Editbox portion of ComboBox gets selected automatically

Question

I have a small problem that has been annoying me for some hours.

In my WinForms (.NET 3.5) application I create some ComboBoxes (DropDownStyle = DropDown) in a Table

Answer 1

Worked for me to change the selectionLength to 0 when the WM_WINDOWPOSCHANGED gets called. Works even with the tableLayoutPanel set to %.

protected override void WndProc(ref Message m) {
    base.WndProc(ref m);

    if(m.Msg == 0x0047) {   // WM_WINDOWPOSCHANGED = 0x0047 
        if (SelectionLength != 0) {
            SelectionLength = 0;
        }
    }
}

Answer 2

Handle the Resize event for the ComboBox's parent container. Put this line in there:

MyComboBox.SelectionLength = 0

An Example (VB, obviously):

Private Sub MyControl_Resize(sender As Object, e As EventArgs) Handles Me.Resize

    MyComboBox.SelectionLength = 0

End Sub

Good Luck to you!

--BP

Answer 3

This appears to be a bug in the native Windows implementation of ComboBox with DropDownStyle of DropDown.

The fix detailed in the other answers here (setting the SelectionLength property to 0 (zero) in the ComboBox's Resize event) works well most of the time.

However, I found that even that fix to work around this bug does not always work. If the ComboBox is in a TableLayoutPanel, and if that TableLayoutPanel has more than one column with a Percent Size Type, then that fix often does not work.

A picture is worth a thousand words. See the following screen shot of a form I made to demonstrate the problem.

Answer 4

Wow. Thank you guys!

Apparently this bug has persisted many years. I'm building a UserControl with .Net 4 (Visual Studio 2010). Here's is my slightlty modified version of bsneeze's code.

Cheers

using System.Windows.Forms;
using System.Linq;

public MyUserControlCtor()
{
    InitializeComponent();

    foreach( Control ctrl in Controls)
    {
        ComboBox cb = ctrl as ComboBox;
        if (cb != null)
        {
            cb.Resize += (sender, e) =>
            {
                if (!cb.Focused)
                    this.FCHZ_ComboBox.SelectionLength = 0;
            };
        }
    } 
}

Answer 5

This is an old question, but I found it searching for an answer and ended up implementing my own solution. Might as well post it here, right?

    foreach (var cb in Controls.OfType<ComboBox>())
    {
        cb.Resize += (sender, e) => {
            if (!cb.Focused)
                cb.SelectionLength = 0;
        };
    }

intentionally selected text became deselected

This WinForms bug doesn't affect selected ComboBoxes, so by ignoring the ones with Focus, we take care of the problem of losing current selections.

I would have to add the event handler to each and every ComboBox on my dialog.

Taken care of by the foreach loop. Put it in InitializeComponent() or your .ctor if you don't want to break the designer, or have the designer break this.

there was a lot of flicker

I'm only seeing flicker if I resize very fast, but I'm on Win7 so it might be different on XP.

Answer 6

None of the answers so far worked for me. The only reliable method I have found was to post a message asynchronously via BeginInvoke that sets SelectionLength back to zero after all other activity on the control has completed. The amount of flicker is very annoying and unprofessional, but it is the best I could come up with...so far.

internal class FixedComboBox : ComboBox
{
    protected override void OnResize(EventArgs e)
    {
        if (IsHandleCreated && !Focused)
        {
            BeginInvoke((Action)(() =>
                {
                    SelectionLength = 0;
                }));
        }
        base.OnResize(e);
    }
}