System.MulticastDelegate 类

System.MulticastDelegate 类例子

下面的示例说明如何使用从 MulticastDelegate 派生的类。

using System;

    // This class contains strings. It has a member method that
    // accepts a multicast delegate as a parameter and calls it.

    class HoldsStrings
    {
        // The following line causes the compiler to generate
        // a new delegate class named CheckAndPrintDelegate that
        // inherits from System.MulticastDelegate.
        public delegate void CheckAndPrintDelegate(string str);

        // An ArrayList that holds strings
        private System.Collections.ArrayList myStringArray = new System.Collections.ArrayList();

        // A method that adds more strings to the Collection
        public void addstring( string str) {
            myStringArray.Add(str);
        }

        // Iterate through the strings and invoke the method(s) that the delegate points to
        public void PrintAllQualified(CheckAndPrintDelegate myDelegate) {
            foreach (string str in myStringArray) {
                myDelegate(str);
            }
        }
    }   //end of class HoldsStrings

    // This class contains a few sample methods
    class StringFuncs
    {
        // This method prints a string that it is passed if the string starts with a vowel
        public static void ConStart(string str) {
            if (!(str[0]=='a'||str[0]=='e'||str[0]=='i'||str[0]=='o'||str[0]=='u'))
                Console.WriteLine(str);
        }

        // This method prints a string that it is passed if the string starts with a consonant
        public static void VowelStart(string str) {
            if ((str[0]=='a'||str[0]=='e'||str[0]=='i'||str[0]=='o'||str[0]=='u'))
                Console.WriteLine(str);
        }
    }

    // This class demonstrates using Delegates, including using the Remove and
    // Combine methods to create and modify delegate combinations.
    class Test
    {
        static public void Main()
        {
            // Declare the HoldsStrings class and add some strings
            HoldsStrings myHoldsStrings = new HoldsStrings();
            myHoldsStrings.addstring("This");
            myHoldsStrings.addstring("is");
            myHoldsStrings.addstring("a");
            myHoldsStrings.addstring("multicast");
            myHoldsStrings.addstring("delegate");
            myHoldsStrings.addstring("example");

            // Create two delegates individually using different methods
            HoldsStrings.CheckAndPrintDelegate ConStartDel =
                new HoldsStrings.CheckAndPrintDelegate(StringFuncs.ConStart);
            HoldsStrings.CheckAndPrintDelegate VowStartDel =
                new HoldsStrings.CheckAndPrintDelegate(StringFuncs.VowelStart);

            // Demonstrate that MulticastDelegates may store only one delegate
            Delegate [] DelegateList;

            // Returns an array of all delegates stored in the linked list of the
            // MulticastDelegate. In these cases the lists will hold only one (Multicast) delegate
            DelegateList = ConStartDel.GetInvocationList();
            Console.WriteLine("ConStartDel contains " + DelegateList.Length + " delegate(s).");
            DelegateList = VowStartDel.GetInvocationList();
            Console.WriteLine("ConStartVow contains " + DelegateList.Length + " delegate(s).");

            // Determine whether the delegates are System.Multicast delegates
            // if (ConStartDel is System.MulticastDelegate && VowStartDel is System.MulticastDelegate) {
                Console.WriteLine("ConStartDel and ConStartVow are System.MulticastDelegates");
            // }

            // Run the two single delegates one after the other
            Console.WriteLine("Running ConStartDel delegate:");
            myHoldsStrings.PrintAllQualified(ConStartDel);
            Console.WriteLine("Running VowStartDel delegate:");
            myHoldsStrings.PrintAllQualified(VowStartDel);

            // Create a new, empty MulticastDelegate
            HoldsStrings.CheckAndPrintDelegate MultiDel;

            // Delegate.Combine receives an unspecified number of MulticastDelegates as parameters
            MultiDel = (HoldsStrings.CheckAndPrintDelegate) Delegate.Combine(ConStartDel, VowStartDel);

            // How many delegates is this delegate holding?
            DelegateList = MultiDel.GetInvocationList();
            Console.WriteLine("\nMulitDel contains " + DelegateList.Length + " delegates.");

            // What happens when this mulitcast delegate is passed to PrintAllQualified
            Console.WriteLine("Running the multiple delegate that combined the first two");
            myHoldsStrings.PrintAllQualified(MultiDel);

            // The Remove and Combine methods modify the multiple delegate
            MultiDel = (HoldsStrings.CheckAndPrintDelegate) Delegate.Remove(MultiDel, VowStartDel);
            MultiDel = (HoldsStrings.CheckAndPrintDelegate) Delegate.Combine(MultiDel, ConStartDel);

            // Finally, pass the combined delegates to PrintAllQualified again
            Console.WriteLine("\nRunning the multiple delegate that contains two copies of ConStartDel:");
            myHoldsStrings.PrintAllQualified(MultiDel);

            return;
        }   //end of main
    }   //end of Test

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