image.png

首页 ui是这样

技术点分析

首页.gif

可以看到首页需要这种可以滚动分页切换的 采用 tabbar+TabBarView

问题:但是tabbar 下面的indicator(指示器)默认不是圆角的 而且不能自定义 宽度 系统默认只提供了2种

//根据文字宽度
TabBarIndicatorSize.label
//根据tab的宽度
TabBarIndicatorSize.tab

1. flutter 自定义 indicator(指示器)

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

// 默认高度从46改为40
const double _kTabHeight = 40.0;
const double _kTextAndIconTabHeight = 72.0;
 
class RoundUnderlineTabIndicator extends Decoration {
  /// Create an underline style selected tab indicator.
  ///
  /// The [borderSide] and [insets] arguments must not be null.
  const RoundUnderlineTabIndicator({
    this.borderSide = const BorderSide(width: 2.0, color: Colors.white),
    this.insets = EdgeInsets.zero,
  }) : assert(borderSide != null),
        assert(insets != null);
 
  /// The color and weight of the horizontal line drawn below the selected tab.
  final BorderSide borderSide;
 
  /// Locates the selected tab's underline relative to the tab's boundary.
  ///
  /// The [TabBar.indicatorSize] property can be used to define the
  /// tab indicator's bounds in terms of its (centered) tab widget with
  /// [TabIndicatorSize.label], or the entire tab with [TabIndicatorSize.tab].
  final EdgeInsetsGeometry insets;
 
  @override
  Decoration lerpFrom(Decoration a, double t) {
    if (a is UnderlineTabIndicator) {
      return UnderlineTabIndicator(
        borderSide: BorderSide.lerp(a.borderSide, borderSide, t),
        insets: EdgeInsetsGeometry.lerp(a.insets, insets, t),
      );
    }
    return super.lerpFrom(a, t);
  }
 
  @override
  Decoration lerpTo(Decoration b, double t) {
    if (b is UnderlineTabIndicator) {
      return UnderlineTabIndicator(
        borderSide: BorderSide.lerp(borderSide, b.borderSide, t),
        insets: EdgeInsetsGeometry.lerp(insets, b.insets, t),
      );
    }
    return super.lerpTo(b, t);
  }
 
  @override
  _UnderlinePainter createBoxPainter([ VoidCallback onChanged ]) {
    return _UnderlinePainter(this, onChanged);
  }
}
 
class _UnderlinePainter extends BoxPainter {
  _UnderlinePainter(this.decoration, VoidCallback onChanged)
      : assert(decoration != null),
        super(onChanged);
 
  final RoundUnderlineTabIndicator decoration;
 
  BorderSide get borderSide => decoration.borderSide;
  EdgeInsetsGeometry get insets => decoration.insets;
 
  Rect _indicatorRectFor(Rect rect, TextDirection textDirection) {
    assert(rect != null);
    assert(textDirection != null);
    final Rect indicator = insets.resolve(textDirection).deflateRect(rect);
//    return Rect.fromLTWH(
//      indicator.left,
//      indicator.bottom - borderSide.width,
//      indicator.width,
//      borderSide.width,
//    );
    //希望的宽度
    double wantWidth = 25;
    //取中间坐标
    double cw = (indicator.left + indicator.right) / 2;
    return Rect.fromLTWH(cw - wantWidth / 2,
        indicator.bottom - borderSide.width, wantWidth, borderSide.width);
  }
 
  @override
  void paint(Canvas canvas, Offset offset, ImageConfiguration configuration) {
    assert(configuration != null);
    assert(configuration.size != null);
    final Rect rect = offset & configuration.size;
    final TextDirection textDirection = configuration.textDirection;
    final Rect indicator = _indicatorRectFor(rect, textDirection).deflate(borderSide.width / 2.0);
//    final Paint paint = borderSide.toPaint()..strokeCap = StrokeCap.square;
    // 改为圆角
    final Paint paint = borderSide.toPaint()..strokeCap = StrokeCap.round;
    canvas.drawLine(indicator.bottomLeft, indicator.bottomRight, paint);
  }
}

