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  • C++ Implicit Conversion Operators

    - by Imbue
    I'm trying to find a nice inheritance solution in C++. I have a Rectangle class and a Square class. The Square class can't publicly inherit from Rectangle, because it cannot completely fulfill the rectangle's requirements. For example, a Rectangle can have it's width and height each set separately, and this of course is impossible with a Square. So, my dilemma. Square obviously will share a lot of code with Rectangle; they are quite similar. For examlpe, if I have a function like: bool IsPointInRectangle(const Rectangle& rect); it should work for a square too. In fact, I have a ton of such functions. So in making my Square class, I figured I would use private inheritance with a publicly accessible Rectangle conversion operator. So my square class looks like: class Square : private Rectangle { public: operator const Rectangle&() const; }; However, when I try to pass a Square to the IsPointInRectangle function, my compiler just complains that "Rectangle is an inaccessible base" in that context. I expect it to notice the Rectangle operator and use that instead. Is what I'm trying to do even possible? If this can't work I'm probably going to refactor part of Rectangle into MutableRectangle class. Thanks.

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  • How can I improve the performance of LinqToSql queries that use EntitySet properties?

    - by DanM
    I'm using LinqToSql to query a small, simple SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of what makes LinqToSql so appealing. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance besides resorting to doing all the joins manually? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view. Update Here are the table definitions for the example I used in my question: create table Order ( Id int identity(1, 1) primary key, ProductName ntext null ) create table Customer ( Id int identity(1, 1) primary key, OrderId int null references Order (Id) )

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  • What is an efficient strategy for multiple threads posting jobs and waiting for response from a single thread?

    - by jakewins
    In java, what is an efficient solution to the following problem: I have multiple threads (10-20 or so) generating jobs ("Job Creators"), and a single thread capable of performing them ("The worker"). Once a job creator has posted a job, it should wait for the job to finish, yielding no result other than "it's done", before it keeps going. For sending the jobs to the worker thread, I think a ring buffer or similar standard fan-in setup would perhaps be a good approach? But for a Job Creator to find out that her job has been done, I'm not so sure.. The job creators could sleep, and the worker interrupt them when done.. Or each job creator could have an atomic boolean that it checks, and that the worker sets. I dunno, neither of those feel very nice. I'd like to do it with as few (none, if possible) locks as absolutely possible. So to be clear: What I'm looking for is speed, not necessarily simplicity. Does anyone have any suggestions? Links to reading about concurrency strategies would also be very welcome!

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  • How good is the memory mapped Circular Buffer on Wikipedia?

    - by abroun
    I'm trying to implement a circular buffer in C, and have come across this example on Wikipedia. It looks as if it would provide a really nice interface for anyone reading from the buffer, as reads which wrap around from the end to the beginning of the buffer are handled automatically. So all reads are contiguous. However, I'm a bit unsure about using it straight away as I don't really have much experience with memory mapping or virtual memory and I'm not sure that I fully understand what it's doing. What I think I understand is that it's mapping a shared memory file the size of the buffer into memory twice. Then, whenever data is written into the buffer it appears in memory in 2 places at once. This allows all reads to be contiguous. What would be really great is if someone with more experience of POSIX memory mapping could have a quick look at the code and tell me if the underlying mechanism used is really that efficient. Am I right in thinking for example that the file in /dev/shm used for the shared memory always stays in RAM or could it get written to the hard drive (performance hit) at some point? Are there any gotchas I should be aware of? As it stands, I'm probably going to use a simpler method for my current project, but it'd be good to understand this to have it in my toolbox for the future. Thanks in advance for your time.

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  • Do all the HTML5 storage systems work together ?

    - by azera
    While there are a lot of good stuff about html5, one thing I don't get is the redondant storage mechanism, first there is localstorage and sessionstorage, which are key value stores, one is for one instance of the app ("one tab"), and the other works for all the instances of that application so they can share data. Both are saved when you close your browser and have a limited size (usually 5MB), that's great and everything would be nice if we stopped there. But then there is the "Web SQL Database", which has the same security system as the localstorage, the same size limit, the same everything except it works like/is sqlite, with tables and sql syntax and all of that. And the bummer is, they don't work on the same data at all ! This is not two way to access your data, this is really two storage for every html 5 app out there (not created by default yes, but still you see my point). What I would like to know is, is there a reason for both of this mechanisms to exist at the same time ? Or did they just look at sql and nosql movement to pick the best then went "screw it let's add both !" ? Why not implement local/session storage as a table inside web sql db ?

