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• Hashing Function for Map C++

  - by Josh

  I am trying to determine a hash function which takes an input (i, k) and determines a unique solution. The possible inputs for (i, k) range from 0 to 100. Consider each (i, k) as a position of a node in a trinomial tree. Ex: (0, 0) can diverge to (1, 1) (1, 0) (1, -1). (1, 1) can diverge to (2, 2) (2, 1) (2, 0). Sample given here: http://www.google.com/imgres?imgurl=http://sfb649.wiwi.hu-berlin.de/fedc_homepage/xplore/tutorials/stfhtmlimg1156.gif&imgrefurl=http://sfb649.wiwi.hu-berlin.de/fedc_homepage/xplore/tutorials/stfhtmlnode41.html&h=413&w=416&sz=4&tbnid=OegDZu-yeVitZM:&tbnh=90&tbnw=91&zoom=1&usg=__9uQWDNYNLV14YioWWbrqPgfa3DQ=&docid=2hhitNyRWjI_DM&hl=en&sa=X&ei=xAfFUIbyG8nzyAHv2YDICg&ved=0CDsQ9QEwAQ I am using a map map <double, double> hash_table I need a key value to be determined from pairs (i, k) to hash to to value for that (i, k) So far I was only able to come up with linear functions such as: double Hash_function(int i, int k) { //double val = pow(i, k) + i; //return (val % 4294967296); return (i*3.1415 + k*i*9.12341); } However, I cannot determine a unique key with a certain (i, k). What kind of functions can I use to help me do so?

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• Howw to add new value with generic Repository if there are foreign keys (EF-4)?

  - by Phsika

  i try to write a kind of generic repository to add method. Everything is ok to add but I have table which is related with two tables with FOREIGN KEY.But Not working because of foreign key public class DomainRepository<TModel> : IDomainRepository<TModel> where TModel : class { #region IDomainRepository<T> Members private ObjectContext _context; private IObjectSet<TModel> _objectSet; public DomainRepository() { } public DomainRepository(ObjectContext context) { _context = context; _objectSet = _context.CreateObjectSet<TModel>(); } //do something..... public TModel Add<TModel>(TModel entity) where TModel : IEntityWithKey { EntityKey key; object originalItem; key = _context.CreateEntityKey(entity.GetType().Name, entity); _context.AddObject(key.EntitySetName, entity); _context.SaveChanges(); return entity; } //do something..... } Calling REPOSITORY: //insert-update-delete public partial class AddtoTables { public table3 Add(int TaskId, int RefAircraftsId) { using (DomainRepository<table3> repTask = new DomainRepository<table3>(new TaskEntities())) { return repTask.Add<table3>(new table3() { TaskId = TaskId, TaskRefAircraftsID = RefAircraftsId }); } } } How to add a new value if this table includes foreign key relation

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• codeigniter active record and mysql

  - by sea_1987

  I am running a query with Active Record in a modal of my codeigniter application, the query looks like this, public function selectAllJobs() { $this->db->select('*') ->from('job_listing') ->join('job_listing_has_employer_details', 'job_listing_has_employer_details.employer_details_id = job_listing.id', 'left'); //->join('employer_details', 'employer_details.users_id = job_listing_has_employer_details.employer_details_id'); $query = $this->db->get(); return $query->result_array(); } This returns an array that looks like this, [0]=> array(13) { ["id"]=> string(1) "1" ["job_titles_id"]=> string(1) "1" ["location"]=> string(12) "Huddersfield" ["location_postcode"]=> string(7) "HD3 4AG" ["basic_salary"]=> string(19) "£20,000 - £25,000" ["bonus"]=> string(12) "php, html, j" ["benefits"]=> string(11) "Compnay Car" ["key_skills"]=> string(1) "1" ["retrain_position"]=> string(3) "YES" ["summary"]=> string(73) "Lorem Ipsum is simply dummy text of the printing and typesetting industry" ["description"]=> string(73) "Lorem Ipsum is simply dummy text of the printing and typesetting industry" ["job_listing_id"]=> NULL ["employer_details_id"]=> NULL } } The job_listing_id and employer_details_id return as NULL however if I run the SQL in phpmyadmin I get full set of results, the query i running in phpmyadmin is, SELECT * FROM ( `job_listing` ) LEFT JOIN `job_listing_has_employer_details` ON `job_listing_has_employer_details`.`employer_details_id` LIMIT 0 , 30 Is there a reason why I am getting differing results?

