Silverlight TextBox, moving caret position

Question

Hi,

I am trying to make a TextBox behavior for an on-screen keyboard, it can update the text in the textbox but I can't get it to focus the textbox and move the caret to the end of the text once it's done updating.

I have tried using TextBox.Focus() and TextBox.Select() in both orders with no luck.

Thanks for your time

Answer 1

Changing the focus from within an input event handler (i.e. mouse click on a virtual key) will fail, since the mouse-up event (or key-up) will return the focus to the original element. In order to make it work, you have to dispatch the focus command to a later time using the Dispatcher object.

Example:

Dispatcher.Invoke(new Action(() =>
{
    textBox1.Focus();
    textBox1.SelectionStart = textBox1.Text.Length;
    // or textBox1.Select(textBox1.Text.Length,0);
}), System.Windows.Threading.DispatcherPriority.Background);

Answer 2

Here is a simple example of moving the cursor to the end of a TextBox once you have updated it.

TextBox.Focus();
TextBox.Text = "sometext ";
TextBox.SelectionStart = TextBox.Text.Length;

Answer 3

I've tried the following basic code and it still doesn't even set the focus on the text box, the FocusAction method does get called though:

    private delegate void FocusDelegate();

    private void FocusAction()
    {
        Target.Focus();
    }

    public void KeyPressed(KeystrokeInformation keystrokeInformation)
    {
        Target.Text += keystrokeInformation.Key;

        Dispatcher.BeginInvoke(new FocusDelegate(FocusAction));
    }

Answer 4

I had a similar situation and I attached a "TextChanged" Handler to my textbox as shown here.

<TextBox Name="tbTextEntry" Width="200" HorizontalAlignment="Center" Background="Plum" Text="{Binding Entered_text,Mode=TwoWay}" TextChanged="OnTextChanged_Handler"></TextBox>

And handled the event like this(thanks Jeff Beck from comment above):

protected void OnTextChanged_Handler(object sender, RoutedEventArgs e)
{
    TextBox my_text_box = (TextBox)sender;
    my_text_box.SelectionStart = my_text_box.Text.Length;
    Debug.WriteLine("OnTextChanged_Handler called !");
    return;
}

This is inefficient for the cases when a person leaves the onscreen keyboard and start to use the real keyboard because each new character will then cause this handler to be invoked needlessly as the cursor works just fine with real keyboard. Any more efficient solution welcome !

Hope that helps. Thanks.