How should I pass the view model to long press command?

[nicholasyin]

Type of issue

Missing information

Description

I'm using this behavior in a collection view to display images, and I want to handle the long press command.
LongPressCommandParameter="{Binding .}" However, the currently touched image's bound view model can't be passed to the command, where it shows null as the view model's value.

Page URL

https://learn.microsoft.com/en-us/dotnet/communitytoolkit/maui/behaviors/touch-behavior?tabs=toucheffect-xaml%2Ctouchbehavior-xaml#properties

Content source URL

https://github.com/MicrosoftDocs/CommunityToolkit/blob/main/docs/maui/behaviors/touch-behavior.md

Document Version Independent Id

98a8e0a6-ef8e-7427-100f-7b4448e0ffce

Platform Id

28950eda-3f84-b0ac-bd2b-243cce75aa34

Article author

Shaun Lawrence (@bijington)

Metadata

• ID: 98a8e0a6-ef8e-7427-100f-7b4448e0ffce
• PlatformId: 28950eda-3f84-b0ac-bd2b-243cce75aa34
• Service: dotnet-communitytoolkit
• Sub-service: dotnet-maui-community-toolkit

[bijington]

Can you share you code to make it easier to understand what you are trying to achieve?

[nicholasyin]

                <DataTemplate x:DataType="data:PhotoItemViewModel">
                    <Border StrokeThickness="1"
                            Padding="0">
                        <VerticalStackLayout>
                            <Grid>
                                <Image
                                    Source="{Binding ThumbnailImageSource}"
                                    Aspect="AspectFill"
                                    HeightRequest="120"
                                    WidthRequest="120">
                                    <Image.Behaviors>
                                        <toolkit:TouchBehavior
                                            
                                            LongPressCommand="{Binding x:DataType=ContentPage, Source={x:Reference Page}, Path=BindingContext.LongPressCommand}"
                                            LongPressCommandParameter="{Binding .}"/>
                                    </Image.Behaviors>
                                </Image>
                                
                                <CheckBox
                                    IsChecked="{Binding IsSelected}"
                                    IsVisible="{Binding x:DataType=ContentPage,Source={x:Reference Page}, Path=BindingContext.IsSelectionMode}"
                                    VerticalOptions="Start"
                                    HorizontalOptions="End"
                                    Margin="5"
                                    BackgroundColor="White"
                                    Opacity="0.8"/>
                            </Grid>
                        </VerticalStackLayout>
                    </Border>
                </DataTemplate>
            </CollectionView.ItemTemplate>
        </CollectionView>

Here I'm using a collection view to display a list of images, with the support of long press gesture on each image, implemented using CommunityToolkit.Maui's TouchBehavior. And my view model's LongPressCommand command is initialized with this method:

private void OnPhotoLongPressed(PhotoItemViewModel photo)
    {
        IsSelectionMode = true;
        // photo.IsSelected = true;
    }

The photo passed from the command is always null.

[bijington]

What if you try something like this:

LongPressCommandParameter="{Binding}"

or

LongPressCommandParameter="{Binding, x:DataType=namespace:Type}"

or

LongPressCommandParameter="{Binding Path=., x:DataType=namespace:Type}"

[nicholasyin]

What if you try something like this:

LongPressCommandParameter="{Binding}"
or

LongPressCommandParameter="{Binding, x:DataType=namespace:Type}"
or

LongPressCommandParameter="{Binding Path=., x:DataType=namespace:Type}"

Doesn't work.