如何在 Flutter 中制作前后图像滑块视图

Question

我想创建一个包含两张堆叠图像的前后视图，并在我的 Flutter 应用中为用户提供前后视图的体验。

如何创建像 https://iosexample.com/fancy-slider-for-before-after-images-with-swift/ 这样的 Before/After 控件

图片来源https://iosexample.com

Answer 1

这是我自己的问题的答案，以传播知识

创建一个 BeforeAfter 类

import 'package:flutter/material.dart';

import 'RectClipper.dart';

class BeforeAfter extends StatefulWidget {
  final Widget beforeImage;
  final Widget afterImage;
  final double imageHeight;
  final double imageWidth;
  final double imageCornerRadius;
  final Color thumbColor;
  final double thumbRadius;
  final Color overlayColor;
  final bool isVertical;

  const BeforeAfter({
    Key key,
    @required this.beforeImage,
    @required this.afterImage,
    this.imageHeight,
    this.imageWidth,
    this.imageCornerRadius = 8.0,
    this.thumbColor = Colors.white,
    this.thumbRadius = 16.0,
    this.overlayColor,
    this.isVertical = false,
  })  : assert(beforeImage != null),
        assert(afterImage != null),
        super(key: key);

  @override
  _BeforeAfterState createState() => _BeforeAfterState();
}

class _BeforeAfterState extends State<BeforeAfter> {
  double _clipFactor = 0.5;

  @override
  Widget build(BuildContext context) {
    return Stack(
      alignment: Alignment.center,
      children: <Widget>[
        Padding(
          padding: widget.isVertical ? const EdgeInsets.symmetric(vertical: 24.0) : const EdgeInsets.symmetric(horizontal: 24.0),
          child: SizedImage(
            widget.afterImage,
            widget.imageHeight,
            widget.imageWidth,
            widget.imageCornerRadius,
          ),
        ),
        Padding(
          padding: widget.isVertical ? const EdgeInsets.symmetric(vertical: 24.0) : const EdgeInsets.symmetric(horizontal: 24.0),
          child: ClipPath(
            clipper: widget.isVertical ? RectClipperVertical(_clipFactor) : RectClipper(_clipFactor),
            child: SizedImage(
              widget.beforeImage,
              widget.imageHeight,
              widget.imageWidth,
              widget.imageCornerRadius,
            ),
          ),
        ),
        Positioned.fill(
          child: SliderTheme(
            data: SliderThemeData(
              trackHeight: 0.0,
              overlayColor: widget.overlayColor,
              thumbShape: CustomThumbShape(widget.thumbRadius, widget.thumbColor),
            ),
            child: widget.isVertical
                ? RotatedBox(
                    quarterTurns: 1,
                    child: Slider(
                      value: _clipFactor,
                      onChanged: (double factor) => setState(() => this._clipFactor = factor),
                    ),
                  )
                : Slider(
                    value: _clipFactor,
                    onChanged: (double factor) => setState(() => this._clipFactor = factor),
                  ),
          ),
        ),
      ],
    );
  }
}

class SizedImage extends StatelessWidget {
  final Widget _image;
  final double _height, _width, _imageCornerRadius;

  const SizedImage(this._image, this._height, this._width, this._imageCornerRadius, {Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return ClipRRect(
      borderRadius: BorderRadius.circular(_imageCornerRadius),
      child: SizedBox(
        height: _height,
        width: _width,
        child: _image,
      ),
    );
  }
}

class CustomThumbShape extends SliderComponentShape {
  final double _thumbRadius;
  final Color _thumbColor;

  CustomThumbShape(this._thumbRadius, this._thumbColor);

  @override
  Size getPreferredSize(bool isEnabled, bool isDiscrete) {
    return Size.fromRadius(_thumbRadius);
  }

  @override
  void paint(
    PaintingContext context,
    Offset center, {
    Animation<double> activationAnimation,
    Animation<double> enableAnimation,
    bool isDiscrete,
    TextPainter labelPainter,
    RenderBox parentBox,
    SliderThemeData sliderTheme,
    TextDirection textDirection,
    double value,
    double textScaleFactor,
    Size sizeWithOverflow,
  }) {
    final Canvas canvas = context.canvas;

    final Paint paint = Paint()
      ..isAntiAlias = true
      ..strokeWidth = 4.0
      ..color = _thumbColor
      ..style = PaintingStyle.fill;

    final Paint paintStroke = Paint()
      ..isAntiAlias = true
      ..strokeWidth = 4.0
      ..color = _thumbColor
      ..style = PaintingStyle.stroke;

    canvas.drawCircle(
      center,
      _thumbRadius,
      paintStroke,
    );

    canvas.drawCircle(
      center,
      _thumbRadius - 6,
      paint,
    );

    canvas.drawRect(Rect.fromCenter(center: center, width: 4.0, height: parentBox.size.height), paint);
  }
}

然后创建一个 RectClipper 类

import 'package:flutter/material.dart';

class RectClipper extends CustomClipper<Path> {
  final double clipFactor;

  RectClipper(this.clipFactor);

  @override
  Path getClip(Size size) {
    Path path = Path();
    path.lineTo(size.width * clipFactor, 0.0);
    path.lineTo(size.width * clipFactor, size.height);
    path.lineTo(0.0, size.height);
    path.close();
    return path;
  }

  @override
  bool shouldReclip(CustomClipper<Path> oldClipper) => true;
}

class RectClipperVertical extends CustomClipper<Path> {
  final double clipFactor;

  RectClipperVertical(this.clipFactor);

  @override
  Path getClip(Size size) {
    Path path = Path();
    path.lineTo(0.0, size.height * clipFactor);
    path.lineTo(size.width, size.height * clipFactor);
    path.lineTo(size.width, 0.0);
    path.close();
    return path;
  }

  @override
  bool shouldReclip(CustomClipper<Path> oldClipper) => true;
}

最后在你的屏幕上使用这些类

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

class BeforeAfterImageScreen extends StatefulWidget {
  static String tag = '/BeforeAfterImageScreen';

  @override
  BeforeAfterImageScreenState createState() => BeforeAfterImageScreenState();
}

class BeforeAfterImageScreenState extends State<BeforeAfterImageScreen> {
  @override
  Widget build(BuildContext context) {
    changeStatusColor(appColorPrimary);
    return Scaffold(
      appBar: appBar(context, "Before After Image"),
      body: Center(
        child: BeforeAfter(
          beforeImage: Image.asset('images/integrations/img/after.jpg'),
          afterImage: Image.asset('images/integrations/img/before.jpg'),
        ),
      ),
    );
  }
}

Answer 2

这就是答案，一个很酷的库 唯一的问题是不支持像 remini 这样的放大图像

https://pub.dev/packages/before_after