业务类中的PropertyChanged事件

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业务类中的PropertyChanged事件

为了提供一致的用户界面，当您的XAF应用程序的属性值更改时，必须从业务类接收通知。例如，当用户修改某个值时，条件外观和验证模块可能需要立即更新UI。本主题描述如何提供来自XPO，实体框架和非持久性业务类的通知。

通知机制基于支持标准INotifyPropertyChanged接口并实现其声明的PropertyChanged事件。要将通知发送到内部XAF代码，请从业务类中的属性集访问器触发PropertyChanged。

XPO中的PropertyChanged事件

无需在XPO业务类中手动实现INotifyPropertyChanged接口。声明XPO业务类时，您将继承已经支持此接口的BaseObject（或另一个基本持久性类）。您可以通过执行XPBaseObject.OnChanged或PersistentBase.SetPropertyValue帮助器方法，从属性集访问器触发PropertyChanged事件。

C＃
VB.NET

public class Department : BaseObject {
    // ...
    private string title;
    public string Title {
        get {
            return title;
        }
        set {
            SetPropertyValue(nameof(Title), ref title, value);
        }
    }
}

Public Class Department
    Inherits BaseObject
    ' ...
    Private _title As String
    Public Property Title() As String
        Get
            Return _title
        End Get
        Set(ByVal value As String)
            SetPropertyValue(NameOf(Title), _title, value)
        End Set
    End Property
End Class

另请参见： 简化的属性语法

实体框架中的PropertyChanged事件

在实现EntityFramework业务类时，您不会继承任何标准基类。因此，您应该手动实现INotifyPropertyChanged接口。XAF提供XAF业务对象| EF Business Object 项目项模板可简化此任务。

EFBusinessOblect

在现有的类中，可以如下实现INotifyPropertyChanged。

C＃
VB.NET

public class Customer : INotifyPropertyChanged {
    // ...
    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged([System.Runtime.CompilerServices.CallerMemberName] string propertyName = null) {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

Public Class Customer
    Implements INotifyPropertyChanged
    ' ...
    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
    Protected Sub OnPropertyChanged( _
        <System.Runtime.CompilerServices.CallerMemberName> Optional propertyName As String = Nothing)
        Dim args As New PropertyChangedEventArgs(propertyName)
        RaiseEvent PropertyChanged(Me, args)
    End Sub
End Class

您可以使用OnPropertyChanged帮助程序方法从属性集访问器触发PropertyChanged事件。

C＃
VB.NET

public class Customer : INotifyPropertyChanged {
    // ...
    private CustomerStatus status;
        public CustomerStatus Status {
        get { return status; }
        set {
            if(status != value) {
                status = value;
                OnPropertyChanged();
            }
        }
    }
}

Public Class Customer
    Implements INotifyPropertyChanged
    ' ...
    Private _status As CustomerStatus
        Public Property Status() As CustomerStatus
        Get
            Return _status
        End Get
        Set(ByVal value As CustomerStatus)
            If _status IsNot value Then
                _status = value
                OnPropertyChanged()
            End If
        End Set
        End Property
End Class

非持久类中的PropertyChanged事件

要在非持久类中使用PropertyChanged事件，请遵循上面针对实体框架描述的相同方法。

C＃
VB.NET

public class NonPersistentObject1 : INotifyPropertyChanged {
    // ...
    private string sampleProperty; 
    public string SampleProperty {
        get { return sampleProperty; }
        set {
            if (sampleProperty != value) {
                sampleProperty = value;
                OnPropertyChanged();
            }
        }
    }
    private void OnPropertyChanged([System.Runtime.CompilerServices.CallerMemberName] string propertyName = null) {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
    public event PropertyChangedEventHandler PropertyChanged;
}

Public Class NonPersistentObject1
    Implements INotifyPropertyChanged
    ' ...
    Private _sampleProperty As String
    Public Property SampleProperty() As String
        Get
            Return _sampleProperty
        End Get
        Set(ByVal value As String)
            If _sampleProperty <> value Then
                _sampleProperty = value
                OnPropertyChanged()
            End If
        End Set
    End Property
    Private Sub OnPropertyChanged( _
        <System.Runtime.CompilerServices.CallerMemberName> Optional propertyName As String = Nothing)
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
    End Sub
    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
End Class

要创建支持INotifyPropertyChanged的新的非持久类，请使用XAF Business Object | XAF。非持久对象 项目项目模板。

非持久对象

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