原文转载自http://www.51testing.com/?uid-175761-action-viewspace-itemid-227073

一、调用 Windows API。
 C#下调用Windows API方法如下:
 1、引入命名空间:using System.Runtime.InteropServices;
 2、引用需要使用的方法,格式:[DllImport("DLL文件")]方法的声明;
 [DllImport("user32.dll")]private static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
 [DllImport("user32.dll")]private static extern bool SetForegroundWindow(IntPtr hWnd);
 [DllImport("user32.dll")]private static extern IntPtr FindWindow(string lpClassName,string lpWindowName);
 [DllImport("user32.dll")]private static extern int SendMessage(IntPtr hWnd,int Msg,int wParam,int lParam);
 [DllImport("user32.dll")]private static extern bool SetCursorPos(int X, int Y);
 [DllImport("user32.dll")]private static extern void mouse_event(int dwFlags, int dx, int dy, int dwData, int dwExtraInfo);
 [DllImport("user32.dll")]private static extern void keybd_event(byte bVk, byte bScan, uint dwFlags, uint dwExtraInfo);
  [DllImport("user32.dll")]private static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndlnsertAfter, int X, int Y, int cx, int cy, uint Flags);
 //ShowWindow参数
 private const int SW_SHOWNORMAL = 1;
 private const int SW_RESTORE = 9;
 private const int SW_SHOWNOACTIVATE = 4;
 //SendMessage参数
 private const int WM_KEYDOWN = 0X100;
 private const int WM_KEYUP = 0X101;
 private const int WM_SYSCHAR = 0X106;
 private const int WM_SYSKEYUP = 0X105;
 private const int WM_SYSKEYDOWN = 0X104;
 private const int WM_CHAR = 0X102;

二、找到目标窗口
1)、根据窗口的标题得到句柄
 IntPtr myIntPtr = FindWindow(null,"窗口名"); //null为类名,可以用Spy++得到,也可以为空
 ShowWindow(myIntPtr, SW_RESTORE); //将窗口还原
 SetForegroundWindow(myIntPtr); //如果没有ShowWindow,此方法不能设置最小化的窗口
2)、遍历所有窗口得到句柄
1 定义委托方法CallBack,枚举窗口API(EnumWindows),得到窗口名API(GetWindowTextW)和得到窗口类名API(GetClassNameW)
 public delegate bool CallBack(int hwnd, int lParam);
 [DllImport("user32")]public static extern int EnumWindows(CallBack x, int y);
  [DllImport("user32.dll")]private static extern int GetWindowTextW(IntPtr hWnd, [MarshalAs(UnmanagedType.LPWStr)]StringBuilder lpString, int nMaxCount);
 [DllImport("user32.dll")]private static extern int GetClassNameW(IntPtr hWnd, [MarshalAs(UnmanagedType.LPWStr)]StringBuilder lpString, int nMaxCount);
2 调用EnumWindows遍历窗口
 CallBack myCallBack = new CallBack(Recall);
 EnumWindows(myCallBack, 0);
3 回调方法Recall
 public bool Recall(int hwnd, int lParam)
 {
  StringBuilder sb = new StringBuilder(256);
  IntPtr PW = new IntPtr(hwnd);

  GetWindowTextW(PW,sb,sb.Capacity); //得到窗口名并保存在strName中
  string strName = sb.ToString();

  GetClassNameW(PW,sb,sb.Capacity); //得到窗口类名并保存在strClass中
  string strClass = sb.ToString();

  if (strName.IndexOf("窗口名关键字") >= 0 && strClass.IndexOf("类名关键字") >= 0)
  {
   return false; //返回false中止EnumWindows遍历
  }
  else
  {
   return true; //返回true继续EnumWindows遍历
  }
 }
3)、打开窗口得到句柄
1 定义设置活动窗口API(SetActiveWindow),设置前台窗口API(SetForegroundWindow)
 [DllImport("user32.dll")]static extern IntPtr SetActiveWindow(IntPtr hWnd);
 [DllImport("user32.dll")][return: MarshalAs(UnmanagedType.Bool)]static extern bool SetForegroundWindow(IntPtr hWnd);
2 打开窗口
 Process proc = Process.Start(@"目标程序路径");
 SetActiveWindow(proc.MainWindowHandle);
 SetForegroundWindow(proc.MainWindowHandle);

三、向指定的窗口输入数据
1 利用发送消息API(SendMessage)向窗口发送数据
 InputStr(myIntPtr, _GameID); //输入游戏ID
 SendMessage(myIntPtr, WM_SYSKEYDOWN, 0X09, 0); //输入TAB(0x09)
 SendMessage(myIntPtr, WM_SYSKEYUP, 0X09, 0);
 InputStr(myIntPtr, _GamePass); //输入游戏密码
 SendMessage(myIntPtr, WM_SYSKEYDOWN, 0X0D, 0); //输入ENTER(0x0d)
 SendMessage(myIntPtr, WM_SYSKEYUP, 0X0D, 0);

 /// <summary>
 /// 发送一个字符串
 /// </summary>
 /// <param name="myIntPtr">窗口句柄</param>
 /// <param name="Input">字符串</param>
 public void InputStr(IntPtr myIntPtr, string Input)
 {
  byte[] ch = (ASCIIEncoding.ASCII.GetBytes(Input));
  for (int i = 0; i < ch.Length; i++)
  {
   SendMessage(PW, WM_CHAR, ch, 0);
  }
 }
2 利用鼠标和键盘模拟向窗口发送数据
 SetWindowPos(PW, (IntPtr)(-1), 0, 0, 0, 0, 0x0040 | 0x0001); //设置窗口位置
 SetCursorPos(476, 177); //设置鼠标位置
 mouse_event(0x0002, 0, 0, 0, 0); //模拟鼠标按下操作
 mouse_event(0x0004, 0, 0, 0, 0); //模拟鼠标放开操作
 SendKeys.Send(_GameID);   //模拟键盘输入游戏ID
 SendKeys.Send("{TAB}"); //模拟键盘输入TAB
 SendKeys.Send(_GamePass); //模拟键盘输入游戏密码
 SendKeys.Send("{ENTER}"); //模拟键盘输入ENTER

另:上面还提到了keybd_event方法,用法和mouse_event方法类似,作用和SendKeys.Send一样。