C# – WPF: OnKeyDown() not being called for space key in control derived from WPF TextBox

conkeydowntextboxwpf

In a WPF application, I have a control that I have derived from TextBox like this:

public class SelectableTextBlock : TextBox
{
    protected override void OnKeyDown(KeyEventArgs e)
    {
        base.OnKeyDown(e);
        e.Handled = false;
    }
}

The OnKeyDown method is not called when entering a space into the TextBox, nor when hitting Backspace, but does fire for other input including normal printable characters (e.g. 'a') and modifier keys (e.g. ).

I'm using this control with IsReadOnly set to true so I can display selectable, uneditable text. The control used within WPFToolkit's DataGrid, and I want KeyDown events to propagate up the data grid, even if the SelectableTextBlock has focus, which is why I am using a custom control to explicitly mark the event as unhandled.

The problem is that the event isn't even making it to my control for certain keys. I can't just use OnPreviewKeyDown in the DataGrid to get round this, since I do want other controls used in the data grid to swallow the space KeyDown event.

Does anyone know how I can get the KeyDown event for the space key to propagate up?

Thanks.

Best Answer

The PreviewKeyDown event exists exactly for this sort of thing.

private void spacebarHandler_PreviewKeyDown(object sender, KeyEventArgs e)
{
    if (e.Key == Key.Space)
        e.Handled = true;
}

Your KeyDown handler will never receive the KeyDown event for spacebar.

Related Solutions

WPF TextBox not accepting Input when in ElementHost in Window Forms

I finally figured it out after 2 days of head scatching...

The MFC Dialog window was taking the WM_CHAR messages and preventing the control from handling the input. So in order to prevent this, I hook the HwndSource and whenever I receive the WM_GETDLGCODE message I respond back with the types of input to accept, and then mark the event as handled.

I created my own TextBox in order to prevent having to fix every textbox (see Below):

    /// <summary>
    /// Interop Enabled TextBox : This TextBox will properly handle WM_GETDLGCODE Messages allowing Key Input
    /// </summary>
    class IOTextBox : TextBox
    {
        private const UInt32 DLGC_WANTARROWS = 0x0001;
        private const UInt32 DLGC_WANTTAB = 0x0002;
        private const UInt32 DLGC_WANTALLKEYS = 0x0004;
        private const UInt32 DLGC_HASSETSEL = 0x0008;
        private const UInt32 DLGC_WANTCHARS = 0x0080;
        private const UInt32 WM_GETDLGCODE = 0x0087;

        public IOTextBox() : base()
        {
            Loaded += delegate
                          {
                              HwndSource s = HwndSource.FromVisual(this) as HwndSource;
                              if (s != null)
                                  s.AddHook(new HwndSourceHook(ChildHwndSourceHook));
                          };
        }

        IntPtr ChildHwndSourceHook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
        {
            if (msg == WM_GETDLGCODE)
            {
                handled = true;
                return new IntPtr(DLGC_WANTCHARS | DLGC_WANTARROWS | DLGC_HASSETSEL);
            }
            return IntPtr.Zero;
        }
    }

C# – How to handle text edition from the KeyDown event

KeyPress is the best way to handle text input.

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