CODEWITHSUNDEEP
silverlightdependenciespropertiesdependency-propertiesconverters
Donovan Groeneweegen
Donovan Groeneweegen

Reputation: 63

Using a Converter in conjunction with a DependencyProperty

I've created a DependencyProperty on my derived AutoCompleteBox control --> IsReadOnly

From there, I'm trying to set the value (T/F) via a converter. Based on the converter value, I would like to update the nested TextBox style in the setter of the DependencyProperty. Explicitly setting the property in the XAML (IsReadOnly="True") works fine, and the setter fires and updates the style. However, doing this via the converter does NOT fire of the setter of the DependencyProperty. I seem to be having trouble pasting code snippets here (first time poster).. so I'll do my best to give an quick code run through:

Property on AutoCompleteBox:

IsReadOnly="{Binding Converter={StaticResource IsReadOnlyVerifier}, ConverterParameter='Edit Client'}"

Which calls out to the Converter, which returns either true or false based on the User's permissions. This however does not call the setter of the registered DependencyProperty.

.. set

        {
            if (value)
            {
                var style = StyleController.FindResource("ReadOnlyTextBox") as Style;
                TextBoxStyle = style;
            }
            else
            {
                TextBoxStyle = null;
            }
            SetValue(IsReadOnlyProperty, value);
        }

Upvotes: 3

Views: 721

Answers (1)

AnthonyWJones
AnthonyWJones

Reputation: 189457

This is a classic newbie gotcha. Bindings will set the target DependencyProperty using SetValue directly, they don't assign a value via the POCO property setter method.

Your IsReadOnly property should look like this:-

  #region public bool IsReadOnly
  public bool IsReadOnly
  {
       get { return (bool)GetValue(IsReadOnlyProperty); }
       set { SetValue(IsReadOnlyProperty, value); }
  }

  public static readonly DependencyProperty IsReadOnlyProperty =
     DependencyProperty.Register(
         "IsReadOnly",
         typeof(bool),
         typeof(MyAutoCompleteBox),
         new PropertyMetaData(false, OnIsReadOnlyPropertyChanged) );

  private static void OnIsReadOnlyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
  {
       MyAutoCompleteBox source = d as MyAutoCompleteBox;
       source.OnIsReadOnlyChanged((bool)e.OldValue, (bool)e.NewValue);    
  }

  private void OnIsReadOnlyChanged(bool oldValue, bool newValue)
  {
       TextBoxStyle = newValue ? StyleControlller.FindResource("ReadOnlyTextBox") as Style ? null;
  }
  #endregion

It affect any other changes when a dependency property is set you should supply a PropertyChangedCallback delegate to the PropertyMetaData when registering the DependencyProperty. This will be called whenever SetValue is used to assign a value for this property.

Upvotes: 3

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