Help "?" button - wpf

Question

How can add this button to the title bar in WPF, by it being so used in a lot of applications I thought it would be built in or something, but looks like it isn't. Anyway let me know if you know anything about this.
Thanks.
Edit:
Isn't there anything equivalent to this?
Basically, to have the ? icon in win forms, all you need to do is this:
public Form1()
{
InitializeComponent();
this.HelpButton = true;
this.MaximizeBox = false;
this.MinimizeBox = false;
}
Doesn't WPF have anything like that?

Answer 1

It's simple, just inset this code into your Window class.
This code uses interop to remove the WS_MINIMIZEBOX and WS_MAXIMIZEBOX styles and add the WS_EX_CONTEXTHELP extended style (the question mark will only show up if you remove the minimize and maximize buttons).
EDIT: added click detection on the help button, this is done by hooking into the WndProc using HwndSource.AddHook and listening for a WM_SYSCOMMAND message with wParam of SC_CONTEXTHELP.
When a click is detected this code will show a message box, changing this into an event, routed event or even a command (for MVVM apps) is left as an exercise for the reader.
private const uint WS_EX_CONTEXTHELP = 0x00000400;
private const uint WS_MINIMIZEBOX = 0x00020000;
private const uint WS_MAXIMIZEBOX = 0x00010000;
private const int GWL_STYLE = -16;
private const int GWL_EXSTYLE = -20;
private const int SWP_NOSIZE = 0x0001;
private const int SWP_NOMOVE = 0x0002;
private const int SWP_NOZORDER = 0x0004;
private const int SWP_FRAMECHANGED = 0x0020;
private const int WM_SYSCOMMAND = 0x0112;
private const int SC_CONTEXTHELP = 0xF180;
[DllImport("user32.dll")]
private static extern uint GetWindowLong(IntPtr hwnd, int index);
[DllImport("user32.dll")]
private static extern int SetWindowLong(IntPtr hwnd, int index, uint newStyle);
[DllImport("user32.dll")]
private static extern bool SetWindowPos(IntPtr hwnd, IntPtr hwndInsertAfter, int x, int y, int width, int height, uint flags);
protected override void OnSourceInitialized(EventArgs e)
{
base.OnSourceInitialized(e);
IntPtr hwnd = new System.Windows.Interop.WindowInteropHelper(this).Handle;
uint styles = GetWindowLong(hwnd, GWL_STYLE);
styles &= 0xFFFFFFFF ^ (WS_MINIMIZEBOX | WS_MAXIMIZEBOX);
SetWindowLong(hwnd, GWL_STYLE, styles);
styles = GetWindowLong(hwnd, GWL_EXSTYLE);
styles |= WS_EX_CONTEXTHELP;
SetWindowLong(hwnd, GWL_EXSTYLE, styles);
SetWindowPos(hwnd, IntPtr.Zero, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_NOZORDER | SWP_FRAMECHANGED);
((HwndSource)PresentationSource.FromVisual(this)).AddHook(HelpHook);
}
private IntPtr HelpHook(IntPtr hwnd,
int msg,
IntPtr wParam,
IntPtr lParam,
ref bool handled)
{
if (msg == WM_SYSCOMMAND &&
((int)wParam & 0xFFF0) == SC_CONTEXTHELP)
{
MessageBox.Show("help");
handled = true;
}
return IntPtr.Zero;
}

Answer 2

No help buttons come out of the box with WPF. Should'nt be a push to roll your own however.