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  • Process: Unable to start service com.google.android.gms.checkin.CheckinService with Intent

    - by AndyRoid
    I'm trying to build a Google map application but keep receiving this in my LogCat. I have all the permissions and meta-data set in my manifest, but am still dumbfounded by this error. Have looked everywhere on SO for this specific error but found nothing relating to com.google.android.gms.checkin A little bit about my structural hierarchy. MainActivity extends ActionBarActivity with three tabs underneath actionbar. Each tab has it's own fragment. On the gMapFragment I create a GPSTrack object from my GPSTrack class which extends Service and implements LocationListener. The problem is that when I start the application I get this message: I have all my libraries imported properly and I even added the google-play-services.jar into my libs folder. I also installed Google Play Services APKs through CMD onto my emulator. Furthermore the LocationManager lm = = (LocationManager) mContext.getSystemService(LOCATION_SERVICE); in my GPSTrack class always returns null. Why is this and how can I fix these issues? Would appreciate an explanation along with solution too, I want to understand what's going on here. ============== Code: gMapFragment.java public class gMapFragment extends SupportMapFragment { private final String TAG = "gMapFragment"; private GoogleMap mMap; protected SupportMapFragment mapFrag; private Context mContext = getActivity(); private static View view; @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { if (view != null) { ViewGroup parent = (ViewGroup) view.getParent(); if (parent != null) { parent.removeView(view); } } try { super.onCreateView(inflater, container, savedInstanceState); view = inflater.inflate(R.layout.fragment_map, container, false); setupGoogleMap(); } catch (Exception e) { /* * Map already there , just return as view */ } return view; } private void setupGoogleMap() { mapFrag = (SupportMapFragment) getFragmentManager().findFragmentById( R.id.mapView); if (mapFrag == null) { FragmentManager fragManager = getFragmentManager(); FragmentTransaction fragTransaction = fragManager .beginTransaction(); mapFrag = SupportMapFragment.newInstance(); fragTransaction.replace(R.id.mapView, mapFrag).commit(); } if (mapFrag != null) { mMap = mapFrag.getMap(); if (mMap != null) { setupMap(); mMap.setOnMapClickListener(new OnMapClickListener() { @Override public void onMapClick(LatLng point) { // TODO your click stuff on map } }); } } } @Override public void onAttach(Activity activity) { super.onAttach(activity); Log.d("Attach", "on attach"); } @Override public void onDetach() { super.onDetach(); } @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); } @Override public void onResume() { super.onResume(); } @Override public void onPause() { super.onPause(); } @Override public void onDestroy() { super.onDestroy(); } private void setupMap() { GPSTrack gps = new GPSTrack(mContext); // Enable MyLocation layer of google map mMap.setMyLocationEnabled(true); Log.d(TAG, "MyLocation enabled"); // Set Map type mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL); // Grab current location **ERROR HERE/Returns Null** Location location = gps.getLocation(); Log.d(TAG, "Grabbing location..."); if (location != null) { Log.d(TAG, "location != null"); // Grab Latitude and Longitude double latitude = location.getLatitude(); double longitude = location.getLongitude(); Log.d(TAG, "Getting lat, long.."); // Initialize LatLng object LatLng latLng = new LatLng(latitude, longitude); Log.d(TAG, "LatLng initialized"); // Show current location on google map mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng)); // Zoom in on google map mMap.animateCamera(CameraUpdateFactory.zoomTo(20)); mMap.addMarker(new MarkerOptions().position( new LatLng(latitude, longitude)).title("You are here.")); } else { gps.showSettingsAlert(); } } } GPSTrack.java public class GPSTrack extends Service implements LocationListener{ private final Context mContext; private boolean isGPSEnabled = false; //See if network is connected to internet private boolean isNetworkEnabled = false; //See if you can grab the location private boolean canGetLocation = false; protected Location location = null; protected double latitude; protected double longitude; private static final long MINIMUM_DISTANCE_CHANGE_FOR_UPDATES = 10; //10 Meters private static final long MINIMUM_TIME_CHANGE_FOR_UPDATES = 1000 * 60 * 1; //1 minute protected LocationManager locationManager; public GPSTrack(Context context) { this.mContext = context; getLocation(); } public Location getLocation() { try { //Setup locationManager for controlling location services **ERROR HERE/Return Null** locationManager = (LocationManager) mContext.getSystemService(LOCATION_SERVICE); //See if GPS is enabled isGPSEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER); //See if Network is connected to the internet or carrier service isNetworkEnabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER); if (!isGPSEnabled && !isNetworkEnabled) { Toast.makeText(getApplicationContext(), "No Network Provider Available", Toast.LENGTH_SHORT).show(); } else { this.canGetLocation = true; if (isNetworkEnabled) { locationManager.requestLocationUpdates( LocationManager.NETWORK_PROVIDER, MINIMUM_TIME_CHANGE_FOR_UPDATES, MINIMUM_DISTANCE_CHANGE_FOR_UPDATES, this); Log.d("GPS", "GPS Enabled"); if (locationManager != null) { location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER); if (location != null) { latitude = location.getLatitude(); longitude = location.getLongitude(); } } } } } catch (Exception e) { e.printStackTrace(); } return location; } public void stopUsingGPS() { if (locationManager != null) { locationManager.removeUpdates(GPSTrack.this); } } public double getLatitude() { if (location != null) { latitude = location.getLatitude(); } return latitude; } public double getLongitude() { if (location != null) { longitude = location.getLongitude(); } return longitude; } public boolean canGetLocation() { return this.canGetLocation; } public void showSettingsAlert() { AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext); //AlertDialog title alertDialog.setTitle("GPS Settings"); //AlertDialog message alertDialog.setMessage("GPS is not enabled. Do you want to go to Settings?"); alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub Intent i = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS); mContext.startActivity(i); } }); alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub dialog.cancel(); } }); alertDialog.show(); } @Override public void onLocationChanged(Location location) { // TODO Auto-generated method stub } @Override public void onStatusChanged(String provider, int status, Bundle extras) { // TODO Auto-generated method stub } @Override public void onProviderEnabled(String provider) { // TODO Auto-generated method stub } @Override public void onProviderDisabled(String provider) { // TODO Auto-generated method stub } @Override public IBinder onBind(Intent intent) { // TODO Auto-generated method stub return null; } } logcat 06-08 22:35:03.441: E/AndroidRuntime(1370): FATAL EXCEPTION: main 06-08 22:35:03.441: E/AndroidRuntime(1370): Process: com.google.android.gms, PID: 1370 06-08 22:35:03.441: E/AndroidRuntime(1370): java.lang.RuntimeException: Unable to start service com.google.android.gms.checkin.CheckinService@b1094e48 with Intent { cmp=com.google.android.gms/.checkin.CheckinService }: java.lang.SecurityException: attempting to read gservices without permission: Neither user 10053 nor current process has com.google.android.providers.gsf.permission.READ_GSERVICES. 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2719) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ActivityThread.access$2100(ActivityThread.java:135) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1293) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.os.Handler.dispatchMessage(Handler.java:102) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.os.Looper.loop(Looper.java:136) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ActivityThread.main(ActivityThread.java:5017) 06-08 22:35:03.441: E/AndroidRuntime(1370): at java.lang.reflect.Method.invokeNative(Native Method) 06-08 22:35:03.441: E/AndroidRuntime(1370): at java.lang.reflect.Method.invoke(Method.java:515) 06-08 22:35:03.441: E/AndroidRuntime(1370): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 06-08 22:35:03.441: E/AndroidRuntime(1370): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 06-08 22:35:03.441: E/AndroidRuntime(1370): at dalvik.system.NativeStart.main(Native Method) 06-08 22:35:03.441: E/AndroidRuntime(1370): Caused by: java.lang.SecurityException: attempting to read gservices without permission: Neither user 10053 nor current process has com.google.android.providers.gsf.permission.READ_GSERVICES. 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ContextImpl.enforce(ContextImpl.java:1685) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ContextImpl.enforceCallingOrSelfPermission(ContextImpl.java:1714) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.content.ContextWrapper.enforceCallingOrSelfPermission(ContextWrapper.java:572) 06-08 22:35:03.441: E/AndroidRuntime(1370): at imq.c(SourceFile:107) 06-08 22:35:03.441: E/AndroidRuntime(1370): at imq.a(SourceFile:121) 06-08 22:35:03.441: E/AndroidRuntime(1370): at imq.a(SourceFile:227) 06-08 22:35:03.441: E/AndroidRuntime(1370): at bwq.c(SourceFile:166) 06-08 22:35:03.441: E/AndroidRuntime(1370): at com.google.android.gms.checkin.CheckinService.a(SourceFile:237) 06-08 22:35:03.441: E/AndroidRuntime(1370): at com.google.android.gms.checkin.CheckinService.onStartCommand(SourceFile:211) 06-08 22:35:03.441: E/AndroidRuntime(1370): at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2702) AndroidManifest <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.app" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="14" android:targetSdkVersion="19" /> <uses-permission android:name="com.curio.permission.MAPS_RECEIVE" /> <uses-permission android:name="android.permission.CAMERA" /> <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> <uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES" /> <uses-permission android:name="android.permission.ACCESS_MOCK_LOCATION" /> <uses-feature android:name="android.hardware.camera" android:required="true" /> <uses-feature android:glEsVersion="0x00020000" android:required="true" /> <application android:allowBackup="true" android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" > <activity android:name="com.app.MainActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <meta-data android:name="com.google.android.gms.version" android:value="@integer/google_play_services_version" /> <meta-data android:name="com.google.android.maps.v2.API_KEY" android:value="AI........................" /> </application>

