C# 3.0 Cookbook, 3rd Edition

9.3. Handling Exceptions Individually for Each Delegate in a Multicast Delegate

Problem

You have added multiple delegates to a single multicast delegate. Each of these individual delegates must be invoked, regardless of whether an unhandled exception is thrown within one of the delegates. But once a delegate in a multicast delegate throws an unhandled exception, no more delegates are invoked. You need a way to trap unhandled exceptions within each individual delegate while still allowing the rest of the delegates to fire.

Solution

Use the GetInvocationList method as shown in Recipe 9.1. This method returns each individual delegate from a multicast delegate and, by doing so, allows you to invoke each delegate within the try block of an exception handler.

The following delegate defines the MyDelegateOperation delegate type:

	public delegate int MyDelegateOperation();

The method shown in Example 9-1 creates a multicast delegate called allInstances and then uses GetInvocationList to retrieve each delegate individually. Each delegate is then invoked within the try block of an exception handler.

Example 9-1. Handling exceptions individually for each delegate in a multicast delegate

public static void TestIndividualInvokesExceptions() { Func<int> myDelegateInstance1 = TestInvokeIntReturn.Method1; Func<int> myDelegateInstance2 = TestInvokeIntReturn.Method2; Func<int> myDelegateInstance3 = TestInvokeIntReturn.Method3; Func<int> allInstances = myDelegateInstance1 + myDelegateInstance2 + myDelegateInstance3; ...