Question

I have some nested SplitContainers and there is one undesired behaviour happening. Every time the splitter moves, the controls get their text selected (the text gets highlighted), specially the ComboBoxes.

I don’t know why thios happens. The problem is fairly easy to reproduce. You just need to:

1. Create the form.
2. A put a split container in it.
3. Add a ComboBox with some items.
4. Anchor the left and right sides of the ComboBox.
5. Compile
6. Move the Splitter

You will see that the ComboBox will have its text highlighted.

How can I prevent this from happening? Or at least, remove the highlight from the ComboBoxes?

Thanks a lot for your help!

Answer 1

This is an age-old bug in the Windows native combobox control. Yes, it selects the text when it gets the WM_SIZE message. This is specific to DropDownStyle = DropDown.

This is a possible workaround:

using System;
using System.Windows.Forms;

class MyComboBox : ComboBox {
    protected override void OnResize(EventArgs e) {
        if (!this.Focused && this.DropDownStyle == ComboBoxStyle.DropDown) {
            this.SelectionLength = 0;
        }
        base.OnResize(e);
    }
}