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  • How to return a record from function, executed by INSERT/UPDATE rule (trigger)?

    - by seas
    Do the following scheme for my database: create sequence data_sequence; create table data_table { id integer primary key; field varchar(100); }; create view data_view as select id, field from data_table; create function data_insert(_new data_view) returns data_view as $$declare _id integer; _result data_view%rowtype; begin _id := nextval('data_sequence'); insert into data_table(id, field) values(_id, _new.field); select * into _result from data_view where id = _id; return _result; end; $$ language plpgsql; create rule insert as on insert to data_view do instead select data_insert(new); Then type in psql: insert into data_view(field) values('abc'); Would like to see something like: id | field ----+--------- 1 | abc Instead see: data_insert ------------- (1, "abc") Is it possible to fix this somehow? Thanks for any ideas. Ultimate idea is to use this in other functions, so that I could obtain id of just inserted record without selecting for it from scratch. Something like: insert into data_view(field) values('abc') returning id into my_variable would be nice but doesn't work with error: ERROR: cannot perform INSERT RETURNING on relation "data_view" HINT: You need an unconditional ON INSERT DO INSTEAD rule with a RETURNING clause. I don't really understand that HINT. I use PostgreSQL 8.4.

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  • Java: which configuration framework to use?

    - by Laimoncijus
    Hi, I need to decide which configuration framework to use. At the moment I am thinking between using properties files and XML files. My configuration needs to have some primitive grouping, e.g. in XML format would be something like: <configuration> <group name="abc"> <param1>value1</param1> <param2>value2</param2> </group> <group name="def"> <param3>value3</param3> <param4>value4</param4> </group> </configuration> or a properties file (something similar to log4j.properties): group.abc.param1 = value1 group.abc.param2 = value2 group.def.param3 = value3 group.def.param4 = value4 I need bi-directional (read and write) configuration library/framework. Nice feature would be - that I could read out somehow different configuration groups as different objects, so I could later pass them to different places, e.g. - reading everything what belongs to group "abc" as one object and "def" as another. If that is not possible I can always split single configuration object into smaller ones myself in the application initialization part of course. Which framework would best fit for me?

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  • Creating a Linq->HQL provider

    - by Mike Q
    Hi all, I have a client application that connects to a server. The server uses hibernate for persistence and querying so it has a set of annotated hibernate objects for persistence. The client sends HQL queries to the server and gets responses back. The client has an auto-generated set of objects that match the server hibernate objects for query results and basic persistence. I would like to support using Linq to query as well as Hql as it makes the queries typesafe and quicker to build (no more typos in HQL string queries). I've looked around at the following but I can't see how to get them to fit with what I have. NHibernate's Linq provider - requires using NHibernate ISession and ISessionFactory, which I don't have LinqExtender - requires a lot of annotations on the objects and extending a base type, too invasive What I really want is something that will generate give me a nice easy to process structure to build the HQL queries from. I've read most of a 15 page article written by one of the C# developers on how to create custom providers and it's pretty fraught, mainly because of the complexity of the expression tree. Can anyone suggest an approach for implementing Linq - HQL translation? Perhaps a library that will the cleanup of the expression tree into something more SQL/HQLish. I would like to support select/from/where/group by/order by/joins. Not too worried about subqueries.

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  • Why does jQuery fadeOut not work inside this setInterval loop?

    - by Clay McClure
    I'm trying to load random items into a div every few seconds, with a nice fadeOut/fadeIn transition between each load. Here's the code: <html> <body> <div id="item"></div> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script> <script type="text/javascript"> // Load a random item var item = $('#item'); function load_item() { item.fadeOut(5000, function() { item.load('http://dynamic.xkcd.com/comic/random/ #middleContent img', null, function() { item.fadeIn(5000); }); }); }; // Load initial featured item load_item(); // Schedule repeated loading setInterval(load_item, 15000); </script> </body> </html> This works fine the first time through, but on subsequent calls to load_item, the fadeOut() seems to stop working. It doesn't actually fade the #item div out, but jumps immediately into the callback function, ignoring the 5000 delay. What am I doing wrong?

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  • Tfs 2010: how to set up a corporate source server?

