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  • linker error in simple program: multiple definition of function

    - by BillyJean
    My function test is added to two different .cpp-files and the functions are private to their respective files as shown below test1.cpp #include <iostream> using namespace std; void test() { cout << "test" << endl; } test2.cpp #include <iostream> using namespace std; void test() { cout << "test" << endl; } main.cpp #include <iostream> using namespace std; int main() { return 0; } During linking I get the error multiple definition of test() - but how is that possible, considering that the two files have their own private scope!? I could understand it if I included the function prototype in each .cpp-files' corresponding header, but there is no such thing in this example.

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  • Getting "value is not defined" while inheriting a type

    - by James Black
    I can't see what I am doing wrong, as the files are in the correct order. In this case it is: BaseDAO.fs CreateDatabase.fs They are in the same namespace, but even when I had them in different modules, and opened the module in CreateDatabase the same error. The error is: Error 1 The value or constructor 'execNonQuery' is not defined I am trying to inherit BaseDAO and use a member that will be common to several files, and I don't see why I get the error above. namespace RestaurantServiceDAO open MySql.Data.MySqlClient type BaseDAO() = let connString = @"Server=localhost;Database=mysql;Uid=root;Pwd=$$$$;" let conn = new MySqlConnection(connString) member self.execNonQuery(sqlStr) = conn.Open() let comm = new MySqlCommand(sqlStr, conn, CommandTimeout = 10) comm.ExecuteNonQuery |> ignore comm.Dispose |> ignore The type that does inherit is here, and execNonQuery is not defined. namespace RestaurantServiceDAO open MySql.Data.MySqlClient type CreateDatabase() = inherit BaseDAO() let createRestaurantTable conn = execNonQuery "CREATE TABLE restaurant(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, name VARCHAR(100), cur_timestamp TIMESTAMP(8))"

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  • Using clojure.contrib functions in slime REPL

    - by Tyler
    I want to use the functions in the clojure.contrib.trace namespace in slime at the REPL. How can I get slime to load them automatically? A related question, how can I add a specific namespace into a running repl? On the clojure.contrib API it describes usage like this: (ns my-namespace (:require clojure.contrib.trace)) But adding this to my code results in the file being unable to load with an "Unable to resolve symbol" error for any function from the trace package. I use leiningen 'lein swank' to start the ServerSocket and the project.clj file looks like this (defproject test-project "0.1.0" :description "Connect 4 Agent written in Clojure" :dependencies [[org.clojure/clojure "1.2.0-master-SNAPSHOT"] [org.clojure/clojure-contrib "1.2.0-SNAPSHOT"]] :dev-dependencies [[leiningen/lein-swank "1.2.0-SNAPSHOT"] [swank-clojure "1.2.0"]]) Everything seems up to date, i.e. 'lein deps' doesn't produce any changes. So what's up?

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  • Error when using SharpDevelop

    - by Sebastian
    I have some code: Outlook.Application outLookApp = new Outlook.Application(); Outlook.Inspector inspector = outLookApp.ActiveInspector(); Outlook.NameSpace nameSpace = outLookApp.GetNamespace("MAPI"); Outlook.MAPIFolder inbox = nameSpace.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderInbox); String sCriteria = "[SenderEmailAddress] = '[email protected]'"; Outlook.Items filteredItems = inbox.Items.Restrict(sCriteria); // totaly sure that count > 0; Outlook.MailItem item = filteredItems[1]; In the last line I have error: "Cannot implicitly convert type 'object' to 'Microsoft.Office.Interop.Outlook.MailItem'. An explicit conversion exists (are you missing a cast?)". I don't know why. Previous I used VisualStudio 2010 but my trial has expired. Is there any hope to run this on SharpDevelop?

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  • What does Ruby have that Python doesn't, and vice versa?

