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Keep Focus back to the previous Textbox on failed validation

Anonymous User 1917 26-Mar-2014
I want Focus back to the previous Textbox if validation gets failed. I am validating the Textbox control value on lostFocus event. 

Need some help.
c# c# 
Updated on 26-Mar-2014
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1 Answers

Pravesh Singh

Pravesh Singh

26-Mar-2014
Hi Ankit,

If you attempt to focus an element inside its own LostFocus handler you will face a StackOverflowException, I'm not sure about the root cause (I suspect the focus kind of bounces around) but there is an easy workaround: dispatch it.

private void TextBoLostFocus(object sender,RoutedEventArgs e)
{
    var element =(sender as TextBox);
    if(!theTextBoxWasValidated())
    {
        // doing this would cause a StackOverflowException
        //
element.Focus();
        var restoreFocus = (System.Threading.ThreadStart)delegate { element.Focus(); };
       
Dispatcher.BeginInvoke(restoreFocus);
    }
}

Through Dispatcher.BeginInvoke you make sure that restoring the focus doesn't get in the way of the in-progress loss of focus (and avoid the nasty exception you'd face otherwise)

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