用C#实现了一个切换当前活动窗口的功能
说明，按钮一打开播放器，按钮二实现切换播放器为活动窗口并代替键盘按下CTRL+U。
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.Windows.Forms;using System.Diagnostics;namespace testKMPlayerWinForm{    public partial class Form1 : Form    {        [System.Runtime.InteropServices.DllImport("user32.dll")]        public static extern bool SetForegroundWindow(IntPtr hWnd);        System.Diagnostics.Process Proc;        String pn;        public Form1()        {            InitializeComponent();        }        private void button1_Click(object sender, EventArgs e)        {            Proc = new System.Diagnostics.Process();            Proc.StartInfo.FileName = "C:/Program Files/The KMPlayer/KMPlayer.exe";            Proc.Start();            pn = Proc.ProcessName;            System.Threading.Thread.Sleep(1000);            SendKeys.Send("^u");        }        private void button2_Click(object sender, EventArgs e)        {            System.Diagnostics.Process[] p = System.Diagnostics.Process.GetProcessesByName(pn);            if (p.Length > 0)            {                SetForegroundWindow(p[0].MainWindowHandle);                System.Threading.Thread.Sleep(1000);                SendKeys.Send("^u");            }            else            {                button1_Click(sender, e);            }        }    }}