Have a ComboBox not “use” the F4 key

Question

I have an application where the user wants F4 to be the "Process Orders" button. (There is a long history around that key performing this feature.)

Today I found out that if the focus is in a ComboBox then F4 makes the ComboBox perform a dropdown.

Is there a way to make that not happen?

Update: I tried this using Delphi and it happens there too. While I am still curious, this seems to be a "baked in" Windows thing. I am going to ask the users to pick another shortcut.

Answer 1

use this

cboTest.PreviewKeyDown += (o,e) => {
    if (e.Key == Key.F4)
        e.Handled = true;
};

cboTest is your ComboBox Name

Answer 2

The Solution: Use a combobox like this:

  public class myComboBox : ComboBox
    {
        protected override void OnKeyDown(KeyEventArgs e)
        {
            if (e.Key != Key.F4)
            {
                base.OnKeyDown(e);
            }
        }
    }

this is all you want.

Answer 3

In addition to the answers above, here is a reusable solution without the need to create a custom control:

public static class ComboBoxHelper
{
    public static readonly DependencyProperty DisableF4HotKeyProperty =
        DependencyProperty.RegisterAttached("DisableF4HotKey", typeof(bool),
            typeof(ComboBoxHelper), new PropertyMetadata(false, OnDisableF4HotKeyChanged));

    public static bool GetDisableF4HotKey(DependencyObject obj)
    {
        return (bool)obj.GetValue(DisableF4HotKeyProperty);
    }

    public static void SetDisableF4HotKey(DependencyObject obj, bool value)
    {
        obj.SetValue(DisableF4HotKeyProperty, value);
    }

    private static void OnDisableF4HotKeyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var box = d as ComboBox;
        if (d == null) return;

        box.PreviewKeyDown -= OnComboBoxKeyDown;
        box.PreviewKeyDown += OnComboBoxKeyDown;
    }

    private static void OnComboBoxKeyDown(object _, KeyEventArgs e)
    {
        if (e.Key == System.Windows.Input.Key.F4)
        {
            e.Handled = true;
        }
    }
}

In your xaml file, add a namespace reference to the ComboBoxHelper class and set the attached property on your ComboBox:

 <ComboBox h:ComboBoxHelper.DisableF4HotKey="True" />

Answer 4

How are you catching the F4 key? If you use the keypreview, you can override it from bubbling down to the combo box:

private void Form1_Load(object sender, EventArgs e)
{
    this.KeyPreview = true;
    this.KeyDown += new KeyEventHandler(Form1_KeyDown);
}

void Form1_KeyDown(object sender, KeyEventArgs e)
{
    if (e.KeyCode == Keys.F4)
    {
        e.Handled = true;
        MessageBox.Show("F4 Pressed");
    }
}

Answer 5

By default the F4 key opens or closes the dropdown list of a combo box. This behavior can be altered to ignore the F4 key and open the list using the down arrow key instead. This is done by sending a CB_SETEXTENDEDUI to the combo box providing a TRUE parameter. This is assuming that WPF does in fact use the native common controls internally.