Flutter - Why onVerticalDragEnd does not work?

Question

I am trying to get if the user is swiping horizontally or vertically using a GestureDetector widget. For some reason I am unable to make the onVerticalDragEnd property work. HorizontalDragEnd works just fine.

Am I supposed to add anything else?

`

child: new GestureDetector(
                  onHorizontalDragEnd: (DragEndDetails details) {
                    print("horizontal drag");
                  },
                  onVerticalDragEnd : (DragEndDetails details) {
                    print("vertical drag");
                  } ,
                  child: new GridView.count(..

`

Solution 1

Instead of GestureDetector, you can use Listener, it worked for me. Here's how I implemented it -

import 'dart:math';

double radians(double degree) {
    return ((degree * 180) / pi);
  }

void swipe(moveEvent) {
double angle = radians(moveEvent.delta.direction);
    if (angle >= -45 && angle <= 45) {
      print("Swipe Right");
    } else if (angle >= 45 && angle <= 135) {
      print("Swipe Down");
    } else if (angle <= -45 && angle >= -135) {
      print("Swipe Up");
    } else {
      print("Swipe Left");
    }
}

child: Listener(
  onPointerMove: (moveEvent) => swipe(moveEvent),
  child: GridView.count(...),
)

But this calls function multiple times on a single swipe

Solution 2

Try logging when your GestureDetector and/or parent components are being created, and see if it's being re-rendered before the End event. I had the same problem, and it was due to side effects of the Update event I used causing a re-render. After making some modifications to prevent that from happening, the End event started working.

Comments

[Rémi Rousselet]

You most likely have another widget somewhere that catch this gesture. Such as ListView.

[Adi Albu]

If I delete onHorizontalDrag it still doesn't execute the vertical one. Furthermore, both horizontal and vertical drag work together just fine if I don't use GridView as a child. Is this a bug or just a constraint?

[Nash]

The reason it works is because you are using a grid view :P