    - by Lennart Regebro
    There is a lot of discussions of Python vs Ruby, and I all find them completely unhelpful, because they all turn around why feature X sucks in language Y, or that claim language Y doesn't have X, although in fact it does. I also know exactly why I prefer Python, but that's also subjective, and wouldn't help anybody choosing, as they might not have the same tastes in development as I do. It would therefore be interesting to list the differences, objectively. So no "Python's lambdas sucks". Instead explain what Ruby's lambdas can do that Python's can't. No subjectivity. Example code is good! Don't have several differences in one answer, please. And vote up the ones you know are correct, and down those you know are incorrect (or are subjective). Also, differences in syntax is not interesting. We know Python does with indentation what Ruby does with brackets and ends, and that @ is called self in Python. UPDATE: This is now a community wiki, so we can add the big differences here. Ruby has a class reference in the class body In Ruby you have a reference to the class (self) already in the class body. In Python you don't have a reference to the class until after the class construction is finished. An example: class Kaka puts self end self in this case is the class, and this code would print out "Kaka". There is no way to print out the class name or in other ways access the class from the class definition body in Python. All classes are mutable in Ruby This lets you develop extensions to core classes. Here's an example of a rails extension: class String def starts_with?(other) head = self[0, other.length] head == other end end Ruby has Perl-like scripting features Ruby has first class regexps, $-variables, the awk/perl line by line input loop and other features that make it more suited to writing small shell scripts that munge text files or act as glue code for other programs. Ruby has first class continuations Thanks to the callcc statement. In Python you can create continuations by various techniques, but there is no support built in to the language. Ruby has blocks With the "do" statement you can create a multi-line anonymous function in Ruby, which will be passed in as an argument into the method in front of do, and called from there. In Python you would instead do this either by passing a method or with generators. Ruby: amethod { |here| many=lines+of+code goes(here) } Python: def function(here): many=lines+of+code goes(here) amethod(function) Interestingly, the convenience statement in Ruby for calling a block is called "yield", which in Python will create a generator. Ruby: def themethod yield 5 end themethod do |foo| puts foo end Python: def themethod(): yield 5 for foo in themethod: print foo Although the principles are different, the result is strikingly similar. Python has built-in generators (which are used like Ruby blocks, as noted above) Python has support for generators in the language. In Ruby you could use the generator module that uses continuations to create a generator from a block. Or, you could just use a block/proc/lambda! Moreover, in Ruby 1.9 Fibers are, and can be used as, generators. docs.python.org has this generator example: def reverse(data): for index in range(len(data)-1, -1, -1): yield data[index] Contrast this with the above block examples. Python has flexible name space handling In Ruby, when you import a file with require, all the things defined in that file will end up in your global namespace. This causes namespace pollution. The solution to that is Rubys modules. But if you create a namespace with a module, then you have to use that namespace to access the contained classes. In Python, the file is a module, and you can import its contained names with from themodule import *, thereby polluting the namespace if you want. But you can also import just selected names with from themodule import aname, another or you can simply import themodule and then access the names with themodule.aname. If you want more levels in your namespace you can have packages, which are directories with modules and an __init__.py file. Python has docstrings Docstrings are strings that are attached to modules, functions and methods and can be introspected at runtime. This helps for creating such things as the help command and automatic documentation. def frobnicate(bar): """frobnicate takes a bar and frobnicates it >>> bar = Bar() >>> bar.is_frobnicated() False >>> frobnicate(bar) >>> bar.is_frobnicated() True """ Python has more libraries Python has a vast amount of available modules and bindings for libraries. Python has multiple inheritance Ruby does not ("on purpose" -- see Ruby's website, see here how it's done in Ruby). It does reuse the module concept as a sort of abstract classes. Python has list/dict comprehensions Python: res = [x*x for x in range(1, 10)] Ruby: res = (0..9).map { |x| x * x } Python: >>> (x*x for x in range(10)) <generator object <genexpr> at 0xb7c1ccd4> >>> list(_) [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] Ruby: p = proc { |x| x * x } (0..9).map(&p) Python: >>> {x:str(y*y) for x,y in {1:2, 3:4}.items()} {1: '4', 3: '16'} Ruby: >> Hash[{1=>2, 3=>4}.map{|x,y| [x,(y*y).to_s]}] => {1=>"4", 3=>"16"} Python has decorators Things similar to decorators can be created in Ruby, and it can also be argued that they aren't as necessary as in Python.

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  • Linq to Sql Data class in dbml

    - by Simon
    I am abit curious about dbml.... Should I create one dbml file for one database or separated into different parts e.g. User dbml (only tables relate to users) etc? When I do this I will have abit of problems. Assume the User dbml has a User table and if the Order dbml has a User table as well, this won't be allowed if the entity namespace are the same. If I have set a different entity namespace for each of the dbml, it works but this will gives me a different entity of User table. When a single data returns to Business Logic layer, there is a difficulty of knowing which entity namespace of the user table to be used. If I built one dbml file instead of having separate dbml, will single dbml appear slower than the separated dbml version when fetching the data from the database.

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  • How to create a SOAP REQUEST using ASP.NET (VB) without using Visual

    - by user311691
    Hi all , I urgently need your help . I am new to consuming a web service using SOAP protocol. I have been given a demo webservice URL which ends in .WSDL and NOT .asml?WSDL. The problem is I cannot add a web reference using Visual studio OR Disco.exe or Wsdl.exe - This webservice has been created on a java platform and for security reasons the only way to make a invoke the webservice is at runtime using SOAP protocol IN asp.net (VB). I I have created some code but cannot seem to send the soap object to the receiving web service. If I could get a solution with step by step instructions on how I can send a SOAP REQUEST. Below is my code and all am trying to do is send a SOAP REQUEST and receive a SOAP RESPONSE which I will display in my browser. <%@ page language="vb" %> <%@ Import Namespace="System.Data"%> <%@ Import Namespace="System.Xml"%> <%@ Import Namespace="System.Net"%> <%@ Import Namespace="System.IO"%> <%@ Import Namespace="System.Text"%> <script runat=server> Private Sub Page_Load() Dim objHTTPReq As HttpWebRequest Dim WebserviceUrl As String = "http://xx.xx.xx:8084/asy/wsdl/asy.wsdl" objHTTPReq = CType(WebRequest.Create(WebserviceUrl), HttpWebRequest) Dim soapXML As String soapXML = "<?xml version='1.0' encoding='utf-8'?>" & _ " <soap:Envelope xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'" & _ " xmlns:xsd='http://www.w3.org/2001/XMLSchema'"& _ " xmlns:soap='http://schemas.xmlsoap.org/soap/envelope/' >"& _ " <soap:Body> "& _ " <validatePaymentData xmlns='http://asybanks.webservices.asycuda.org'> " & _ " <bankCode>"& bankCode &"</bankCode> " & _ " <PaymentDataType>" & _ " <paymentType>"& payment_type &"</paymentType> " & _ " <amount>"& ass_amount &"</amount> " & _ " <ReferenceType>" & _ " <year>"& year &"</year> " & _ " <customsOfficeCode>"& station &"</customsOfficeCode> " & _ " </ReferenceType>" & _ " <accountNumber>"& zra_account &"</accountNumber> " & _ " </PaymentDataType> " & _ " </validatePaymentData> " & _ " </soap:Body> " & _ " </soap:Envelope> " objHTTPReq.Headers.Add("SOAPAction", "http://asybanks.webservices.asycuda.org") objHTTPReq.ContentType = "text/xml; charset=utf-8" objHTTPReq.ContentLength = soapXML.Length objHTTPReq.Accept = "text/xml" objHTTPReq.Method = "POST" Dim objHTTPRes As HttpWebResponse = CType(objHTTPReq.GetResponse(), HttpWebResponse) Dim dataStream As Stream = objHTTPRes.GetResponseStream() Dim reader As StreamReader = new StreamReader(dataStream) Dim responseFromServer As String = reader.ReadToEnd() OurXml.text = responseFromServer End Sub </script> <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title> XML TRANSACTION SIMULATION - N@W@ TJ </title> </head> <body> <form id="form1" runat="server"> <div> <p>ZRA test Feedback:</p> <asp:label id="OurXml" runat="server"/> </div> </form> </body> </html> the demo webservice looks like this: <?xml version="1.0" encoding="UTF-8" ?> - <!-- WEB SERVICE JAVA DEMO --> - <definitions targetNamespace="http://asybanks.webservices.asycuda.org" xmlns="http://schemas.xmlsoap.org/wsdl/" xmlns:apachesoap="http://xml.apache.org/xml-soap" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:y="http://asybanks.webservices.asycuda.org"> - <types> - <xs:schema elementFormDefault="qualified" targetNamespace="http://asybanks.webservices.asycuda.org" xmlns="http://www.w3.org/2001/XMLSchema"> SOME OTHER INFORMATION AT THE BOTTOM <soap:address location="http://xx.xx.xx:8084/asy/services/asy" /> </port> </service> </definitions> From the above excerpt of the wsdl url webservice, I am not sure which namespace to use for soapACTION - please advise.... Please if you could comment every stage of a soap request and provide a working demo - I would be most grateful as I would be learning rather than just assuming stuff :)

