How to hide close button in WPF window?

Question

I'm writing a modal dialog in WPF. How do I set a WPF window to not have a close button? I'd still like for its WindowState to have a normal title bar.

I found ResizeMode, WindowState, and WindowStyle, but none of those properties allow me to hide the close button but show the title bar, as in modal dialogs.

Answer 1

WPF doesn't have a built-in property to hide the title bar's Close button, but you can do it with a few lines of P/Invoke.

First, add these declarations to your Window class:

private const int GWL_STYLE = -16;
private const int WS_SYSMENU = 0x80000;
[DllImport("user32.dll", SetLastError = true)]
private static extern int GetWindowLong(IntPtr hWnd, int nIndex);
[DllImport("user32.dll")]
private static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

Then put this code in the Window's Loaded event:

var hwnd = new WindowInteropHelper(this).Handle;
SetWindowLong(hwnd, GWL_STYLE, GetWindowLong(hwnd, GWL_STYLE) & ~WS_SYSMENU);

And there you go: no more Close button. You also won't have a window icon on the left side of the title bar, which means no system menu, even when you right-click the title bar - they all go together.

Note that Alt+F4 will still close the Window. If you don't want to allow the window to close before the background thread is done, then you could also override OnClosing and set Cancel to true, as Gabe suggested.