Xamarin.Forms - Binding on ContextMenu

Question

I have a list with songs as items. A long press on the element should display a context menu.

AllSongsViewModel.xaml:

<DataTemplate x:Key="SongTemplate">
    <ViewCell>
        <ViewCell.ContextActions>
            <MenuItem Text="Edit" />
            <MenuItem Text="Delete"/>
        </ViewCell.ContextActions>

        <StackLayout Padding="15,5" VerticalOptions="Center">

            <Label Text="{Binding Title}"
                   FontSize="16"/>
            <Label Text="{Binding Performer}"
                   FontSize="12"/>
        </StackLayout>
    </ViewCell>
</DataTemplate>

This works well, but I need to bind now so that the context menu opens depending on bool IsAdmin, which lies in AllSongsViewModel

AllSongsViewModel.cs:

public bool IsAdmin => _authService.LoggedUser.Role == "Admin";

But I don’t know how to bind this property to the context menu

Answer 1

Unfortunately you can't do this on your ViewModel. But you can set a BindingContextChange event on your View Cell and change it there like this:

XAML:

<DataTemplate x:Key="SongTemplate">
 <ViewCell BindingContextChanged="OnBindingContextChanged">
    <StackLayout Padding="15,5" VerticalOptions="Center">

        <Label Text="{Binding Title}"
               FontSize="16"/>
        <Label Text="{Binding Performer}"
               FontSize="12"/>
    </StackLayout>
</ViewCell>

In your code behind:

 private void OnBindingContextChanged(object sender, EventArgs e)
    {
        base.OnBindingContextChanged();

        if (BindingContext == null)
            return;

        ViewCell theViewCell = ((ViewCell)sender);
        var viewModel = this.BindingContext.DataContext as AllSongsViewModel;
        theViewCell.ContextActions.Clear();

        if (viewModel.IsAdmin)
        {
            theViewCell.ContextActions.Add(new MenuItem()
            {
                Text = "Delete",
            });

            theViewCell.ContextActions.Add(new MenuItem()
            {
                Text = "Edit",
            });
        }
    }