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  • Python unicode problem

    - by Somebody still uses you MS-DOS
    I'm receiving some data from a ZODB (Zope Object Database). I receive a mybrains object. Then I do: o = mybrains.getObject() and I receive a "Person" object in my project. Then, I can do b = o.name and doing print b on my class I get: José Carlos and print b.name.__class__ <type 'unicode'> I have a lot of "Person" objects. They are added to a list. names = [o.nome, o1.nome, o2.nome] Then, I trying to create a text file with this data. delimiter = ';' all = delimiter.join(names) + '\n' No problem. Now, when I do a print all I have: José Carlos;Jonas;Natália Juan;John But when I try to create a file of it: f = open("/tmp/test.txt", "w") f.write(all) I get an error like this (the positions aren't exaclty the same, since I change the names) UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in position 84: ordinal not in range(128) If I can print already with the "correct" form to display it, why I can't write a file with it? Which encode/decode method should I use to write a file with this data? I'm using Python 2.4.5 (can't upgrade it)

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  • Is there a "vim runtime log"?

    - by Somebody still uses you MS-DOS
    Sometimes I try a customization/command in my vimrc. Everything seens to be correct, but it just doesn't work. It's difficult to know what's happening when vim starts, and know which command failed or not, so it's really difficult to debug what can be causing a problem in my vimrc. It's a trial-error approach, which is time consuming and really a PITA. For example, I'm having problems with snipmate plugin in some files and just don't have a clue on how to discover the problem. Is there a "runtime log" when vim starts, telling which commands it executed, which ones failed and such? This would help me a lot.

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  • How do you use indent in vim for web development?

    - by Somebody still uses you MS-DOS
    I'm starting to use Linux and Vim at work. I'm starting to read vims documentation and creating my own .vimrc file and such. I'm a web developer working with HTML, XML, CSS, JS, Python, PHP, ZPT, DTML and SQL. I would like to have an indent feature like this one: for each language/set, a corresponding indent solution. So, in js, writing function test(){|} would turn in function test(){ | } If php, writing <?php function test(){|}: <?php function test(){ | } <?php> ...and such. Writing a function definition in Python, and then creating a for loop sentece, it would automatically create an indent. I'm starting with autoindent, smartindent, cindent but I'm a little confused about their differences. How do the indent in vim works? Am I supposed to download plugins for each language? Is the behavior I described possible with already existing plugins you're used to or do I have to create it? I keep seeing people using Vim and I'm trying to do this as well since the machine I'm using is too limited, but I'm afraid I won't be able to have a decent auto indenting solution in it. (I have used autoindenting in a little small project in Visual Studio, and really liked their approach. Is there a plugin for that?)

