Unable to focus a button that resides in a DataTemplate

Question

I have a button which is in a DataTemplate on the extended toolkit BusyIndicator control. I have a data trigger (and I've tried a style trigger) bound to the visibility of the BusyIndicator control to have the FocusManager set focus to the button when the BusyIndicator is visible.
This does not work. I've also tried to handle the IsVisibleChanged event on the BusyIndicator to set the focus on the button in the code-behind by traversing the visual tree and that did not work either. Is there some special way to set the keyboard focus on a button?

Answer 1

I think I have had this same problem. Here is the code I used:

public delegate void SimpleDelegate();
private void grid_IsVisibleChanged(object sender, DependencyPropertyChangedEventArgs e)
{
    if (grid.Visibility == System.Windows.Visibility.Visible)
    {
        TextBox tb = (TextBox)(sender as Grid).FindName("theTextbox");

        tb.SelectAll();
        Dispatcher.BeginInvoke(DispatcherPriority.Input, new SimpleDelegate(delegate { tb.Focus(); }));
    }
}

This code also selects all the text when the grid containing the textbox is shown.

Maybe there is a better way to do it, but using the Dispatcher to set the focus seemed to work for me.

Answer 2

This SO article describes how you can select the container of an item in an ItemsControl and navigate the tree to select the item you want to alter (in this case focusing it).

Revising my code from below:

public void WhateverMethodForShowingBusy ()
{
    //Get a reference to your View
    FrameworkElement myView = this.View;  // I generally have a reference to the view living on the ViewModel set at construction time
    // Get a reference to your ItemsControl - in this example by name
    ListBox custListBox = myView.ListBoxName;
    // Get the currently selected Item which will be a CustomerViewModel 
    // (not a DataTemplate or ListBoxItem)
    CustomerViewModel cvm = custListBox.SelectedItem;

    //Generate the ContentPresenter
    ContentPresenter cp = custListBox.ItemContainerGenerator.ContainerFromItem(cvm) as ContentPresenter;

    //Now get the button and focus it.
    Button myButton = cp.FindName("MyButtonName");
    myButton.Focus();
}

The information below is incorrect based on the mistake that IsFocused was a read/write property that would set focus. It is not applicable.

This is another place where MVVM really works well. If you are unfamiliar with MVVM I would highly suggest looking into it. It solves a lot of problems like this and if implemented properly it can make your code much more maintainable.

If you are using an MVVM approach, just host a boolean property (we'll call it IsFocused) on the ViewModel that is sitting behind the DataTemplate. For example we have a Customer class, a CustomerViewModel class which contains an instance of customer, and then your MainViewModel which contains a collection of CustomerViewModels. Your ItemsControl's ItemsSource property is bound to the CustomerViewModels collection, and the DataTemplate button's IsFocused property is bound to the IsFocused property on the CustomerViewModel.

I am unsure of your workflow, but you can essentially do something like so:

public void WhateverMethodForShowingBusy ()
{
    //Get a reference to your View
    FrameworkElement myView = this.View;  // I generally have a reference to the view living on the ViewModel set at construction time
    // Get a reference to your ItemsControl - in this example by name
    ListBox custListBox = myView.ListBoxName;
    // Get the currently selected Item which will be a CustomerViewModel 
    // (not a DataTemplate or ListBoxItem)
    CustomerViewModel cvm = custListBox.SelectedItem;

    //Finally set the property.
    cvm.IsFocused = true;
}

As with all things in MVVM, be sure that you are implementing INotifyPropertyChanged.