步步为营-27-事件

1:先用委托演示

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace Event_PlayMusic
{
    //声明委托
    public delegate string delPlay();
    class PlayMusic
    {
        //定义委托
        public delPlay del;
        private string name;

        public string Name
        {
            get { return name; }
            set { name = value; }
        }

        public PlayMusic(string name)
        {
            this.name = name;
        }

        public void PlaySongs()
        {
            Thread.Sleep(3000);
            if (del != null)
            {
                del();
            }
        }

    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Event_PlayMusic
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnPlaySong_Click(object sender, EventArgs e)
        {
            string songName = "小天狼";
            //事件--先触发后响应
            PlayMusic p = new PlayMusic(songName);
            MessageBox.Show("开始播放" + songName);
            p.del = () => { return "播放完毕"; };
            p.PlaySongs();
            MessageBox.Show(p.del());
         
        }
    }
}

效果
将委托改为事件

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Event_PlayMusic
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnPlaySong_Click(object sender, EventArgs e)
        {
            string songName = "小天狼";
            //事件--先触发后响应
            PlayMusic p = new PlayMusic(songName);
            MessageBox.Show("开始播放" + songName);
            p.del += () => { return "播放完毕"; };            
           string str = p.PlaySongs();
           MessageBox.Show(str);
         
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace Event_PlayMusic
{
    //声明委托
    public delegate string delPlay();
    class PlayMusic
    {
        //定义委托
        public event delPlay del;
        private string name;

        public string Name
        {
            get { return name; }
            set { name = value; }
        }

        public PlayMusic(string name)
        {
            this.name = name;
        }

        public string PlaySongs()
        {
            Thread.Sleep(3000);
            if (del != null)
            {
               return  del();
            }

            return "事件为空!";
        }

    }
}