UWP - How to bind a ContentPresenter's element to the main ViewModel? - xaml

Question

I work on an app where the user can edit a "big" form:
The form contains a lot of fields: it is displayed in a Pivot, where each PivotItem represents a category of the form.
Some categories contain one or more child items: they are displayed through a Master-Detail presentation.
To display the items of the Detail part, I use a ContentPresenter that is binded directly to the Model:
<ContentPresenter
x:Name="DetailContentPresenter"
Grid.Column="1"
Grid.RowSpan="2"
BorderThickness="1,0,0,0"
Padding="24,0"
BorderBrush="{ThemeResource SystemControlForegroundBaseLowBrush}"
Content="{x:Bind MasterListView.SelectedItem, Mode=OneWay}">
<ContentPresenter.ContentTemplate>
<DataTemplate x:DataType="models:Form_Parts">
<...>
</DataTemplate>
</ContentPresenter.ContentTemplate>
</ContentPresenter>
This works fine, but there is a "third" level in the main form: a list of photos, that I display in the ContentPresenter through a GridView. This works also great, but I would like to use an "Add" button or the "ItemClick" event to interact with the photos: I don't see how I could bind a Command in the main ViewModel, instead of the ContentPresenter's DataContext. The other fields of this form bind well on this ViewModel.
I did some tests without any result:
<StackPanel Orientation="Horizontal" Grid.Row="1">
<GridView ItemsSource="{Binding images}"
ItemClick="{Binding PhotoClickCommand}">
<GridView.ItemTemplate>
<DataTemplate>
<Border BorderBrush="Gray" BorderThickness="1"
Padding="10"
Height="150" Width="190">
<Image Stretch="UniformToFill"
Source="{Binding bitmap_image}" />
</Border>
</DataTemplate>
</GridView.ItemTemplate>
</GridView>
<Border BorderBrush="Gray" BorderThickness="1"
Padding="10"
Height="150" Width="190">
<Button Command="{Binding Path=DataContext.AddPhotoCommand, ElementName=DetailsPage}"
Height="100" Width="100">
<Viewbox>
<SymbolIcon Symbol="Add"/>
</Viewbox>
</Button>
</Border>
</StackPanel>
=> is there a way to doing this?
Edit :
I solved my problem for the "Add" button thanks Alteik with:
<Button Command="{Binding ElementName=Root, Path=DataContext.AddPhotoCommand}" Height="100" Width="100">
But I always get a problem with the ItemClick of the GridView. I tried this:
<GridView ItemsSource="{Binding images}"
IsItemClickEnabled="True"
SelectionMode="None">
<i:Interaction.Behaviors>
<core:EventTriggerBehavior EventName="Tapped">
<core:InvokeCommandAction Command="{Binding ElementName=Root, Path=DataContext.EditPhotoCommand}"
CommandParameter="{Binding Mode=OneWay}"/>
</core:EventTriggerBehavior>
</i:Interaction.Behaviors>
<...>
</GridView>
But I don't get the expected parameter in the ViewModel:
private void EditPhoto(object sender)
{
Images sImage = (Images)sender;
if (sImage != null)
{
NavigationService.NavigateTo<CommentImageViewModel>(this, new Object[] { sImage }, true);
}
}
The sender is the current Form_Parts (the DataTemplate of the ContentPresenter), whereas I would get the selected item of my images collection, that is binded to the GridView...
=> Whad could I do to fix this?

Answer 1

You should be able to change the DataContext in a child element doing this:
Command"{Binding ElementName=Root, Path=DataContext.TheCommandFromRoot}"
Obviously you need to set the name of the parent's element to "Root"