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  • Why does Sql Server recommends creating an index when it already exist?

    - by Pierre-Alain Vigeant
    I ran a very basic query against one of our table and I noticed that the execution plan query processor is recommending that we create an index on a column The query is SELECT SUM(DATALENGTH(Data)) FROM Item WHERE Namespace = 'http://some_url/some_namespace/' After running, I get the following message // The Query Processor estimates that implementing the following index could improve the query cost by 96.7211%. CREATE NONCLUSTERED INDEX [<Name of Missing Index, sysname,>] ON [dbo].[Item] ([Namespace]) My problem is that I already have such index on that column: CREATE NONCLUSTERED INDEX [IX_ItemNamespace] ON [dbo].[Item] ( [Namespace] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] Why is Sql Server recommending me to create such index when it already exist?

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  • Implement a generic C++/CLI interface in a C# generic interface

    - by Florent
    I have a C++/CLI generic interface like this : using namespace System::Collections::Generic; namespace Test { generic <class T> public interface class IElementList { property List<T>^ Elements; }; } and I want to implement it in a C# generic interface like this : using Test; namespace U { public interface IElementLightList<T> : IElementList<T> where T : IElementLight { bool isFrozen(); bool isPastable(); } } This don't work, Visual Studio is not able to see C++/CLI IElementList interface ! I tested with a not generic C++/CLI interface and this work. What I missed ?

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  • Rails routing/polymorphism issue - how to model the following

    - by 46and2
    Hi all, I have an app where a 'user' belong to a 'client' or a 'vendor' (and client and vendor has_many users). In the admin namespace, I want to administer these users - so an admin would choose a client or a vendor, then nav to that client's or vendor's users. My question is, short of making the user model polymorphic, how could I model/route this? Here is what I have in terms of routing: map.namespace :admin do |admin| admin.resources :clients admin.resources :vendors end I know I could do something like: map.namespace :admin do |admin| admin.resources :clients do |client| client.resources :users admin.resources :vendors do |vendor| vendor.resources :users end end But the above would definitely need me to treat the User as polymorphic. I'm just wondering what you would recommend or what my options are. Thanks.

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  • How can one use the "Add view" dialog in Visual Studio efficiently when working with ASP.NET MVC?

    - by Marek
    Does anyone else think that the add view dialog in VS is useless or is it just me? Why is there no search/filtering in there? I can not even paste the type name (without namespace) there to speed up the view creation. Plus, there are a lot of irrelevant classes there, including classes from all referenced libraries. Am I missing something or Microsoft never did any usability testing with that?? Is it possible to filter out types/assemblies in the dialog and/or better navigation compared to manually scrolling the combobox with all the types listed? Is it possible to include only types from a particular directory/assembly/namespace? (the ViewModels namespace for example) EDIT: As it seems from the answers that there is no usable workaround for this, I have filed a suggestion at Connect: https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=507784 Please vote for the suggestion if you find this is an important issue.

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  • What are the main advantages of adding your custom functions to a javascript libraries namepsace?

    - by yaya3
    It is fairly well known in JavaScript that declaring variables within the global scope is a bad thing. So code I tend to work on contains namespaced JavaScript. There seems to be two different approaches taken to this - Adding your application specific functions to the libraries' namespace e.g. $.myCarouselfunction Creating your own namespace e.g. MyApplication.myCarouselFunction I wanted to know whether or not there is a 'better' solution or if they tend to meet somewhere close in terms of pros and cons. The reason for me personally deciding not to go with the library is for Seperation / Isolation / Lack of conflict with library code and potential plugins that are likely to share that namespace. But I am sure there is more to this. Thanks

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  • Why is generated XAML spitting out namespaces that are not asked for?

    - by Matt Holmes
    I have a very simple XAML form, that has one namespace definition. For some reason, when Visual Studio processes that XAML file in to it's component .g.cs, it's sticking a bunch of namespace definitions at the top that I have not asked for in the XAML, or the code behind, and they are namespaces that no longer exist in my project. Thus the project is failing to compile. Why is Visual Studio sticking arbitrary namespace 'using' statements in my generated XAML .g.cs files? It's caused my entire project to break. Not one time did this .xaml file ever reference the namespaces in question, so it's doubly annoying.

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  • Is it possible to modify ASP.NET to no longer require runat="server"?

    - by sean2078
    I know why runat="server" is currently required (ASP.NET why runat="server"), but the consensus is that it should not be required if you incorporate a simple default into the design (I agree of course). Would it be possible to modify, extend, decompile and recreate, intercept or otherwise change the behavior of how ASP.NET parses ASPX and ASCX files so that runat="server" would no longer be required? For instance, I assume that a version of Mono could be branched to accomplish this goal. In case specific requirements are helpful, the following highlights one design: During parsing, when configured namespace tags are encountered (such as "asp"), default the element's runat property to "server" During parsing, when configured namespace tags are encountered (such as "asp"), if the element's runat property value is available, then that value should be used in place of the default New page-level setting introduced (can be set in the page directive or web.config) that specifies the default runat value for a specific namespace tag

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  • Twitter feed appears to be both RSS 2.0 and Atom?