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  • How to make a file with .pt extension, with xml syntax highlighting and vim's plugin snipmate load p

    - by Somebody still uses you MS-DOS
    I have the following in my .vimrc: au BufNewFile,BufRead *.pt set filetype=xml This is needed because although I'm editing a file with *.pt extension, it's indeed a valid xml file: setting the filetype like this I can have syntax highlighting. I'm using vim's snipmate plugin, and tried to create pt.snippets to specific needs since these files are Zope Page Templates (ZPT with TAL). Now, I have a problem: I don't want to create these snippets in xml.snippets, since they aren't really generic xml snippets, but my *.pt files are set to xml, so when I define my pt snippets they aren't loaded unless I run :set filetype=pt on my pt file on vim - but then I lose syntax highlighting. I would like to be able to have a pt file, with xml syntax highlighting, to be able to load a pt.snippets file from snipmate. How can I do it? (I would like to avoid putting my snippets in a generic snippet file, I would like it to be present only in pt.snippets to be easier to maintain.)

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  • How to create a cross-plataform application, doing the interface modules (Mac/Qt/GTK+) in a totally

    - by Somebody still uses you MS-DOS
    I'm amazed at Transmission, a BT client. It has a Mac, a GTK+, a QT, a Web Client and a CLI interface to it. I tried reading some of it's source to understand how he creates all these interfaces, but no luck. Does the developer creates them using a single ide? Or does he create the interface logic in each specific environment (specially mac), "exports" this window code and integrates with the main logic? Is it possible to create that mac interface in another OS using an IDE? How did the developers create this software with so many interfaces, in a independent way?

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  • CVS in cmd/gui works only the third time I run a command.

    - by Somebody still uses you MS-DOS
    I'm using CVS in the command line. I'm in my repository folder. When I call a CVS command, I get... cvs [log aborted]: unrecognized auth response from localhost: -f [pserver aborted]: /opt/cvs/XXXXXX: no such repository ...2 times. The third time I run the command, it works with no problems. I tried to use a GUI client (CrossVC) and the same problem occurs. I tried inside gVim and Vim using VCSCommand and I'm having the same issues as well. I've tested with different times between each command, but I still have the same problems. I'm using a CVS configuration with stunnel. Why am I having problem with this setup? Why every time just the third time that I try to run the command that actually works?

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  • How does exactly Qt works?

    - by Somebody still uses you MS-DOS
    I have seen that you can write your application in Qt, and it can be run in different operating systems. And - correct me if I'm wrong - you don't need to have Qt already installed in all of these platforms. How exactly this approach works? Does Qt compiles to the desired platform, does it bundle some "dlls" (libs), how does it do it? Is different from programming a Java application for the sake of cross-platform? If you use Python to write a Qt application with Python bindings, does the final user needs to have Python installed?

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  • Is it possible to run a SQL-only file from a "rake db:create"?

    - by Somebody still uses you MS-DOS
    I'm trying to install a software called Teambox in my Dreamhost shared account. I have no experience with Rails. I just want to install the software in the shared hosting. In this shared hosting, all dependencies are ok, but I have to create the dabatase from their panel. I can't create in command line (ssh). So, when I run "rake db:create" these's an error, because the db already exists (because I created in panel). I've already contacted support. They can't change this policy. How do I populate my tables "by hand" in this case? Which files should I look inside Teambox's folder... Thanks!

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  • Need help/guidance about creating a desktop application with gui

    - by Somebody still uses you MS-DOS
    I'm planning to do an Desktop application using Python, to learn some Desktop concepts. I'm going to use GTK or Qt, I still haven't decided which one. Fact is: I would like to create an application with the possibility to be called from command line, AND using a GUI. So it would be useful for cmd fans, and GUI users as well. It would be interesting to create a web interface too in the future, so it could be run in a server somewhere using an html interface created with a template language. I'm thinking about two approaches: - Creating a "model" with a simple interface which is called from a desktop/web implementation; - Creating a "model" with an html interface, and embeb a browser component so I could reuse all the code in both desktop/web scenarios. My question is: which exactly concepts are involved in this project? What advantages/disadvantages each approach has? Are they possible? By naming "interface", I'm planning to just do some interfaces.py files with def calls. Is this a bad approach? I would like to know some book recommendations, or resources to both options - or source code from projects which share the same GUI/cmd/web goals I'm after. Thanks in advance!

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  • Using Wordpress as a CMS to a site AND blog (two completely different layouts for each). Duplicate i

    - by Somebody still uses you MS-DOS
    I'm going to create a website using Wordpress static pages feature. It's going to have a menu for all the created pages. A blog is going to be created as well. This blog has a completely different layout/menu from the main site, but within the same domain: "http://www.domain.com" is the website url, and "http://www.domain.com/blog/" is the blog url. I was thinking of installing two different Wordpress instances: /var/www/public_html/ and /var/www/public_html/blog/. Although it's a simple solution, users are going to be duplicated: if you change password in one system, you need to change in the other. So, I would like to know from you which other approaches are possible: create a "dynamic" theme (call a theme when in root domain, another whern /blog - dont even know if this is possible), or for example a plugin to syncronize users from both instances? Does Wordpress MU solve this problem for me? Thanks!

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  • How does transmission created it's cross plataform app? It has from Qt/Mac to CLI interfaces!

    - by Somebody still uses you MS-DOS
    I'm amazed at Transmission, a BT client. It has a Mac, a GTK+, a QT, a Web Client and a CLI interface to it. I tried reading some of it's source to understand how he creates all these interfaces, but no luck. Does the developer creates them using a single ide? Or does he create the interface logic in each specific environment (specially mac), "exports" this window code and integrates with the main logic? How did the developers create this software with so many interfaces?

