WPF ViewModel DataContext between UserControl Windows

Question

Hi,
have anyone a small sample for me like this:

1. Master Window
2. Sub Window
3. In the Sub Window is a UserControl Window

How can i send data via datacontext from the Master Window to the UserControl Window?
I can set the first data easy from the Master Window to the Sub Window
But from the Sub Window i can not set the datacontext with my data from the Sub Window

Have anyone a small sample how i can send an get data from the UserControl Window?

Best regards

Bernd

Answer 1

Hi, if you use the same instance of ViewModel for Master and Child Window you can bind Controls to the same property in ViewModel (instance).

Try following demo:

<Window x:Class="Window030"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp1"
        mc:Ignorable="d"
        Title="Master Window" Height="450" Width="800">
  <StackPanel>
    <TextBox Text="{Binding Info, UpdateSourceTrigger=PropertyChanged}"/>
  </StackPanel>
</Window>

---

Imports System.ComponentModel
Imports System.Runtime.CompilerServices

Public Class Window030

  Public Sub New()

    ' This call is required by the designer.
    InitializeComponent()

    ' Add any initialization after the InitializeComponent() call.
    Dim vm As New WpfApp030.ViewModel
    Me.DataContext = vm
    Call (New Window030Child With {.DataContext = vm}).Show()
  End Sub

End Class

Namespace WpfApp030

  Public Class ViewModel
    Implements INotifyPropertyChanged

    Private _info As String
    Public Property Info As String
      Get
        Return Me._info
      End Get
      Set(value As String)
        Me._info = value
        OnPropertyChanged()
      End Set
    End Property

    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
    Friend Sub OnPropertyChanged(<CallerMemberName> Optional propName As String = "")
      RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propName))
    End Sub

  End Class

---

<Window x:Class="Window030Child"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp1"
        mc:Ignorable="d"
        Title="Child Window" Height="450" Width="800">
  <StackPanel>
    <TextBox Text="{Binding Info, UpdateSourceTrigger=PropertyChanged}"/>
  </StackPanel>
</Window>