Qfyilyi

I'm trying to reliably detect when focus leaves a group of controls. So if I tab or click between two controls in the group, that's considered not leaving, but as soon as I click on a control outside the group, it raises an event. Here's how I'm currently doing it:

public class LeaveTracker

{

    private HashSet<Control> trackedControls = new HashSet<Control>();

    public void Track(Control ctrl)

    {

        ctrl.Leave += Ctrl_Leave;

        trackedControls.Add(ctrl);

    }



    private void Ctrl_Leave(object sender, EventArgs e)

    {

        foreach (var ctrl in trackedControls)

            if (ctrl.ContainsFocus)

                return;

        if (LeftControlGroup != null)

            LeftControlGroup(this, EventArgs.Empty);

    }

    public event EventHandler LeftControlGroup;

}

Sometimes it works perfectly, but occasionally it seems to stop raising events. Is there a more reliable way to do this?

Apparently, the Leave event gets triggered before the control actually loses focus. You can confirm that by checking the value of (sender as Control).ContainsFocus in your event handler.

Either use the Control.LostFocus event instead:

private void Ctrl_LostFocus(object sender, EventArgs e)

{

    foreach (var ctrl in trackedControls)

        if (ctrl.ContainsFocus)

            return;

    Debug.Print("The tracked controls are not focused anymore!");

    //..

}

Or if you want to use the Leave event, you can wait for a little while until the control actually loses focus. This also worked fine for me:

private async void Ctrl_Leave(object sender, EventArgs e)

{

    while ((sender as Control).ContainsFocus)

        await Task.Delay(50);



    foreach (var ctrl in trackedControls)

        if (ctrl.ContainsFocus)

            return;

    Debug.Print("The tracked controls are not focused anymore!");

    //..

}

A better alternative to using await is to wrap the code under Ctrl_Leave in a BeginInvoke delegate as suggested by Hans Passant:

private void Ctrl_Leave(object sender, EventArgs e)

{

    BeginInvoke((Action)(() =>

    {

        foreach (var ctrl in trackedControls)

            if (ctrl.ContainsFocus)

                return;

        Debug.Print("The tracked controls are not focused anymore!");

        //..

    }));

}