image.png

首頁 ui是這樣

技術(shù)點(diǎn)分析

首頁.gif

可以看到首頁需要這種可以滾動(dòng)分頁切換的 采用 tabbar+TabBarView

問題:但是tabbar 下面的indicator(指示器)默認(rèn)不是圓角的 而且不能自定義 寬度 系統(tǒng)默認(rèn)只提供了2種

//根據(jù)文字寬度
TabBarIndicatorSize.label
//根據(jù)tab的寬度
TabBarIndicatorSize.tab

1. flutter 自定義 indicator(指示器)

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

// 默認(rèn)高度從46改為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,
//    );
    //希望的寬度
    double wantWidth = 25;
    //取中間坐標(biāo)
    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;
    // 改為圓角
    final Paint paint = borderSide.toPaint()..strokeCap = StrokeCap.round;
    canvas.drawLine(indicator.bottomLeft, indicator.bottomRight, paint);
  }
}

Copy一份系統(tǒng)的 從新命名一個(gè) RoundUnderlineTabIndicator 類 修改 修改參數(shù)即可

使用方式

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

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

問題2

image.png

上面區(qū)域有陰影,可以自己寫,我這是用的ui給的一張背景圖,這時(shí)候就涉及到 圖片拉伸的問題 需要指定區(qū)域拉伸, 就和iOS原生的 Show Slicing ,android 的.9處理 是一樣的效果,當(dāng)然你可以選擇用card組件去實(shí)現(xiàn)

使用image的centerSlice 拉伸指定區(qū)域 這里需要 Rect.fromLTRB 或者 Rect.fromLTWH,這里需要注意的是
1.組件不能比你圖片大
2.fromLTRB 和 fromLTWH 指定位置的問題

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"));

上圖 Rect.fromLTRB(60, 60, 71, 71) 我以為 會(huì)是這樣的

image.png

但實(shí)際上卻不是這樣的 實(shí)際上是這樣的

image.png

為啥會(huì)是這樣呢 Rect.fromLTRB ltrb都是距離左上角的距離

fromLTWH 這個(gè)就更好理解一點(diǎn)了

image.png

問題3

指示器.gif

這里的搭配 pageView+Indicator 可以看出指示器需要自定義 而且?guī)?dòng)畫的

flutter 自定義指示器(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,   //注意這個(gè)controller是 PageController 
            itemCount: 3,

/*  
            如需要點(diǎn)擊 指示器切換pageView  需要實(shí)現(xiàn)此事件,我上面用不上,所以不實(shí)現(xiàn)
             onPageSelected: (int page) {
               pageCtr.animateToPage(
                 page,
               duration:time,
                curve:curve,
          );
*/
          )

以上理解如有誤請(qǐng)大佬能夠指出,3q

ok,以夢為馬,不負(fù)韶華

image.png