大家好，我是阿辉。
创建线程一种简单的方式是委托的异步调用，Delegate类提供了BeginInvoke方法，该方法可以传递委托类型定义的参数(所以BeginInvoke参数数量是可变的)，另外还有2个固定的参数 回调函数委托AsynsCallBack和类型Object(如果不使用可直接赋值为null)。
BeginInvoke() 的返回值为IAsynResult，通过它的IsComplete属性可以判断异步调用是否完成。.
static void Main(string[] args)
{
Func<int, int> act1 = new Func<int, int>(Calculate);
Console.WriteLine("Main Start....");
IAsyncResult ar = act1.BeginInvoke(20,null, null);
while (!ar.IsCompleted)
{
Console.WriteLine("Main is waiting");
Thread.Sleep(500);
}
int result = act1.EndInvoke(ar);
Console.WriteLine("Result is " + result);
Console.ReadLine();
}
private static int Calculate(int total)
{
int sum = 0;
for (int i = 0; i < total;i++ )
{
sum += i;
Thread.Sleep(100);
}
return sum;
}
运行返回结果：
Main Start....
Main is waiting
Main is waiting
Main is waiting
Main is waiting
Main is waiting
Result is 190
事实上，EndInvoke也是会等到异步调用结束，返回结果的。此外，IAsynResult的AsyncWaitHandle属性是WaitHandle类型，利用WaitOne()能够达到上述同样的效果，我觉得有一个好处就是可以利用WaitAll()等待多个异步调用同时完成：
static void Main(string[] args)
{
Func<int, int> act1 = new Func<int, int>(Calculate);
Func<int, int> act2 = new Func<int, int>(Calculate);
Console.WriteLine("Main Start....");
IAsyncResult ar1 = act1.BeginInvoke(20,null, null);
IAsyncResult ar2 = act2.BeginInvoke(30, null, null);
if(WaitHandle.WaitAll(new WaitHandle[]{ar1.AsyncWaitHandle,ar2.AsyncWaitHandle},5000))
{
Console.WriteLine("Waiting is over");
}
int result1 = act1.EndInvoke(ar1);
int result2 = act2.EndInvoke(ar2);
Console.WriteLine("Result1 is {0},Result2 is {1}", result1, result2);
Console.ReadLine();
}
private static int Calculate(int total)
{
int sum = 0;
for (int i = 0; i < total;i++ )
{
sum += i;
Thread.Sleep(100);
}
return sum;
}
我声明了act1和act2两个委托对象，并同时进行异步调用，WaitHandle.WaitAll(new WaitHandle[]{ar1.AsyncWaitHandle,ar2.AsyncWaitHandle},5000) 等待同时完成，最后返回结果：
Main Start....
Waiting is over
Result1 is 190,Result2 is 435
除了以上2种方式返回运行结果，还可以使用AsynsCallBack回调，BeginInvoke()的最后一个参数可以用ar.Asynstate访问，以便在回调函数中使用，例如传递委托实例获取运行结果：
static void Main(string[] args)
{
Func<int, int> act1 = new Func<int, int>(Calculate);
Console.WriteLine("Main Start....");
IAsyncResult ar1 = act1.BeginInvoke(20, new AsyncCallback(CalculateComplete), act1);
while(!ar1.IsCompleted){
Console.WriteLine("Main is waiting");
Thread.Sleep(500);
}
Console.ReadLine();
}
private static int Calculate(int total)
{
int sum = 0;
for (int i = 0; i < total;i++ )
{
sum += i;
Thread.Sleep(100);
}
return sum;
}
private static void CalculateComplete(IAsyncResult ar)
{
Console.WriteLine("Counting is over...........");
Func<int, int> act = ar.AsyncState as Func<int, int>;
Console.WriteLine("Result is "+act.EndInvoke(ar));
}
运行结果：
Main Start....
Main is waiting
Main is waiting
Main is waiting
Main is waiting
Main is waiting
Counting is over...........
Result is 190
回调函数是在委托线程中完成的，还可以使用Lamda表达式，更加简便，传入最后一个参数，因为Lamda表达式可以访问域外变量：
static void Main(string[] args)
{
Func<int, int> act1 = new Func<int, int>(Calculate);
Console.WriteLine("Main Start....");
IAsyncResult ar1 = act1.BeginInvoke(20, ar => { Console.WriteLine("Result is " + act1.EndInvoke(ar)); }, null);
while(!ar1.IsCompleted){
Console.WriteLine("Main is waiting");
Thread.Sleep(500);
}
Console.ReadLine();
} 