Initialize a Property After Creating an Object创建对象后初始化属性 即如何设置对象的默认值（EF）

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 (EF) lesson. To initialize it, assign a value to this property in the constructor.

在本课中，您将学习如何为 Business 类的特定属性设置默认值。为此，优先级属性将添加到在"设置多对多关系 （EF）"一课中创建的 DemoTask 类中。要初始化它，请为构造函数中的此属性赋值。

Note

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

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

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

• 注意
  
  在继续之前，请花点时间复习以下课程：

• 从业务类库类 （EF） 继承

• 设置多对多关系 （EF）

• 将"优先级"属性添加到 DemoTask 类并声明优先级枚举，如下所示：

  namespace MySolution.Module.BusinessObjects {
      //...
      public class DemoTask : Task {
          //...
          public Priority Priority { get; set; }
      }
  
      public enum Priority {
          Low = 0,
          Normal = 1,
          High = 2
      }
  }

   

• In the Module.cs (Module.vb) file, register the Priority enumeration type in the constructor of your ModuleBase descendant using the EnumProcessingHelper.RegisterEnum method as follows.

• 在Module.cs（Module.vb）文件中，使用枚举处理帮助器.寄存器Enum方法，在ModuleBase后代的构造函数中注册优先级枚举类型，如下所示。

  using DevExpress.Data.Filtering;
  //...
  public sealed partial class MySolutionModule : ModuleBase {
      public MySolutionModule() {
          InitializeComponent();
          EnumProcessingHelper.RegisterEnum(typeof(MySolution.Module.BusinessObjects.DemoTask.Priority));
          //...
      }
      //...
  }

   

• Use the code below to initialize the newly added Priority property when a DemoTask object is created.

• 在创建 DemoTask 对象时，使用以下代码初始化新添加的"优先"属性。

public class DemoTask : Task {
    public DemoTask() : base() {
        //...
        Priority = Priority.Normal; 
    }
    //...
}

 

• The constructor will be executed when the new DemoTask object is created. As a result, the Priority property will be initialized with the specified value.

• 创建新的 DemoTask 对象时，将执行构造函数。因此，将用指定的值初始化"Priority"属性。

• 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.

• 运行 WinForms 或ASP.NET应用程序。通过在"新建（new_dropdown_btn）"按钮的下拉列表中选择"演示任务"，创建新的"演示任务"对象。（在表示新创建的 DemoTask 对象的详细信息视图中，请注意，优先级属性设置为"正常"，如上述代码中声明的那样。请注意，枚举属性由组合框编辑器自动显示。

  

You can see the code demonstrated in this lesson in the MySolution.Module | Business Objects | DemoTask.cs (DemoTask.vb) file of the EF Demo (Code First) installed with XAF. By default, the EF Demo (Code First) application is installed in %PUBLIC%\Documents\DevExpress Demos 19.2\Components\eXpressApp Framework\EFDemoCodeFirst.

您可以在 MySolution.模块中看到本课中演示的代码。业务对象 |DemoTask.cs （DemoTask.vb） 文件与 XAF 一起安装的 EF 演示（代码优先）文件。默认情况下，EF 演示（代码优先）应用程序安装在 %PUBLIC%\Documents\DevExpress Demos 19.2\Components\eXpressApp Framework\EFDemoCodeFirst 中。