How to make CheckBox focus border appear when calling CheckBox.Focus()?

问题

When the user tabs into a CheckBox to give it focus, a dotted border appears around the CheckBox to indicate that it has focus.

When the CheckBox gets focused by code calling myCheckBox.Focus(), no such indicator appears (even though pressing the space bar toggles the state).

How can I make the CheckBox focus border appear when I have programmatically focused the CheckBox?

回答1:

The border is intentionally only shown if you are navigating by the keyboard (Tab key). The MSDN page on this topic has further details:

Focus visual styles act only when the focus action was initiated by the keyboard. Any mouse action or programmatic focus change disables the mode for focus visual styles.

If you want to show a border, you could use a Trigger on the IsFocused- Property to do some visual changes (although you can't set the border with this) or if you actually want a border, you would have to create your own ControlTemplate.

There is also a thread here on SO on a somewhat related topic where the suggestion is to simulate a key press, but I would suggest not to use this solution for your problem.

回答2:

'initially set chkCheckBox.Appearance = 1

'on Got Focus set appearance = 0 - Flat
Private Sub chkCheckBox_GotFocus()
  chkCheckBox.Appearance = 0
End Sub

'on Lost Focus set appearance = 1 - 3D
Private Sub chkCheckBox_LostFocus()
  chkCheckBox.Appearance = 1
End Sub

回答3:

By editing the KeyboardNavigationEx file from ControlzEx I managed to solve the issue (full credit goes, as always, to punker76).

Just call the KeyboardHelper.Focus method passing the UIElement that shoud be focused (e.g. KeyboardHelper.Focus(myCheckBox))

Here's the KeyboardHelper class:

public sealed class KeyboardHelper
{
    private static KeyboardHelper _Instance;

    private readonly PropertyInfo _AlwaysShowFocusVisual;
    private readonly MethodInfo _ShowFocusVisual;

    // Explicit static constructor to tell C# compiler
    // not to mark type as beforefieldinit
    static KeyboardHelper()
    {
    }

    private KeyboardHelper()
    {
        var type = typeof(KeyboardNavigation);

        _AlwaysShowFocusVisual = type.GetProperty("AlwaysShowFocusVisual", BindingFlags.NonPublic | BindingFlags.Static);
        _ShowFocusVisual = type.GetMethod("ShowFocusVisual", BindingFlags.NonPublic | BindingFlags.Static);
    }

    internal static KeyboardHelper Instance => _Instance ?? (_Instance = new KeyboardHelper());

    internal void ShowFocusVisualInternal()
    {
        _ShowFocusVisual.Invoke(null, null);
    }

    internal bool AlwaysShowFocusVisualInternal
    {
        get { return (bool)_AlwaysShowFocusVisual.GetValue(null, null); }
        set { _AlwaysShowFocusVisual.SetValue(null, value, null); }
    }

    public static void Focus(UIElement element)
    {
        element?.Dispatcher.BeginInvoke(DispatcherPriority.Background, new Action(() =>
        {
            var keybHack = KeyboardHelper.Instance;
            var oldValue = keybHack.AlwaysShowFocusVisualInternal;

            keybHack.AlwaysShowFocusVisualInternal = true;

            try
            {
                Keyboard.Focus(element);
                keybHack.ShowFocusVisualInternal();
            }
            finally
            {
               keybHack.AlwaysShowFocusVisualInternal = oldValue;
            }
        }));
    }
}

来源：https://stackoverflow.com/questions/5400570/how-to-make-checkbox-focus-border-appear-when-calling-checkbox-focus

标签

wpf

checkbox

focus

border

indicator