    - by bwerks
    Hi all, I'm looking for guidance in setting up a corporate source server, but when I google this topic the best I can come up with is articles and walkthrough concerned with configuring VS to use microsoft's public symbol servers for use with debugging .NET assemblies. Provided for background info, the environment I'm concerned with using is Vs2010/Tfs2010. Basically, the workflow I'm looking to facilitate is this: 1) customer reports problem with application 2) application of the appropriate version is installed on a virtual machine 3) developer repros bug attaching to process on virtual machine and leveraging source server (symbol server?) on corporate domain. This is the step I'm concerned with. 4) developer pinpoints problem fixes bug in workspace. 5) developer performs a dll swap on VM to test changes? (side topic, not sure on this) 6) normal development/source control workflows. Any advice is welcome! Edit: since writing this, I have stumbled on this article, which is a nice writeup on the configuration of source server for TFS 2008. Has anyone adapted this for Tfs 2010?

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  • To OpenID or not to OpenID? Is it worth it?

    - by Eloff
    Does OpenID improve the user experience? Edit Not to detract from the other comments, but I got one really good reply below that outlined 3 advantages of OpenID in a rational bottom line kind of way. I've also heard some whisperings in other comments that you can get access to some details on the user through OpenID (name? email? what?) and that using that it might even be able to simplify the registration process by not needing to gather as much information. Things that definitely need to be gathered in a checkout process: Full name Email (I'm pretty sure I'll have to ask for these myself) Billing address Shipping address Credit card info There may be a few other things that are interesting from a marketing point of view, but I wouldn't ask the user to manually enter anything not absolutely required during the checkout process. So what's possible in this regard? /Edit (You may have noticed stackoverflow uses OpenID) It seems to me it is easier and faster for the user to simply enter a username and password in a signup form they have to go through anyway. I mean you don't avoid entering a username and password either with OpenID. But you avoid the confusion of choosing a OpenID provider, and the trip out to and back from and external site. With Microsoft making Live ID an OpenID provider (More Info), bringing on several hundred million additional accounts to those provided by Google, Yahoo, and others, this question is more important than ever. I have to require new customers to sign up during the checkout process, and it is absolutely critical that the experience be as easy and smooth as possible, every little bit harder it becomes translates into lost sales. No geek factor outweighs cold hard cash at the end of the day :) OpenID seems like a nice idea, but the implementation is of questionable value. What are the advantages of OpenID and is it really worth it in my scenario described above?

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  • What good open source programs exist for fuzzing popular image file types?

    - by JohnnySoftware
    I am looking for a free, open source, portable fuzzing tool for popular image file types that is written in either Java, Python, or Jython. Ideally, it would accept specifications for the fuzzable fields using some kind of declarative constraints. Non-procedural grammar for specifying constraints are greatly preferred. Otherwise, might as well write them all in Python or whatever. Just specifying ranges of valid values or expressions for them. Ideally, it would support some kind of generative programming to export the fuzzer into various programming languages to suit cases where more customization was required. If it supported a direct-manipulation GUI for controlling parameter values and ranges, that would be nice too. The file formats that should be supported are: GIF JPEG PNG So basically, it should be sort of a toolkit consisting of ready-to-run utility, a framework or library, and be capable of generating the fuzzed files directly as well as from programs it generates. It needs to be simple so that test images can be created quickly. It should have a batch capability for creating a series of images. Creating just one at a time would be too painful. I do not want a hacking tool, just a QA tool. Basically, I just want to address concerns that it is taking too long to get commonplace image rendering/parsing libraries stable and trustworthy.

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  • Installing Mercurial on Windows Apache XAMPP Tutorial

    - by Tim Dellas
    After asking this question (http://stackoverflow.com/questions/2675764/xampp-mercurial-installation-on-windows-apache-hgwebdir-cgi-script-error) and reading though the whole internet including this question (http://stackoverflow.com/questions/644322/how-do-i-get-mercurials-hgwebdir-working-on-windows) and all its links for about 10 hours, I seem to not be able to find a solution. I begun with this tutorial http://mercurial.selenic.com/wiki/HgWebDirStepByStep ... and I really don't want to install ancient versions of Mercurial. I got my windows-apache to run Python scripts, CGI-Scripts, publish them in the wild, but hgwebdir just won't work. Question 1: Can someone please enrich his personal blog with a tutorial on how to install MERCURIAL on a WINDOWS XAMPP installation and make it visible to the world? I guarantee a lot of pageviews, as this is not a trivial problem. And this would sincerely help a lot of other people I guess. Question 2: For example, even after browsing half a day through everywhere, I just cannot find out, which version of python I need to pair with the freshest version of mercurial, and I get the "magic number is wrong"-error. This would be my question, if noone has time to make up a nice blogpost. Sorry for being a bit frustrated.