    - by Greg K
    I'm parsing various site feeds, and putting together a small library to help me do it. Looking at the Atom RFC and RSS 2.0 specification, feeds from Twitter seem to be a combination. Twitter specifies an Atom namespace in an RSS 2.0 structure? GitHub uses Atom, whereas Flickr (offers multiple but the default 'Latest' feed from user profiles) appears to be RSS 2.0. How can Twitter specify a Atom namespace and then use RSS? This makes parsing feeds a little ambiguous, unless I ignore any specified namespace and just examine the document structure.

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  • Unnamed/anonymous namespaces vs. static functions

    - by Head Geek
    A little-used feature of C++ is the ability to create anonymous namespaces, like so: namespace { int cannotAccessOutsideThisFile() { ... } } // namespace You would think that such a feature would be useless -- since you can't specify the name of the namespace, it's impossible to access anything within it from outside. But these unnamed namespaces are accessible within the file they're created in, as if you had an implicit using-clause to them. My question is, why or when would this be preferable to using static functions? Or are they essentially two ways of doing the exact same thing?

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  • LInq to SQL - Partial Class - C#

    - by Mark Comix
    Hi, I have a system with 2 different projects, one is called LINQ_Extensions and the other is ORM_Linq. On ORM_Linq i have the LINQ diagram with the SQL tables "converted" in clases. One of the Class is called "Tipos_Pago" In the other project i have another class (partial class) "Tipos_Pago". I want to use the method OnValidate to validate the properties include in the class "Tipos_Pago", so i create this partial class. In the 2 projects i put the same NameSpace "ORM_Linq"(I changed the NameSpace of the project "LINQ_Extensions" to have the same of the project "ORM_Linq") After those chages, Visual Studio give me this error: Error 1 No defining declaration found for implementing declaration of partial method 'ORM_Linq.Tipos_Pago.OnValidate(System.Data.Linq.ChangeAction)' C..\Tipos_Pago.cs 13 22 Extensiones_Linq I don't have any Idea of what happend, can someone help me? Thanks, sorry for my poor english This is the code in the partial class: namespace ORM_Linq { public partial class Tipos_Pago { partial void OnValidate(System.Data.Linq.ChangeAction action) { //Valid code } } }

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  • c++/cli pass (managed) delegate to unmanaged code

    - by Ron Klein
    How do I pass a function pointer from managed C++ (C++/CLI) to an unmanaged method? I read a few articles, like this one from MSDN, but it describes two different assemblies, while I want only one. Here is my code: 1) Header (MyInterop.ManagedCppLib.h): #pragma once using namespace System; namespace MyInterop { namespace ManagedCppLib { public ref class MyManagedClass { public: void DoSomething(); }; }} 2) CPP Code (MyInterop.ManagedCppLib.cpp) #include "stdafx.h" #include "MyInterop.ManagedCppLib.h" #pragma unmanaged void UnmanagedMethod(int a, int b, void (*sum)(const int)) { int result = a + b; sum(result); } #pragma managed void MyInterop::ManagedCppLib::MyManagedClass::DoSomething() { System::Console::WriteLine("hello from managed C++"); UnmanagedMethod(3, 7, /* ANY IDEA??? */); } I tried creating my managed delegate and then I tried to use Marshal::GetFunctionPointerForDelegate method, but I couldn't compile.

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  • Zend autloading different namespaces from the same directory?

    - by Sled
    Hey guys, I have a models directory in my project, and I would like to save/files classes there with different namespaces. Example: models/User.php with classname Model_User models/Table_User.php with classname Model_Table_User For the first namespace I have this in bootstrap.php $resourceLoader->addResourceTypes(array( 'model' => array( 'namespace' => 'Model', 'path' => 'models' ) )); I can't figure out how to add the second namespace so it detects files starting with Table_ Any ideas? For now I've added a second directory named 'tables' but it's getting confusing because I have each model name twice (once in the models diretory and once in the tables directory)

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  • PHP 5.3 Namespaces should i use every PHP function with backslash?

    - by lhwparis
    Hi, im now using namespaces in PHP 5.3 now there is a fallback mechanism for functions which dont exist in the namespace. so php every time checks if the function exists in namespace and then tries to load it from global space. So what about all php internal functions? strstr for example? Should i now use every php internal function with a \ ? to avoid php first checking the namespace? is this fallback a huge performance drop? what do you think?

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  • Is there a "concise" way to do namespacing in JavaScript?

    - by olliej
    I've frequently encountered sites that put all of their javascript inside a "namespace" structure along the lines of namespaces = { com : { example: { example.com's data} } But setting this up safely with respect to other namespaced frameworks seems to require a relatively hefty amount of code (defined as 2 lines). I was wondering whether anyone knows of a concise way to do this? and whether there's a relatively standard/consistent way to structure it? eg. is the "com" namespace directly attached to the global object, or is it attached through a namespace object? [Edit: whoops, obviously {com = { ... } } wouldn't accomplish anything close to what i intended, thanks to Shog9 for pointing that out. :D]

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  • Problem using a costum server control in a aspx

    - by gre3ns0ul
    Hi guys, i am having a issue. I already developed one class (my custom gridview) and i want use it on a .aspx That class is defined in app_code and compiled to the dll of the project. namespace MyCostumControls{  public class DropDownPagingGridView : GridView{ ... I already registered the control on the aspx page using <%@ Register Namespace="MyCostumControls" TagPrefix="ctrl" % and i can use in the page and works ok.. But i'm watching one problem. That class contains methods defined by me, than when i try to call them in code-behind sayd to me than they're not defined. In designed i don't see the reference to MyCostumControls, and when i try declare one field using protected global::MyCostumControls.MyCostumControls ddl_gv_errors, i cannot access to MyCostumControls namespace, Is because he's compiled to the project dll? I can access to all namespaces than are not contained in app_code. Solutions? Apreciate. Thanks

