wpf - Help "?" button

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;
}