失去焦点后在 ElementHost 中的 WPF RichTextBox 中显示选择

Question

I'm currently developing a windows forms application (basically a document editor) with a WPF RichTextBox. Of course, since all the rest is a windows forms app, I host the WPF RichTextBox inside an ElementHost.

The problem is that I want to keep the selection in the RichTextBox visible, even if it doesn't have focus. For example, I have several text formatting buttons (bold, italic, ...) in the toolbar, and when I press one of them, I currently can't see the selection anymore because the RichTextBox loses focus.

Unfortunately, the RichTextBox doesn't have a HideSelection property like some WinForms controls.

I have already tried cancelling the LostFocus event as described in other posts. However, this doesn't seem to work when the RichTextBox is hosted inside an ElementHost (I tried and it did work in a WPF-only project).

I also experimented a bit with setting/resetting selection background colors when losing/gaining focus, but this seems very hackish and it's much effort to make it work reliably.

Does anyone have an idea how this could be achieved?

Thank you!

Answer 1

I found a solution:

Add a second RichTextBox to your ElementHost (with a height of 0).
In the LostFocus of your RichTextBox do this:

bool firstLost = true;

void yourRichTextBox_LostFocus(object sender, RoutedEventArgs e)
{
        e.Handled = true;

        if (firstLost)
        {
            yourRichTextBox.Focus();
            firstLost = false;
        }
        else
        {
            firstLost = true;
        }

        invisibleRichTextBox.Focus();
}

So it gets the Focus, gives it to the invisible RichTextBox (so the e.Handled = true; works correct) and then you can do whatever you want in your WinForms-controls.

Does only work it the focus is set to a control of the same form - if you leave the parentform directly from your WPF-RichTextBox it loses the selection-highlight. (The LostFocus-Event seems not to be raised.)

Edit: You can catch the Deactivate-event from your form and focus the yourRichTextBox and then focus the invisivleRichTextBox . So you con directly leave your form.