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  • (g)Vim with version control like Eclipse

    - by Somebody still uses you MS-DOS
    I was an Eclipse user, now I have to use Vim in my machine. I used to "compare" a file I edited with a CVS repository to do merges an commit the files, using a context menu and my mouse. Is this possible in Vim? Opening a vimdiff for a file before commiting, and commit it from vim itself? And how is that supposed to work? I'm supposing I would be editing a file. Then, I want to see the modifications. I run vimdiff in gvim, and a new window (or buffer) is opened. I run the modifications, save what is applicable (using vimdiff commands), and commit running another command. Is this all transparent in vim? Do I have to keep getting out of vim to my terminal, or can all be done inside it? Do I need to use some plugins, or just really simple functions inside my vimrc?

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  • CVS Diff to output only modified files?

    - by Somebody still uses you MS-DOS
    Is it possible? Run a cvs diff in terminal at the project root that outputs only modified files (like local files that aren't in source control and local modified files). I'm running cvs diff --brief but I still have too many results since my project is large, and with a lot of subdirectories - it shows the whole hierarchy and I just want to know which files are different from HEAD revision. I'm using Linux.

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  • How does exactly Qt work?

    - by Somebody still uses you MS-DOS
    I have seen that you can write your application in Qt, and can be run in different operating systems. And - correct me if I'm wrong - you don't need to have Qt installed in all of these plataforms. How does exactly this works? Does Qt compiles to the desired plataform, it bundles some "dlls" (libs), how? Is different from programming a Java application for the sake of cross-plataform? If you use Python to write a Qt application with Python bindings, does the final user needs to have Python installed?

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  • My google map android app keeps crashing

    - by Manny264
    I have followed about two tutorials from vogella and some other tutorial that looked similar...very similar but to no avail. I load the app on my nexus 7 and it just crashes "Unfortunately MyMapView has stopped working" on launch.This is the manifest: ` <uses-sdk android:minSdkVersion="17" android:targetSdkVersion="17" /> <uses-feature android:glEsVersion="0x00020000" android:required="true"/> <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> <uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES"/> <application android:allowBackup="true" android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" > <uses-library android:name="com.google.android.maps" /> <activity android:name="com.macmozart.mymapview.MainActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <meta-data android:name="com.google.android.maps.v2.API_KEY" android:value="AIzaSyBZ1Bt7rjB863Jy-B05zls6k8XZsBGQ6-4" /> </application> ` Followed by my main layout: <fragment android:id="@+id/map" android:layout_width="match_parent" android:layout_height="match_parent" class="com.google.android.gms.maps.MapFragment" /> and finally my java class: package com.macmozart.mymapview; import android.app.Activity; import android.os.Bundle; import com.google.android.gms.maps.CameraUpdateFactory; import com.google.android.gms.maps.GoogleMap; import com.google.android.gms.maps.MapFragment; import com.google.android.gms.maps.model.BitmapDescriptorFactory; import com.google.android.gms.maps.model.LatLng; import com.google.android.gms.maps.model.Marker; import com.google.android.gms.maps.model.MarkerOptions; import com.google.android.maps.*; public class MainActivity extends Activity { static final LatLng HAMBURG = new LatLng(53.558, 9.927); static final LatLng KIEL = new LatLng(53.551, 9.993); private GoogleMap map; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); map = ((MapFragment) getFragmentManager().findFragmentById(R.id.map)) .getMap(); if (map != null) { Marker hamburg = map.addMarker(new MarkerOptions() .position(HAMBURG).title("Hamburg")); Marker kiel = map.addMarker(new MarkerOptions() .position(KIEL) .title("Kiel") .snippet("Kiel is cool") .icon(BitmapDescriptorFactory .fromResource(R.drawable.ic_launcher))); map.moveCamera(CameraUpdateFactory.newLatLngZoom(HAMBURG, 15)); // Zoom in, animating the camera. map.animateCamera(CameraUpdateFactory.zoomTo(10), 2000, null); } } } Any idea what im doing wrong I really need this to work

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  • Big Data – Buzz Words: Importance of Relational Database in Big Data World – Day 9 of 21

    - by Pinal Dave
    In yesterday’s blog post we learned what is HDFS. In this article we will take a quick look at the importance of the Relational Database in Big Data world. A Big Question? Here are a few questions I often received since the beginning of the Big Data Series - Does the relational database have no space in the story of the Big Data? Does relational database is no longer relevant as Big Data is evolving? Is relational database not capable to handle Big Data? Is it true that one no longer has to learn about relational data if Big Data is the final destination? Well, every single time when I hear that one person wants to learn about Big Data and is no longer interested in learning about relational database, I find it as a bit far stretched. I am not here to give ambiguous answers of It Depends. I am personally very clear that one who is aspiring to become Big Data Scientist or Big Data Expert they should learn about relational database. NoSQL Movement The reason for the NoSQL Movement in recent time was because of the two important advantages of the NoSQL databases. Performance Flexible Schema In personal experience I have found that when I use NoSQL I have found both of the above listed advantages when I use NoSQL database. There are instances when I found relational database too much restrictive when my data is unstructured as well as they have in the datatype which my Relational Database does not support. It is the same case when I have found that NoSQL solution performing much better than relational databases. I must say that I am a big fan of NoSQL solutions in the recent times but I have also seen occasions and situations where relational database is still perfect fit even though the database is growing increasingly as well have all the symptoms of the big data. Situations in Relational Database Outperforms Adhoc reporting is the one of the most common scenarios where NoSQL is does not have optimal solution. For example reporting queries often needs to aggregate based on the columns which are not indexed as well are built while the report is running, in this kind of scenario NoSQL databases (document database stores, distributed key value stores) database often does not perform well. In the case of the ad-hoc reporting I have often found it is much easier to work with relational databases. SQL is the most popular computer language of all the time. I have been using it for almost over 10 years and I feel that I will be using it for a long time in future. There are plenty of the tools, connectors and awareness of the SQL language in the industry. Pretty much every programming language has a written drivers for the SQL language and most of the developers have learned this language during their school/college time. In many cases, writing query based on SQL is much easier than writing queries in NoSQL supported languages. I believe this is the current situation but in the future this situation can reverse when No SQL query languages are equally popular. ACID (Atomicity Consistency Isolation Durability) – Not all the NoSQL solutions offers ACID compliant language. There are always situations (for example banking transactions, eCommerce shopping carts etc.) where if there is no ACID the operations can be invalid as well database integrity can be at risk. Even though the data volume indeed qualify as a Big Data there are always operations in the application which absolutely needs ACID compliance matured language. The Mixed Bag I have often heard argument that all the big social media sites now a days have moved away from Relational Database. Actually this is not entirely true. While researching about Big Data and Relational Database, I have found that many of the popular social media sites uses Big Data solutions along with Relational Database. Many are using relational databases to deliver the results to end user on the run time and many still uses a relational database as their major backbone. Here are a few examples: Facebook uses MySQL to display the timeline. (Reference Link) Twitter uses MySQL. (Reference Link) Tumblr uses Sharded MySQL (Reference Link) Wikipedia uses MySQL for data storage. (Reference Link) There are many for prominent organizations which are running large scale applications uses relational database along with various Big Data frameworks to satisfy their various business needs. Summary I believe that RDBMS is like a vanilla ice cream. Everybody loves it and everybody has it. NoSQL and other solutions are like chocolate ice cream or custom ice cream – there is a huge base which loves them and wants them but not every ice cream maker can make it just right  for everyone’s taste. No matter how fancy an ice cream store is there is always plain vanilla ice cream available there. Just like the same, there are always cases and situations in the Big Data’s story where traditional relational database is the part of the whole story. In the real world scenarios there will be always the case when there will be need of the relational database concepts and its ideology. It is extremely important to accept relational database as one of the key components of the Big Data instead of treating it as a substandard technology. Ray of Hope – NewSQL In this module we discussed that there are places where we need ACID compliance from our Big Data application and NoSQL will not support that out of box. There is a new termed coined for the application/tool which supports most of the properties of the traditional RDBMS and supports Big Data infrastructure – NewSQL. Tomorrow In tomorrow’s blog post we will discuss about NewSQL. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Big Data, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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  • GCM: onMessage() from GCMIntentService is never called [migrated]

