Set focus on textbox in WPF from view model (C#) & wPF

Question

I have a textbox and a button in my view.

Now I am checking a condition upon button click and if the condition turns out to be false, displaying the message to the user, and then I have to set the cursor to the text box control.

if (companyref == null)
{
Lipper.Nelson.AdminClient.Main.Views.ContactPanels.CompanyAssociation cs = new Lipper.Nelson.AdminClient.Main.Views.ContactPanels.CompanyAssociation(); 

MessageBox.Show("Company does not exist.", "Error", MessageBoxButton.OK,
                    MessageBoxImage.Exclamation);

    cs.txtCompanyID.Focusable = true;

    System.Windows.Input.Keyboard.Focus(cs.txtCompanyID);

}

The above code is in view model.

The CompanyAssociation is the view name.

But the cursor is not getting set in the textbox.

The xaml is as under

<igEditors:XamTextEditor KeyDown="xamTextEditorAllowOnlyNumeric_KeyDown" Name="txtCompanyID" ValueChanged="txtCompanyID_ValueChanged" Text="{Binding Company.CompanyId, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Width="{Binding ActualWidth, ElementName=border}" Grid.Column="1" Grid.Row="0" VerticalAlignment="Top" Margin="0,5,0,0" HorizontalAlignment="Stretch" IsEnabled="{Binding Path=IsEditable}" />

<Button Template="{StaticResource buttonTemp1}" Command="{Binding ContactCommand}" CommandParameter="searchCompany" Content="Search" Width="80" Grid.Column="2" Grid.Row="0" VerticalAlignment="Top" Margin="0" HorizontalAlignment="Left" IsEnabled="{Binding Path=IsEditable}" />

Please help

Answer 1

Hey Pewned!

Let me answer to your question in three parts.

1. I'm wondering what is "cs.txtCompanyID" in your example? Is it a TextBox control? If yes, then you are on a wrong way. Generally speaking it's not a good idea to have any reference to UI in your ViewModel. You can ask "Why?" but this is another question to post on Stackoverflow :).

2. The best way to track down issues with Focus is... debugging .Net source code. No kidding. It saved me a lot of time many times. To enable .net source code debugging refer to Shawn Bruke's blog.

3. Finally, general approach that I use to set focus from ViewModel is Attached Properties. I wrote very simple attached property, which can be set on any UIElement. And it can be bound to ViewModel's property "IsFocused" for example. Here it is:

   public static class FocusExtension
   {
    public static bool GetIsFocused(DependencyObject obj)
   {
    return (bool)obj.GetValue(IsFocusedProperty);
   }
   
   
    public static void SetIsFocused(DependencyObject obj, bool value)
    {
     obj.SetValue(IsFocusedProperty, value);
    }
   
   
    public static readonly DependencyProperty IsFocusedProperty =
     DependencyProperty.RegisterAttached(
      "IsFocused", typeof(bool),  typeof(FocusExtension),
      new UIPropertyMetadata(false, OnIsFocusedPropertyChanged));
   
   
    private static void OnIsFocusedPropertyChanged(DependencyObject d,
     DependencyPropertyChangedEventArgs e)
    {
     var uie = (UIElement) d;
     if ((bool)e.NewValue)
     {
      uie.Focus(); // Don't care about false values.
     }
    }
   }
   

Now in your View (in XAML) you can bind this property to your ViewModel:

<TextBox local:FocusExtension.IsFocused="{Binding IsUserNameFocused}" />

Hope this helps :). If it doesn't refer to the answer #2.

Cheers.

Answer 2

Hey anvaka,

your focusextension class works great. Thank you for this.

Unfortunately the focus was not visible at my textbox (blinking cursor). Calling DoEvents() helped me out. http://nmarian.blogspot.com/2007/09/doevents-in-wpf.html

Maybe this also works for you, Pewned.

CU

Answer 3

Hi Scott,

Where exactly I have to call DoEvents, so I can get the blinking cursor in the textbox?

Answer 4

        System.Windows.Forms.Application.DoEvents();
        Keyboard.Focus(tbxLastName);

Answer 5

The problem is that once the IsUserNameFocused is set to true, it will never be false. This solves it by handling the GotFocus and LostFocus for the FrameworkElement.

I was having trouble with the source code formatting so here is a link