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Posted 8 Sep 2009

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How to Implement a DependencyProperty?

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4.48/5 (26 votes)
8 Sep 2009CPOL1 min read
A DependencyProperty is set to enable declarative code to alter the properties of an object which reduces the data requirements by providing a more powerful notification system regarding the change of data in a very specific way.

A DependencyProperty is set to enable declarative code to alter the properties of an object which reduces the data requirements by providing a more powerful notification system regarding the change of data in a very specific way. In .NET, there are two types of properties: the normal property, and a Dependency Property which adds functionality over the normal property.

Now, let us discuss on how to implement such a Dependency Property to give a powerful notification on a data change.

First of all, implement the UserControl class from the INotifyPropertyChanged interface:

C#
public partial class MyUserControl : UserControl, INotifyPropertyChanged 
{ 
    public event PropertyChangedEventHandler PropertyChanged; 
    protected void OnPropertyChanged(string propertyName) 
    { 
        if (PropertyChanged != null) 
        { 
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); 
        } 
    } 
}

Create your own normal property. Let's say the name of the property is “Caption”.

C#
public string Caption 
{  
    get { return GetValue(CaptionProperty).ToString(); }  
    set { SetValue(CaptionProperty, value); } 
}

Now, register the DependencyProperty to the CLR by calling the Register method and by passing the property field that you used to store the data in the earlier step:

C#
public static readonly DependencyProperty CaptionProperty = 
  DependencyProperty.Register("Caption", typeof(string), typeof(MyUserControl), 
  new PropertyMetadata(string.Empty, OnCaptionPropertyChanged));

The name of the identifier field of the DependencyProperty will be same as you used in the property after appending “Property” at the end. In this example, our property name is “Caption”, hence our identifier field name is “CaptionProperty”. Add the PropertyMetaData with the default value and the callback event handler within the Register method as mentioned in the above code. Mark the identifier as static and readonly so that this will be unique to the CLR.

Now, implement the OnCaptionPropertyChanged event handler:

C#
private static void OnCaptionPropertyChanged(DependencyObject dependencyObject, 
               DependencyPropertyChangedEventArgs e) 
{  
    MyUserControl myUserControl = dependencyObject as MyUserControl;  
    myUserControl.OnPropertyChanged("Caption");  
    myUserControl.OnCaptionPropertyChanged(e); 
}
private void OnCaptionPropertyChanged(DependencyPropertyChangedEventArgs e) 
{ 
    txbCaption.Text = Caption; 
}

The implementation of the Dependency Property is complete. You can either call it from XAML:

XML
<local:MyUserControl Caption="My First Dependency Property Example" />

or from the code-behind:

C#
MyUserControl myUserControl = new MyUserControl(); 
myUserControl.SetValue(MyUserControl.CaptionProperty, 
              "My First Dependency Property Example");

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Technical Lead
India India

Kunal Chowdhury is a former Microsoft "Windows Platform Development" MVP (Most Valuable Professional, 2010 - 2018), a Codeproject Mentor, Speaker in various Microsoft events, Author, passionate Blogger and a Senior Technical Lead by profession.

He is currently working in an MNC located in India. He has a very good skill over XAML, C#, Silverlight, Windows Phone, WPF and Windows app development. He posts his findings, articles, tutorials in his technical blog (www.kunal-chowdhury.com) and CodeProject.


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Comments and Discussions

 
QuestionMy vote of 5 Pin
Tim Butler18-Apr-17 13:54
Tim Butler18-Apr-17 13:54 
QuestionCode behind doesn't work Pin
Member 1063968028-Apr-16 12:09
Member 1063968028-Apr-16 12:09 
QuestionSmall clarification on code. Pin
Member 956059124-Oct-14 20:29
Member 956059124-Oct-14 20:29 
AnswerRe: Small clarification on code. Pin
rahul_tripathikanpur2-Oct-16 22:45
rahul_tripathikanpur2-Oct-16 22:45 
GeneralMy vote of 1 Pin
alamgir15-May-14 19:35
alamgir15-May-14 19:35 
GeneralMy vote of 3 Pin
StewBob18-Aug-13 5:46
StewBob18-Aug-13 5:46 
GeneralMy vote of 5 Pin
mhdnour14-Apr-12 9:00
mhdnour14-Apr-12 9:00 
GeneralMy vote of 5 Pin
Member 476816328-Feb-12 1:40
Member 476816328-Feb-12 1:40 
GeneralMy vote of 4 Pin
bluetiger092013-Apr-11 18:57
bluetiger092013-Apr-11 18:57 
GeneralMy vote of 2 Pin
Patel Kalpesh15-Feb-11 20:54
Patel Kalpesh15-Feb-11 20:54 
GeneralMy vote of 1 Pin
mahendra varman29-Dec-10 20:00
mahendra varman29-Dec-10 20:00 
QuestionWhat the Identifier should be defined readonly ??? Pin
Member 330120119-Nov-10 1:33
Member 330120119-Nov-10 1:33 
GeneralMy vote of 1 Pin
phobik26-Oct-10 15:15
phobik26-Oct-10 15:15 
GeneralRe: My vote of 1 Pin
Kunal Chowdhury «IN»7-Nov-10 22:50
professionalKunal Chowdhury «IN»7-Nov-10 22:50 
Generalone small correction Pin
Shanbhag uday20-Mar-10 4:52
Shanbhag uday20-Mar-10 4:52 
AnswerRe: one small correction Pin
Kunal Chowdhury «IN»10-Jul-10 3:09
professionalKunal Chowdhury «IN»10-Jul-10 3:09 

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