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  • What database strategy to choose for a large web application

    - by Snoopy
    I have to rewrite a large database application, running on 32 servers. The hardware is up to date, each machine has two quad core Xeon and 32 GByte RAM. The database is multi-tenant, each customer has his own file, around 5 to 10 GByte each. I run around 50 databases on this hardware. The app is open to the web, so I have no control on the load. There are no really complex queries, so SQL is not required if there is a better solution. The databases get updated via FTP every day at midnight. The database is read-only. C# is my favourite language and I want to use ASP.NET MVC. I thought about the following options: Use two big SQL servers running SQL Server 2012 to serve the 32 servers with data. On the 32 servers running IIS hosting providing REST services. Denormalize the database and use Redis on each webserver. Use booksleeve as a Redis client. Use a combination of SQL Server and Redis Use SQL Server 2012 together with Hadoop Use Hadoop without SQL Server What is the best way for a read-only database, to get the best performance without loosing maintainability? Does Map-Reduce make sense at all in such a scenario? The reason for the rewrite is, the old app written in C++ with ISAM technology is too slow, the interfaces are old fashioned and not nice to use from an website, especially when using ajax. The app uses a relational datamodel with many tables, but it is possible to write one accerlerator table where all queries can be performed on, and all other information from the other tables are possible by a simple key lookup.

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  • Run Javascript on the body of a Gmail message

    - by saturn
    I want to display LaTeX math in the gmail messages that I receive, so that for example $\mathbb P^2$ would show as a nice formula. Now, there are several Javascripts available (for example, this one, or MathJax which would do the job, I just need to call them at the right time to manipulate the gmail message. I know that this is possible to do in "basic HTML" and "print" views. Is it possible to do in the standard Gmail view? I tried to insert a call to the javascript right before the "canvas_frame" iframe, but that did not work. My suspicion is that manipulating a Gmail message by any Javascript would be a major security flaw (think of all the malicious links one could insert) and that Google does everything to prevent this. And so the answer to my question is probably 'no'. Am I right in this? Of course, it would be very easy for Google to implement viewing of LaTeX and MathML math simply by using MathJax on their servers. I made the corresponding Gmail Lab request, but no answer, and no interest from Google apparently. So, again: is this possible to do without Google's cooperation, on the client side?

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  • Javascript Getting Objects to Fallback to One Another

    - by Ian
    Here's a ugly bit of Javascript it would be nice to find a workaround. Javascript has no classes, and that is a good thing. But it implements fallback between objects in a rather ugly way. The foundational construct should be to have one object that, when a property fails to be found, it falls back to another object. So if we want a to fall back to b we would want to do something like: a = {sun:1}; b = {dock:2}; a.__fallback__ = b; then a.dock == 2; But, Javascript instead provides a new operator and prototypes. So we do the far less elegant: function A(sun) { this.sun = sun; }; A.prototype.dock = 2; a = new A(1); a.dock == 2; But aside from elegance, this is also strictly less powerful, because it means that anything created with A gets the same fallback object. What I would like to do is liberate Javascript from this artificial limitation and have the ability to give any individual object any other individual object as its fallback. That way I could keep the current behavior when it makes sense, but use object-level inheritance when that makes sense. My initial approach is to create a dummy constructor function: function setFallback(from_obj, to_obj) { from_obj.constructor = function () {}; from_obj.constructor.prototype = to_obj; } a = {sun:1}; b = {dock:2}; setFallback(a, b); But unfortunately: a.dock == undefined; Any ideas why this doesn't work, or any solutions for an implementation of setFallback? (I'm running on V8, via node.js, in case this is platform dependent)

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  • Delivering activity feed items in a moderately scalable way

