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POHow can I avoid having to pass around/store a delegate when using BeginInvoke and EndInvoke?
 

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  1. POHow can I avoid having to pass around/store a delegate when using BeginInvoke and EndInvoke?
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    <p><strong>Edit</strong>: Moved the actual question to the top.</p> <p><strong>Update</strong>: Found an example by Microsoft, tucked on some more code at the end.</p> <p>My questions are these:</p> <ol> <li>Is it safe to call multiple BeginInvoke calls on the same delegate instance, or do I have to construct a new delegate instance for each in-flight method call?</li> <li>If I have to construct new instances for each, is there some way to get hold of the original delegate out of the IAsyncResult value?</li> <li>Is there some other, better, way to add asynchronous support to my class than using delegates?</li> </ol> <p>More info follows.</p> <p>I am adding asynchronous support to a class of mine, and thought I'd do it simple.</p> <p>Take this class:</p> <pre><code>public class Calculator { public Int32 Add(Int32 a, Int32 b) { return a + b; } } </code></pre> <p>I thought I could simply do this:</p> <pre><code>public class Calculator { private delegate Int32 AddDelegate(Int32 a, Int32 b); public Int32 Add(Int32 a, Int32 b) { return a + b; } public IAsyncResult BeginAdd(Int32 a, Int32 b, AsyncCallback callback, Object obj) { return new AddDelegate(Add).BeginInvoke(a, b, callback, obj); } public Int32 EndAdd(IAsyncResult ar) { return new AddDelegate(Add).EndInvoke(ar); } } </code></pre> <p>This doesn't work, as the two methods each construct their own delegate object, and the .EndInvoke call checks to see if the delegate instance i call it on is the same as the one I originally called BeginInvoke on.</p> <p>The simplest way to handle this would be to just store a reference into a variable, like this:</p> <pre><code>public class Calculator { private delegate Int32 AddDelegate(Int32 a, Int32 b); private AddDelegate _Add; public Calculator() { _Add = new AddDelegate(Add); } public Int32 Add(Int32 a, Int32 b) { return a + b; } public IAsyncResult BeginAdd(Int32 a, Int32 b, AsyncCallback callback, Object obj) { return _Add.BeginInvoke(a, b, callback, obj); } public Int32 EndAdd(IAsyncResult ar) { return _Add.EndInvoke(ar); } } </code></pre> <p>Note that I'm fully aware of problems with allowing multiple instance methods on the same class to execute at the same time, with regards to shared state, etc.</p> <hr> <p><strong>Update</strong>: I found this example here by Microsoft on <a href="http://msdn.microsoft.com/en-us/library/h80ttd5f(VS.71).aspx" rel="nofollow noreferrer">Asynchronous Delegates Programming Sample</a>. It shows casting the <a href="http://msdn.microsoft.com/en-us/library/system.iasyncresult.aspx" rel="nofollow noreferrer">IAsyncResult</a> reference back to an <a href="http://msdn.microsoft.com/en-us/library/system.runtime.remoting.messaging.asyncresult.aspx" rel="nofollow noreferrer">AsyncResult</a> object, and then I can get the original delegate instance through the <a href="http://msdn.microsoft.com/en-us/library/system.runtime.remoting.messaging.asyncresult.asyncdelegate.aspx" rel="nofollow noreferrer">AsyncDelegate</a> property.</p> <p>Is this a safe approach?</p> <p>In other words, is the following class fine?</p> <pre><code>public class Calculator { private delegate Int32 AddDelegate(Int32 a, Int32 b); public Int32 Add(Int32 a, Int32 b) { return a + b; } public IAsyncResult BeginAdd(Int32 a, Int32 b, AsyncCallback callback, Object obj) { return new AddDelegate(Add).BeginInvoke(a, b, callback, obj); } public Int32 EndAdd(IAsyncResult ar) { AddDelegate del = (AddDelegate)((AsyncResult)ar).AsyncDelegate; return del.EndInvoke(ar); } } </code></pre>
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