c#调用winAPI向某一程序发送按键

[DllImport("USER32.DLL")]
public static extern IntPtr FindWindow(string lpClassName,string lpWindowName);
[DllImport("USER32.DLL")]
public static extern bool SetForegroundWindow(IntPtr hWnd);

IntPtr calculatorHandle = FindWindow(null, "Form1");//窗口名称
if (calculatorHandle == IntPtr.Zero)
{
MessageBox.Show("not running.");
return;
}

SetForegroundWindow(calculatorHandle);
SendKeys.SendWait("111");
SendKeys.SendWait("*");
SendKeys.SendWait("11");
SendKeys.SendWait("=");