    - by sotangochips
    The application I'm working on has an activity feed where each user can see their friends' activity (much like Facebook). I'm looking for a moderately scalable way to show a given users' activity stream on the fly. I say 'moderately' because I'm looking to do this with just a database (Postgresql) and maybe memcached. For instance, I want this solution to scale to 200k users each with 100 friends. Currently, there is a master activity table that stores the rendered html for the given activity (Jim added a friend, George installed an application, etc.). This master activity table keeps the source user, the html, and a timestamp. Then, there's a separate ('join') table that simply keeps a pointer to the person who should see this activity in their friend feed, and a pointer to the object in the main activity table. So, if I have 100 friends, and I do 3 activities, then the join table will then grow to 300 items. Clearly this table will grow very quickly. It has the nice property, though, that fetching activity to show to a user takes a single (relatively) inexpensive query. The other option is to just keep the main activity table and query it by saying something like: select * from activity where source_user in (1, 2, 44, 2423, ... my friend list) This has the disadvantage that you're querying for users who may never be active, and as your friend list grows, this query can get slower and slower. I see the pros and the cons of both sides, but I'm wondering if some SO folks might help me weigh the options and suggest one way or they other. I'm also open to other solutions, though I'd like to keep it simple and not install something like CouchDB, etc. Many thanks!

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  • check properties of two objects for changes

    - by k-hoffmann
    Hi, i have to develop a mechanism to check two object properties for changes. All properties which are needed to check are marked with an attribute. Atm i - read all properties from acutal object via linq - read the corresponding property from old object - fill an own object with the two properties (old and new value) In Code the call to the workerclass looks like this public void CreateHistoryMap(BaseEntity actual, BaseEntity old) { CreateHistoryMap(actualEntity, oldEntity) .ForEach(mapEntry => CreateHistoryEntry(mapEntry), mapEntry => IfChangesDetected(mapEntry)); } CreateHistoryMap builds up the HistoryMapEntry which contains the two properties. CreateHistoryEntry build up the object which is saved to database, the IfChangesDetected check the object for changes. I have to handle own special application types to generate history values to database (like concatinating list values and so on). My problem is now, that i have to read the values of the properties twice - for change detection - and for the concreate CreateHistoryEntry How can i eliminate this problem or how can i implement the change tracking scenario with the nice c# 3.5 features? Thanks a lot.

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  • How to see external libraries code when debugging

    - by Sanva
    Hello!! First of all... this is my message #1 in this place, so... please be nice with me ;) I just started recently to study Gnome apps/libraries and I found that debuggers are an excellent way to learn, because seeing the code running helps a lot in understanding the structure of the program. But I have a problem. For example, debugging gnome-panel I found a lot of calls to external functions (basically the GTK+ functions), and although pretending to see all the code of all the functions applications like this call would be crazy, there are a lot that will be very interesting to see in action. The problem is that the debugger hasn't the code of those libraries loaded and it can't show it to me —at most it shows the line number where the execution is. I'm using Nemiver and when it tries to enter in an external function it claims because it can't find a file it supposed to be somewhere. For example, trying to enter in gtk_window_set_default_icon_name it tries to load /build/buildd/gtk+2.0-2.16.1/gtk/gtkwindow.c, and calling XSetIOErrorHandler, ../../src/ErrHndlr.c. So now I think that I'm doing something wrong... Why Nevimer are looking for those source files in those places?? My system does not even have the /build/buildd/ folders... and I don't know if I'm doing something wrong or I need to install somethig or what. Any suggestion? How do you debug this kind of applications? Best regards and thanks a lot for your time —and forgive me if my English is bad.

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  • How do I implement aasm in Rails 3 for what I want it to do?

    - by marcamillion
    I am a Rails n00b and have been advised that in order for me to keep track of the status of my user's accounts (i.e. paid, unpaid (and therefore disabled), free trial, etc.) I should use an 'AASM' gem. So I found one that seems to be the most popular: https://github.com/rubyist/aasm But the instructions are pretty vague. I have a Users model and a Plan model. User's model manages everything you might expect (username, password, first name, etc.). Plan model manages the subscription plan that users should be assigned to (with the restrictions). So I am trying to figure out how to use the AASM gem to do what I want to do, but no clue where to start. Do I create a new model ? Then do I setup a relationship between my User model and the model for AASM ? How do I setup a relationship? As in, a user 'has_many' states ? That doesn't seem to make much sense to me. Any guidance would be really appreciated. Thanks. Edit: If anyone else is confused by AASMs like myself, here is a nice explanation of their function in Rails by the fine folks at Envy Labs: http://blog.envylabs.com/2009/08/the-rails-state-machine/ Edit2: How does this look: include AASM aasm_column :current_state aasm_state :paid aasm_state :free_trial aasm_state :disabled #this is for accounts that have exceed free trial and have not paid #aasm_state :free_acct aasm_event :pay do transitions :to => :paid, :from => [:free_trial, :disabled] transitions :to => :disabled, :from => [:free_trial, :paid] end

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  • No GPS Update retrieved? Problem in Code?

