WPF tab control and MVVM selection

Question

I have a TabControl in an MVVM WPF application. It is defined as follows.

<TabControl Style="{StaticResource PortfolioSelectionTabControl}" SelectedItem="{Binding SelectedParameterTab}" >
    <TabItem Header="Trades" Style="{StaticResource PortfolioSelectionTabItem}">
        <ContentControl Margin="0,10,0,5" Name="NSDetailTradeRegion" cal:RegionManager.RegionName="NSDetailTradeRegion" />
    </TabItem>
    <TabItem Header="Ccy Rates" Style="{StaticResource PortfolioSelectionTabItem}">
        <ContentControl Margin="0,10,0,5" Name="NSDetailCcyRegion" cal:RegionManager.RegionName="NSDetailCcyRegion" />
    </TabItem>
    <TabItem Header="Correlations / Shocks" Style="{StaticResource PortfolioSelectionTabItem}">
        <ContentControl Name="NSDetailCorrelationRegion" cal:RegionManager.RegionName="NSDetailCorrelationRegion" />
    </TabItem>
    <TabItem Header="Facility Overrides" Style="{StaticResource PortfolioSelectionTabItem}" IsEnabled="False">
        <ContentControl Name="NSDetailFacilityOverrides" cal:RegionManager.RegionName="NSDetailFacilityOverrides" />
    </TabItem>
</TabControl>

So each tab item content has its own view associated with it. Each of those views has the MEF [Export] attribute and is associated with the relevant region through view discovery, so the above code is all I need to have the tab control load and switch between them. They all reference the same shared ViewModel object behind them and so all interact seamlessly.

My problem is that when the user navigates to the parent window, I want the tab control to default to the second tab item. That is easy enough to do when the window is first loaded, by specifying in XAML IsSelected="True" in TabItem number 2. It is less easy to do when the user navigates away from the screen and then comes back to it.

I thought about having a SelectedItem={Binding SelectedTabItem} property on the tab control, so I could programmatically set the selected tab in the ViewModel, but the problem is I have no knowledge of the TabItem objects in the ViewModel as they are declared above in the XAML only, so I have no TabItem object to pass to the setter property.

One idea I had was to make the child Views (that form the content of each of the tab items above) have a style on the UserControl level of their XAML, something along the following.

<Style TargetType={x:Type UserControl}>
    <Style.Triggers>
        <DataTrigger Property="IsSelected" Value="True">
             <Setter Property="{ElementName={FindAncestor, Parent, typeof(TabItem)}, Path=IsSelected", Value="True" />
        </DataTrigger>
    </Style.Triggers>
</Style>

I know the findancestor bit isn't correct; I've just put it there to specify my intent, but I am not sure of the exact syntax. Basically for each UserControl to have a trigger that listens to a property on the ViewModel (not sure how I would distinguish each different UserControl as obviously they can't all listen to the same property or they would all select simultaneously when the property is set to True, but having a property for each usercontrol seems ugly) and then finds its parent TabItem container and sets the IsSelected value to true.

Am I on the right track with a solution here? Is it possible to do what I am pondering? Is there a tidier solution?

Answer 1

If you look at the TabControl Class page on MSDN, you'll find a property called SelectedIndex which is an int. Therefore, simply add an int property into your view model and Bind it to the TabControl.SelectedIndex property and then you can select whichever tab you like at any time from the view model:

<TabControl SelectedIndex="{Binding SelectedIndex}">
    ...
</TabControl>

---

UPDATE >>>

Setting a 'startup' tab is even easier using this method:

In view model:

private int selectedIndex = 2; // Set the field to whichever tab you want to start on

public int SelectedIndex { get; set; } // Implement INotifyPropertyChanged here