Question

I am banging my head on what looks like such a simple problem to fix in wpf but i have yet to discover why i can’t get my app to behave according to my plan.

I have a small search box that pops-up in my wpf application when user presses ctrl+f. All i want is for the caret to be flashing inside the search box text box, ready to take whatever user input without the user having to click on it. Here is the xaml code for the text box which is visible, enabled, hit testable, tabstopable and focusable.

   <TextBox x:Name="SearchCriteriaTextBox" Text="{Binding SearchCriteria}" Focusable="True" IsEnabled="True" IsTabStop="True" IsHitTestVisible="True" Style="{DynamicResource SearchTextBoxStyle}" Grid.Column="1" Margin="5,10,0,5" />

In the code behind, i have this method called when the visibility of the search box is affected. the search box is loaded at the start of the app.

    /// <summary>
    /// Handles events triggered from focusing on this view.
    /// </summary>
    /// <param name="sender">The sender.</param>
    /// <param name="dependencyPropertyChangedEventArgs">The key event args.</param>
    private void OnIsVisibleChanged(object sender, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
    {
        if (!((bool) dependencyPropertyChangedEventArgs.NewValue))
        {
            return;
        }

        SearchCriteriaTextBox.Focus();
        Keyboard.Focus(SearchCriteriaTextBox);
        SearchCriteriaTextBox.Select(0, 0);

        if (SearchCriteriaTextBox.Text.Length > 0)
        {
            SearchCriteriaTextBox.SelectAll();
        }
    }

The problem is, code gets called, component becomes IsFocused=true but does not gain keyboard focus.
Am I missing something? Unless another control keeps hold ferociously to the keyboard focus which i am pretty sure i didn’t code, why would this piece of rather simple code would not work properly.

Answer 1

As a workaround, you could try using the Dispatcher to set the focus at a later DispatcherPriority, such as Input

Dispatcher.BeginInvoke(DispatcherPriority.Input,
    new Action(delegate() { 
        SearchCriteriaTextBox.Focus();         // Set Logical Focus
        Keyboard.Focus(SearchCriteriaTextBox); // Set Keyboard Focus
     }));

From the description of your problem, it sounds like you don’t have Keyboard focus set. WPF can have multiple Focus Scopes, so multiple elements can have Logical Focus (IsFocused = true), however only one element can have Keyboard Focus and will receive keyboard input.

The code you posted should set the focus correctly, so something must be occurring afterwards to move Keyboard Focus out of your TextBox. By setting focus at a later dispatcher priority, you’ll be ensuring that setting keyboard focus to your SearchCriteriaTextBox gets done last.