Monday, 6 May 2013

Difference Between Dependency Property and Normal CLR Property in WPF

Difference Between Dependency Property and Normal CLR Property in WPF

The Normal CLR property and the dependency property look quite similar but the dependency property is more powerful and has more features. In WPF, dependency properties are used in Animation, Styles, Triggers, Templates, Validation, Data Binding, Layout etc.

Syntax Difference Between Dependency Property and Normal CLR Property

Syntax of Normal CLR Property

private int count;
public int Count
{
   get
   {
      return count;
   }
   set
   {
      count = value;
   }
}

Syntax of Dependency Property

public static DependencyProperty PageSizeProperty =
DependencyProperty.RegisterAttached("PageSize",
typeof(int), typeof(AttachedPropertySample),
             new PropertyMetadata(25,
             new PropertyChangedCallback(OnPageSizePropertyChanged)));

public int PageSize
{
    get
    {
        return (int) GetValue(PageSizeProperty);
    }
    set
    {
        SetValue(PageSizeProperty, value);
    }
}

In Built Change Notification

Dependency provides change notification when its value has been changed. You can specify Call Back while registering dependency property so user will get notification. This is mainly used in Data Binding. But CLR property has not any inbuilt change notification. So if you want your normal CLR proprety also notify changes, you have to implement INotifyPropertyChanged.

Value Resolution

CLR property reads value directly from private member while dependency property dynamically resolves value when you call GetValue() method of dependency property. The GetValue and SetValue methods are inherited from Dependency Object.

Value Inheritance

If you specify dependency property to top element it will be inherited to all child elements until child element specifically override the property. Dependency property value is resolved at runtime when you call GetValue() method. 

Suggestion: If your property will commonly be the source of a databinding (e.g. providing the Text for a TextBlock), I would recommend using a standard CLR property and having the containing class implement INotifyPropertyChanged.

2 comments:

  1. Reliance provides modify alert when its value has been modified. You can specify Contact Returning while applying dependency residence so customer will get alert. This is mainly used in Information Executed. But CLR residence has not any integrated modify alert. So if you want your regular CLR proprety also inform changes

    ReplyDelete
  2. How will i decide, when to use dependency property and when to use CLR property. With INotifyPropertyChanged in CLR we get most of things done. So when to go for dependecy property?

    ReplyDelete