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It is clear to me why dependency property are static and the question still remain on my mind is why we need to use Readonly keyword at the time of declaration of Dependency Property.
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DependencyProperty has to be static (Class level) because when we create multiple objects of the class which has that property and want to refer the default value for that property the value has to come from that static instance of DependencyProperty.
Existing read-only dependency properties For example, the Windows Presentation Foundation (WPF) framework implements the IsMouseOver property as read-only because its value should only be determined by mouse input. If IsMouseOver allowed other inputs, its value might become inconsistent with mouse input.
Dependency properties and the WPF property system extend property functionality by providing a type that backs a property, as an alternative to the standard pattern of backing a property with a private field. The name of this type is DependencyProperty.
Arguably the biggest feature of a dependency property is its built-in ability to provide change notification. The motivation for adding such intelligence to properties is to enable rich functionality directly from declarative markup.
Conceptually a dependency property is something that a dependency object simply has and that does not depend on when you use the property. Just like a CLR property, if you ask does this object have a Total property, you know it cannot be a double now but an int later. As a result, we'd make the dependency property const if we could, but we cannot, so readonly is the next best thing.
Using the readonly keyword has at least three effects:
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Because it makes it obvious, that the value of this property cannot be changed after initialization.
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