委托(1)

委托本质上是一种类型跟int、float、string一样，int、float、string可以作为参数传递，声明了委托之后方法也可以像int、float、string一样作为参数传递。
委托一般以EventHandler结尾。

委托的简单使用

public delegate string SayHiEventHandler(string name);
public class DelegateHelper
{
    public void SimpleDelegate()
    {
        //完整形式
        SayHiEventHandler sayHi = new SayHiEventHandler(SayHiByChinese);
        //隐式调用委托
        string result = sayHi("蝈蝈");
        Console.WriteLine("result=" + result);
        sayHi = new SayHiEventHandler(SayHiByEnglish);
        //显示调用委托sayHi.Invoke("guoguo");等价于sayHi("guoguo");
        result = sayHi.Invoke("guoguo");
        Console.WriteLine("result=" + result);

        //简写形式
        SayHiEventHandler sayHiSimple = SayHiByChinese;
        result = sayHiSimple("蝈蝈");
        Console.WriteLine("result=" + result);
        sayHiSimple = SayHiByEnglish;
        result = sayHiSimple.Invoke("guoguo");
        Console.WriteLine("result=" + result);
    }

    public string SayHiByEnglish(string name)
    {
        Console.WriteLine("Hello：" + name);
        return "success";
    }
    public string SayHiByChinese(string name)
    {
        Console.WriteLine("你好：" + name);
        return "成功";
    }
}

运行结果如下：

委托链

委托只能操作与之定义的返回值类型、参数类型、个数都一样的方法。

public delegate string SayHiEventHandler(string name);
public class DelegateHelper
{
    public void DelegateLink()
    {
        SayHiEventHandler sayHi = SayHiByChinese;
        sayHi += SayHiByEnglish;
        //此时调用委托链sayHi("蝈蝈")相当于连续执行SayHiByChinese("蝈蝈");SayHiByEnglish("蝈蝈");
        string result = sayHi("蝈蝈");
        //result是最后一个方法SayHiByEnglish方法的返回值
        Console.WriteLine("result=" + result);
        Console.WriteLine("---------------");
        //委托链能加也能减
        sayHi -= SayHiByEnglish;
        result = sayHi("蝈蝈");
        //result是SayHiByChinese方法的返回值
        Console.WriteLine("result=" + result);
        Console.WriteLine("---------------");
    }
}

运行结果如下：

传递委托类型参数

当方法需要委托类型的参数时，传递过去的方法的返回值类型、参数个数、类型必须与委托完全一致。

//Program.cs文件代码
class Program
{
    static void Main(string[] args)
    {
        new DelegateHelper().SayHi("蝈蝈",new DelegateHelper().SayHiByChinese);
        new DelegateHelper().SayHi("guoguo", new DelegateHelper().SayHiByEnglish);
        Console.ReadKey();
    }
}
//DelegateHelper.cs文件代码
public delegate string SayHiEventHandler(string name);
public class DelegateHelper
{
    public void SayHi(string name,SayHiEventHandler sayHi)
    {
        sayHi(name);
    }
}

运行结果如下：