> 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