Mvvm. Textbox never change with System.Threading.Thread.Sleep - vb.net

Question

I want change a textbox value, but this code doesn't work. I see only the last value.
If you want to help me copy and paste the code .
Thanks a lot
This is XAML
<TextBox HorizontalAlignment="Left" Height="46"
Margin="4,4,4,4" VerticalAlignment="Top" Width="162"
Text="{Binding Path=Msg,
Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
This is VB code.
Imports System.Threading
Imports System.Collections.ObjectModel
Imports System.ComponentModel
Imports System
Class MainWindow
Private Sub Window_Loaded(sender As Object, e As RoutedEventArgs)
Dim x As New Abc
Me.DataContext = x
End Sub
End Class
Public Class Abc
Implements INotifyPropertyChanged
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Private Sub OnPropertyChanged(ByVal info As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(info))
End Sub
Protected Sub OnNotifyPropertyChanged(propertyName As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
End Sub
Private Property _Msg As String
Public Property Msg As String
Get
Return _Msg
End Get
Set(value As String)
_Msg = value
OnPropertyChanged("Msg")
End Set
End Property
Private m_ButtonCommand As ICommand
Public Property ButtonCommand() As ICommand
Get
Return m_ButtonCommand
End Get
Set(value As ICommand)
m_ButtonCommand = value
End Set
End Property
Public Sub displayMessage(ByVal param As Object)
Msg = "How"
System.Threading.Thread.Sleep(1000)
Msg = "Are"
System.Threading.Thread.Sleep(1000)
Msg = "you"
System.Threading.Thread.Sleep(1000)
Msg = "?"
System.Threading.Thread.Sleep(1000)
End Sub
Private Function CandisplayMessage(ByVal param As Object) As Boolean
Return True
End Function
Public Sub New()
m_ButtonCommand = New DelegateCommand(AddressOf displayMessage, AddressOf CandisplayMessage)
End Sub
End Class
Public Class DelegateCommand
Implements ICommand
Private m_canExecute As Func(Of Object, Boolean)
Private m_executeAction As Action(Of Object)
Private m_canExecuteCache As Boolean
Public Event CanExecuteChanged(ByVal sender As Object, ByVal e As System.EventArgs) Implements ICommand.CanExecuteChanged
Public Sub New(ByVal executeAction As Action(Of Object), ByVal canExecute As Func(Of Object, Boolean))
Me.m_executeAction = executeAction
Me.m_canExecute = canExecute
End Sub
Public Function CanExecute(ByVal parameter As Object) As Boolean Implements ICommand.CanExecute
Dim temp As Boolean = m_canExecute(parameter)
If m_canExecuteCache <> temp Then
m_canExecuteCache = temp
RaiseEvent CanExecuteChanged(Me, New EventArgs())
End If
Return m_canExecuteCache
End Function
Public Sub Execute(ByVal parameter As Object) Implements ICommand.Execute
m_executeAction(parameter)
End Sub
End Class
.............................................

Answer 1

When you use Thread.Sleep on UI Thread you block the UI thread, So nothing can happen in UI. If you want to show a 1 second wait after each message you have two choices.
1 - Using the Delay command in an Async method. https://msdn.microsoft.com/en-us/library/hh194873(v=vs.110).aspx?cs-save-lang=1&cs-lang=vb#code-snippet-4
2 - Using a dispatcher frame, which can let the dispatcher work while your method waits. http://www.codeproject.com/Articles/152137/DispatcherFrame-Look-in-Depth
Unfortunately I'm not a VB programmer, But the code in c# would be like this.
Async Sample:
public Task displayMessage(object param){
Msg = "How";
await Task.Delay(1000);
Msg = "Are";
await Task.Delay(1000);
Msg = "you";
await Task.Delay(1000);
Msg = "?";
await Task.Delay(1000);
}
DispatcherFrame sample:
public void displayMessage(object param){
Msg = "How";
Wait(1000);
Msg = "Are";
Wait(1000);
Msg = "you";
Wait(1000);
Msg = "?";
Wait(1000);
}
public void Wait(int sleep)
{
var dFrame = new DispatcherFrame();
ThreadPool.QueueUserWorkItem(state => {
Thread.Sleep(sleep);
dFrame.Continue = false;
});
Dispatcher.PushFrame(dFrame);
}