搞明白 委托 本质

委托是风，委托是雨，委托是唯一的神话。呵呵。

定义一个委托

public delegate int TakesAWhileDelegate(int data,int ms);在正统的.NET语言里这是个不伦不类的东西，去掉delegate关键字

public int TakesAWhileDelegate(int data,int ms);

就是个方法，加上个关键字就变成了一个委托。就这么一句，反射工具反射后会看到他的一些东西

Base Types:基类 。一个正常的方法被加上一个delegate之后就成了一个委托，该方法名变成了一个类名,它的基类是System.MulticastDelegate,MuticastDelegate的基类是Delegate，先看System.MuticastDelegate类的定义，这个类有2个私有变量

IntPtr _invocationCount: 类型是整形指针类型，invocationCount表示调用次数。

object _invocationList:表示调用列表，类型是一个object。

[Serializable, ComVisible(true)]
public abstract class MulticastDelegate : Delegate
{
    // Fields
    private IntPtr _invocationCount;
    private object _invocationList;

    // Methods
    // 构造函数,参数类型是object和string。 
    protected MulticastDelegate(object target, string method);
    protected MulticastDelegate(Type target, string method);
    // 将此委托与指定的委托合并以形成新的委托,follow表示要被合并的委托。
    protected sealed override Delegate CombineImpl(Delegate follow);
    [DebuggerNonUserCode] //DebuggerNonUserCode的属性，这表明这段代码将在调试运行时，调试器不会进入其中。
    private void CtorClosed(object target, IntPtr methodPtr);
    [DebuggerNonUserCode]
    private void CtorClosedStatic(object target, IntPtr methodPtr);
    [DebuggerNonUserCode]
    private void CtorOpened(object target, IntPtr methodPtr, IntPtr shuffleThunk);
    [DebuggerNonUserCode]
    private void CtorRTClosed(object target, IntPtr methodPtr);
    [DebuggerNonUserCode]
    private void CtorSecureClosed(object target, IntPtr methodPtr, IntPtr callThunk, IntPtr assembly);
    [DebuggerNonUserCode]
    private void CtorSecureClosedStatic(object target, IntPtr methodPtr, IntPtr callThunk, IntPtr assembly);
    [DebuggerNonUserCode]
    private void CtorSecureOpened(object target, IntPtr methodPtr, IntPtr shuffleThunk, IntPtr callThunk, IntPtr assembly);
    [DebuggerNonUserCode]
    private void CtorSecureRTClosed(object target, IntPtr methodPtr, IntPtr callThunk, IntPtr assembly);
    [DebuggerNonUserCode]
    private void CtorSecureVirtualDispatch(object target, IntPtr methodPtr, IntPtr shuffleThunk, IntPtr callThunk, IntPtr assembly);
    [DebuggerNonUserCode]
    private void CtorVirtualDispatch(object target, IntPtr methodPtr, IntPtr shuffleThunk);
    private object[] DeleteFromInvocationList(object[] invocationList, int invocationCount, int deleteIndex, int deleteCount);
    private bool EqualInvocationLists(object[] a, object[] b, int start, int count);
    public sealed override bool Equals(object obj);
    public sealed override int GetHashCode();
    public sealed override Delegate[] GetInvocationList();
    protected override MethodInfo GetMethodImpl();
    public override void GetObjectData(SerializationInfo info, StreamingContext context);
    internal override object GetTarget();
    private bool InvocationListEquals(MulticastDelegate d);
    internal bool IsUnmanagedFunctionPtr();
    internal MulticastDelegate NewMulticastDelegate(object[] invocationList, int invocationCount);
    internal MulticastDelegate NewMulticastDelegate(object[] invocationList, int invocationCount, bool thisIsMultiCastAlready);
    public static bool operator ==(MulticastDelegate d1, MulticastDelegate d2);
    public static bool operator !=(MulticastDelegate d1, MulticastDelegate d2);
    protected sealed override Delegate RemoveImpl(Delegate value);  //从一个委托的调用列表中移除另一个委托的调用列表。
    internal void StoreDynamicMethod(MethodInfo dynamicMethod);
    [DebuggerNonUserCode]
    private void ThrowNullThisInDelegateToInstance();
    private bool TrySetSlot(object[] a, int index, object o);
}

 
Expand Methods
 

下面着重看几个比较重要的：

MulticastDelegate 是一个特殊类。编译器和其他工具可以从此类派生，但是您不能显式地从此类进行派生。Delegate 类也是如此。

    protected MulticastDelegate(object target, string method) : base(target, method)
    {
    }

什么是 target ,什么是 method，:base(target,method)又是什么意思？

举个例子：

public delegate int TakesAWhileDelegate(int data, int ms);

static int TakesAWhile(int data, int ms)
        {
            Console.WriteLine("begin");
            System.Threading.Thread.Sleep(ms);
            Console.WriteLine("completed");
            return ++data;
        }

 static void Main(string[] args)
        {

           TakesAWhileDelegate dl = TakesAWhile;

           dl.GetType();  //设置断点，运行。

        }

可以看出,Method描述了一个方法，{Method={Int32 TakesAWhile(Int32,Int32)}}

鼠标继续悬在base{System.Delegate}这一行。

_methodBase:类型是MethodBase类，提供有关方法和构造函数的信息。这边表示方法的信息{Int32 TakesAWhile(Int32,Int32)}

_methodPtr:这边表示方法的指针，IntPtr型。

_methodPtrAux:Aux辅助的意思。

Target什么时候不为null呢？

继续，public virtual Delegate[] GetInvocationList();

            public delegate void del(object sender, EventArgs e);
            public static event del evt;

            del handler = new del(method1);
            handler += new del(method2);
            foreach (del d in handler.GetInvocationList())
            {
                d(null, null);
            }

            //扩展下
            evt += new del(method1);
            evt += new del(method2);
            foreach (del d in evt.GetInvocationList())
            {
                d(null, null);
            }

        public static void method1(object sender, EventArgs e)
        { Console.WriteLine("方法一"); }
        public static void method2(object sender, EventArgs e)
        { Console.WriteLine("方法二"); }

结果是一致的。