    - by Shrikant
    I am implementing GCM (Google Cloud Messaging- PUSH Notifications) in my application. I have followed all the steps given in GCM tutorial from developer.android.com My application's build target is pointing to Goolge API 8 (Android 2.2 version). I am able to get the register ID from GCM successfully, and I am passing this ID to my application server. So the registration step is performed successfully. Now when my application server sends a PUSH message to my device, the server gets the message as SUCCESS=1 FAILURE=0, etc., i.e. Server is sending message successfully, but my device never receives the message. After searching alot about this, I came to know that GCM pushes messages on port number 5228, 5229 or 5230. Initially, my device and laptop was restricted for some websites, but then I was granted all the permissions to access all websites, so I guess these port numbers are open for my device. So my question is: I never receive any PUSH message from GCM. My onMessage() from GCMIntenService class is never called. What could be the reason? Please see my following code and guide me accordingly: I have declared following in my manifest: <uses-sdk android:minSdkVersion="8" android:targetSdkVersion="8" /> <permission android:name="package.permission.C2D_MESSAGE" android:protectionLevel="signature" /> <!-- App receives GCM messages. --> <uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" /> <!-- GCM connects to Google Services. --> <uses-permission android:name="android.permission.INTERNET" /> <!-- GCM requires a Google account. --> <uses-permission android:name="android.permission.GET_ACCOUNTS" /> <!-- Keeps the processor from sleeping when a message is received. --> <uses-permission android:name="android.permission.WAKE_LOCK" /> <uses-permission android:name="package.permission.C2D_MESSAGE" /> <uses-permission android:name="android.permission.INTERNET" /> <receiver android:name="com.google.android.gcm.GCMBroadcastReceiver" android:permission="com.google.android.c2dm.permission.SEND" > <intent-filter> <action android:name="com.google.android.c2dm.intent.RECEIVE" /> <action android:name="com.google.android.c2dm.intent.REGISTRATION" /> <category android:name="packageName" /> </intent-filter> </receiver> <receiver android:name=".ReceiveBroadcast" android:exported="false" > <intent-filter> <action android:name="GCM_RECEIVED_ACTION" /> </intent-filter> </receiver> <service android:name=".GCMIntentService" /> /** * @author Shrikant. * */ public class GCMIntentService extends GCMBaseIntentService { /** * The Sender ID used for GCM. */ public static final String SENDER_ID = "myProjectID"; /** * This field is used to call Web-Service for GCM. */ SendUserCredentialsGCM sendUserCredentialsGCM = null; public GCMIntentService() { super(SENDER_ID); sendUserCredentialsGCM = new SendUserCredentialsGCM(); } @Override protected void onRegistered(Context arg0, String registrationId) { Log.i(TAG, "Device registered: regId = " + registrationId); sendUserCredentialsGCM.sendRegistrationID(registrationId); } @Override protected void onUnregistered(Context context, String arg1) { Log.i(TAG, "unregistered = " + arg1); sendUserCredentialsGCM .unregisterFromGCM(LoginActivity.API_OR_BROWSER_KEY); } @Override protected void onMessage(Context context, Intent intent) { Log.e("GCM MESSAGE", "Message Recieved!!!"); String message = intent.getStringExtra("message"); if (message == null) { Log.e("NULL MESSAGE", "Message Not Recieved!!!"); } else { Log.i(TAG, "new message= " + message); sendGCMIntent(context, message); } } private void sendGCMIntent(Context context, String message) { Intent broadcastIntent = new Intent(); broadcastIntent.setAction("GCM_RECEIVED_ACTION"); broadcastIntent.putExtra("gcm", message); context.sendBroadcast(broadcastIntent); } @Override protected void onError(Context context, String errorId) { Log.e(TAG, "Received error: " + errorId); Toast.makeText(context, "PUSH Notification failed.", Toast.LENGTH_LONG) .show(); } @Override protected boolean onRecoverableError(Context context, String errorId) { return super.onRecoverableError(context, errorId); } }

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  • JSF managed bean question

    - by Nitesh Panchal
    Hello, I have one page which uses <ui:insert> called master.xhtml which uses one managedbean named MasterBean.java and its of viewScoped. It calls webservice and has all useful data which will be useful in master.xhtml as well as page which is built using master.xhtml (which uses <ui:include>). When i visit data.xhtml (which uses template as master.xhtml) and which uses managed bean as DataBean.java which is also of view scoped, how do i use MasterBean? If i directly use #{Masterbean.property}, won't it create a new instance again? or will it use the bean which is already in view scope? Also how do i use MasterBean in DataBean in such a way that existing MasterBean's instance is used in DataBean. I don't want new instance of MasterBean in DataBean. Thanks in advance. If i am not clear please let me know.

