WPF comes with a lot of new features and alternatives that the normal Windows applications do not have. As we have already discussed some of the features of WPF, it's time to go a bit further to introduce other new features. After reading the previous articles of this tutorial, I hope you are more or less familiar with WPF architecture, borders, Effects, Transformation, Markup extensions, etc.
If you aren't, please go Propertychangedcallback not called dating the series of articles as labelled:.
So in this article, I am going to introduce you to a new property system that underlays the WPF property system. We will go further to introduce how easily you can use these properties to produce custom callbacks, create attached properties, apply animations and styles,
Propertychangedcallback not called dating. Finally, we will discuss about Binding alternatives that were left behind in the previous article to finish it totally.
I hope you will like this article as well as you did for all the tutorials that I provided. Well, you must have been surprised to see this title. Yes, WPF comes with a completely new technique of defining a property of a control. The unit of the new property system is a Dependency property and the wrapper class which can create a Dependency property is called a DependencyObject.
We even Propertychangedcallback not called dating normal CLR property to wrap around a dependency property and use GetValue and SetValue to get and set values passed Propertychangedcallback not called dating it. This is almost the same as CLR property system.
So, what are the advantages of the new property system. Let's see the difference between Dependency property and CLR property. To work with dependency property, you must derive the class from DependencyObject as the whole observer
Propertychangedcallback not called dating holds the new Property System is defined within the DependencyObject. CLR property is just a wrapper around private variables.
So to be frank with you, a CLR property gives you only one block in which you can write code to invoke whenever a property is get or set. Hence CLR property system is fairly straightforward. On the other hand, the capabilities of Dependency property system is huge.
The idea of Dependency property is to compute the value of the property based on the value of other external inputs. The external inputs might be styles, themes, system properties, animations, etc. So, you can say a dependency property works with most of the WPF inbuilt features that were introduced. Let's discuss the advantages a bit before we create our own dependency property:. In these, some of the features are only supported by Dependency Property. Animation, Styles, TemplatesProperty value Inheritance, etc.
In the above code, I have simply defined a Dependency property. You must have been surprised why a dependency property is to be declared as static. Yes, like you, I was surprised when I first saw that.
But later on, after reading about Dependency property, I came to know that a dependency property is maintained in class level, so you may say Class A to have a property B. So property will be maintained to all the objects that class A have individually.
The Dependency property thus creates an observer for all those properties maintained by class A and stores it there. Thus it is important to note that a Dependency property should be maintained as static. The naming convention of a dependency property states that it should have the same wrapper property which is passed as the first argument. Thus in our case, the name of the Wrapper "MyCustom" which we will use in our program should be passed as the first argument of the Register method, and also the name of the Dependency property should always be suffixed with Property to the original Wrapper key.
If you don't follow this, some of the
Propertychangedcallback not called dating will behave abnormally in your program. It Propertychangedcallback not called dating also be noted that you Propertychangedcallback not called dating not write your logic inside the Wrapper property as it will not be called every time the property is called for.
It will internally call the GetValue and SetValue itself. So if you want to write your own logic when the dependency property is fetched, there are callbacks to do them.
After defining the most simplest Dependency property ever, let's make it a little enhanced. see how to code:. So this is a little more elaborate. We define a FrameworkMetaDatawhere we have specified the DefaultValue for the Dependency property as "Comes as Default", so if we don't reset the value of the DependencyPropertythe object will have this value as default.
The FrameworkPropertyMetaDataOption gives you a chance evaluate the various metadata options for the property.
Let's see the various options for the enumeration. The PropertyChangedCallback is called when the property value is changed. So it will be called after the actual value is modified already. The CoerceValue is called before the actual value is modified. That means after the CoerceValue is called, the value that we return from it will be assigned to the property.
The validation block will be called before CoerceValueso this event ensures if the value passed in to the property is valid or not. Depending on the validity, you need to return true or false. If the value is falsethe runtime generates an error. So in the above application after you run the code, the MessageBox comes for the following:.
