WPF - Set Focus when a button is clicked - No Code Behind

Is there a way to set Focus from one control to another using WPF Triggers?

Like the following example:

<Page
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Grid>  
    <Grid.RowDefinitions>
      <RowDefinition/>
      <RowDefinition/>
      <RowDefinition/>
    </Grid.RowDefinitions>

    <TextBox Name="txtName"></TextBox>    
    <TextBox Grid.Row="1" Name="txtAddress"></TextBox>
    <Button Grid.Row="2" Content="Finish">
        <Button.Triggers>
            <EventTrigger RoutedEvent="Button.Click">

                <!-- Insert cool code here-->  

            </EventTrigger>
        </Button.Triggers>
    </Button>
  </Grid>
</Page>

Is there a way for this EventTrigger to put to focus on the textBox "txtName"?

I am trying to find the way to do something like this using strict MVVM. If this is something that should not be done via the XAML (in MVVM) then that is fine. But I would like to see some kind of documentation as to how it fit in the MVVM pattern doing it outside the XAML.

Have you considered using an attached behaviour. They are simple to implement and use AttachedProperty's. Although it still requires code, this code is abstracted away in a class and be reused. They can eliminate the need 'code behind' and are often used with the MVVM pattern.

Try this one and see if it works for you.

public class EventFocusAttachment
{
    public static Control GetElementToFocus(Button button)
    {
        return (Control)button.GetValue(ElementToFocusProperty);
    }

    public static void SetElementToFocus(Button button, Control value)
    {
        button.SetValue(ElementToFocusProperty, value);
    }

    public static readonly DependencyProperty ElementToFocusProperty =
        DependencyProperty.RegisterAttached("ElementToFocus", typeof(Control), 
        typeof(EventFocusAttachment), new UIPropertyMetadata(null, ElementToFocusPropertyChanged));

    public static void ElementToFocusPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        var button = sender as Button;
        if (button != null)
        {
            button.Click += (s, args) =>
                {
                    Control control = GetElementToFocus(button);
                    if (control != null)
                    {
                        control.Focus();
                    }
                };
        }
    }
}

And then in your XAML do something like...

<Button 
    Content="Click Me!" 
    local:EventFocusAttachment.ElementToFocus="{Binding ElementName=textBox}" 
    />
<TextBox x:Name="textBox" />

I'm not near visual studio so I can't actually try this right now, but off the top of my head, you should be able to do something like this:

FocusManager.FocusedElement="{Binding ElementName=txtName}">

Edit:

There is a followup question (asked more recently) about this here: How to set autofocus only in xaml? which contains this method, and a few different ideas on how to use it.

You could also use a WPF Behavior...

    public class FocusElementAfterClickBehavior : Behavior<ButtonBase>
{
    private ButtonBase _AssociatedButton;

    protected override void OnAttached()
    {
        _AssociatedButton = AssociatedObject;

        _AssociatedButton.Click += AssociatedButtonClick;
    }

    protected override void OnDetaching()
    {
        _AssociatedButton.Click -= AssociatedButtonClick;
    }

    void AssociatedButtonClick(object sender, RoutedEventArgs e)
    {
        Keyboard.Focus(FocusElement);
    }

    public Control FocusElement
    {
        get { return (Control)GetValue(FocusElementProperty); }
        set { SetValue(FocusElementProperty, value); }
    }

    // Using a DependencyProperty as the backing store for FocusElement.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty FocusElementProperty =
        DependencyProperty.Register("FocusElement", typeof(Control), typeof(FocusElementAfterClickBehavior), new UIPropertyMetadata());
}

Here is the XAML to use the behavior.

Include namespaces:

xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity" 
xmlns:local="clr-namespace:WpfApplication1"

Attach WPF Behavior to button and bind element you want to set focus to:

<Button Content="Focus" Width="75">
    <i:Interaction.Behaviors>
        <local:FocusElementAfterClickBehavior FocusElement="{Binding ElementName=CheckBoxComboBox, Mode=OneWay}"/>
    </i:Interaction.Behaviors>
</Button>
<ComboBox x:Name="CheckBoxComboBox" HorizontalAlignment="Center" VerticalAlignment="Center" Width="120" Grid.Row="1"/>

So this way you have no code behind and it is reusable on any control that inherits from ButtonBase.

Hope this helps someone.

you need a TriggerAction to invoke the Focus() method on the desired control.

public class SetFocusTrigger : TargetedTriggerAction<Control>
{
 protected override void Invoke(object parameter)
 {
    if (Target == null) return;

    Target.Focus();
 }
}

To have the focus set to a Control , you place a Triggers collection after your LayoutRoot (or any control really), select the event as the trigger, and select the SetFocusTrigger as the class to run. In the SetFocusTrigger declaration, you put the name of the control that you want to receive the focus by using the TargetName property.

<Button x:Name="LayoutRoot" >
<i:Interaction.Triggers>
    <i:EventTrigger EventName="Clicked">
        <local:SetFocusTrigger TargetName="StartHere"/>
    </i:EventTrigger>
</i:Interaction.Triggers>

<TextBox x:Name="StartHere"/>
</Button>