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  • Converting C# class to JavaScript

    - by AgileMeansDoAsLittleAsPossible
    Take a look at this basic class: namespace AcmeWeb { public string FirstName { get; set; } public class Person { public Person(string firstName, string lastName) { if (String.IsNullOrEmpty(firstName)) { throw new ArgumentNullException(firstName); } this.FirstName = firstName; } } } What's the best translation of this into JavaScript? This is what I'm thinking: (function(namespace) { namespace.Person = function(firstName, lastName) { // Constructor (function() { if (!firstName) { throw "'firstName' argument cannot be null or empty"; } })(); // Private memberts var _ = { firstName: firstName }; // Public members this.firstName = function(value) { if (typeof(value) === "undefined") { return _.firstName; } else { _.firstName = value; return this; } }; }; })(AcmeWeb);

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  • Using LINQ Distinct: With an Example on ASP.NET MVC SelectListItem

    - by Joe Mayo
    One of the things that might be surprising in the LINQ Distinct standard query operator is that it doesn’t automatically work properly on custom classes. There are reasons for this, which I’ll explain shortly. The example I’ll use in this post focuses on pulling a unique list of names to load into a drop-down list. I’ll explain the sample application, show you typical first shot at Distinct, explain why it won’t work as you expect, and then demonstrate a solution to make Distinct work with any custom class. The technologies I’m using are  LINQ to Twitter, LINQ to Objects, Telerik Extensions for ASP.NET MVC, ASP.NET MVC 2, and Visual Studio 2010. The function of the example program is to show a list of people that I follow.  In Twitter API vernacular, these people are called “Friends”; though I’ve never met most of them in real life. This is part of the ubiquitous language of social networking, and Twitter in particular, so you’ll see my objects named accordingly. Where Distinct comes into play is because I want to have a drop-down list with the names of the friends appearing in the list. Some friends are quite verbose, which means I can’t just extract names from each tweet and populate the drop-down; otherwise, I would end up with many duplicate names. Therefore, Distinct is the appropriate operator to eliminate the extra entries from my friends who tend to be enthusiastic tweeters. The sample doesn’t do anything with the drop-down list and I leave that up to imagination for what it’s practical purpose could be; perhaps a filter for the list if I only want to see a certain person’s tweets or maybe a quick list that I plan to combine with a TextBox and Button to reply to a friend. When the program runs, you’ll need to authenticate with Twitter, because I’m using OAuth (DotNetOpenAuth), for authentication, and then you’ll see the drop-down list of names above the grid with the most recent tweets from friends. Here’s what the application looks like when it runs: As you can see, there is a drop-down list above the grid. The drop-down list is where most of the focus of this article will be. There is some description of the code before we talk about the Distinct operator, but we’ll get there soon. This is an ASP.NET MVC2 application, written with VS 2010. Here’s the View that produces this screen: <%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<TwitterFriendsViewModel>" %> <%@ Import Namespace="DistinctSelectList.Models" %> <asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">     Home Page </asp:Content><asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">     <fieldset>         <legend>Twitter Friends</legend>         <div>             <%= Html.DropDownListFor(                     twendVM => twendVM.FriendNames,                     Model.FriendNames,                     "<All Friends>") %>         </div>         <div>             <% Html.Telerik().Grid<TweetViewModel>(Model.Tweets)                    .Name("TwitterFriendsGrid")                    .Columns(cols =>                     {                         cols.Template(col =>                             { %>                                 <img src="<%= col.ImageUrl %>"                                      alt="<%= col.ScreenName %>" />                         <% });                         cols.Bound(col => col.ScreenName);                         cols.Bound(col => col.Tweet);                     })                    .Render(); %>         </div>     </fieldset> </asp:Content> As shown above, the Grid is from Telerik’s Extensions for ASP.NET MVC. The first column is a template that renders the user’s Avatar from a URL provided by the Twitter query. Both the Grid and DropDownListFor display properties that are collections from a TwitterFriendsViewModel class, shown below: using System.Collections.Generic; using System.Web.Mvc; namespace DistinctSelectList.Models { /// /// For finding friend info on screen /// public class TwitterFriendsViewModel { /// /// Display names of friends in drop-down list /// public List FriendNames { get; set; } /// /// Display tweets in grid /// public List Tweets { get; set; } } } I created the TwitterFreindsViewModel. The two Lists are what the View consumes to populate the DropDownListFor and Grid. Notice that FriendNames is a List of SelectListItem, which is an MVC class. Another custom class I created is the TweetViewModel (the type of the Tweets List), shown below: namespace DistinctSelectList.Models { /// /// Info on friend tweets /// public class TweetViewModel { /// /// User's avatar /// public string ImageUrl { get; set; } /// /// User's Twitter name /// public string ScreenName { get; set; } /// /// Text containing user's tweet /// public string Tweet { get; set; } } } The initial Twitter query returns much more information than we need for our purposes and this a special class for displaying info in the View.  