Inheritance of DataContext in WPF

Question

2.50/5 (2 votes)

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Hi,

I have a User Control in a Window. I need a DataContext for the Window and another one for the UserControl. The problem is that the DataContext from the Window inherits to the DataContext from the User Control. That means, after initializing the application I lost my DataContext from the UserControl, but have the DataContext from the Window at both, Window and UserControl.

When I don't set the DataContext of the Window then my User Control gets the right one. That means, each DataContext allocation works for it's own, but not together.

My Xaml for the window:

XML

<Window x:Class="myproj.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:sys="clr-namespace:System;assembly=mscorlib"
        xmlns:my="clr-namespace:myproj.Controls"
        xmlns:myBehaviour="clr-namespace:Behaviour"
        Title="window" WindowState="Maximized" myBehaviour:Behaviour.Command="{Binding Command}">

        <Grid>
 <Grid.ColumnDefinitions>            
            <ColumnDefinition x:Name="TreeViewColumn" Width="250" />
            <ColumnDefinition x:Name="MainColumn" MinWidth="200" />
 </Grid.ColumnDefinition>
 <Grid.RowDefinitions>
            <RowDefinition x:Name="MenuBarRow" Height="56" />            
            <RowDefinition x:Name="MainRow" MinHeight="200" Height="200*" />
  </Grid.RowDefinition>

        <my:UserControl Grid.Column="0" Grid.Row="1" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
        </Grid>
        </Window>

My Code - behind constructor for the window

C#

public MainWindow()
   {
       this.DataContext = new MainViewModel();
       InitializeComponent();
   }

My Xaml for the UserControl

XML

<UserControl x:Class="myproj.Controls.myUserControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             mc:Ignorable="d"
             d:DesignHeight="300" d:DesignWidth="300" >

    <DockPanel>
        <TextBox  TextWrapping="Wrap" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Text="{Binding myProperty, UpdateSourceTrigger=PropertyChanged}" DockPanel.Dock="Top" />
    </DockPanel>
</UserControl>

My Code - behind constructor for the User Control

C#

public UserControl()
   {
      InitializeComponent();
      this.DataContext = new UserControlViewModel;
   }

I hope someone can give me a piece of advice.

Thank you.

Posted 8-May-13 2:49am

pd1989

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Comments

Irina Pykhova 8-May-13 9:37am

set UserControl DataContext in the MainWindow after call to InitializeComponent()

pd1989 8-May-13 10:04am

Thanks!

Sandeep Mewara 8-May-13 11:08am

Is your problem resolved?

2 solutions

Solution 1

Yes, it's solved,

now my constructor of my mainwindow looks like this...

C#

public MainWindow()
   {
       this.DataContext = new MainViewModel();
       InitializeComponent();
       myUserControlName.DataContext = new UserControlViewModel();
   }

Posted 9-May-13 3:19am

pd1989

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milannaughty · Accepted Answer · 2013-05-09T04:20:00

Hello pd1989,

You are right but,
By the way its not a good way to use datacontext properties. Better way to initiate UserControlViewModel in MainViewModel's constructor. Look This,

C#

class MainViewModel : BaseViewModel
{
    public UserControlViewModel UserControlVM {get; set;} 

    public MainViewModel()
    {
        UserControlVM = new UserControlViewModel();
    }
}

and use XAML code in MainWindow like this,

HTML

<my:usercontrol grid.column="0" grid.row="1" horizontalalignment="Stretch" verticalalignment="Stretch" datacontext="{Binding" xmlns:my="#unknown"></my:usercontrol>

Thanks.