> Pete

> On Mon, Mar 15, 2010 at 2:24 PM, Josh Smith <flappleja...@gmail.com>wrote:

>> Thanks.  Any pitfalls or gotchas sticking their heads out?

>> On Mon, Mar 15, 2010 at 1:03 AM, Peter O'Hanlon <pete.ohan...@gmail.com>wrote:

>>> I like it - I know that it feels "dirty", but it's actually pretty darn
>>> cool.

>>>  On Mon, Mar 15, 2010 at 3:54 AM, Josh Smith <flappleja...@gmail.com>wrote:

>>>> A while back Dr. WPF graced us with his clever hack of controlling input
>>>> focus from VM objects.  It involved hijacking the VM's IDataErrorInfo
>>>> implementation, and doing all sorts of evil-genius stuff to make the input
>>>> caret move to the correct element.  Today while I was *trying* to read
>>>> a great novel, I couldn't stop thinking about another way to control input
>>>> focus from a viewmodel object.

>>>> I put the novel down and did a quick spike of the idea.  The source code
>>>> is attached (rename it from .DOC to .ZIP since gmail is terrified of ZIP
>>>> files for some reason).  Here's the general idea...

>>>> Implement this interface on your VM class:

>>>>  /// <summary>
>>>> /// Implemented by a ViewModel that needs to control
>>>> /// where input focus is in a View.
>>>> /// </summary>
>>>> public interface IFocusController
>>>> {
>>>>     /// <summary>
>>>>     /// Raised when the input focus should move to
>>>>     /// a control whose 'active' dependency property
>>>>     /// is bound to the specified property.
>>>>     /// </summary>
>>>>     event EventHandler<MoveFocusEventArgs> MoveFocus;
>>>> }

>>>> Next, in your VM object (which might implement IDataErrorInfo), do
>>>> something like this to support a Save button:

>>>>  public ICommand SaveCommand
>>>> {
>>>>     get { return new RelayCommand(this.Save); }
>>>> }

>>>> void Save()
>>>> {
>>>>     if (this.HasError)
>>>>     {
>>>>         // The Error property knows which property is invalid.
>>>>         this.RaiseMoveFocus(this.Error);
>>>>     }
>>>>     else
>>>>     {
>>>>         // Save to database...
>>>>         System.Windows.MessageBox.Show("Saved");
>>>>     }
>>>> }

>>>> bool HasError
>>>> {
>>>>     get { return _validatedProperties.Any(prop =>
>>>> !String.IsNullOrEmpty(this[prop])); }
>>>> }

>>>>  public event EventHandler<MoveFocusEventArgs> MoveFocus;

>>>> void RaiseMoveFocus(string focusedProperty)
>>>> {
>>>>     var handler = this.MoveFocus;
>>>>     if (handler != null)
>>>>     {
>>>>         handler(this, new MoveFocusEventArgs(focusedProperty));
>>>>     }
>>>> }

>>>> Lastly, in your View, use my terribly(?) named attached property to
>>>> specify which DP on your elements is bound to the validated property of the
>>>> VM, for example:

>>>>  <TextBox
>>>>     Text="{Binding Path=FirstName, ValidatesOnDataErrors=True}"
>>>>     *local:FocusControl.ValidatedProperty="TextBox.Text"*
>>>>     />

>>>> I'm not sure that I like this approach yet.  It's a pretty important
>>>> topic, so I thought I'd share this out amongst the Disciples for feedback.

>>>> Thanks,
>>>> Josh

>>> --
>>> Peter O'Hanlon

> --
> Peter O'Hanlon