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  • Default Parameters vs Method Overloading

    - by João Angelo
    With default parameters introduced in C# 4.0 one might be tempted to abandon the old approach of providing method overloads to simulate default parameters. However, you must take in consideration that both techniques are not interchangeable since they show different behaviors in certain scenarios. For me the most relevant difference is that default parameters are a compile time feature while method overloading is a runtime feature. To illustrate these concepts let’s take a look at a complete, although a bit long, example. What you need to retain from the example is that static method Foo uses method overloading while static method Bar uses C# 4.0 default parameters. static void CreateCallerAssembly(string name) { // Caller class - Invokes Example.Foo() and Example.Bar() string callerCode = String.Concat( "using System;", "public class Caller", "{", " public void Print()", " {", " Console.WriteLine(Example.Foo());", " Console.WriteLine(Example.Bar());", " }", "}"); var parameters = new CompilerParameters(new[] { "system.dll", "Common.dll" }, name); new CSharpCodeProvider().CompileAssemblyFromSource(parameters, callerCode); } static void Main() { // Example class - Foo uses overloading while Bar uses C# 4.0 default parameters string exampleCode = String.Concat( "using System;", "public class Example", "{{", " public static string Foo() {{ return Foo(\"{0}\"); }}", " public static string Foo(string key) {{ return \"FOO-\" + key; }}", " public static string Bar(string key = \"{0}\") {{ return \"BAR-\" + key; }}", "}}"); var compiler = new CSharpCodeProvider(); var parameters = new CompilerParameters(new[] { "system.dll" }, "Common.dll"); // Build Common.dll with default value of "V1" compiler.CompileAssemblyFromSource(parameters, String.Format(exampleCode, "V1")); // Caller1 built against Common.dll that uses a default of "V1" CreateCallerAssembly("Caller1.dll"); // Rebuild Common.dll with default value of "V2" compiler.CompileAssemblyFromSource(parameters, String.Format(exampleCode, "V2")); // Caller2 built against Common.dll that uses a default of "V2" CreateCallerAssembly("Caller2.dll"); dynamic caller1 = Assembly.LoadFrom("Caller1.dll").CreateInstance("Caller"); dynamic caller2 = Assembly.LoadFrom("Caller2.dll").CreateInstance("Caller"); Console.WriteLine("Caller1.dll:"); caller1.Print(); Console.WriteLine("Caller2.dll:"); caller2.Print(); } And if you run this code you will get the following output: // Caller1.dll: // FOO-V2 // BAR-V1 // Caller2.dll: // FOO-V2 // BAR-V2 You see that even though Caller1.dll runs against the current Common.dll assembly where method Bar defines a default value of “V2″ the output show us the default value defined at the time Caller1.dll compiled against the first version of Common.dll. This happens because the compiler will copy the current default value to each method call, much in the same way a constant value (const keyword) is copied to a calling assembly and changes to it’s value will only be reflected if you rebuild the calling assembly again. The use of default parameters is also discouraged by Microsoft in public API’s as stated in (CA1026: Default parameters should not be used) code analysis rule.

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  • Multiple dex files define Lcom/google/api/client/auth/oauth/AbstractOAuthGetToken;

    - by Elad Benda
    I have just followed this tutorial: https://developers.google.com/drive/quickstart-android so I don't see a reason for duplicated libs in my project. I have added the drive Client lib via Google plugin for eclipse When I build my android app with this manifest <uses-sdk android:minSdkVersion="15" android:targetSdkVersion="16" /> <uses-permission android:name="android.permission.READ_CALENDAR" /> <uses-permission android:name="android.permission.WRITE_CALENDAR" /> <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/> <uses-permission android:name="android.permission.GET_ACCOUNTS"/> <uses-permission android:name="android.permission.INTERNET" /> <application android:icon="@drawable/todo" android:label="@string/app_name" > <activity android:name=".TodosOverviewActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name=".TodoDetailActivity" android:windowSoftInputMode="stateVisible|adjustResize" > <intent-filter> <action android:name="android.intent.action.SEND" /> <category android:name="android.intent.category.DEFAULT" /> <data android:mimeType="image/*" /> </intent-filter> </activity> <provider android:name=".contentprovider.MyTodoContentProvider" android:authorities="de.vogella.android.todos.contentprovider" > </provider> </application> I get the following error: [2013-10-27 00:43:58 - Dex Loader] Unable to execute dex: Multiple dex files define Lcom/google/api/client/auth/oauth/AbstractOAuthGetToken; [2013-10-27 00:43:58 - de.vogella.android.todos] Conversion to Dalvik format failed: Unable to execute dex: Multiple dex files define Lcom/google/api/client/auth/oauth/AbstractOAuthGetToken; how can I fix this?

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  • XML Serialization and Deserialization in C#

    - by SOF User
    <job id="ID00004" name="PeakValCalcO"> <uses file="Seismogram_FFI_0_1_ID00003.grm" link="input" /> <uses file="PeakVals_FFI_0_1_ID00003.bsa" link="output" /> </job> <job id="ID00005" name="SeismogramSynthesis" > <uses file="FFI_0_1_txt.variation-s07930-h00000" link="input" /> <uses file="Seismogram_FFI_0_1_ID00005.grm" link="output" /> </job> Let say I have this XML I want to convert into .net Object how can do this i tried it but it doesn't work correct... public class jobs : List<job> { } public class job { public string id { get; set; } public string name { get; set; } public List<uses> Files { get; set; } } public class uses { public string file { get; set; } public string link { get; set; } } private void Form1_Load(object sender, EventArgs e) { XmlSerializer serializer = new XmlSerializer(typeof(jobs)); TextReader tr = new StreamReader("CyberShake_100.xml"); job b = (job)serializer.Deserialize(tr); tr.Close(); }

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  • wifi provider onLocationChanged is never called

    - by Kelsie
    I got a weird problem. I uses wifi to retrieve user location. I have tested on several phones; on some of them, I could never get a location update. it seemed that the method onLocationChanged is never called. My code is attached below.. Any suggestions appreciated!!! @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); LocationManager locationManager; locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE); String provider = locationManager.NETWORK_PROVIDER; Location l = locationManager.getLastKnownLocation(provider); updateWithNewLocation(l); locationManager.requestLocationUpdates(provider, 0, 0, locationListener); } private void updateWithNewLocation(Location location) { TextView myLocationText; myLocationText = (TextView)findViewById(R.id.myLocationText); String latLongString = "No location found"; if (location != null) { double lat = location.getLatitude(); double lng = location.getLongitude(); latLongString = "Lat:" + lat + "\nLong:" + lng; } myLocationText.setText("Your Current Position is:\n" + latLongString); } private final LocationListener locationListener = new LocationListener() { public void onLocationChanged(Location location) { updateWithNewLocation(location); Log.i("onLocationChanged", "onLocationChanged"); Toast.makeText(getApplicationContext(), "location changed", Toast.LENGTH_SHORT).show(); } public void onProviderDisabled(String provider) {} public void onProviderEnabled(String provider) {} public void onStatusChanged(String provider, int status, Bundle extras) {} }; Manifest <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/> <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/> <uses-permission android:name="android.permission.INTERNET"/>

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  • Design by Contract with Microsoft .Net Code Contract

