Question

I have a master view and two subviews. I would like to switch from SubViewA to SubViewB when clicking on the button on SubViewA. The masterview contains a contentpresenter which is binded to View, and initialized to SubViewB when loaded. When clicking on the button on SubViewA the SubViewB constructor is called, but the control is never loaded. What am I missing? I’ve also tried by just setting the contenttemplate:

<ContentPresenter x:Name="contentPresenter" Content="{Binding View, PresentationTraceSources.TraceLevel=High}" />

which does not work either.

MainWindow:

<Window x:Class="WpfApplication2.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"
    xmlns:local="clr-namespace:WpfApplication2">

<Grid>

    <TextBlock Text="MasterViewPage" />

    <ContentControl x:Name="content" Content="{Binding View}">
        <ContentControl.Resources>
            <DataTemplate DataType="{x:Type local:SubViewModelA}">
                <local:SubViewA></local:SubViewA>
            </DataTemplate>
            <DataTemplate DataType="{x:Type local:SubViewModelB}">
                <local:SubViewB></local:SubViewB>
            </DataTemplate>
        </ContentControl.Resources>
    </ContentControl>

</Grid>
</Window>

public partial class MainWindow
{
    public MainWindow()
    {
        Loaded += MainWindow_Loaded;
        InitializeComponent();
    }

    private void MainWindow_Loaded(object sender, System.Windows.RoutedEventArgs e)
    {
        DataContext = new MainViewModel();
    }      
}

SubViewA:

<UserControl x:Class="WpfApplication2.SubViewA"
         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">

<Grid Margin="0,40,0,0">
    <TextBlock Text="Subview A" />

    <Button Height="50" Width="120" Content="Open View B" Command="{Binding OpenViewCommand}" />
</Grid>
</UserControl>

public partial class SubViewA
{
    public SubViewA()
    {
        Loaded += SubViewA_Loaded;
        InitializeComponent();
    }

    private void SubViewA_Loaded(object sender, System.Windows.RoutedEventArgs e)
    {
        DataContext = new SubViewModelA();
    }
}

ViewModels:

public class MainViewModel : NotifyPropertyChanged
{
    private object _view;

    public object View
    {
        get { return _view; }
        set
        {
            _view = value;
            RaisePropertyChanged(() => View);
        }
    }

    public MainViewModel()
    {
        View = new SubViewA();
    }
}

public class SubViewModelA : MainViewModel
{
    public ICommand OpenViewCommand
    {
        get { return new DelegatingCommand(OpenView); }
    }

    private void OpenView()
    {
        View = new SubViewB();
    }
}

public class SubViewModelB : MainViewModel
{
}

Thanks in advance.

Answer 1

OK, the solution that worked for me was:

MainView.xaml:

    <ContentControl x:Name="content">
        <ContentControl.Style>
            <Style TargetType="{x:Type ContentControl}">
                <Style.Triggers>
                    <DataTrigger Binding="{Binding View, PresentationTraceSources.TraceLevel=High}" Value="SubViewA">
                            <Setter Property="ContentTemplate">
                            <Setter.Value>
                                    <DataTemplate>
                                        <local:SubViewA />
                                    </DataTemplate>
                            </Setter.Value>
                        </Setter>
                    </DataTrigger>
                    <DataTrigger Binding="{Binding View, PresentationTraceSources.TraceLevel=High}" Value="SubViewB">
                            <Setter Property="ContentTemplate">
                            <Setter.Value>
                                    <DataTemplate>
                                        <local:SubViewB />
                                    </DataTemplate>
                                </Setter.Value>
                        </Setter>
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </ContentControl.Style>
    </ContentControl>

and in SubViewA.xaml:

<Button Height="50" Width="120" Content="Open View B" Command="{Binding Path=DataContext.OpenViewCommand, RelativeSource={RelativeSource AncestorType={x:Type Window}}, PresentationTraceSources.TraceLevel=High}" />

Reason was that View wasn’t set on MainViewModel, but on the subview instead (which inherited from MainViewModel). When removing the inheritance to actually set the view on MainViewModel everything worked.