Question

I want to close window with some name (any application, for example, calculator and etc.). How to do it in C#? Import WinAPI functions?

Answer 1

Yes, you should import the Windows API functions: FindWindow(), SendMessage(); and WM_CLOSE constant.

Native definitions of the Windows API functions:

[DllImport("user32.dll", SetLastError = true)]
static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

/// <summary>
/// Find window by Caption only. Note you must pass IntPtr.Zero as the first parameter.
/// </summary>
[DllImport("user32.dll", EntryPoint = "FindWindow", SetLastError = true)]
static extern IntPtr FindWindowByCaption(IntPtr ZeroOnly, string lpWindowName);

[DllImport("user32.dll", CharSet = CharSet.Auto)]
static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam);

const UInt32 WM_CLOSE = 0x0010;

Client code:

IntPtr windowPtr = FindWindowByCaption(IntPtr.Zero, "Untitled - Notepad");
if (windowPtr == IntPtr.Zero)
{
    Console.WriteLine("Window not found");
    return;
}

SendMessage(windowPtr, WM_CLOSE, IntPtr.Zero, IntPtr.Zero);