Now you know about the View and how it’s constructed. Let’s look at the controller next. The controller for this demo performs authentication, data retrieval, data manipulation, and view selection. I’ll skip the description of the authentication because it’s a normal part of using OAuth with LINQ to Twitter. Instead, we’ll drill down and focus on the Distinct operator. However, I’ll show you the entire controller, below,  so that you can see how it all fits together: using System.Linq; using System.Web.Mvc; using DistinctSelectList.Models; using LinqToTwitter; namespace DistinctSelectList.Controllers { [HandleError] public class HomeController : Controller { private MvcOAuthAuthorization auth; private TwitterContext twitterCtx; /// /// Display a list of friends current tweets /// /// public ActionResult Index() { auth = new MvcOAuthAuthorization(InMemoryTokenManager.Instance, InMemoryTokenManager.AccessToken); string accessToken = auth.CompleteAuthorize(); if (accessToken != null) { InMemoryTokenManager.AccessToken = accessToken; } if (auth.CachedCredentialsAvailable) { auth.SignOn(); } else { return auth.BeginAuthorize(); } twitterCtx = new TwitterContext(auth); var friendTweets = (from tweet in twitterCtx.Status where tweet.Type == StatusType.Friends select new TweetViewModel { ImageUrl = tweet.User.ProfileImageUrl, ScreenName = tweet.User.Identifier.ScreenName, Tweet = tweet.Text }) .ToList(); var friendNames = (from tweet in friendTweets select new SelectListItem { Text = tweet.ScreenName, Value = tweet.ScreenName }) .Distinct() .ToList(); var twendsVM = new TwitterFriendsViewModel { Tweets = friendTweets, FriendNames = friendNames }; return View(twendsVM); } public ActionResult About() { return View(); } } } The important part of the listing above are the LINQ to Twitter queries for friendTweets and friendNames. Both of these results are used in the subsequent population of the twendsVM instance that is passed to the view. Let’s dissect these two statements for clarification and focus on what is happening with Distinct. The query for friendTweets gets a list of the 20 most recent tweets (as specified by the Twitter API for friend queries) and performs a projection into the custom TweetViewModel class, repeated below for your convenience: var friendTweets = (from tweet in twitterCtx.Status where tweet.Type == StatusType.Friends select new TweetViewModel { ImageUrl = tweet.User.ProfileImageUrl, ScreenName = tweet.User.Identifier.ScreenName, Tweet = tweet.Text }) .ToList(); The LINQ to Twitter query above simplifies what we need to work with in the View and the reduces the amount of information we have to look at in subsequent queries. Given the friendTweets above, the next query performs another projection into an MVC SelectListItem, which is required for binding to the DropDownList.  This brings us to the focus of this blog post, writing a correct query that uses the Distinct operator. The query below uses LINQ to Objects, querying the friendTweets collection to get friendNames: var friendNames = (from tweet in friendTweets select new SelectListItem { Text = tweet.ScreenName, Value = tweet.ScreenName }) .Distinct() .ToList(); The above implementation of Distinct seems normal, but it is deceptively incorrect. After running the query above, by executing the application, you’ll notice that the drop-down list contains many duplicates.  This will send you back to the code scratching your head, but there’s a reason why this happens. To understand the problem, we must examine how Distinct works in LINQ to Objects. Distinct has two overloads: one without parameters, as shown above, and another that takes a parameter of type IEqualityComparer<T>.  In the case above, no parameters, Distinct will call EqualityComparer<T>.Default behind the scenes to make comparisons as it iterates through the list. You don’t have problems with the built-in types, such as string, int, DateTime, etc, because they all implement IEquatable<T>. However, many .NET Framework classes, such as SelectListItem, don’t implement IEquatable<T>. So, what happens is that EqualityComparer<T>.Default results in a call to Object.Equals, which performs reference equality on reference type objects.  You don’t have this problem with value types because the default implementation of Object.Equals is bitwise equality. However, most of your projections that use Distinct are on classes, just like the SelectListItem used in this demo application. So, the reason why Distinct didn’t produce the results we wanted was because we used a type that doesn’t define its own equality and Distinct used the default reference equality. This resulted in all objects being included in the results because they are all separate instances in memory with unique references. As you might have guessed, the solution to the problem is to use the second overload of Distinct that accepts an IEqualityComparer<T> instance. If you were projecting into your own custom type, you could make that type implement IEqualityComparer<T>, but SelectListItem belongs to the .NET Framework Class Library.  Therefore, the solution is to create a custom type to implement IEqualityComparer<T>, as in the SelectListItemComparer class, shown below: using System.Collections.Generic; using System.Web.Mvc; namespace DistinctSelectList.Models { public class SelectListItemComparer : EqualityComparer { public override bool Equals(SelectListItem x, SelectListItem y) { return x.Value.Equals(y.Value); } public override int GetHashCode(SelectListItem obj) { return obj.Value.GetHashCode(); } } } The SelectListItemComparer class above doesn’t implement IEqualityComparer<SelectListItem>, but rather derives from EqualityComparer<SelectListItem>. Microsoft recommends this approach for consistency with the behavior of generic collection classes. However, if your custom type already derives from a base class, go ahead and implement IEqualityComparer<T>, which will still work. EqualityComparer is an abstract class, that implements IEqualityComparer<T> with Equals and GetHashCode abstract methods. For the purposes of this application, the SelectListItem.Value property is sufficient to determine if two items are equal.   Since SelectListItem.Value is type string, the code delegates equality to the string class. The code also delegates the GetHashCode operation to the string class.You might have other criteria in your own object and would need to define what it means for your object to be equal. Now that we have an IEqualityComparer<SelectListItem>, let’s fix the problem. The code below modifies the query where we want distinct values: var friendNames = (from tweet in friendTweets select new SelectListItem { Text = tweet.ScreenName, Value = tweet.ScreenName }) .Distinct(new SelectListItemComparer()) .ToList(); Notice how the code above passes a new instance of SelectListItemComparer as the parameter to the Distinct operator. Now, when you run the application, the drop-down list will behave as you expect, showing only a unique set of names. In addition to Distinct, other LINQ Standard Query Operators have overloads that accept IEqualityComparer<T>’s, You can use the same techniques as shown here, with SelectListItemComparer, with those other operators as well. Now you know how to resolve problems with getting Distinct to work properly and also have a way to fix problems with other operators that require equality comparisons. @JoeMayo

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  • Access violation in DirectX OMSetRenderTargets

