Chained Delegates

Delegate chaining allows you to create a linked list of delegates such that when the delegate at the head of the list is called, all of the delegates in the chain are called. The System.Delegate class provides a few static methods to manage lists of delegates.

Delegate.Combine(), Delegate.Remove() & Delegate.RemoveAll()

  • The result that comes out from chained invocation is the result of the last delegate.

  • Any exception in chained invocation terminates the chained invocation process.

  • You can also pass value by reference, but be aware that each delegate that uses the reference parameter will see the changes made by the previous delegate in the chain.

  • Before invoking the delegate chain, you must cast the delegate back into the explicit delegate type.

Code…

   public delegate int ProgressChanged(int value);        
   public class TestChainedInvocation     
   {     
       public void Process()     
       {                
             ProgressChanged[] ProgessDelegates=new ProgressChanged[]{ 
                  new ProgressChanged(1), 
                  new ProgressChanged(2),   
                 new ProgressChanged(3)};   
              ProgressChanged Result = (ProgressChanged)Delegate.Combine(ProgessDelegates);                              
           //simple invocation  
            Result.Invoke(10);             
           //OR    
            Result(10);        
           //Get invocation list         
           int Total;     
           foreach (ProgressChanged  ProgressDelegate in Result.GetInvocationList())     
           {     
               Total+=ProgressDelegate.Invoke(2);  
              }     
          }       
     }
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