Flutter Skeleton Text with Shimmer Animation

Skeleton text is a strategy that improves the perceived load time of content by rendering a blank placeholder that roughly matches the size of the expected content. This method was originally made popular by Facebook, but is now used on many popular apps and websites.

Use this skeleton text widget as a placeholder when loading data from an external source.

The skeleton text effect can be created in Flutter with an animated loop over a color gradient. It simply moves the starting point of the gradient from left to right. In addition, it makes the height and width configurable to fit different content types.

skeleton.dart

class Skeleton extends StatefulWidget {
  final double height;
  final double width;

  Skeleton({Key key, this.height = 20, this.width = 200 }) : super(key: key);

  createState() => SkeletonState();
}

class SkeletonState extends State<Skeleton> with SingleTickerProviderStateMixin {
  AnimationController _controller;

  Animation gradientPosition;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(duration: Duration(milliseconds: 1500), vsync: this);

    gradientPosition = Tween<double>(
      begin: -3,
      end: 10,
    ).animate(
      CurvedAnimation(
        parent: _controller,
        curve: Curves.linear
      ),
    )..addListener(() {
      setState(() {});
    });

    _controller.repeat();
  }

  @override
  void dispose() {
    super.dispose();
    _controller.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
        width:  widget.width,
        height: widget.height, 
        decoration: BoxDecoration(
          gradient: LinearGradient(
            begin: Alignment(gradientPosition.value, 0),
            end: Alignment(-1, 0),
            colors: [Colors.black12, Colors.black26, Colors.black12]
          )
        ),
    );
  }
}

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