事件于委托

一、事件
（1）需要一个表示时间参数的对象
class BallEventArgs:EventArgs
    {
        public int Trajectory{get; private set;}
        public int Distence{get; private set;}
        public BallEventArgs(int Trajectoty, int Distence){
            this.Trajectory = Trajectory;
            this.Distence = Distence;
        }
    }
（2）在产生事件的类专用定义这个事件
//产生事件的类
    class Ball
    {
        //定义事件
        //EventHandler告诉事件订购对象它的事件处理方法应该是什么样的
       public event EventHandler BallInPlay;
       
        //产生事件
        public void OnBallInPlay(BallEventArgs e){
            if (BallInPlay != null)
                BallInPlay(this,e);
        }

    }
（3）订购类需要处理事件的方法，各个对象订购事件
class Pitcher
    {//订购事件
        public Pitcher(Ball ball) {
           ball.BallInPlay += new EventHandler(ball_BallInPlay);
        }
        //事件处理程序
        void ball_BallInPlay(object sender, EventArgs e) {
            if (e is BallEventArgs) {
                BallEventArgs ballEventArgs = e as BallEventArgs;
                if (ballEventArgs.Distence < 95 && ballEventArgs.Trajectory < 60)
                    CatchBall();
                else
                    CoverFirstBase();
            }
        }

        private void CatchBall() {
            MessageBox.Show("Pitcher: I catch the ball!");
        }

        private void CoverFirstBase(){
            MessageBox.Show("Pitcher: I cover first base!");
        }
    }
（4）测试
public partial class Form1 : Form
    {
        Ball ball = new Ball();
        Pitcher pitcher;
        public Form1()
        {
            InitializeComponent();
            pitcher = new Pitcher(ball);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            BallEventArgs ballEventArgs = new BallEventArgs((int)numericUpDown1.Value, (int)numericUpDown2.Value);
            ball.OnBallInPlay(ballEventArgs);
        }
    }