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• Linear Search with Jagged Array?

  - by Nerathas

  Hello, I have the following program that creates 100 random elements trough a array. Those 100 random value's are unique, and every value only gets displayed once. Although with the linear search it keeps looking up the entire array. How would i be able to get a Jagged Array into this, so it only "scans" the remaining places left? (assuming i keep the table at 100 max elements, so if one random value is generated the array holds 99 elements with linear search scans and on...) I assume i would have to implent the jagged array somewhere in the FoundLinearInArray? Hopefully this made any sence. Regards. private int ValidNumber(int[] T, int X, int Range) { Random RndInt = new Random(); do { X = RndInt.Next(1, Range + 1); } while (FoundLinearInArray(T, X)); return X; }/*ValidNumber*/ private bool FoundLinearInArray(int[] A, int X) { byte I = 0; while ((I < A.Length) && (A[I] != X)) { I++; } return (I < A.Length); }/*FoundInArray*/ public void FillArray(int[] T, int Range) { for (byte I = 0; I < T.Length; I++) { T[I] = ValidNumber(T, I, Range); } }/*FillArray*/

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• mysql_affected_rows() returns 0 for UPDATE statement even when an update actually happens

  - by Alex Moore

  I am trying to get the number of rows affected in a simple mysql update query. However, when I run this code below, PHP's mysql_affected_rows() always equals 0. No matter if foo=1 already (in which case the function should correctly return 0, since no rows were changed), or if foo currently equals some other integer (in which case the function should return 1). $updateQuery = "UPDATE myTable SET foo=1 WHERE bar=2"; mysql_query($updateQuery); if (mysql_affected_rows() > 0) { echo "affected!"; } else { echo "not affected"; // always prints not affected } The UPDATE statement itself works. The INT gets changed in my database. I have also double-checked that the database connection isn't being closed beforehand or anything funky. Keep in mind, mysql_affected_rows doesn't necessarily require you to pass a connection link identifier, though I've tried that too. Details on the function: mysql_affected_rows Any ideas? SOLUTION The part I didn't mention turned out to be the cause of my woes here. This PHP file was being called ten times consecutively in an AJAX call, though I was only looking at the value returned on the last call, ie. a big fat 0. My apologies!

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• Function to even out multiple arrays

  - by Moak

  Assume I have a function evenOut($array, $limit){ //returns exactly $limit items } and this data $animals = array(); $animals['barn'] = array_fill(0,20, 'b'); $animals['forest'] = array_fill(0,20, 'f'); $animals['house'] = array_fill(0,20, 'h'); $animals['mountain'] = array_fill(0,20, 'm'); I want to return a maximum of 10 animals, however they should be spread out evenly among the locations they come from. so if i did evenOut($animals,8); i'd get 2 of each('b','b','f','f','h','h','m','m',) evenOut($animals,2); should return ('b','f') if I have this data $animals = array(); $animals['barn'] = array_fill(0,1, 'b'); $animals['forest'] = array_fill(0,3, 'f'); $animals['house'] = array_fill(0,8, 'h'); $animals['mountain'] = array_fill(0,1, 'm'); evenOut($animals,8); expected result would be ('b','f','f','f','h','h','h','m',) evenOut($animals,10); expected result would be ('b','f','f','f','h','h','h','h','h','m',) $animals = array(); $animals['barn'] = array_fill(0,0, 'b'); $animals['forest'] = array_fill(0,3, 'f'); evenOut($animals,10); expected result would be ('f','f','f') I'm not sure how I should approach this, I am hoping there is a simple way

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• How do I pass dependency to object with Castle Windsor and MS Test?

