C#声明一个接口IPlayer,包含5个接口方法：播放、停止、暂停、上一首和下一首

声明一个接口IPlayer,包含5个接口方法：播放、停止、暂停、上一首和下一首。设计一个Windows应用程序，在该程序中定义一个MP3播放器类和一个AVI播放器类，以实现该接口，最后创建相应类的实例测试程序，图

所示为单击“MP3”按钮后，再点击“播放”按钮的效果。如果点击“AVI”按钮后，再点击“播放”按钮，则应显示“正在播放AVI视频！”。

代码如下：

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 Text5
{
    public partial class Form3 : Form
    {
        IPlayer iplayer;
        MP3 mp3;
        AVI avi;
        public Form3()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            mp3 = new MP3();
            iplayer = (IPlayer)mp3;
        }

        private void button7_Click(object sender, EventArgs e)
        {
            avi = new AVI();
            iplayer = (IPlayer)avi;
        }
        private void button2_Click(object sender, EventArgs e)
        {
            lblshow.Text = iplayer.Pre();
        }

        private void button3_Click(object sender, EventArgs e)
        {
            lblshow.Text = iplayer.Stop ();
        }

        private void button4_Click(object sender, EventArgs e)
        {
            lblshow.Text = iplayer.Play();
        }

        private void button5_Click(object sender, EventArgs e)
        {
            lblshow.Text = iplayer.Pause();

        }

        private void button6_Click(object sender, EventArgs e)
        {
            lblshow.Text = iplayer.Next();
        }
    }
    interface IPlayer
    {
        string Play();
        string Stop();
        string Pause();
        string Pre();
        string Next();
    }
    public class MP3 : IPlayer
    {
     //copy from iotword.com
        public string Play() {
            return "正在播放MP3歌曲！";
        }
        public string Stop()
        {
            return "停止播放MP3歌曲！";
        }
        public string Pause()
        {
            return "暂停播放MP3歌曲！";
        }
        public string Pre()
        {
            return "播放上一首MP3歌曲！";
        }
        public string Next()
        {
            return "播放下一首MP3歌曲！";
        }
    }
    public class AVI : IPlayer
    {
        public string Play()
        {
            return "正在播放AVI视频！";
        }
        public string Stop()
        {
            return "停止播放AVI视频！";
        }
        public string Pause()
        {
            return "暂停播放AVI视频！";
        }
        public string Pre()
        {
            return "播放上一个AVI视频！";
        }
        public string Next()
        {
            return "播放下一个AVI视频！";
        }
    }
}