Question

I have a WPF app that starts another application, I’d like for my application to change the Icon of this second app. I am able to use GetWindowText and SetWindowText to change the title. Is it possible to do this for the Icon as well?

update

I have no control of the second app.

Answer 1

To change the window title of another application:

Definitions of Win32 API functions and constants:

[DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
public static extern bool SetWindowText(IntPtr hwnd, String lpString);

[DllImport("user32.dll")]
public static extern int SendMessage(IntPtr hwnd, int message, int wParam, IntPtr lParam);

private const int WM_SETICON = 0x80;
private const int ICON_SMALL = 0;
private const int ICON_BIG = 1;

Usage:

Process process = Process.Start("notepad");
// If you have just started a process and want to use its main window handle,
// consider using the WaitForInputIdle method to allow the process to finish starting,
// ensuring that the main window handle has been created.
// Otherwise, an exception will be thrown.
process.WaitForInputIdle();
SetWindowText(process.MainWindowHandle, "Hello!");
Icon icon = new Icon(@"C:\Icon\File\Path.ico");
SendMessage(process.MainWindowHandle, WM_SETICON, ICON_BIG, icon.Handle);