  - by Nick

  I am trying to use Castle Windsor with MS Test. The test class only seems to use the default constructor. How do I configure Castle to resolve the service in the constructor? Here is the Test Class' constructors: private readonly IWebBrowser _browser; public DepressionSummaryTests() { } public DepressionSummaryTests(IWebBrowser browser) { _browser = browser; } My component in the app config looks like so: <castle> <components> <component id="browser" service="ConversationSummary.IWebBrowser, ConversationSummary" type="ConversationSummary.Browser" /> </components> </castle> Here is my application container: public class ApplicationContainer : WindsorContainer { private static IWindsorContainer container; static ApplicationContainer() { container = new WindsorContainer(new XmlInterpreter(new ConfigResource("castle"))); } private static IWindsorContainer Container { get { return container; } } public static IWebBrowser Browser { get { return (IWebBrowser) Container.Resolve("browser"); } } } MS test requires the default constructor. What am I missing? Thanks!

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• Insertion sort invariant assertion fails

  - by user1661211

  In the following code at the end of the for loop I use the assert function in order to test that a[i+1] is greater than or equal to a[i] but I get the following error (after the code below). Also in c++ the assert with the following seems to work just fine but in python (the following code) it does not seem to work...anyone know why? import random class Sorting: #Precondition: An array a with values. #Postcondition: Array a[1...n] is sorted. def insertion_sort(self,a): #First loop invariant: Array a[1...i] is sorted. for j in range(1,len(a)): key = a[j] i = j-1 #Second loop invariant: a[i] is the greatest value from a[i...j-1] while i >= 0 and a[i] > key: a[i+1] = a[i] i = i-1 a[i+1] = key assert a[i+1] >= a[i] return a def random_array(self,size): b = [] for i in range(0,size): b.append(random.randint(0,1000)) return b sort = Sorting() print sort.insertion_sort(sort.random_array(10)) The Error: Traceback (most recent call last): File "C:\Users\Albaraa\Desktop\CS253\Programming 1\Insertion_Sort.py", line 27, in <module> print sort.insertion_sort(sort.random_array(10)) File "C:\Users\Albaraa\Desktop\CS253\Programming 1\Insertion_Sort.py", line 16, in insertion_sort assert a[i+1] >= a[i] AssertionError

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• Time complexity of a powerset generating function

  - by Lirik

  I'm trying to figure out the time complexity of a function that I wrote (it generates a power set for a given string): public static HashSet<string> GeneratePowerSet(string input) { HashSet<string> powerSet = new HashSet<string>(); if (string.IsNullOrEmpty(input)) return powerSet; int powSetSize = (int)Math.Pow(2.0, (double)input.Length); // Start at 1 to skip the empty string case for (int i = 1; i < powSetSize; i++) { string str = Convert.ToString(i, 2); string pset = str; for (int k = str.Length; k < input.Length; k++) { pset = "0" + pset; } string set = string.Empty; for (int j = 0; j < pset.Length; j++) { if (pset[j] == '1') { set = string.Concat(set, input[j].ToString()); } } powerSet.Add(set); } return powerSet; } So my attempt is this: let the size of the input string be n in the outer for loop, must iterate 2^n times (because the set size is 2^n). in the inner for loop, we must iterate 2*n times (at worst). 1. So Big-O would be O((2^n)*n) (since we drop the constant 2)... is that correct? And n*(2^n) is worse than n^2. if n = 4 then (4*(2^4)) = 64 (4^2) = 16 if n = 100 then (10*(2^10)) = 10240 (10^2) = 100 2. Is there a faster way to generate a power set, or is this about optimal?

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• Returning reference to object is not changing the address in c++

  - by ashish-sangwan

  I am trying to understand functions returning a reference. For that I have written a simple program: #include<iostream> using namespace std; class test { int i; friend test& func(); public: test(int j){i=j;} void show(){cout<<i<<endl;} }; test& func() { test temp(10); return temp; //// Address of temp=0xbfcb2874 } int main() { test obj1(50); // Address of obj1=0xbfcb28a0 func()=obj1; <= Problem:The address of obj1 is not changing obj1.show(); // // Address of obj1=0xbfcb28a0 return 0; } I ran the program using gdb and observed that the address of obj1 still remains same, but I expect it to get changed to 0xbfcb2874. I am not clear with the concept. Please help.

