带有渐变的颤振滑块

Question

我想知道是否有一种方法可以在 Flutter 中创建具有渐变颜色的滑块小部件。 Here 是滑块类的链接，但没有“SliderTheme”或类似的东西。

Answer 1

我现在基于this youtube 视频创建了一个自定义轨道形状类，并在构造函数中添加了渐变属性。

使用方法：

渐变：

LinearGradient gradient = LinearGradient(
 colors: <Color> [
  Colors.red,
  Colors.orange,
  Colors.yellow,
  Colors.green,
  Colors.blue,
  Colors.blue[900],
  Colors.purple
 ]
);

滑块：
（属性 darkenInactive = false 用于不使非活动侧的滑块变暗。）

SliderTheme(
 data: SliderThemeData(
  trackShape: GradientRectSliderTrackShape(gradient: gradient, darkenInactive: false),
 ),
 child: Slider(
  min: 0,
  max: 10,
  value: value,
  onChanged: (double value) {},
  )
),

形状类：

import 'package:flutter/material.dart';

/// Based on https://www.youtube.com/watch?v=Wl4F5V6BoJw

class GradientRectSliderTrackShape extends SliderTrackShape
    with BaseSliderTrackShape {
  const GradientRectSliderTrackShape({
    this.gradient = const LinearGradient(
      colors: [
        Colors.red,
        Colors.yellow,
      ],
    ),
    this.darkenInactive = true,
  });

  final LinearGradient gradient;
  final bool darkenInactive;

  @override
  void paint(
      PaintingContext context,
      Offset offset,
      {
        required RenderBox parentBox,
        required SliderThemeData sliderTheme,
        required Animation<double> enableAnimation,
        required TextDirection textDirection,
        required Offset thumbCenter,
        bool isDiscrete = false,
        bool isEnabled = false,
        double additionalActiveTrackHeight = 2,
      }
    ) {
    assert(sliderTheme.disabledActiveTrackColor != null);
    assert(sliderTheme.disabledInactiveTrackColor != null);
    assert(sliderTheme.activeTrackColor != null);
    assert(sliderTheme.inactiveTrackColor != null);
    assert(sliderTheme.thumbShape != null);
    assert(sliderTheme.trackHeight != null && sliderTheme.trackHeight! > 0);

    final Rect trackRect = getPreferredRect(
      parentBox: parentBox,
      offset: offset,
      sliderTheme: sliderTheme,
      isEnabled: isEnabled,
      isDiscrete: isDiscrete,
    );

    final activeGradientRect = Rect.fromLTRB(
      trackRect.left,
      (textDirection == TextDirection.ltr)
          ? trackRect.top - (additionalActiveTrackHeight / 2)
          : trackRect.top,
      thumbCenter.dx,
      (textDirection == TextDirection.ltr)
          ? trackRect.bottom + (additionalActiveTrackHeight / 2)
          : trackRect.bottom,
    );

    // Assign the track segment paints, which are leading: active and
    // trailing: inactive.
    final ColorTween activeTrackColorTween = ColorTween(
        begin: sliderTheme.disabledActiveTrackColor,
        end: sliderTheme.activeTrackColor);
    final ColorTween inactiveTrackColorTween = darkenInactive
        ? ColorTween(
          begin: sliderTheme.disabledInactiveTrackColor,
          end: sliderTheme.inactiveTrackColor
        )
        : activeTrackColorTween;
    final Paint activePaint = Paint()
      ..shader = gradient.createShader(activeGradientRect)
      ..color = activeTrackColorTween.evaluate(enableAnimation)!;
    final Paint inactivePaint = Paint()
      ..color = inactiveTrackColorTween.evaluate(enableAnimation)!;
    final Paint leftTrackPaint;
    final Paint rightTrackPaint;
    switch (textDirection) {
      case TextDirection.ltr:
        leftTrackPaint = activePaint;
        rightTrackPaint = inactivePaint;
        break;
      case TextDirection.rtl:
        leftTrackPaint = inactivePaint;
        rightTrackPaint = activePaint;
        break;
    }

