委托

class Program
    {
        static void Main(string[] args)
        {
           DelegateIntro.Go();
            Console.ReadKey();
        }
    }


    internal sealed class DelegateIntro
    {
        //声明一个委托类型，它的实例引用一个方法,
        // 该方法获取一个Int32参数,返回void
        //创建一个Feedback类（包含4个方法，构造方法，Invoke，BeginInvoke，EndInvoke）,派生自MulticastDelegate。
        internal delegate void Feedback(Int32 value);

        public static void Go()
        {
            StaticDelegateDemo();
            InstanceDelegateDemo();
            ChainDelegateDemo1(new DelegateIntro());
            ChainDelegateDemo2(new DelegateIntro());
        }

        private static void StaticDelegateDemo()
        {
            Console.WriteLine("----- Static Delegate Demo -----");
            Counter(1, 3, null);
            Counter(1, 3, new Feedback(DelegateIntro.FeedbackToConsole));
            Counter(1, 3, new Feedback(FeedbackToMsgBox)); // "Program." is optional
            Console.WriteLine();
        }

        private static void InstanceDelegateDemo()
        {
            Console.WriteLine("----- Instance Delegate Demo -----");
            DelegateIntro di = new DelegateIntro();

            Counter(1, 3, new Feedback(di.FeedbackToFile));
            Feedback f1 = di.FeedbackToFile;
            
            Console.WriteLine();
        }

        private static void ChainDelegateDemo1(DelegateIntro di)
        {
            Console.WriteLine("----- Chain Delegate Demo 1 -----");
            Feedback fb1 = new Feedback(FeedbackToConsole);
            Feedback fb2 = new Feedback(FeedbackToMsgBox);
            Feedback fb3 = new Feedback(di.FeedbackToFile);

            Feedback fbChain = null;
            fbChain = (Feedback)Delegate.Combine(fbChain, fb1);
            fbChain = (Feedback)Delegate.Combine(fbChain, fb2);
            fbChain = (Feedback)Delegate.Combine(fbChain, fb3);
            Counter(1, 2, fbChain);

            Console.WriteLine();
            fbChain = (Feedback)Delegate.Remove(fbChain, new Feedback(FeedbackToMsgBox));
            Counter(1, 2, fbChain);
        }


        private static void ChainDelegateDemo2(DelegateIntro di)
        {
            Console.WriteLine("----- Chain Delegate Demo 2 -----");
            Feedback fb1 = new Feedback(FeedbackToConsole);
            Feedback fb2 = new Feedback(FeedbackToMsgBox);
            Feedback fb3 = new Feedback(di.FeedbackToFile);

            Feedback fbChain = null;
            fbChain += fb1;
            fbChain += fb2;
            fbChain += fb3;
            Counter(1, 2, fbChain);

            Console.WriteLine();
            fbChain -= new Feedback(FeedbackToMsgBox);
            Counter(1, 2, fbChain);
        }

        private static void Counter(Int32 from, Int32 to, Feedback fb)
        {
            for (Int32 val = from; val <= to; val++)
            {
                // If any callbacks are specified, call them
                if (fb != null)
                    fb(val);
            }
        }

        private static void FeedbackToConsole(Int32 value)
        {
            Console.WriteLine("ItemC=" + value);
        }

        private static void FeedbackToMsgBox(Int32 value)
        {
            Console.WriteLine("ItemB=" + value);
        }

        private void FeedbackToFile(Int32 value)
        {
            StreamWriter sw = new StreamWriter("Status", true);
            sw.WriteLine("Item=S" + value);
            sw.Close();
        }
    }



    #region 显示调用委托链
    internal static class GetInvocationList
    {
        // Define a Light component.
        internal sealed class Light
        {
            // This method returns the light's status.
            public String SwitchPosition()
            {
                return "The light is off";
            }
        }

        // Define a Fan component.
        internal sealed class Fan
        {
            // This method returns the fan's status.
            public String Speed()
            {
                throw new InvalidOperationException("The fan broke due to overheating");
            }
        }

        // Define a Speaker component.
        internal sealed class Speaker
        {
            // This method returns the speaker's status.
            public String Volume()
            {
                return "The volume is loud";
            }
        }

        // Definition of delegate that allows querying a component's status.
        private delegate String GetStatus();

        public static void Go()
        {
            // Declare(声明) an empty delegate chain.
            GetStatus getStatus = null;

            // Construct the three components, and add their status methods 
            // to the delegate chain.
            getStatus += new GetStatus(new Light().SwitchPosition);
            getStatus += new GetStatus(new Fan().Speed);
            getStatus += new GetStatus(new Speaker().Volume);

            // Show consolidated status report reflecting 
            // the condition of the three components.
            Console.WriteLine(GetComponentStatusReport(getStatus));
        }

        // Method that queries several components and returns a status report
        private static String GetComponentStatusReport(GetStatus status)
        {

            // If the chain is empty, there抯 is nothing to do.
            if (status == null) return null;

            // Use this to build the status report.
            StringBuilder report = new StringBuilder();

            // Get an array where each element is a delegate from the chain.
            Delegate[] arrayOfDelegates = status.GetInvocationList();

            // Iterate over each delegate in the array. 
            foreach (GetStatus getStatus in arrayOfDelegates)
            {

                try
                {
                    // Get a component's status string, and append it to the report.
                    report.AppendFormat("{0}{1}{1}", getStatus(), Environment.NewLine);
                }
                catch (InvalidOperationException e)
                {
                    
                    // Generate an error entry in the report for this component.
                    Object component = getStatus.Target;
                    report.AppendFormat(
                       "Failed to get status from {1}{2}{0}   Error: {3}{0}{0}",
                       Environment.NewLine,
                       ((component == null) ? "" : component.GetType() + "."),
                       getStatus.Method.Name, e.Message);
                }
            }
            
            // Return the consolidated report to the caller.
            return report.ToString();
        }
    }
    #endregion

    #region 局部变量不需要手动包装到类中传给回掉函数
     sealed class AClass2
    {
        private static void UsingLocalVariablesInTheCallbackCode(Int32 numToDo)
        {

            // Some local variables
            Int32[] squares = new Int32[numToDo];
            AutoResetEvent done = new AutoResetEvent(false);

            // Do a bunch of tasks on other threads
            for (Int32 n = 0; n < squares.Length; n++)
            {
                ThreadPool.QueueUserWorkItem(
                   delegate (Object obj)
                   {
                       Int32 num = (Int32)obj;

                   // This task would normally more time consuming
                   squares[num] = num * num;

                   // If last task, let main thread continue running
                   if (Interlocked.Decrement(ref numToDo) == 0)
                           done.Set();
                   }, n);
            }

            // Wait for all the other threads to finish
            done.WaitOne();

            // Show the results
            for (Int32 n = 0; n < squares.Length; n++)
                Console.WriteLine("Index {0}, Square={1}", n, squares[n]);
        }
    }
    #endregion