WPF MVVM Binding Relative Source

Question

I'm struggling with relative Sources. I'm inside Tab Items and I want to reach the parent ModelView. The goal is to make some context menu items invisble, if the item is the last tab.

ViewModel:

public bool IsLastTab => ItemCollection.Count > 1;

xaml:

<Window x:Name="MainWinodw"
    ...
    xmlns:ct="clr-namespace:ChromeTabs;assembly=ChromeTabs"
    xmlns:vm="clr-namespace:Main.ViewModel"
    xmlns:conv="clr-namespace:Main.Converters"
    xmlns:ctConv="clr-namespace:ChromeTabs.Converters;assembly=ChromeTabs"
    xmlns:usercontrols="clr-namespace:Main.UserControls"
    xmlns:sys="clr-namespace:System;assembly=mscorlib"
    ...
    DataContext="{Binding Source={StaticResource Locator},Path=Main}" ">
<Window.Resources>
    <conv:InverseBooleanToVisibilityConverter x:Key="InverseBooleanToVisibilityConverter" />
    ...
</Window.Resources >
<Grid>
    <ct:ChromeTabControl x:Name="MyChromeTabControl"
                         TabPersistBehavior="Timed"
                         TabPersistDuration="0:0:0:5"
                         AddTabButtonBehavior="OpenNewTab"
                         Background="AliceBlue"
                         ItemsSource="{Binding ItemCollection}"
                          ...">
        ...
        <ct:ChromeTabControl.ItemTemplate>
            <DataTemplate>
                <Grid Tag="{Binding RelativeSource={RelativeSource AncestorType={x:Type ct:ChromeTabItem}}}">
                    ...
                    <Grid.ContextMenu>
                        <ContextMenu>
                            <MenuItem Header="Close"
                                      Command="{Binding Path=PlacementTarget.Tag.CloseTabCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
                                      Visibility="{Binding IsLastTab,  
                                                    RelativeSource={RelativeSource AncestorType={x:Type vm:ViewModelChromeTabs}}, 
                                                    Mode=OneWay, 
                                                    Converter={StaticResource InverseBooleanToVisibilityConverter}}"
                                      CommandTarget="{Binding Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}" />
                            ...
                            <Separator />
                            <MenuItem Header="{Binding IsPinned, Converter={StaticResource BooleanToPinTabTextConverter}}"
                                      Command="{Binding Path=PlacementTarget.Tag.PinTabCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
                                      CommandTarget="{Binding Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}"
                                      CommandParameter="{Binding}" />
                        </ContextMenu>
                    </Grid.ContextMenu>
                </Grid>
            </DataTemplate>
        </ct:ChromeTabControl.ItemTemplate>
    </ct:ChromeTabControl>
</Grid>
</Window>

It's working when I put it in the Item Class but there I have no Info about how many Tabs are left, and it seems counter logic to implement a messenger here for this.

Your ViewModel is probably not in the LogicalTree. You should bind to the datacontext of your window instead: `{Binding DataContext.IsLastTab, RelativeSource={RelativeSource AncestorType={x:Type Window}}` — Freggar, Jun 18 '18 at 10:57
Hellor Freggar, didn't help. The Viewmodel works with `ItemsSource="{Binding ItemCollection}"` but after the tag its only applying the items model — k4yaman, Jun 18 '18 at 11:01
Then it's time to create a [Minimal, Complete, and Verifiable example](https://stackoverflow.com/help/mcve). Because I have no clue other than that why the binding does not work. You could also look at the debug console for any Binding Expression errors. — Freggar, Jun 18 '18 at 11:11
Oh I'm stupid. `RelativeSource` won't work since a `ContextMenu` does not share the same VisualTree. See https://stackoverflow.com/questions/3583507/wpf-binding-a-contextmenu-to-an-mvvm-command for more info — Freggar, Jun 18 '18 at 11:17
Thanks, thats exactly my question. Didn't find this one before. I'll try this one — k4yaman, Jun 18 '18 at 11:28

FrankM · Accepted Answer · 2018-06-18T11:05:49.897

2

You have defined IsLastTab like this:

public bool IsLastTab => ItemCollection.Count > 1;

This does not seem to determine whether the current tab is the last one.

You need something like that:

public bool IsLastTab => ReferenceEquals(this, ItemCollection.LastOrDefault());

(Since you did not post the underlying view models, this is just a guess. The exact code might change.)

And you also need to call INotifyPropertyChanged.PropertyChanged for the property "IsLastTab" for each tab item whenever the tab collection changes.

edited Jun 18 '18 at 11:05

answered Jun 18 '18 at 11:03

FrankM

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15

Well it doesn't reach the getter anyway yet. I could probably notify the last item in the list with the PropertyChanged Event. Thanks for this, i'll try it but it isn't my desired solution – k4yaman Jun 18 '18 at 11:05

WPF MVVM Binding Relative Source

1 Answers1