    final Radius trackRadius = Radius.circular(trackRect.height / 2);
    final Radius activeTrackRadius = Radius.circular(trackRect.height / 2 + 1);

    context.canvas.drawRRect(
      RRect.fromLTRBAndCorners(
        trackRect.left,
        (textDirection == TextDirection.ltr)
            ? trackRect.top - (additionalActiveTrackHeight / 2)
            : trackRect.top,
        thumbCenter.dx,
        (textDirection == TextDirection.ltr)
            ? trackRect.bottom + (additionalActiveTrackHeight / 2)
            : trackRect.bottom,
        topLeft: (textDirection == TextDirection.ltr)
            ? activeTrackRadius
            : trackRadius,
        bottomLeft: (textDirection == TextDirection.ltr)
            ? activeTrackRadius
            : trackRadius,
      ),
      leftTrackPaint,
    );
    context.canvas.drawRRect(
      RRect.fromLTRBAndCorners(
        thumbCenter.dx,
        (textDirection == TextDirection.rtl)
            ? trackRect.top - (additionalActiveTrackHeight / 2)
            : trackRect.top,
        trackRect.right,
        (textDirection == TextDirection.rtl)
            ? trackRect.bottom + (additionalActiveTrackHeight / 2)
            : trackRect.bottom,
        topRight: (textDirection == TextDirection.rtl)
            ? activeTrackRadius
            : trackRadius,
        bottomRight: (textDirection == TextDirection.rtl)
            ? activeTrackRadius
            : trackRadius,
      ),
      rightTrackPaint,
    );
  }
}

(Github Gist)

Answer 2

你可以试试这个；

Widget get gradientContainer => Container(
    width: double.infinity,
    height: height,
    decoration: BoxDecoration(
        gradient: gradient
    ),
  );

Widget get slider =>SliderTheme(
  data: SliderThemeData(
      trackShape: CustomTrackShape(),
      activeTrackColor: Colors.transparent,
      inactiveTrackColor: Colors.red,
      thumbColor: Colors.white,
      overlayColor: Colors.transparent
  ),
  child: Slider(
      value: value,
      max: max,
      min: min,
      onChanged: (double newValue){
        setState(() {
          value=newValue;
        });
      }
  )

);

为了在滑块上添加轨道填充，我们的自定义轨道形状类也在这里；

class CustomTrackShape extends RoundedRectSliderTrackShape {
  Rect getPreferredRect({
    @required RenderBox parentBox,
    Offset offset = Offset.zero,
    @required SliderThemeData sliderTheme,
    bool isEnabled = false,
    bool isDiscrete = false,
  }) {
    final double trackHeight = sliderTheme.trackHeight;
    final double trackLeft = offset.dx;
    final double trackTop = offset.dy + (parentBox.size.height - trackHeight) / 2;
    final double trackWidth = parentBox.size.width;
    return Rect.fromLTWH(trackLeft, trackTop, trackWidth, trackHeight);
  }
}

我们终于可以合并它们了；

  Widget get gradientSlider=>Padding(
  child: SizedBox(
    child: Stack(
      children: [
        gradientContainer,
        slider,
      ],
      alignment: Alignment.center,
    ),
  ),
  padding: padding

);

最后你只需要填充填充、宽度、高度、渐变按钮容器高度属性，就可以了。

结果；

Answer 3

使用这个库。用它来实现真的很容易，

https://pub.dev/packages/flutter_xlider

        FlutterSlider(
          values: [40],
          max: 100,
          min: 0,
          trackBar: FlutterSliderTrackBar(
            activeTrackBar: BoxDecoration(
              gradient: AppColors.sliderGradient,
              borderRadius: BorderRadius.circular(5)
            ),
            activeTrackBarHeight: 6,
          ),
          onDragging: (handlerIndex, lowerValue, upperValue) {
            
          },
        );

**更新
似乎 pub 版本尚未更新为空安全。但是主分支有它。如下使用 null 安全版本

flutter_xlider:
  git:
    url: https://github.com/Ali-Azmoud/flutter_xlider.git
    ref: master