[3][1]System.Windows.DependencyObject

[3][1]System.Windows.DependencyObject

Represents an object that participates in the dependency property system.

• Dependency property is used throughout the platform to enable styling, automatic data binding, animation, etc.
• One of the primary architectural philosophies used in building WPF was a preference for properties over methods or events.

• In order to enable two way binding, you need both sides of the bind to support change notification.
  
• INotifyPropertyChange allows an object to publish change notifications (it is optional).
  
• WPF provides a richer property system, derived from the DependencyObject type. For example, if you have a property that inherits (like FontSize), the system is automatically updated if the property changes on a parent of an element that inherits the value.
• The GetValue and SetValue methods work within the dependency property system to store and retrieve property values, and trigger notification when such properties change.
• DependencyProperty.Register method:
  
• Sample: public static readonly DependencyProperty CaptionProperty = DependencyProperty.Register("StatViewer.Stat.Caption", typeof(string), typeof(Stat));
• Optionally you can pass metadata that customizes how the property is treated by WPF, as well as callbacks for handling property value changes, coercing values, and validating values
• The dependency property system provides support for streamlined property storage.
• A dependency property depends on multiple providers for determining its value
  
• It provides change notifications.
• The dependency property system is based on the concept of inherited property values, and allows cascading changes to various UI element properties.
• Dependency Properties:
• The ability for controls to inherit their container element’s properties (such as coordinates, size, and so on)Object-independent storage
• Tracking the changes made to elements in order to control the state of a control or element for undo commands to be used
• Complex data binding
• Constructs for animation routines for a control
• Sample:

public static readonly DependencyProperty CaptionProperty = DependencyProperty.Register("StatViewer.Stat.Caption", typeof(string), typeof(Stat));

public string Caption

{

get { return GetValue(CaptionProperty) as string; }

set { SetValue(CaptionProperty, value); }

}

• By convention all DependencyProperty fields are public, static, and have a Property suffix.
• Note the static modifier of a DependencyProperty .
• Steps performed by WPF to calculate the value of a dependency value:
• Determine the base value
• There are eight providers that can set the value of most dependency properties, in order from highest to lowest precedence:
• Local value
• Style triggers
• Template triggers
• Style setters
• Theme style triggers
• Theme style setters
• Property value inheritance
• Default value
• Use DependencyPropertyHelper.GetValueSource method to figure out where a given dependency property is getting its current value from
  
• it returns a ValueSource
• it contains IsExpression, IsAnimated, and IsCoerced properties
• Evaluate (if it is an expression - an object deriving from System.Windows.Expression)
• Apply animation
• If one or more animations are running, they have the power to alter the current property value (using the value after step 2 as input) or completely replace it
• Coerce
• ProgressBar use CoerceValueCallback delegate to constrain its Value dependency property to a value between its Minimum and Maximum values, returning Minimum if the input value is less than Minimum or Maximum if the input value is greater than Maximum.
• Validate
• The potentially-coerced value is passed to a ValidateValueCallback delegate
• Returning false causes an exception to be thrown, cancelling the entire process.
• ClearValue() method
  
• _button.ClearValue(Button.ForegroundProperty);