    - by IDWMaster
    I receive the following error (Unhandled exception at 0x527DAE81 (d3d11_1sdklayers.dll) in Lesson2.Triangles.exe: 0xC0000005: Access violation reading location 0x00000000) when running the Triangle sample application for DirectX 11 in D3D_FEATURE_LEVEL_9_1. This error occurs at the OMSetRenderTargets function, as shown below, and does not happen if I remove that function from the program (but then, the screen is blue, and does not render the triangle) //// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF //// ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO //// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A //// PARTICULAR PURPOSE. //// //// Copyright (c) Microsoft Corporation. All rights reserved #include #include #include "DirectXSample.h" #include "BasicMath.h" #include "BasicReaderWriter.h" using namespace Microsoft::WRL; using namespace Windows::UI::Core; using namespace Windows::Foundation; using namespace Windows::ApplicationModel::Core; using namespace Windows::ApplicationModel::Infrastructure; // This class defines the application as a whole. ref class Direct3DTutorialViewProvider : public IViewProvider { private: CoreWindow^ m_window; ComPtr m_swapChain; ComPtr m_d3dDevice; ComPtr m_d3dDeviceContext; ComPtr m_renderTargetView; public: // This method is called on application launch. void Initialize( _In_ CoreWindow^ window, _In_ CoreApplicationView^ applicationView ) { m_window = window; } // This method is called after Initialize. void Load(_In_ Platform::String^ entryPoint) { } // This method is called after Load. void Run() { // First, create the Direct3D device. // This flag is required in order to enable compatibility with Direct2D. UINT creationFlags = D3D11_CREATE_DEVICE_BGRA_SUPPORT; #if defined(_DEBUG) // If the project is in a debug build, enable debugging via SDK Layers with this flag. creationFlags |= D3D11_CREATE_DEVICE_DEBUG; #endif // This array defines the ordering of feature levels that D3D should attempt to create. D3D_FEATURE_LEVEL featureLevels[] = { D3D_FEATURE_LEVEL_11_1, D3D_FEATURE_LEVEL_11_0, D3D_FEATURE_LEVEL_10_1, D3D_FEATURE_LEVEL_10_0, D3D_FEATURE_LEVEL_9_3, D3D_FEATURE_LEVEL_9_1 }; ComPtr d3dDevice; ComPtr d3dDeviceContext; DX::ThrowIfFailed( D3D11CreateDevice( nullptr, // specify nullptr to use the default adapter D3D_DRIVER_TYPE_HARDWARE, nullptr, // leave as nullptr if hardware is used creationFlags, // optionally set debug and Direct2D compatibility flags featureLevels, ARRAYSIZE(featureLevels), D3D11_SDK_VERSION, // always set this to D3D11_SDK_VERSION &d3dDevice, nullptr, &d3dDeviceContext ) ); // Retrieve the Direct3D 11.1 interfaces. DX::ThrowIfFailed( d3dDevice.As(&m_d3dDevice) ); DX::ThrowIfFailed( d3dDeviceContext.As(&m_d3dDeviceContext) ); // After the D3D device is created, create additional application resources. CreateWindowSizeDependentResources(); // Create a Basic Reader-Writer class to load data from disk. This class is examined // in the Resource Loading sample. BasicReaderWriter^ reader = ref new BasicReaderWriter(); // Load the raw vertex shader bytecode from disk and create a vertex shader with it. auto vertexShaderBytecode = reader-ReadData("SimpleVertexShader.cso"); ComPtr vertexShader; DX::ThrowIfFailed( m_d3dDevice-CreateVertexShader( vertexShaderBytecode-Data, vertexShaderBytecode-Length, nullptr, &vertexShader ) ); // Create an input layout that matches the layout defined in the vertex shader code. // For this lesson, this is simply a float2 vector defining the vertex position. const D3D11_INPUT_ELEMENT_DESC basicVertexLayoutDesc[] = { { "POSITION", 0, DXGI_FORMAT_R32G32_FLOAT, 0, 0, D3D11_INPUT_PER_VERTEX_DATA, 0 }, }; ComPtr inputLayout; DX::ThrowIfFailed( m_d3dDevice-CreateInputLayout( basicVertexLayoutDesc, ARRAYSIZE(basicVertexLayoutDesc), vertexShaderBytecode-Data, vertexShaderBytecode-Length, &inputLayout ) ); // Load the raw pixel shader bytecode from disk and create a pixel shader with it. auto pixelShaderBytecode = reader-ReadData("SimplePixelShader.cso"); ComPtr pixelShader; DX::ThrowIfFailed( m_d3dDevice-CreatePixelShader( pixelShaderBytecode-Data, pixelShaderBytecode-Length, nullptr, &pixelShader ) ); // Create vertex and index buffers that define a simple triangle. float3 triangleVertices[] = { float3(-0.5f, -0.5f,13.5f), float3( 0.0f, 0.5f,0), float3( 0.5f, -0.5f,0), }; D3D11_BUFFER_DESC vertexBufferDesc = {0}; vertexBufferDesc.ByteWidth = sizeof(float3) * ARRAYSIZE(triangleVertices); vertexBufferDesc.Usage = D3D11_USAGE_DEFAULT; vertexBufferDesc.BindFlags = D3D11_BIND_VERTEX_BUFFER; vertexBufferDesc.CPUAccessFlags = 0; vertexBufferDesc.MiscFlags = 0; vertexBufferDesc.StructureByteStride = 0; D3D11_SUBRESOURCE_DATA vertexBufferData; vertexBufferData.pSysMem = triangleVertices; vertexBufferData.SysMemPitch = 0; vertexBufferData.SysMemSlicePitch = 0; ComPtr vertexBuffer; DX::ThrowIfFailed( m_d3dDevice-CreateBuffer( &vertexBufferDesc, &vertexBufferData, &vertexBuffer ) ); // Once all D3D resources are created, configure the application window. // Allow the application to respond when the window size changes. m_window-SizeChanged += ref new TypedEventHandler( this, &Direct3DTutorialViewProvider::OnWindowSizeChanged ); // Specify the cursor type as the standard arrow cursor. m_window-PointerCursor = ref new CoreCursor(CoreCursorType::Arrow, 0); // Activate the application window, making it