在此处查看有关如何使用完整源代码执行此操作的示例：

http://www.csharphelp.com/2006/08/get-current-window-handle-and-caption-with-
windows-api-in-c/

[DllImport("user32.dll")]
static extern IntPtr GetForegroundWindow();

[DllImport("user32.dll")]
static extern int GetWindowText(IntPtr hWnd, StringBuilder text, int count);

private string GetActiveWindowTitle()
{
    const int nChars = 256;
    StringBuilder Buff = new StringBuilder(nChars);
    IntPtr handle = GetForegroundWindow();

    if (GetWindowText(handle, Buff, nChars) > 0)
    {
        return Buff.ToString();
    }
    return null;
}

*使用@Doug McClean注释进行 *编辑， 以获得更好的正确性。