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• Unit-testing a directive with isolated scope and bidirectional value

  - by unludo

  I want to unit test a directive which looks like this: angular.module('myApp', []) .directive('myTest', function () { return { restrict: 'E', scope: { message: '='}, replace: true, template: '<div ng-if="message"><p>{{message}}</p></div>', link: function (scope, element, attrs) { } }; }); Here is my failing test: describe('myTest directive:', function () { var scope, compile, validHTML; validHTML = '<my-test message="message"></my-test>'; beforeEach(module('myApp')); beforeEach(inject(function($compile, $rootScope){ scope = $rootScope.$new(); compile = $compile; })); function create() { var elem, compiledElem; elem = angular.element(validHTML); compiledElem = compile(elem)(scope); scope.$digest(); return compiledElem; } it('should have a scope on root element', function () { scope.message = 'not empty'; var el = create(); console.log(el.text()); expect(el.text()).toBeDefined(); expect(el.text()).not.toBe(''); }); }); Can you spot why it's failing? The corresponding jsFiddle Thanks :)

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• Ajax request not receiving xml from Django

  - by amougeot

  I have a Django server which handles requests to a URL which will return some HTML for use in an image gallery. I can navigate to the URL and the browser will display the HTML that is returned, but I can't get that same HTML by doing an AJAX call (using jQuery) to the same URL. This is the view that generates the response: def gallery_images(request, gallery_name): return render_to_response('galleryimages.html', {'images': get_images_of_gallery(gallery_name)}, mimetype='text/xml') This is the 'galleryimages.html' template: {% for image in images %} <div id="{{image.name}}big"> <div class="actualImage" style="background-image:url({{image.image.name}});"> <h1>{{image.caption|safe}}</h1> </div> </div> {% endfor %} This is the jQuery call I am making: $("#allImages").load("http://localhost:8000/galleryimages/Web"); However, this loads nothing into my #allImages div. I've used firebug and ran jQuery's Ajax method .get("http://localhost:8000/galleryimages/Web") and firebug says that the response text is completely empty. When I check my Django server log, this is the entry I see for when I navigate to the URL manually, through my browser: [16/Jan/2010 17:34:10] "GET /galleryimages/Web HTTP/1.1" 200 215 This is the entry in the server log for when I make the AJAX call: [16/Jan/2010 17:36:19] "OPTIONS /galleryimages/Web HTTP/1.1" 200 215 Why does the AJAX request not get the xml that my Django page is serving?

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• Java Days & Bookings

  - by sys_debug

  Ok this is an extension of a question I asked about earlier yet this is the next step that is unclear to me. Everything else will be ready and this part is driving me mad! some members provided great help and I already made progress with that info, but this is just another obstacle. I am creating a booking object (as was suggested) that will have a start date and end date. each booking will also have a number of seats associated with it (that I require to reserve). The total available number of seats any given day 46 (as the total capacity of the hall is 46 seats). so in assumption that I have a booking to be made in the system, and start date is 1st jan and end date is 10th jan. The question is how can I check the remaining seats in all those days between the range to see if requested number could be hosted or not? and then when the second booking is made, it will have to see that the days in this range already have less than 46 and decrement further if possible to host the reservation. one of the members, and I appreciate his effort, gladly contributed a method to compare if this booking is after or before the existing bookings. The code provided is here: public boolean overlapsWithExisting(Booking booking) { final Date early = booking.getStart(); final Date late = booking.getEnd(); for(Booking existing : existingBookings) { if(!(early.isAfter(existing.getEnd() || late.isBefore(existing.getStart())) return true; } return false; } I just want to know how to associate 46 with each day and keep record of days that are decremented by bookings. Thanks and reallllllly appreciated :D

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• Garbage data from serial port.

  - by sasayins

  Hi I wrote a code in Linux platform that read the data in serial port, my code below: int fd; char *rbuff=NULL; struct termios new_opt, old_opt; int ret; fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY); if( fd == -1 ) { printf("Can't open file: %s\n", strerror(errno)); return -1; } tcgetattr(fd, &old_opt); new_opt.c_cflag = B115200 | CS8 | CLOCAL | CREAD; new_opt.c_iflag = IGNPAR /*| ICRNL*/; new_opt.c_oflag = 0; new_opt.c_lflag = ICANON; tcsetattr(fd, TCSANOW, &new_opt); rbuff = malloc(NBUFF); printf("reading..\n"); memset(rbuff,0x00,NBUFF); ret = read(fd, rbuff, NBUFF); printf("value:%s",rbuff); if(ret == -1) { printf("Read error:%s\n",strerror(errno)); return -1; } tcsetattr(fd, TCSANOW, &old_opt); close(fd); My problem is the code above doesn't read the first data that was transmitted, then the second transmission the data is garbage, then the third is the normal data. Did I missed a setting in the serial port? Thanks.

