> 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