#133 – Where a Dependency Property Gets Its Value

Since the value of a dependency property can come from a variety of different sources, WPF uses a predetermined precedence for each possible source of a property value in order to determine the final value.

WPF determines the final value for a dependency property as follows:

• Determine the base value, using the precedence rules listed below
• Evaluate expressions
• Apply animations
• Coerce value  (implementing class might coerce to valid value)
• Validate (implementing class may throw exception if value is invalid)

The base value of a property is obtained from one of the following sources, listed from highest to lowest precedence:

• Local value (set in code or XAML)
• Parent template trigger
• Parent template
• Implicit style (for Style property)
• Style triggers
• Template triggers
• Style setters
• Theme style triggers
• Theme style
• Inheritance
• Default value

WPF works down the list until it finds a source that provides a value for the property.