Method to highlighting Text in TextBox is inconsistent

Question

Currently I am using this method to highlight text inside a TextBox, but it works just sometimes.

This code has to verify if there is contained a space in the entered text. If there is a space in the text the user should be warned, and then the text inside the TextBox has to be highlighted:

if (textBox.Text.Contains(" "))
{
    MessageBox.Show("Sorry, the value entered must not contain any spaces.", "Please enter a valid value", MessageBoxButton.OK, MessageBoxImage.Error);

    //Highlights incorrect text
    textBox.SelectionStart = 0;
    textBox.SelectionLength = textBox.Text.Length;
}

Why isn't this method working for me all the time and what can I do to fix it?

Please consider using a simple keypress javascript event to cancel any spaces the user puts in... makes a much better user experience. — Adam Heeg, Jun 24 '14 at 19:12
Valadate and DataError are much better user experiences. Message box is very obtrusive. — paparazzo, Jun 24 '14 at 19:20

Dmitry Zaets · Accepted Answer · 2014-06-24T20:08:00.450

0

It might be a problem when you are selecting length of textBox which has no focus in current moment.

Can you try to add check for focus?

if (textBox.Text.Contains(" "))
{
    MessageBox.Show("Sorry, the value entered must not contain any spaces.", "Please enter a valid value", MessageBoxButton.OK, MessageBoxImage.Error);

    if(!textBox.Focused)
    {
      textBox.Focus();
    }

    //Highlights incorrect text
    textBox.SelectionStart = 0;
    textBox.SelectionLength = textBox.Text.Length;
}

Also instead of current solution you can use textBox.SelectAll():

if (textBox.Text.Contains(" "))
{
    textBox.SelectAll();
    MessageBox.Show("Sorry, the value entered must not contain any spaces.", "Please enter a valid value", MessageBoxButton.OK, MessageBoxImage.Error);

}

edited Jun 24 '14 at 20:08

answered Jun 24 '14 at 19:13

Dmitry Zaets

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The c# code would be `if(!textBox.Focus())`. I tried it, it worked once and I was hopeful, but then on the other attempts it failed... – Eric after dark Jun 24 '14 at 19:17
Can you describe in which cases it fails? – Dmitry Zaets Jun 24 '14 at 19:18
Actually you should not call Focus method if element already has focus. So check if textbox.Focused - makes sens. – Dmitry Zaets Jun 24 '14 at 19:19
Never mind, it's working now. It was my fault. But just for clarity, when I use `textBox.Focused` it says that `textBox` does not contain a definition for `Focused`. – Eric after dark Jun 24 '14 at 19:20
Ah, ok. And what about textBox.SelectAll() method? Does it exist? – Dmitry Zaets Jun 24 '14 at 19:20
Yep, textBox.SelectAll() exists. – Eric after dark Jun 24 '14 at 19:22
Than you can use SelectAll instead of your code, I think it should even set focus. – Dmitry Zaets Jun 24 '14 at 19:23
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/56228/discussion-between-eric-after-dark-and-u10). – Eric after dark Jun 24 '14 at 19:27

Method to highlighting Text in TextBox is inconsistent

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