Charlie Robbins

Now that I’m back from staycation I’ve been looking around at some miscellany that needs to be done at the Lab. One of those items used my open-source (MIT ftw)Custom Chrome Window library. In the process of using it I came across a little bug that’s discussed on the WPF Window Chrome site here.

Basically, even though the “Caption bar” (aka “Title bar,” aka “Window bar,” aka “Non-client Window area”) was hidden, the Window.Top and Window.Left calculations take it into account. After a colleague of mine did some serious Google-foo on Win32 we found this solution which has been added to the library on GitHub. The solution is outlined below, starting with including some Win32 API calls:

public static class SafeNativeMethods
{
    [DllImport("user32.dll")]
    public static extern int GetWindowLong(IntPtr hwnd, int index);

    [DllImport("user32.dll")]
    public static extern int SetWindowLong(IntPtr hwnd, int index, int newStyle);

    [DllImport("user32.dll")]
    public static extern bool SetWindowPos(IntPtr hwnd, IntPtr hwndInsertAfter, int x, int y, int width, int height, uint flags);

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

    internal const int WS_CHILD = 0x40000000;
    internal const int WS_VISIBLE = 0x10000000;
    internal const int LBS_NOTIFY = 0x00000001;
    internal const int HOST_ID = 0x00000002;
    internal const int LISTBOX_ID = 0x00000001;
    internal const int WS_VSCROLL = 0x00200000;
    internal const int WS_BORDER = 0x00800000;


    public const int GWL_EXSTYLE = -20;
    public const int GWL_STYLE = -16;
    public const int WS_EX_DLGMODALFRAME = 0x0001;
    public const int SWP_NOSIZE = 0x0001;
    public const int SWP_NOMOVE = 0x0002;
    public const int SWP_NOZORDER = 0x0004;
    public const int SWP_FRAMECHANGED = 0x0020;
    public const uint WM_SETICON = 0x0080;
    public const int WS_DLGFRAME = 0x00400000;

    public const int WS_SYSMENU = 0x80000;
    public const int WS_MINIMIZEBOX = 0x20000;
    public const int WS_MAXIMIZEBOX = 0x10000;
}

After which we need to call into these methods in the CustomChromeWindow class:

protected override void OnSourceInitialized(EventArgs e)
{
    base.OnSourceInitialized(e);

    // Get this window's handle
    IntPtr hwnd = new WindowInteropHelper(this).Handle;

    // Change the extended window style to not show a window icon
    int extendedStyle = SafeNativeMethods.GetWindowLong(hwnd, SafeNativeMethods.GWL_EXSTYLE);
    int style = SafeNativeMethods.GetWindowLong(hwnd, SafeNativeMethods.GWL_STYLE);

    SafeNativeMethods.SetWindowLong(
        hwnd, 
        SafeNativeMethods.GWL_STYLE,
        style & ~SafeNativeMethods.WS_SYSMENU & ~SafeNativeMethods.WS_MINIMIZEBOX & ~SafeNativeMethods.WS_MAXIMIZEBOX & SafeNativeMethods.WS_DLGFRAME);

    // Update the window's non-client area to reflect the changes
    SafeNativeMethods.SetWindowPos(
        hwnd, 
        IntPtr.Zero, 
        0, 0, 0, 0,
        SafeNativeMethods.SWP_NOMOVE | SafeNativeMethods.SWP_NOSIZE | SafeNativeMethods.SWP_NOZORDER | SafeNativeMethods.SWP_FRAMECHANGED);
}

Hopefully you’ll never have to wallow in the pain of custom window chrome, but if you do take a look at the library on GitHub.