Question

My application starts up another external application.

I want to remove the title bar of this external application once it has started.

Is this feasible, and if so how would it be done?

Based on the comments I am using the working code below

//Finds a window by class name
[DllImport("USER32.DLL")]
public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

//Sets a window to be a child window of another window
[DllImport("USER32.DLL")]
public static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

//Sets window attributes
[DllImport("USER32.DLL")]
public static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

//Gets window attributes
[DllImport("USER32.DLL")]
public static extern int GetWindowLong(IntPtr hWnd, int nIndex);

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


//assorted constants needed
public static int GWL_STYLE = -16;
public static int WS_CHILD = 0x40000000; //child window
public static int WS_BORDER = 0x00800000; //window with border
public static int WS_DLGFRAME = 0x00400000; //window with double border but no title
public static int WS_CAPTION = WS_BORDER | WS_DLGFRAME; //window with a title bar

public void WindowsReStyle()
{
    Process[] Procs = Process.GetProcesses();
    foreach (Process proc in Procs)
    {
        if (proc.ProcessName.StartsWith("notepad"))
        {
            IntPtr pFoundWindow = proc.MainWindowHandle;
            int style = GetWindowLong(pFoundWindow, GWL_STYLE);
            SetWindowLong(pFoundWindow, GWL_STYLE, (style & ~WS_CAPTION));
        }
    }
}

Answer 1

No need to inject anything, you can just modify the windows style bits as using the API, e.g. this works for Notepad, however YMMV depending on the app you’re playing with.

//Get current style
lCurStyle = GetWindowLong(hwnd, GWL_STYLE)

//remove titlebar elements
lCurStyle = lCurStyle And Not WS_CAPTION
lCurStyle = lCurStyle And Not WS_SYSMENU
lCurStyle = lCurStyle And Not WS_THICKFRAME
lCurStyle = lCurStyle And Not WS_MINIMIZE
lCurStyle = lCurStyle And Not WS_MAXIMIZEBOX

//apply new style
SetWindowLong hwnd, GWL_STYLE, lCurStyle

//reapply a 3d border
lCurStyle = GetWindowLong(hwnd, GWL_EXSTYLE)

SetWindowLong hwnd, GWL_EXSTYLE, lCurStyle Or WS_EX_DLGMODALFRAME

//redraw
SetWindowPos hwnd, 0, 0, 0, 0, 0, SWP_NOMOVE Or SWP_NOSIZE Or SWP_FRAMECHANGED