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• Calling arrays from other methods in a different class

  - by Jake H

  Hello, I need help dealing with an array in my java program. in my first class, "test", I set 4 variables and then send them to my other class (test2). arr[i] = new test2(id, fname, lname, case); at that point, variables are set and then I want to return those variables. So in the test2 class, I have a method that strictly returns one of those variables public int getId(){ return id; } I understand this is a little stupid, but professor gets what professor wants I guess. What I want to do now is in my main method in "test" I want to retrieve that variable and sort the array based on that int. Unfortunately, I have to create my own sort function, but I think this would work for what I want to do. for(j = 0; j < arr.length; j++){ int indexMin =j; for(i = j; i < arr.length;i++){ if(arr[i] < arr[indexMin]){ indexMin = i; } } int tmp = arr[j]; arr[j] = arr[indexMin]; arr[indexMin] = tmp; } I appreciate any help anyone could provide. Thank you

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• Bitmap issue in Samsung Galaxy S3

  - by user1531240

  I wrote a method to change Bitmap from camera shot : public Bitmap bitmapChange(Bitmap bm) { /* get original image size */ int w = bm.getWidth(); int h = bm.getHeight(); /* check the image's orientation */ float scale = w / h; if(scale < 1) { /* if the orientation is portrait then scaled and show on the screen*/ float scaleWidth = (float) 90 / (float) w; float scaleHeight = (float) 130 / (float) h; Matrix mtx = new Matrix(); mtx.postScale(scaleWidth, scaleHeight); Bitmap rotatedBMP = Bitmap.createBitmap(bm, 0, 0, w, h, mtx, true); return rotatedBMP; } else { /* if the orientation is landscape then rotate 90 */ float scaleWidth = (float) 130 / (float) w; float scaleHeight = (float) 90 / (float) h; Matrix mtx = new Matrix(); mtx.postScale(scaleWidth, scaleHeight); mtx.postRotate(90); Bitmap rotatedBMP = Bitmap.createBitmap(bm, 0, 0, w, h, mtx, true); return rotatedBMP; } } It works fine in another Android device, even Galaxy Nexus but in Samsung Galaxy S3, the scaled image doesn't show on screen. I tried to mark the bitmapChange method , let it show the original size Bitmap on screen but S3 also show nothing on screen. The information of variables in eclipse is here. The information of sony xperia is here. xperia and other device is working fine.

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• Binary serialization and deserialization without creating files (via strings)

  - by the_V

  Hi, I'm trying to create a class that will contain functions for serializing/deserializing objects to/from string. That's what it looks like now: public class BinarySerialization { public static string SerializeObject(object o) { string result = ""; if ((o.GetType().Attributes & TypeAttributes.Serializable) == TypeAttributes.Serializable) { BinaryFormatter f = new BinaryFormatter(); using (MemoryStream str = new MemoryStream()) { f.Serialize(str, o); str.Position = 0; StreamReader reader = new StreamReader(str); result = reader.ReadToEnd(); } } return result; } public static object DeserializeObject(string str) { object result = null; byte[] bytes = System.Text.Encoding.ASCII.GetBytes(str); using (MemoryStream stream = new MemoryStream(bytes)) { BinaryFormatter bf = new BinaryFormatter(); result = bf.Deserialize(stream); } return result; } } SerializeObject method works well, but DeserializeObject does not. I always get an exception with message "End of Stream encountered before parsing was completed". What may be wrong here?