    - by poeschlorn
    Hello mates, I've got a serious problem with my GPS on my Nexus One: I wrote a kind of hello world with GPS, but the Toast that should be displayed isn't :( I don't know what I'm doing wrong...maybe you could help me getting this work. Here's my code: package gps.test; import android.app.Activity; import android.content.Context; import android.location.Location; import android.location.LocationListener; import android.location.LocationManager; import android.os.Bundle; import android.widget.Toast; public class GPS extends Activity { private LocationManager lm; private LocationListener locationListener; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // ---use the LocationManager class to obtain GPS locations--- lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE); locationListener = new MyLocationListener(); lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 100, 1, locationListener); } private class MyLocationListener implements LocationListener { @Override public void onLocationChanged(Location loc) { if (loc != null) { Toast.makeText( getBaseContext(), "Location changed : Lat: " + loc.getLatitude() + " Lng: " + loc.getLongitude(), Toast.LENGTH_SHORT).show(); } } @Override public void onProviderDisabled(String provider) { // TODO Auto-generated method stub } @Override public void onProviderEnabled(String provider) { // TODO Auto-generated method stub } @Override public void onStatusChanged(String provider, int status, Bundle extras) { // TODO Auto-generated method stub } } } Theoretically there should be a new toast every 100 milliseconds, shouldn't it? Or at least, when I change my position by one meter!? I've no idea why it doesn't. I must admit I'm new to the topic, maybe I've missed something? It would be great if you could give me a hint :) nice greetings, poeschlorn

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  • PHP OOP: Avoid Singleton/Static Methods in Domain Model Pattern

    - by sunwukung
    I understand the importance of Dependency Injection and its role in Unit testing, which is why the following issue is giving me pause: One area where I struggle not to use the Singleton is the Identity Map/Unit of Work pattern (Which keeps tabs on Domain Object state). //Not actual code, but it should demonstrate the point class Monitor{//singleton construction omitted for brevity static $members = array();//keeps record of all objects static $dirty = array();//keeps record of all modified objects static $clean = array();//keeps record of all clean objects } class Mapper{//queries database, maps values to object fields public function find($id){ if(isset(Monitor::members[$id]){ return Monitor::members[$id]; } $values = $this->selectStmt($id); //field mapping process omitted for brevity $Object = new Object($values); Monitor::new[$id]=$Object return $Object; } $User = $UserMapper->find(1);//domain object is registered in Id Map $User->changePropertyX();//object is marked "dirty" in UoW // at this point, I can save by passing the Domain Object back to the Mapper $UserMapper->save($User);//object is marked clean in UoW //but a nicer API would be something like this $User->save(); //but if I want to do this - it has to make a call to the mapper/db somehow $User->getBlogPosts(); //or else have to generate specific collection/object graphing methods in the mapper $UserPosts = $UserMapper->getBlogPosts(); $User->setPosts($UserPosts); Any advice on how you might handle this situation? I would be loathe to pass/generate instances of the mapper/database access into the Domain Object itself to satisfy DI - At the same time, avoiding that results in lots of calls within the Domain Object to external static methods. Although I guess if I want "save" to be part of its behaviour then a facility to do so is required in its construction. Perhaps it's a problem with responsibility, the Domain Object shouldn't be burdened with saving. It's just quite a neat feature from the Active Record pattern - it would be nice to implement it in some way.

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  • Fun with casting and inheritance

    - by Vaccano
    NOTE: This question is written in a C# like pseudo code, but I am really going to ask which languages have a solution. Please don't get hung up on syntax. Say I have two classes: class AngleLabel: CustomLabel { public bool Bold; // code to allow the label to be on an angle } class Label: CustomLabel { public bool Bold; // Code for a normal label // Maybe has code not in an AngleLabel (align for example). } They both decend from this class: class CustomLabel: Control { protected bool Bold; } The bold field is exposed as public in the descended classes. No interfaces are available on the classes. Now, I have a method that I want to beable to pass in a CustomLabel and set the Bold property. Can this be done without having to 1) find out what the real class of the object is and 2) cast to that object and then 3) make seperate code for each variable of each label type to set bold. Kind of like this: public void SetBold(customLabel: CustomLabel) { AngleLabel angleLabel; NormalLabel normalLabel; if (angleLabel is AngleLabel ) { angleLabel= customLabel as AngleLabel angleLabel.Bold = true; } if (label is Label) { normalLabel = customLabel as Label normalLabel .Bold = true; } } It would be nice to maybe make one cast and and then set bold on one variable. What I was musing about was to make a fourth class that just exposes the bold variable and cast my custom label to that class. Would that work? If so, which languages would it work for? (This example is drawn from an old version of Delphi (Delphi 5)). I don't know if it would work for that language, (I still need to try it out) but I am curious if it would work for C++, C# or Java. If not, any ideas on what would work? (Remember no interfaces are provided and I can not modify the classes.) Any one have a guess?

