Ctrl+Left/Right moves focus to other control

Question

I have a WinForms usercontrol (ZedGraphControl) hosted on a WindowsFormsHost WPF control, placed in a nested Grid. When I attempt to handle Ctrl+Left/Right in the WinForms control code the control looses focus, and focus moves to control in the grid cell to the Left/Right.

What may cause this, and how can the behavior be disabled?

Edit: The behavior is triggered if a DataGrid is in the grid cell to the left or right, with cells displayed that can take focus. Also if a TextBox is there, possibly any control that can take editable focus.

Answer 1

Sounds like something in your WPF universe is intercepting those key combinations and using them to move focus. At first, I thought it might be WPF's built-in directional keyboard navigation, but based on your edits, I think it might be something else.

Whatever is happening, you might be able to prevent it by overriding some keyboard processing behavior in WindowsFormsHost.

public class WindowsFormsHostEx : WindowsFormsHost
{
    protected override bool TranslateAcceleratorCore(ref MSG msg, ModifierKeys modifiers)
    {
        const int vkLeft = 0x25;
        const int vkRight = 0x27;

        if (modifiers == ModifierKeys.Control &&
            ((int)msg.wParam == vkLeft || (int)msg.wParam == vkRight))
        {
            var m = Message.Create(msg.hwnd, msg.message, msg.wParam, msg.lParam);
            this.Child?.WindowTarget?.OnMessage(ref m);
            return true;
        }

        return base.TranslateAcceleratorCore(ref msg, modifiers);
    }
}

Based on my tests, this causes the WindowsFormsHostEx to 'claim' all Ctrl+Left/Right keystrokes when the host has focus. It dispatches them to the hosted WinForms content, with WPF apparently carrying on as if the event never happened.