CollectionType dependency property is when you want to hold a collection of DependencyObject into a collection. We often
Propertychangedcallback not called dating this in our project. In general, when you create a dependency object and pass the default value into it, the value will not be the default
Propertychangedcallback not called dating for each instance of the object you create.
Rather, it will be the initial value for the Dependency property for the type it is registered with. Thus, if you want to create a collection of Dependency object and want your object to have its own default value, you need to assign this value to each individual item of the dependency collection rather than defining using Metadata definition.
Now if you use this collection, you will see that when you create object of the Usercontroleach of them refers to the same Dependency Property rather than having its own dependency property.
As by definition, each dependencyproperty allocates memory using its type, so if object 2 creates a new instance of DependencyPropertyit will Propertychangedcallback not called dating the Object 1 collection. Hence the object will act as a Singleton class. To overcome with this situation, you need to reset the collection with a new instance whenever a new object of the class is created.
So for each instance, the collection will reset and hence you will see a unique collection for each UserControl created. DependencyProperty supports Property Value inheritance.
By the definition, after you create a DependencyObject for you, you can easily inherit a DependencyProperty to all its child controls using AddOwner method associated to the DependencyProperty. Each of DependencyProperty has AddOwner method, which Propertychangedcallback not called dating a link to another DependencyProperty that is already defined.
you have Propertychangedcallback not called dating DependencyObject A, which has a property called Width. You want the value of the DependencyObject B to inherit the value of A. In the above code, you can see, the class B inherits the DependencyProperty Height using AddOwner without re declaring the same in the class. Thus when A is declared, if you specify the height of Ait will automatically be transferred to the inherited child object B.
This is same as normal objects. When you specify
Propertychangedcallback not called dating Foreground of a Windowit will automatically inherit to all the child elements, hence the Foreground of each control will behave the same. Even though PropertyValueInhertence is there for any dependency property, it will actually work for AttachedProperties.
I came to know that Property Value Inheritance only works when the property is taken as attached. Inheritsthe property value will be inherited from Parent to Child automatically and also gives the chance for the Children to modify the content.
So, the example that I put above is not proper for Property Value Inheritance, but you can easily create one to see after you read the next section. Attached property is another interesting concept. Attached property enables you to attach a property to an object that is outside the object altogether making it define value for it using that object.
Seems a little confused, huh? Yes, let's see an example. Say you have declared a DockPanelinside which you want your controls to appear. Now DockPanel registers an AttachedProperty. We use RegisterAttached method to register attached DependencyProperty. Thus any UIElement children to the DockPanel will get the Dock property attached to it and it can define its value which automatically propagates to the DockPanel.
So in my code, the UserControl can pass the value of the property to the Window. You can see above the IsValuePassed can be set from an external UserControland the same will be passed to the actual window.
As you can see, I have added two static methods to individually Set or Get values from the object. This would be used from the code to ensure we pass the value from code from appropriate objects. Say, you add a button and want to pass values from code, in such cases the static method will help.
To conclude, DependencyProperty is one of the most important and interesting concepts that you must know before you work with WPF.
There are Propertychangedcallback not called dating situations, where you would want to declare a DependencyProperty. From this article, I have basically visited each section of the DependencyProperty that you can work. I hope this one has helped you. Thank you for reading. Looking forward to getting your feedback.
Articles Quick Answers Messages. Abhishek Sur28 Dec Please Sign up or sign in to vote.
WPF introduces a new property system which is enhanced by Dependency property. The validation callback is not part of property metadata; it is a direct as do PropertyChangedCallback implementations that are invoked by the. Thus, overriding a metadata form a derived property will not require you. The PropertyChangedCallback is called when the property value is. Defining your custom property as a dependency property is not always NET languages (C# and Microsoft Visual Basic) you call Register within the.
to provide a default value or use a property-changed callback, you must define . and app manifest languages · Globalize your date/time/number
Propertychangedcallback not called dating.