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• C# call a C++ dll get EntryPointNotFoundException

  - by 5YrsLaterDBA

  I was gaven a C++ dll file, a lib file and a header file. I need to call them from my C# application. header file looks like this: class Clog ; class EXPORT_MACRO NB_DPSM { private: string sFileNameToAnalyze ; Clog *pLog ; void write2log(string text) ; public: NB_DPSM(void); ~NB_DPSM(void); void setFileNameToAnalyze(string FileNameToAnalyze) ; int WriteGenbenchData(string& message) ; }; In my C# code, I have those code: internal ReturnStatus correctDataDLL(string rawDataFileName) { if (rawDataFileName == null || rawDataFileName.Length <= 0) { return ReturnStatus.Return_CannotFindFile; } else { setFileNameToAnalyze(rawDataFileName); } string msg = ""; int returnVal = WriteGenbenchData(ref msg); return ReturnStatus.Return_Success; } [DllImport("..\\..\\thirdParty\\cogs\\NB_DPSM.dll")] public static extern void setFileNameToAnalyze(string fileName); [DllImport("..\\..\\thirdParty\\cogs\\NB_DPSM.dll")] public static extern int WriteGenbenchData(ref string message); I got EntryPointNotFoundException at the setFileNameToAnalyze(rawDataFileName); statement. Few questions: do I need to add that lib file into somewhere of my C# project? how? do I need to add the header file into my C# project? how? (no compile error for now) I would like to remove those "..\\..\\thirdParty\\cogs\\" hardcode path. how to this? how to get ride of that EntryPointNotFoundException? thanks,

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• overloading "<<" with a struct (no class) cout style

  - by monkeyking

  I have a struct that I'd like to output using either 'std::cout' or some other output stream. Is this possible without using classes? Thanks #include <iostream> #include <fstream> template <typename T> struct point{ T x; T y; }; template <typename T> std::ostream& dump(std::ostream &o,point<T> p) const{ o<<"x: " << p.x <<"\ty: " << p.y <<std::endl; } template<typename T> std::ostream& operator << (std::ostream &o,const point<T> &a){ return dump(o,a); } int main(){ point<double> p; p.x=0.1; p.y=0.3; dump(std::cout,p); std::cout << p ;//how? return 0; } I tried different syntax' but I cant seem to make it work.

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• android progressBar problem

  - by kostas

  hi.i have a button that on click is loading rss feed.i want to load a progress bar until my list opens.i have created a progressbar,it works,but as i press the return button to return to the main menu the progress bar appears again and it doesnt stop(and not even let me see my menu).this is my code ProgressBar myProgressBar; int myProgress = 0; /** Called when the activity is first created. */ @Override public void onCreate(Bundle icicle) { super.onCreate(icicle); setContentView(R.layout.main1); Button nea = (Button) findViewById(R.id.nea); nea.setOnClickListener(new View.OnClickListener() { public void onClick (View view) { setContentView(R.layout.bar); myProgressBar=(ProgressBar)findViewById(R.id.bar); new Thread(myThread).start(); Intent myIntent = new Intent(view.getContext(), nea.class); startActivityForResult(myIntent, 0); } }); } and then,out of the onCreate private Runnable myThread = new Runnable(){ @Override public void run() { // TODO Auto-generated method stub while (myProgress<100){ try{ myHandle.sendMessage(myHandle.obtainMessage()); Thread.sleep(1000); } catch(Throwable t){ } } } Handler myHandle = new Handler(){ public void handleMessage(Message msg) { // TODO Auto-generated method stub myProgress++; myProgressBar.setProgress(myProgress); } }; };

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• In perl, how can I call a method whose name I have in a string?

  - by Ryan Thompson

  I'm trying to write some abstract code for searching through a list of similar objects for the first one whose attributes match specific values. In order to do this, I need to call a bunch of accessor methods and check all their values one by one. I'd like to use an abstraction like this: sub verify_attribute { my ($object, $attribute_method, $wanted_value) = @_; if ( call_method($object, $attribute_method) ~~ $wanted_value ) { return 1; } else { return; } } Then I can loop through a hash whose keys are accessor method names and whose values are the values I'm looking for for those attributes. For example, if that hash is called %wanted, I might use code like this to find the object I want: my $found_object; FINDOBJ: foreach my $obj (@list_of_objects) { foreach my $accessor (keys %wanted) { next FINDOBJ unless verify_attribute($obj, $accessor, $wanted{$accessor}); } # All attrs verified $found_object = $obj; last FINDOBJ; } Of course, the only problem is that call_method does not exsit. Or does it? How can I call a method if I have a string containing its name? Or is there a better solution to this whole problem?