visible and enabling it to receive events. m_window-Activate(); // Enter the render loop. Note that tailored applications should never exit. while (true) { // Process events incoming to the window. m_window-Dispatcher-ProcessEvents(CoreProcessEventsOption::ProcessAllIfPresent); // Specify the render target we created as the output target. ID3D11RenderTargetView* targets[1] = {m_renderTargetView.Get()}; m_d3dDeviceContext-OMSetRenderTargets( 1, targets, NULL // use no depth stencil ); // Clear the render target to a solid color. const float clearColor[4] = { 0.071f, 0.04f, 0.561f, 1.0f }; //Code fails here m_d3dDeviceContext-ClearRenderTargetView( m_renderTargetView.Get(), clearColor ); m_d3dDeviceContext-IASetInputLayout(inputLayout.Get()); // Set the vertex and index buffers, and specify the way they define geometry. UINT stride = sizeof(float3); UINT offset = 0; m_d3dDeviceContext-IASetVertexBuffers( 0, 1, vertexBuffer.GetAddressOf(), &stride, &offset ); m_d3dDeviceContext-IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST); // Set the vertex and pixel shader stage state. m_d3dDeviceContext-VSSetShader( vertexShader.Get(), nullptr, 0 ); m_d3dDeviceContext-PSSetShader( pixelShader.Get(), nullptr, 0 ); // Draw the cube. m_d3dDeviceContext-Draw(3,0); // Present the rendered image to the window. Because the maximum frame latency is set to 1, // the render loop will generally be throttled to the screen refresh rate, typically around // 60Hz, by sleeping the application on Present until the screen is refreshed. DX::ThrowIfFailed( m_swapChain-Present(1, 0) ); } } // This method is called before the application exits. void Uninitialize() { } private: // This method is called whenever the application window size changes. void OnWindowSizeChanged( _In_ CoreWindow^ sender, _In_ WindowSizeChangedEventArgs^ args ) { m_renderTargetView = nullptr; CreateWindowSizeDependentResources(); } // This method creates all application resources that depend on // the application window size. It is called at app initialization, // and whenever the application window size changes. void CreateWindowSizeDependentResources() { if (m_swapChain != nullptr) { // If the swap chain already exists, resize it. DX::ThrowIfFailed( m_swapChain-ResizeBuffers( 2, 0, 0, DXGI_FORMAT_R8G8B8A8_UNORM, 0 ) ); } else { // If the swap chain does not exist, create it. DXGI_SWAP_CHAIN_DESC1 swapChainDesc = {0}; swapChainDesc.Stereo = false; swapChainDesc.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT; swapChainDesc.Scaling = DXGI_SCALING_NONE; swapChainDesc.Flags = 0; // Use automatic sizing. swapChainDesc.Width = 0; swapChainDesc.Height = 0; // This is the most common swap chain format. swapChainDesc.Format = DXGI_FORMAT_R8G8B8A8_UNORM; // Don't use multi-sampling. swapChainDesc.SampleDesc.Count = 1; swapChainDesc.SampleDesc.Quality = 0; // Use two buffers to enable flip effect. swapChainDesc.BufferCount = 2; // We recommend using this swap effect for all applications. swapChainDesc.SwapEffect = DXGI_SWAP_EFFECT_FLIP_SEQUENTIAL; // Once the swap chain description is configured, it must be // created on the same adapter as the existing D3D Device. // First, retrieve the underlying DXGI Device from the D3D Device. ComPtr dxgiDevice; DX::ThrowIfFailed( m_d3dDevice.As(&dxgiDevice) ); // Ensure that DXGI does not queue more than one frame at a time. This both reduces // latency and ensures that the application will only render after each VSync, minimizing // power consumption. DX::ThrowIfFailed( dxgiDevice-SetMaximumFrameLatency(1) ); // Next, get the parent factory from the DXGI Device. ComPtr dxgiAdapter; DX::ThrowIfFailed( dxgiDevice-GetAdapter(&dxgiAdapter) ); ComPtr dxgiFactory; DX::ThrowIfFailed( dxgiAdapter-GetParent( __uuidof(IDXGIFactory2), &dxgiFactory ) ); // Finally, create the swap chain. DX::ThrowIfFailed( dxgiFactory-CreateSwapChainForImmersiveWindow( m_d3dDevice.Get(), DX::GetIUnknown(m_window), &swapChainDesc, nullptr, // allow on all displays &m_swapChain ) ); } // Once the swap chain is created, create a render target view. This will // allow Direct3D to render graphics to the window. ComPtr backBuffer; DX::ThrowIfFailed( m_swapChain-GetBuffer( 0, __uuidof(ID3D11Texture2D), &backBuffer ) ); DX::ThrowIfFailed( m_d3dDevice-CreateRenderTargetView( backBuffer.Get(), nullptr, &m_renderTargetView ) ); // After the render target view is created, specify that the viewport, // which describes what portion of the window to draw to, should cover // the entire window. D3D11_TEXTURE2D_DESC backBufferDesc = {0}; backBuffer-GetDesc(&backBufferDesc); D3D11_VIEWPORT viewport; viewport.TopLeftX = 0.0f; viewport.TopLeftY = 0.0f; viewport.Width = static_cast(backBufferDesc.Width); viewport.Height = static_cast(backBufferDesc.Height); viewport.MinDepth = D3D11_MIN_DEPTH; viewport.MaxDepth = D3D11_MAX_DEPTH; m_d3dDeviceContext-RSSetViewports(1, &viewport); } }; // This class defines how to create the custom View Provider defined above. ref class Direct3DTutorialViewProviderFactory : IViewProviderFactory { public: IViewProvider^ CreateViewProvider() { return ref new Direct3DTutorialViewProvider(); } }; [Platform::MTAThread] int main(array^) { auto viewProviderFactory = ref new Direct3DTutorialViewProviderFactory(); Windows::ApplicationModel::Core::CoreApplication::Run(viewProviderFactory); return 0; }

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