how to let SpriteAnimationComponent follow BodyComponent

how to let SpriteAnimationComponent follow BodyComponent, which can fall due to gravity. currently SpriteAnimationComponent still keep in the air, here is my code:

  class Chick extends BodyComponent {
      Vector2 fallPosition;
      SpriteAnimationComponent chick = SpriteAnimationComponent();
    
      Chick({
        this.fallPosition,
      });
    
      final spriteSize = Vector2(32, 34) / 2;
    
      @override
      Future<void> onLoad() async {
        await super.onLoad();
        var spriteData = SpriteAnimationData.sequenced(
            amount: 14, stepTime: 0.1, textureSize: Vector2(32, 34));
        chick = SpriteAnimationComponent.fromFrameData(
            spriteSize, ImageTool.image('chicken.png'), spriteData)
          ..x = fallPosition.x
          ..y = fallPosition.y
          ..anchor = Anchor.center
          ..size = spriteSize;
        await addChild(chick);
      }
    
      @override
      void update(double dt) {
        chick.position = body.position;
        print('body.position ! ${body.position} == $fallPosition}');
        super.update(dt);
      }
    
      @override
      Body createBody() {
        debugMode = true;
    
        final shape = CircleShape()..radius = spriteSize.x / 2;
        var position = fallPosition.clone();
        var worldPosition = viewport.getScreenToWorld(position);
        final fixtureDef = FixtureDef()
          ..shape = shape
          ..restitution = 0.1
          ..density = 0.1
          ..friction = 0.1;
    
        final bodyDef = BodyDef()
          ..userData = this
          ..angularDamping = 0.1
          ..position = worldPosition
          ..type = BodyType.DYNAMIC;
    
        return world.createBody(bodyDef)..createFixture(fixtureDef);
      }
    }

I realize fallPosition, fallPosition, and chick.position has different value, but I dont know how to make this SpriteAnimationComponent follow Body, thanks for any help!

Solution

Add the SpriteBodyComponent as a child to the BodyComponent by simply running add, and remove the attempts that you have at synchronizing the positions, this will be done automatically once you have added it as a child.

To do this you also need to upgrade to a newer version of Flame (preferably v1.4.0 or newer) and a new version of flame_forge2d (> 0.12.3). Do note that addChild has been renamed to add.