Question

Using WPF, and VB.net, I want to update a textbox in a textblock with the current date and time. I use a timer, and it seems to be firing, and setting an object property to “Now”.
And I am using iNotifyPropertyChanged.

All I get is an empty textbox with no data in it. Can you help? Maybe my context is off?

XAML

<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
    <TextBlock DataContext="oTime"> 
        <TextBox x:Name="myTextBox" 
                 Width="200" Height="50" Foreground="Black" 
                 Text="{Binding Path=oTime.TimeUpdate}"></TextBox>
    </TextBlock>
</Grid>
</Window>

VB Code

Imports System.ComponentModel
Imports System.Windows.Threading

Class MainWindow
  Public oTime As TimeUpdate = New TimeUpdate
  Private dpTimer As DispatcherTimer

  Private Sub TextBlock_SourceUpdated(ByVal sender As System.Object, ByVal e As System.Windows.Data.DataTransferEventArgs)

  End Sub

  Private Sub MainWindow_Loaded(ByVal sender As Object, ByVal e As System.Windows.RoutedEventArgs) Handles Me.Loaded
      dpTimer = New DispatcherTimer
      dpTimer.Interval = TimeSpan.FromMilliseconds(1000)
      AddHandler dpTimer.Tick, AddressOf TickMe
      dpTimer.Start()
  End Sub

  Private Sub TickMe()
      oTime.TimeUpdate = Now.ToString
      Debug.Print(oTime.TimeUpdate)
  End Sub

End Class

Public Class TimeUpdate
Implements INotifyPropertyChanged

  Private sTime As String

  'Declare the Event
  Public Event PropertyChanged(ByVal sender As Object, ByVal e As System.ComponentModel.PropertyChangedEventArgs) Implements System.ComponentModel.INotifyPropertyChanged.PropertyChanged

  Public Property TimeUpdate() As String
      Get
          Return sTime

      End Get
      Set(ByVal value As String)
          sTime = value
          'Call onPropertyChanged whenever the property is updated
          OnPropertyChanged("TimeUpdate")
      End Set

  End Property

  Protected Sub OnPropertyChanged(ByVal name As String)
      RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(name))
  End Sub

End Class

Answer 1

Few things seem to be missing. First the DataContext of the window is not set. You can do it the constructor:

Public Sub New()
    DataContext = oTime
End Sub

This allows your view to see the contents of the TimeUpdate class.

And then change you XAML (bind directly to the TimeUpdate property):

<Grid> 
    <TextBox x:Name="myTextBox" 
             Width="200" Height="50" Foreground="Black" 
             Text="{Binding Path=TimeUpdate}"></TextBox>
</Grid>

Update:
Alternative way will be to add the DataContext line in the Window tag. This way your MainWindow class becomes visible to the view and you can bind to the public properties.

<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
DataContext="{Binding RelativeSource={RelativeSource Self}}"
Title="MainWindow" Height="350" Width="525">

Now create a public property to access the object:

Public Property OTime() As TimeUpdate
    Get
        Return oTime
    End Get
    Set
        oTime = value
    End Set
End Property

And bind the textbox to it:

<Grid> 
    <TextBox x:Name="myTextBox" 
             Width="200" Height="50" Foreground="Black" 
             Text="{Binding Path=OTime.TimeUpdate}"></TextBox>
</Grid>