    - by Fredrik N
    I have done some talks on different events and summits about Defensive Programming and Design by Contract, last time was at Cornerstone’s Developer Summit 2010. Next time will be at SweNug (Sweden .Net User Group). I decided to write a blog post about of some stuffs I was talking about. Users are a terrible thing! Protect your self from them ”Human users have a gift for doing the worst possible thing at the worst possible time.” – Michael T. Nygard, Release It! The kind of users Michael T. Nygard are talking about is the users of a system. We also have users that uses our code, the users I’m going to focus on is the users of our code. Me and you and another developers. “Any fool can write code that a computer can understand. Good programmers write code that humans can understand.” – Martin Fowler Good programmers also writes code that humans know how to use, good programmers also make sure software behave in a predictable manner despise inputs or user actions. Design by Contract   Design by Contract (DbC) is a way for us to make a contract between us (the code writer) and the users of our code. It’s about “If you give me this, I promise to give you this”. It’s not about business validations, that is something completely different that should be part of the domain model. DbC is to make sure the users of our code uses it in a correct way, and that we can rely on the contract and write code in a way where we know that the users will follow the contract. It will make it much easier for us to write code with a contract specified. Something like the following code is something we may see often: public void DoSomething(Object value) { value.DoIKnowThatICanDoThis(); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Where “value” can be uses directly or passed to other methods and later be used. What some of us can easily forget here is that the “value” can be “null”. We will probably not passing a null value, but someone else that uses our code maybe will do it. I think most of you (including me) have passed “null” into a method because you don’t know if the argument need to be specified to a valid value etc. I bet most of you also have got the “Null reference exception”. Sometimes this “Null reference exception” can be hard and take time to fix, because we need to search among our code to see where the “null” value was passed in etc. Wouldn’t it be much better if we can as early as possible specify that the value can’t not be null, so the users of our code also know it when the users starts to use our code, and before run time execution of the code? This is where DbC comes into the picture. We can use DbC to specify what we need, and by doing so we can rely on the contract when we write our code. So the code above can actually use the DoIKnowThatICanDoThis() method on the value object without being worried that the “value” can be null. The contract between the users of the code and us writing the code, says that the “value” can’t be null.   Pre- and Postconditions   When working with DbC we are specifying pre- and postconditions.  Precondition is a condition that should be met before a query or command is executed. An example of a precondition is: “The Value argument of the method can’t be null”, and we make sure the “value” isn’t null before the method is called. Postcondition is a condition that should be met when a command or query is completed, a postcondition will make sure the result is correct. An example of a postconditon is “The method will return a list with at least 1 item”. Commands an Quires When using DbC, we need to know what a Command and a Query is, because some principles that can be good to follow are based on commands and queries. A Command is something that will not return anything, like the SQL’s CREATE, UPDATE and DELETE. There are two kinds of Commands when using DbC, the Creation commands (for example a Constructor), and Others. Others can for example be a Command to add a value to a list, remove or update a value etc. //Creation commands public Stack(int size) //Other commands public void Push(object value); public void Remove(); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   A Query, is something that will return something, for example an Attribute, Property or a Function, like the SQL’s SELECT.   There are two kinds of Queries, the Basic Queries  (Quires that aren’t based on another queries), and the Derived Queries, queries that is based on another queries. Here is an example of queries of a Stack: //Basic Queries public int Count; public object this[int index] { get; } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } To understand about some principles that are good to follow when using DbC, we need to know about the Commands and different Queries. The 6 Principles When working with DbC, it’s advisable to follow some principles to make it easier to define and use contracts. The following DbC principles are: Separate commands and queries. Separate basic queries from derived queries. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries. For each command, write a postcondition that specifies the value of every basic query. For every query and command, decide on a suitable precondition. Write invariants to define unchanging properties of objects. Before I will write about each of them I want you to now that I’m going to use .Net 4.0 Code Contract. I will in the rest of the post uses a simple Stack (Yes I know, .Net already have a Stack class) to give you the basic understanding about using DbC. A Stack is a data structure where the first item in, will be the first item out. Here is a basic implementation of a Stack where not contract is specified yet: public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } //Is related to Count and this[] Query public object Top() { return this[Count]; } //Creation commands public Stack(uint size) { Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { this[++Count] = value; } public void Remove() { this[Count] = null; Count--; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: The Stack is implemented in a way to demonstrate the use of Code Contract in a simple way, the implementation may not look like how you would implement it, so don’t think this is the perfect Stack implementation, only used for demonstration.   Before I will go deeper into the principles I will simply mention how we can use the .Net Code Contract. I mention before about pre- and postcondition, is about “Require” something and to “Ensure” something. When using Code Contract, we will use a static class called “Contract” and is located in he “System.Diagnostics.Contracts” namespace. The contract must be specified at the top or our member statement block. To specify a precondition with Code Contract we uses the Contract.Requires method, and to specify a postcondition, we uses the Contract.Ensure method. Here is an example where both a pre- and postcondition are used: public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The contract above requires that the Count is greater than 0, if not we can’t get the item at the Top of a Stack. We also Ensures that the results (By using the Contract.Result method, we can specify a postcondition that will check if the value returned from a method is correct) of the Top query is equal to this[Count].   1. Separate Commands and Queries   When working with DbC, it’s important to separate Command and Quires. A method should either be a command that performs an Action, or returning information to the caller, not both. By asking a question the answer shouldn’t be changed. The following is an example of a Command and a Query of a Stack: public void Push(object value) public object Top() .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The Push is a command and will not return anything, just add a value to the Stack, the Top is a query to get the item at the top of the stack.   2. Separate basic queries from derived queries There are two different kinds of queries,  the basic queries that doesn’t rely on another queries, and derived queries that uses a basic query. The “Separate basic queries from derived queries” principle is about about that derived queries can be specified in terms of basic queries. So this principles is more about recognizing that a query is a derived query or a basic query. It will then make is much easier to follow the other principles. The following code shows a basic query and a derived query: //Basic Queries public uint Count; //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   We can see that IsEmpty will use the Count query, and that makes the IsEmpty a Derived query.   3. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries.   When the derived query is recognize we can follow the 3ed principle. For each derived query, we can create a postcondition that specifies what result our derived query will return in terms of one or more basic queries. Remember that DbC is about contracts between the users of the code and us writing the code. So we can’t use demand that the users will pass in a valid value, we must also ensure that we will give the users what the users wants, when the user is following our contract. The IsEmpty query of the Stack will use a Count query and that will make the IsEmpty a Derived query, so we should now write a postcondition that specified what results will be returned, in terms of using a basic query and in this case the Count query, //Basic Queries public uint Count; //Derived Queries public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } The Contract.Ensures is used to create a postcondition. The above code will make sure that the results of the IsEmpty (by using the Contract.Result to get the result of the IsEmpty method) is correct, that will say that the IsEmpty will be either true or false based on Count is equal to 0 or not. The postcondition are using a basic query, so the IsEmpty is now following the 3ed principle. We also have another Derived Query, the Top query, it will also need a postcondition and it uses all basic queries. The Result of the Top method must be the same value as the this[] query returns. //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count and this[] Query public object Top() { Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   4. For each command, write a postcondition that specifies the value of every basic query.   For each command we will create a postconditon that specifies the value of basic queries. If we look at the Stack implementation we will have three Commands, one Creation command, the Constructor, and two others commands, Push and Remove. Those commands need a postcondition and they should include basic query to follow the 4th principle. //Creation commands public Stack(uint size) { Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   As you can see the Create command will Ensures that Count will be 0 when the Stack is created, when a Stack is created there shouldn’t be any items in the stack. The Push command will take a value and put it into the Stack, when an item is pushed into the Stack, the Count need to be increased to know the number of items added to the Stack, and we must also make sure the item is really added to the Stack. The postconditon of the Push method will make sure the that old value of the Count (by using the Contract.OldValue we can get the value a Query has before the method is called)  plus 1 will be equal to the Count query, this is the way we can ensure that the Push will increase the Count with one. We also make sure the this[] query will now contain the item we pushed into the Stack. The Remove method must make sure the Count is decreased by one when the top item is removed from the Stack. The Commands is now following the 4th principle, where each command now have a postcondition that used the value of basic queries. Note: The principle says every basic Query, the Remove only used one Query the Count, it’s because this command can’t use the this[] query because an item is removed, so the only way to make sure an item is removed is to just use the Count query, so the Remove will still follow the principle.   5. For every query and command, decide on a suitable precondition.   We have now focused only on postcondition, now time for some preconditons. The 5th principle is about deciding a suitable preconditon for every query and command. If we starts to look at one of our basic queries (will not go through all Queries and commands here, just some of them) the this[] query, we can’t pass an index that is lower then 1 (.Net arrays and list are zero based, but not the stack in this blog post ;)) and the index can’t be lesser than the number of items in the stack. So here we will need a preconditon. public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Think about the Contract as an documentation about how to use the code in a correct way, so if the contract could be specified elsewhere (not part of the method body), we could simply write “return _array[index]” and there is no need to check if index is greater or lesser than Count, because that is specified in a “contract”. The implementation of Code Contract, requires that the contract is specified in the code. As a developer I would rather have this contract elsewhere (Like Spec#) or implemented in a way Eiffel uses it as part of the language. Now when we have looked at one Query, we can also look at one command, the Remove command (You can see the whole implementation of the Stack at the end of this blog post, where precondition is added to more queries and commands then what I’m going to show in this section). We can only Remove an item if the Count is greater than 0. So we can write a precondition that will require that Count must be greater than 0. public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   6. Write invariants to define unchanging properties of objects.   The last principle is about making sure the object are feeling great! This is done by using invariants. When using Code Contract we can specify invariants by adding a method with the attribute ContractInvariantMethod, the method must be private or public and can only contains calls to Contract.Invariant. To make sure the Stack feels great, the Stack must have 0 or more items, the Count can’t never be a negative value to make sure each command and queries can be used of the Stack. Here is our invariant for the Stack object: [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: The ObjectInvariant method will be called every time after a Query or Commands is called. Here is the full example using Code Contract:   public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } set { Contract.Requires(index >= 1); Contract.Requires(index <= Count); _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } //Is related to Count and this[] Query public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } //Creation commands public Stack(uint size) { Contract.Requires(size > 0); Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Requires(value != null); Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Summary By using Design By Contract we can make sure the users are using our code in a correct way, and we must also make sure the users will get the expected results when they uses our code. This can be done by specifying contracts. To make it easy to use Design By Contract, some principles may be good to follow like the separation of commands an queries. With .Net 4.0 we can use the Code Contract feature to specify contracts.

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