Question

我是MVVM的新手。

我的视图中有一个标签，如下所示：

<Label Content="{Binding Path=ClockTime}" />

我的ViewModel看起来像：

Public Class MainWindowViewModel
  Inherits ViewModelBase

  Dim strClockTime As String
  Dim dstDispatcherTimer As New Windows.Threading.DispatcherTimer

  Public Sub New()
    AddHandler dstDispatcherTimer.Tick, AddressOf TimeDelegate
    dstDispatcherTimer.Interval = New TimeSpan(0, 0, 1)
    dstDispatcherTimer.Start()
  End Sub

  Private Sub TimeDelegate(ByVal sender As Object, ByVal e As System.EventArgs)
    strClockTime = DateTime.Now.ToString("dddd, dd MMMM yyyy h:mm:ss tt")
  End Sub

  Public ReadOnly Property ClockTime As String
    Get
      Return strClockTime
    End Get
  End Property

End Class

我的问题是标签不会与ViewModel中的线程动态更新。是否有一种简单的方法让View知道这个值是动态的？

Answer 1

您需要在ViewModel中实现INotifyPropertyChanged接口，并在设置ClockTime时引发PropertyChanged事件

Answer 2

要扩展托德所说的应该像这样更新你的代码你需要ViewModelBase看起来像这样

Public class ViewModelBase Inherits INotifyPropertyChanged
  protected Sub OnPropertyChanged(PropertyName as string)
    if PropertyChanged is not nothing then
      PropertyChanged(new PropertyChangedEventArgs(PropertyName)
    end if 
  End Sub
End Class

然后修改您的视图模型：

  Private Sub TimeDelegate(ByVal sender As Object, ByVal e As System.EventArgs)
    ClockTime = DateTime.Now.ToString("dddd, dd MMMM yyyy h:mm:ss tt")
  End Sub

  Public Property ClockTime As String
    Get
      Return strClockTime
    End Get
    Private Set
      strClockTime = value
      OnPropertyChanged("ClockTime")
    End Set
  End Property

请注意，我正在分配给ClockTime，当它被设置为WPF时，会通知ClockTime已更改

绑定到在MVVM中的ViewModel中更新的值？

2 个答案: