Disabled horizontal drag recognition over the `panelBuilder`

[s0nerik]

This fixes an issue with horizontally-slideable children in panelBuilder that cause the panel to drag vertically during the horizontal scroll.

Also, multi-touch recognition prevention is implemented just in case.

[emvaized]

Is it also possible to fix this issue using the same approach? Thanks.

[s0nerik]

@emvaized It's very likely that this PR will fix the issue you've mentioned as well.

[emvaized]

@s0nerik Unfortunately, it's not -- I just tried to implement your changes, and issue still persists.

[emvaized]

@s0nerik I've also tried your solution with TabView children of panelBuilder, and it seems not working as well - panel's still reacting to swipe when scrolling between tabs. Maybe I've implemented it wrong?

[emvaized]

@s0nerik UPDATE: It actually solves my problem with Draggable children, but at first you have to move item horizontally, and only after that panel stops to react to the movement of the item.

Maybe your code can be slightly changed in some way, in order to fix it?

[s0nerik]

@emvaized This fix solves only the problem of counting the vertical component of the horizontal scroll.

If I understood your use-case correctly, you have list items within sliding panel that can be dragged both horizontally and vertically. In your case, there're two vertically-draggable components: SlidingUpPanel, LongPressDraggable. I didn't envision such usages when I wrote it, and, from my experience, having more than one draggable component within the same axis is always problematic (two drags within different axes are OK).

Probably what you're seeing is LongPressDraggable being dragged the same amount of vertical pixels as the SlidingUpPanel since AFAIK, Listener doesn't block any gesture detectors from receiving the drag events.

I think that the only way to fix your problem is to have some sort of drag rejection mechanism within the SlidingUpPanel.

The way I envision it to work is the following:

1. You detect that your draggable item has started dragging.
2. You notify SlidingUpPanel that it should stop any drag it's currently tracking. **
3. _VerticalDragListener receives the signal
4. _VerticalDragListener notifies SlidingUpPanel that the drag was canceled
5. SlidingUpPanel animates back to the position before drag occurred (should not be visible at all if you notify the panel early enough)

** There's already an isDraggable parameter, and it should work by simply removing the vertical drag listener from the widget tree, but I'm not sure how the gesture tracking mechanism would react to that. My guess would be that the old Listener callbacks will still be called for the drag that started while it was within the widget tree. Considering the above, probably using something like ValueListenable that's listened within the _VerticalDragListener would be better than a widget property in this case since it won't require the widget tree rebuild to stop the drag from being tracked by the panel, and will definitely work regardless of the way Flutter handles Listener removal from the tree.

[emvaized]

@s0nerik Thanks for extended response! I got your thought. Just as you guessed, simply wrapping SlidingUpPanel into ValueListenableBuilder doesn't help -- panel continues to react to gestures.

Could you please explain, what you mean by this line:

ValueListenable that's listened within the _VerticalDragListener

Do you mean modifying SlidingUpPanel constructor in order to make it accept custom ValueListenable parameter, and then listen to it's value inside _VerticalDragListener?

[s0nerik]

@emvaized Yes. Ignoring the drag upon receiving the event from ValueListenable within the _VerticalDragListener looks like the way out for me.

[emvaized]

@s0nerik Thanks, it seems to work with no issues now :) Not sure if it will be right to ask you to add these changes to your pull request, since they require wrapping SlidingUpPanel widget in the ValueListenableBuilder (at least in my case).

[JulianBissekkou]

Can this be merged? 🤔 We are waiting for this fix

[emvaized]

@JulianBissekkou You can simply import the whole panel.dart file in your project, and rename class to something like CustomSlidingUpPanel. It should work until the creators will merge @s0nerik 's patches.

[aBuder]

Yes can we merge this. I also have the same problem

[TheBarn]

Really useful, thanks!

[shahmirzali49]

@s0nerik Hi, thanks for this fixing, but now it's not working? can you update this fixing? thanks

[shahmirzali49]

Really useful, thanks!

@TheBarn did you solve it? can you help?

[s0nerik]

@Shahmirzali-Huseynov

Unfortunately, I no longer support the lib's fork. My team decided to abandon this lib due to its limitations/problems. Instead, we made a self-written "sliding panel" implementation that satisfied all of our needs. The lib isn't open-source, unfortunately, but, TBH, it was quite straightforward to implement, so I can only suggest you do the same.

[shahmirzali49]

@s0nerik thank you for code, fixed now, it's working