bugfix: Prevent parent ListView widgets from snatching scrolling gestures

[ritikmishra]

Closes #253.

The issue was fixed by using a GestureArenaTeam in conjunction with extra gesture recognizers to ensure that the ScalingGestureRecognizer wins when we would expect it to do so.

[dev-phamquoctrong]

How to add it into my project? Do you have a example code?

[ritikmishra]

If you want to use the fork, put the following in your pubspec.yaml

  flutter_map:
    git:
      url: https://github.com/ritikmishra/flutter_map.git
      ref: fix-listview-scrolling

[jakobkuehne]

Sadly I can't use your git version because of flutter_map_marker_cluster.

Because flutter_map_marker_cluster 0.2.9 depends on flutter_map ^0.10.1+1 and no versions of flutter_map_marker_cluster match >0.2.9 <0.3.0, flutter_map_marker_cluster ^0.2.9 requires flutter_map from hosted.

Or am I doing something wrong? So far, I've never added a package directly from Git. But apart from the possibility to add your great customization via Git, this would be a very important feature and I can't understand why this is still not officially available in flutter_map...

If you want to use the fork, put the following in your pubspec.yaml

  flutter_map:
    git:
      url: https://github.com/ritikmishra/flutter_map.git
      ref: fix-listview-scrolling

[romainpurchla]

Work for me 👍

[sm2017]

It's worked for me. Can you explain how to it works?

@ritikmishra I'm interested to know that how it works

@johnpryan Please accept the PR

[ritikmishra]

The mechanism through which Flutter recognizes gestures is called the gesture arena. Different gesture recognizers compete in the arena, and the first recognizer to accept the gesture, or the last recognizer remaining in the arena (i.e the other recognizers rejected the gesture), is responsible for handling it.

Previously, the map was implicitly using 3 gesture recognizers through GestureDetector: ScaleGestureRecognizer (handling panning and zoom), TapGestureRecognizer, and LongPressGestureRecognizer. If the map is inside a widget that scrolls (i.e a ListView), a fourth gesture recognizer will be in the arena: either a HorizontalDragGestureRecognizer or a VerticalDragGestureRecognizer depending on the direction that it scrolls.

The problem was caused by the ScaleGestureRecognizer taking too long to accept the gesture, resulting in the HorizontalDragGestureRecognizer/VerticalDragGestureRecognizer winning in the gesture arena.

The solution was to use a GestureArenaTeam to utilize a new HorizontalDragGestureRecognizer and a new VerticalDragGestureRecognizer to help the original ScaleGestureRecognizer win faster. A GestureArenaTeam has a captain and members -- whenever any gesture recognizer in the team accepts the gesture, the captain is put in charge of handling it. This way, a user can pan the map when it is inside a ListView/other scrollable widget.

[sm2017]

@ritikmishra as the PR is not merged, is there alternative solution , for example wrapping map with another widget?

[ritikmishra]

I couldn't find a workaround, which is why I made this PR. If you can find some way to stop the ListView from being so greedy in the gesture arena & ensure that the pointer events from gestures that don't go to the ListView do go to the FlutterMap, that should fix the problem.

[gsimko]

@johnpryan can you please take a look?

[kengu]

@ritikmishra Can you resolve the conflict and update this PR? I can review it when this is done.

[ritikmishra]

@kengu i have resolved the conflict

[kengu]

If I understand this correctly @ritikmishra, the TeamGestureRecognizer will always ensure that flutter_map takes precedence over ListView scoll? I don't think we can conclude that this is the only behaviour user expect. I think we need to make this behavior configurable, just as it is for scollables in general. I think we should add something similar (or equal) to scrollPhysics to MapOptions constructor.

@johnpryan? What do you think?

[github-actions]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[BenBitDesign]

Hi guys

I think @kengu makes a good point to make this configurable.

Is anyone looking into this?

[github-actions]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[kengu]

Closing, fixed by #994.