Set focus on TextBox in WPF from view model

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, displ

Answer 1

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:

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

Cheers.