Why is there no command for pan gesture reconizer? tap gesture recognizer has one.

Steve Brooke 40

using gesture recognizer in a graphics view. Tap gesture allows commands, while pan and pinch do not. I need to respond to these in the view model. Is there some technical reason that these gestures do not allow commands?

            <GraphicsView.GestureRecognizers>
                <PanGestureRecognizer Command="{Binding Panned}" />
                <PinchGestureRecognizer Command="{Binding Pinched}" />
                <TapGestureRecognizer Command="{Binding Tapped}"/>
            </GraphicsView.GestureRecognizers>

Leon Lu (Shanghai Wicresoft Co,.Ltd.) 68,661 Reputation points Microsoft Vendor

2023-10-19T06:14:55.0566667+00:00

Pan and Pinch gesture apply for the whole view, not the content in the view. When you get these gestures, you can make the changes in the layout background code directly.

Do you want to detect Pinch and Pan gesture then make the graphic changes in the GraphicsView?

If you want to your view model to get gestures information, you can create methods in the Viewmodel. And add bindingContext in the layout background code. when Pinch event is executed, call methods in the viewmodel.
Steve Brooke 40 Reputation points

2023-10-19T14:19:55.4433333+00:00

The Pan and Pinch apply to the whole view, though they are embedded in the graphics view? That seems misleading in the xaml code. I would think that the pan/pinch gesture recognizers should be allowed only in the content section.

If I happen to have two graphics views on the same page, each with its own pan/pinch handlers, are both handlers called or only the one in which the gesture is performed? Just trying to understand the ramifications.

Yes, I am overlaying buttons which remain fixed while the graphics view underneath is panned or scaled.

I only understand the basics to use ICommand or binding. My work around is to have a pinch and pan handler in the content page code (layout background code?) which in turn sets translation and scale properties in the view model which are bound to the graphics view translate and scale. This seems to work pretty well and I am not sure if this was your recommendation. If not, please clarify?

Thanks so much for taking the time to respond.

Leon Lu (Shanghai Wicresoft Co,.Ltd.) 68,661 Microsoft Vendor

I found graphicsview have some events, you can use EventToCommandBehavior to get these events(such as drop, press and release event), then invoke the command in the viewmodel.

<GraphicsView Drawable="{StaticResource drawable}"
               HeightRequest="300"
             
               WidthRequest="400" >
     <GraphicsView.Behaviors>
         <toolkit:EventToCommandBehavior
              x:TypeArguments="TouchEventArgs"
         EventName="DragInteraction"
         Command="{Binding DragCommand}" />
     </GraphicsView.Behaviors>
</GraphicsView>