绑定和异步操作

Question

我在里面创建了一个带有TextBlock的Window.我绑定了Text属性,一切正常. 但是 当我在任务内部更改有界属性时,没有任何作用!

你知道为什么吗？

Public Async Sub StartProgress()
    Try
       LoadingText = "text 1" 'Works perfect

       Dim fResult As Boolean = Await LoadModules()

       If Not fResult Then
          MessageBox.Show(Me.Error)
       End If

       m_oView.Close()
    Catch ex As Exception
       Msg_Err(ex)
    End Try
End Sub

Public Async Function LoadModules() As Task(Of Boolean)
    Try
        Await Task.Delay(3000)

        LoadingText = "text 2" 'Nothing Happens

        Await Task.Delay(5000)

        LoadingText = "complete" 'Nothing Happens

        Await Task.Delay(3000)

        Return True
    Catch ex As Exception
        Me.Error = ex.Message
        Return False
    End Try
   End Function

文本2和3从未显示过.如果我动态更改textblcok的文本(例如:m_oView.txtLoadingText.Text)它工作正常(但它不是一个解决方案)

编辑 这是ViewModel Base,每个ViewModel实现该类.

Public Class VM_Base
    Implements IDisposable
    Implements INotifyPropertyChanged

    Private m_oDS As MxDataSet
    Public Property [Error] As String

    Public Event PropertyChanged As PropertyChangedEventHandler _
        Implements INotifyPropertyChanged.PropertyChanged

    Protected Sub New()
        m_oDS = New MxDataSet

    End Sub

    Protected Overrides Sub Finalize()
        Try
            Me.Dispose(False)
            Debug.Fail("Dispose not called on ViewModel class.")
        Finally
            MyBase.Finalize()
        End Try
    End Sub

    Public Sub Dispose() Implements IDisposable.Dispose
        Me.Dispose(True)
        GC.SuppressFinalize(Me)
    End Sub

    Protected Overridable Sub Dispose(disposing As Boolean)
    End Sub

    Protected Overridable Sub OnPropertyChanged(propertyName As String)
        Me.EnsureProperty(propertyName)
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
    End Sub

    <Conditional("DEBUG")> _
    Private Sub EnsureProperty(propertyName As String)
        If TypeDescriptor.GetProperties(Me)(propertyName) Is Nothing Then
            Throw New ArgumentException("Property does not exist.", "propertyName")
        End If
    End Sub
End Class

如何调用StartProgress:

<i:Interaction.Triggers>
     <i:EventTrigger EventName="ContentRendered">
         <i:InvokeCommandAction Command="{Binding DataContext.WindowsActivatedCommand,ElementName=fLoading}" />
     </i:EventTrigger>
 </i:Interaction.Triggers>

编辑将 TextBlock绑定到Property

Public Property LoadingText As String
     Get
         Return m_sLoadingText
     End Get
     Set(value As String)
         m_sLoadingText = value
         OnPropertyChanged("LoadingText")
     End Set
 End Property

<TextBlock x:Name="txtLoading" Width="450"
             Grid.Row="1" VerticalAlignment="Center" 
             HorizontalAlignment="Left" 
             TextWrapping="Wrap" Text="{Binding LoadingText}">
    </TextBlock>

Answer 1

以下是有关如何确保源自非 UI 线程的调用正确调用 UI 方法所需执行的操作的详细答案：

确保事物在 WPF 中的 UI 线程上运行