Silverlight dependencyobject and dependencyproperty

We have talked about binding many times before, and it has a notification function. How does this notification function come out? Why didn't we use this notification function in our previous CLR attributes?

That's because we now have two more concepts in SL: dependencyobject and dependencyproperty.

Dependencyproperty is actually used in dependencyobject.

 

The following describes the two items respectively.

1. dependencyobject

1. It is a class defined in SL and has dependencyproperty.

2. It is a data object to be bound.

3. All our interface elements are derived from dependencyobject.

To a UML diagram

 

1. dependencyproperty

• Parameters for registration-name of property-type of owner-propertymetadata • types of registration-simple property 'dependencyproperty. register '-- register the Dependency Property-attach property' dependencyproperty. registerattached '-- register the additional property-sample: canvas. top, grid. column • Principle of dependency Property-DependencyObject.Dictionary <propertyname, propertyvalue> • why use Dependency Property-binding, inherit, multiple value providers, Attachment

 

 

 

Why does dependencyproperty provide binding and inheritance .... Such a function.

The principle is as follows:

In fact, it is a dictionary in the dependencyobject. This dictionary contains a series of propertynames and propertyvalue pairs, that is

Let's say we use a name to get the corresponding value. In this way, the attributes and classes are decoupled. Therefore, when we perform some features on these attributes, we can operate on these attributes separately.

UseCodeTo implement the principles of dependencyobject and dependencyproperty (Note: Only imitation, dependencyproperty in Sl is more complex, but the principle is similar)

Customize a dependencyobject

     Public   Class  Mydependencyobject {  # Region Dependency Property principle code Private Dictionary < String , Object > Properties = New Dictionary < String , Object >();  Protected   Object  Getvalue (mydependencyproperty property ){  If (Property. ownertype = This  . GetType ()){  Return   This  . Properties [property. Name];}  Else  {  // Sample for inherit principle. Mydependencyobject parent = This  . Getparentelement (property. ownertype );  Return  Parent. getvalue (property );}}  Protected   Void Setvalue (mydependencyproperty property, Object  Value ){  This . Properties [property. Name] = Value ;} # Endregion          # Region Private methods Private  Mydependencyobject getparentelement (type ){  //  Todo: Get parent element here.              Return   Null  ;}  # Endregion  } 

 

Define a dependencyproperty

     Public   Class Mydependencyproperty {  # Region Constructor Private Mydependencyproperty ( String Name, type valuetype, type ownertype, Object  Defaultvalue ){  This . Name = Name;  This . Valuetype = Valuetype;  This . Ownertype = Ownertype; This . Defaultvalue = Defaultvalue ;}  Public   Static Mydependencyproperty register ( String Name, type valuetype, type ownertype, Object  Defaultvalue) {mydependencyproperty instance = New  Mydependencyproperty (name, valuetype, ownertype, defaultvalue );  Return  Instance ;} # Endregion          # Region CLR Properties Public   String  Name {  Get  ;  Private   Set  ;}  Public  Type valuetype {  Get  ;  Private  Set  ;}  Public  Type ownertype {  Get  ;  Private   Set  ;}  Public   Object  Defaultvalue {  Get  ;  Private   Set ;}  # Endregion  } 

 

Example:

     Public   Class  Myparentelement: mydependencyobject {  Public   String  Text {  Get { Return ( String  ) Getvalue (textproperty );}  Set {Setvalue (textproperty, value );}}  Public   Static   Readonly Mydependencyproperty textproperty = Mydependencyproperty. Register (  "  Text  " , Typeof ( String ), Typeof (Myparentelement ), "  I'm parent.  " );}  Public   Class  Mychildelement: mydependencyobject {  Public   String  Text {  Get { Return ( String  ) Getvalue (textproperty );}  Set  {Setvalue (textproperty, value );}}  Public  Static   Readonly Mydependencyproperty textproperty = Mydependencyproperty. Register (  "  Text  " , Typeof ( String ), Typeof (Myparentelement ), "  I'm child.  "  );}