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  • What's the best way of accessing a DRb object (e.g. Ruby Queue) from Scala (and Java)?

    - by Tom Morris
    I have built a variety of little scripts using Ruby's very simple Queue class, and share the Queue between Ruby and JRuby processes using DRb. It would be nice to be able to access these from Scala (and maybe Java) using JRuby. I've put together something Scala and the JSR-223 interface to access jruby-complete.jar. import javax.script._ class DRbQueue(host: String, port: Int) { private var engine = DRbQueue.factory.getEngineByName("jruby") private var invoker = engine.asInstanceOf[Invocable] engine.eval("require \"drb\" ") private var queue = engine.eval("DRbObject.new(nil, \"druby://" + host + ":" + port.toString + "\")") def isEmpty(): Boolean = invoker.invokeMethod(this.queue, "empty?").asInstanceOf[Boolean] def size(): Long = invoker.invokeMethod(this.queue, "length").asInstanceOf[Long] def threadsWaiting: Long = invoker.invokeMethod(this.queue, "num_waiting").asInstanceOf[Long] def offer(obj: Any) = invoker.invokeMethod(this.queue, "push", obj.asInstanceOf[java.lang.Object]) def poll(): Any = invoker.invokeMethod(this.queue, "pop") def clear(): Unit = { invoker.invokeMethod(this.queue, "clear") } } object DRbQueue { var factory = new ScriptEngineManager() } (It conforms roughly to java.util.Queue interface, but I haven't declared the interface because it doesn't implement the element and peek methods because the Ruby class doesn't offer them.) The problem with this is the type conversion. JRuby is fine with Scala's Strings - because they are Java strings. But if I give it a Scala Int or Long, or one of the other Scala types (List, Set, RichString, Array, Symbol) or some other custom type. This seems unnecessarily hacky: surely there has got to be a better way of doing RMI/DRb interop without having to use JSR-223 API. I could either make it so that the offer method serializes the object to, say, a JSON string and takes a structural type of only objects that have a toJson method. I could then write a Ruby wrapper class (or just monkeypatch Queue) to would parse the JSON. Is there any point in carrying on with trying to access DRb from Java/Scala? Might it just be easier to install a real message queue? (If so, any suggestions for a lightweight JVM-based MQ?)

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  • How is timezone handled in the lifecycle of an ADO.NET + SQL Server DateTime column?

    - by stimpy77
    Using SQL Server 2008. This is a really junior question and I could really use some elaborate information, but the information on Google seems to dance around the topic quite a bit and it would be nice if there was some detailed elaboration on how this works... Let's say I have a datetime column and in ADO.NET I set it to DateTime.UtcNow. 1) Does SQL Server store DateTime.UtcNow accordingly, or does it offset it again based on the timezone of where the server is installed, and then return it offset-reversed when queried? I think I know that the answer is "of course it stores it without offsetting it again" but want to be certain. So then I query for it and cast it from, say, an IDataReader column to a DateTime. As far as I know, System.DateTime has metadata that internally tracks whether it is a UTC DateTime or it is an offsetted DateTime, which may or may not cause .ToLocalTime() and .ToUniversalTime() to have different behavior depending on this state. So, 2) Does this casted System.DateTime object already know that it is a UTC DateTime instance, or does it assume that it has been offset? Now let's say I don't use UtcNow, I use DateTime.Now, when performing an ADO.NET INSERT or UPDATE. 3) Does ADO.NET pass the offset to SQL Server and does SQL Server store DateTime.Now with the offset metadata? So then I query for it and cast it from, say, an IDataReader column to a DateTime. 4) Does this casted System.DateTime object already know that it is an offset time, or does it assume that it is UTC?

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