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• Predicate usually used for array/list how about here?

  - by amit kohan

  In following code (Josh Smith's article on MVVM), can somebody give me some insight about return _canExecute == null ? true : _canExecute(parameter); ? it is a normal if/else statement but I'm not getting the last part of it. public class RelayCommand : ICommand { #region Fields readonly Action<object> _execute; readonly Predicate<object> _canExecute; #endregion // Fields #region Constructors public RelayCommand(Action<object> execute) : this(execute, null) { } public RelayCommand(Action<object> execute, Predicate<object> canExecute) { if (execute == null) throw new ArgumentNullException("execute"); _execute = execute; _canExecute = canExecute; } #endregion // Constructors #region ICommand Members [DebuggerStepThrough] public bool CanExecute(object parameter) { return _canExecute == null ? true : _canExecute(parameter); } public event EventHandler CanExecuteChanged { add { CommandManager.RequerySuggested += value; } remove { CommandManager.RequerySuggested -= value; } } public void Execute(object parameter) { _execute(parameter); } #endregion // ICommand Members } Thanks.

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• Task Parallel Library exception handling

  - by user1680766

  When handling exceptions in TPL tasks I have come across two ways to handle exceptions. The first catches the exception within the task and returns it within the result like so: var task = Task<Exception>.Factory.StartNew( () => { try { // Do Something return null; } catch (System.Exception e) { return e; } }); task.ContinueWith( r => { if (r.Result != null) { // Handle Exception } }); The second is the one shown within the documentation and I guess the proper way to do things: var task = Task.Factory.StartNew( () => { // Do Something }); task.ContinueWith( r => { if (r.Exception != null) { // Handle Aggregate Exception r.Exception.Handle(y => true); } }); I am wondering if there is anything wrong with the first approach? I have received 'unhandled aggregate exception' exceptions every now and again using this technique and was wondering how this can happen?

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• Why we can't we overload "=" using friend function?

  - by ashish-sangwan

  Why it is not allowed to overload "=" using friend function? I have written a small program but it is giving error. class comp { int real; int imaginary; public: comp(){real=0; imaginary=0;} void show(){cout << "Real="<<real<<" Imaginary="<<imaginary<<endl;} void set(int i,int j){real=i;imaginary=j;} friend comp operator=(comp &op1,const comp &op2); }; comp operator=(comp &op1,const comp &op2) { op1.imaginary=op2.imaginary; op1.real=op2.real; return op1; } int main() { comp a,b; a.set(10,20); b=a; b.show(); return 0; } The compilation gives the following error :- [root@dogmatix stackoverflow]# g++ prog4.cpp prog4.cpp:11: error: ‘comp operator=(comp&, const comp&)’ must be a nonstatic member function prog4.cpp:14: error: ‘comp operator=(comp&, const comp&)’ must be a nonstatic member function prog4.cpp: In function ‘int main()’: prog4.cpp:25: error: ambiguous overload for ‘operator=’ in ‘b = a’ prog4.cpp:4: note: candidates are: comp& comp::operator=(const comp&) prog4.cpp:14: note: comp operator=(comp&, const comp&)

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• Centralizing Messagebox handling for application

  - by DRapp

  I'm wondering how others deal with trying to centralize MessageBox function calling. Instead of having long text embedded all over the place in code, in the past (non .net language), I would put system and application base "messagebox" type of messages into a database file which would be "burned" into the executable, much like a resource file in .Net. When a prompting condition would arise, I would just do call something like MBAnswer = MyApplication.CallMsgBox( IDUserCantDoThat ) then check the MBAnswer upon return, such as a yes/no/cancel or whatever. In the database table, I would have things like what the messagebox title would be, the buttons that would be shown, the actual message, a special flag that automatically tacked on a subsequent standard comment like "Please contact help desk if this happens.". The function would call the messagebox with all applicable settings and just return back the answer. The big benefits of this was, one location to have all the "context" of messages, and via constants, easier to read what message was going to be presented to the user. Does anyone have a similar system in .Net to do a similar approach, or is this just a bad idea in the .Net environment.

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