Initialize a Property After Creating an Object (XPO)

• Nov 17, 2020
• 3 minutes to read

In this lesson, you will learn how to set the default value for a particular property of a business class. For this purpose, the Priority property will be added to the DemoTask class created in the Set a Many-to-Many Relationship (XPO) lesson. To initialize it, the AfterConstruction method will be overridden in this class.

Note

Before proceeding, take a moment to review the following lessons:

• Inherit from the Business Class Library Class (XPO)
• Set a Many-to-Many Relationship (XPO)

• Add the Priority property to the DemoTask class and declare the Priority enumeration, as shown below:

  C#

  public class DemoTask : Task {
      // ...
      private Priority priority;
      public Priority Priority {
          get { return priority; }
          set {
              SetPropertyValue(nameof(Priority), ref priority, value);
          }
      }
      //...
  }
  public enum Priority {
      Low = 0,
      Normal = 1,
      High = 2
  }
  

  VB.NET

  Public Class DemoTask
      Inherits Task
      ' ...
      Private fPriority As Priority
      Public Property Priority() As Priority
          Get
              Return fPriority
          End Get
          Set(ByVal value As Priority)
              SetPropertyValue(NameOf(Priority), fPriority, value)
          End Set
      End Property
      '...
  End Class
  Public Enum Priority
      Low = 0
      Normal = 1
      High = 2
  End Enum
  

• To initialize the newly added Priority property when a DemoTask object is created, override the AfterConstruction method, as shown below:

  C#

  [DefaultClassOptions]
  [Custom("Caption", "Task")]
  public class DemoTask : Task {
      //...
      public override void AfterConstruction() {
          base.AfterConstruction();
          Priority = Priority.Normal;
      }
      //...
  }
  

  VB.NET

  <DefaultClassOptions(), Custom("Caption", "Task")> _
  Public Class DemoTask
      Inherits Task
      '...
      Public Overrides Sub AfterConstruction()
          MyBase.AfterConstruction()
          Priority = Priority.Normal
      End Sub
      '...
  End Class
  

  This method will be executed when the new DemoTask object is created. As a result, the Priority property will be initialized with the specified value. For details on the AfterConstruction method, refer to the PersistentBase.AfterConstruction Method topic in the XPO documentation.

• Run the WinForms or ASP.NET application. Create a new DemoTask object by selecting DemoTask in the drop-down list of the New () button. (In the Detail View that represents the newly created DemoTask object, note that the Priority property is set to Normal, as declared in the code above.) Notice that the enumeration property is automatically displayed by the combo box editor.

  

You can see the code demonstrated in this lesson in the MySolution.Module | Business Objects | DemoTask.cs (DemoTask.vb) file of the Main Demo installed with XAF. The MainDemo application is installed in %PUBLIC%\Documents\DevExpress Demos 20.2\Components.NET Core Desktop Libraries\eXpressApp Framework\MainDemo by default. The ASP.NET Web Forms version is available online at https://demos.devexpress.com/XAF/MainDemo.

Next Lesson: Implement Dependent Reference Properties (XPO)