Copy一份系统的 从新命名一个 RoundUnderlineTabIndicator 类 修改 修改参数即可

使用方式

 TabBar(
         ..............

            indicator: RoundUnderlineTabIndicator(
                borderSide: BorderSide(
              width: 3.5,
              color: ColorsUtils.main_color,
            )),
         ......
        )
           

问题2

image.png

上面区域有阴影,可以自己写,我这是用的ui给的一张背景图,这时候就涉及到 图片拉伸的问题 需要指定区域拉伸, 就和iOS原生的 Show Slicing ,android 的.9处理 是一样的效果,当然你可以选择用card组件去实现

使用image的centerSlice 拉伸指定区域 这里需要 Rect.fromLTRB 或者 Rect.fromLTWH,这里需要注意的是
1.组件不能比你图片大
2.fromLTRB 和 fromLTWH 指定位置的问题

return Container(
        width: 300,
        height: 195,
        decoration: BoxDecoration(
            image: DecorationImage(
                centerSlice: Rect.fromLTRB(60, 60, 71, 71),
                image: AssetImage("assets/images/beijing.png"),
                fit: BoxFit.fill),
            color: Colors.red),
        child: Text("哈哈"));

上图 Rect.fromLTRB(60, 60, 71, 71) 我以为 会是这样的

image.png
但实际上却不是这样的 实际上是这样的
image.png
为啥会是这样呢 Rect.fromLTRB ltrb都是距离左上角的距离

fromLTWH 这个就更好理解一点了

image.png

问题3

指示器.gif

这里的搭配 pageView+Indicator 可以看出指示器需要自定义 而且带动画的

flutter 自定义指示器(Indicator)

    
/// An indicator showing the currently selected page of a PageController
class CSTIndicator extends AnimatedWidget {
  CSTIndicator({
    this.controller,
    this.itemCount,
    this.onPageSelected,
    this.color:ColorsUtils.yelllow_color ,
  }) : super(listenable: controller);

  /// The PageController that this DotsIndicator is representing.
  final PageController controller;

  /// The number of items managed by the PageController
  final int itemCount;

  /// Called when a dot is tapped
  final ValueChanged<int> onPageSelected;

  /// The color of the dots.
  ///
  /// Defaults to `Colors.white`.
  final Color color;

  // The base size of the dots
  static const double _kDotSize = 8.0;

  // The increase in the size of the selected dot
  static const double _kMaxZoom = 2.5;

  // The distance between the center of each dot
  static const double _kDotSpacing = 25.0;

  Widget _buildDot(int index) {
    double selectedness = Curves.easeOut.transform(
      max(
        0.0,
        1.0 - ((controller.page ?? controller.initialPage) - index).abs(),
      ),
    );
    double zoom = 1.0 + (_kMaxZoom - 1.0) * selectedness;
    return new Container(
      width: _kDotSpacing,
      child: new Center(
        child: new Container(
            decoration: BoxDecoration(
              borderRadius: BorderRadius.circular(_kDotSize/2),
              color: color,
            ),
        
            width: _kDotSize * zoom,
            height: _kDotSize ,
            child: new InkWell(
              onTap: () => onPageSelected(index),
            ),
          ),
      ),
    );
  }

  Widget build(BuildContext context) {
    return new Row(
      mainAxisAlignment: MainAxisAlignment.center,
      children: new List<Widget>.generate(itemCount, _buildDot),
    );
  }
}

使用方式

    CSTIndicator(
            controller: pageCtr,   //注意这个controller是 PageController 
            itemCount: 3,

/*  
            如需要点击 指示器切换pageView  需要实现此事件,我上面用不上,所以不实现
             onPageSelected: (int page) {
               pageCtr.animateToPage(
                 page,
               duration:time,
                curve:curve,
          );
*/
          )

以上理解如有误请大佬能够指出,3q

ok,以梦为马,不负韶华

image.png