Trying to change DataContext of main window from usercontrol

Question

On initialization of main window i set DataContext to usercontrol and on this usercontrol i have an event which suppose to change datacontext of main window to another usercontrol but nothing happens.

Here is xaml for main window:

</Window.Resources>
<Grid>
    <ContentControl Content="{Binding}" Width="auto" Height="auto" />
</Grid>

Here is C# for main window:

public MainWindow()
    {
        InitializeComponent();
        DataContext = new LogInViewModel();
    }

Here is xaml for LogInUserControl:

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition/>
        <ColumnDefinition/>
        <ColumnDefinition/>
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition/>
        <RowDefinition/>
        <RowDefinition/>
    </Grid.RowDefinitions>
    <StackPanel Grid.Column="1" Grid.Row="1">
        <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" Width="250">
            <StackPanel Width="125">
                <TextBlock Text="Email:" Margin="5,0,5,0" Width="auto"/>
            </StackPanel>
            <StackPanel Width="125">
                <TextBlock Text="Password:" Margin="5,0,0,0" Width="auto"/>
            </StackPanel>
        </StackPanel>
        <StackPanel Orientation="Horizontal" HorizontalAlignment="Center">
        <TextBox Margin="5,0,5,0" HorizontalAlignment="Center" Height="23" TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
        <PasswordBox Margin="0,0,0,5" HorizontalAlignment="Center" Height="23" VerticalAlignment="Top" Width="120"/>
        </StackPanel>
        <Button Content="Log In" Margin="0,0,0,5" HorizontalAlignment="Center" VerticalAlignment="Top" Width="75"/>
    </StackPanel>
    <Grid Grid.Column="1" Grid.Row="1">
        <StackPanel Orientation="Horizontal" HorizontalAlignment="Center">
        <TextBlock Text="don't have account yet ?" HorizontalAlignment="Center" VerticalAlignment="Bottom" Margin="5"/>
        <TextBlock Name="TBSignUp" Text="Sign Up" HorizontalAlignment="Center" VerticalAlignment="Bottom" Margin="5" PreviewMouseLeftButtonDown="TextBlock_PreviewMouseLeftButtonDown" PreviewMouseLeftButtonUp="TextBlock_PreviewMouseLeftButtonUp" Foreground="#FF0B36F5"/>
        </StackPanel>
    </Grid>
</Grid>

and here is C# for LogInUserControl:

public partial class LogInView : UserControl
{
    string BlackForeground = "#FF000000" ;
    string OriginalForeground = "#FF0B36F5";
    public LogInView()
    {
        InitializeComponent();
    }

    private void TextBlock_PreviewMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
    {
        TBSignUp.Foreground = new SolidColorBrush((Color)ColorConverter.ConvertFromString(OriginalForeground));
        DataContext = new RegisterView();
    }

    private void TextBlock_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        TBSignUp.Foreground = new SolidColorBrush((Color)ColorConverter.ConvertFromString(BlackForeground));
    }
}

Answer 1

In WPF you can get a shell (first) window from anywhere:

System.Windows.Window shell = System.Windows.Application.Current.MainWindow;

OR

 Application.Current.Windows[0];

but I recommend passing the reference if needed.

look at the MVVM pattern, you need to implement property change notification in your view model class to bind properties.