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【Flutter 专题】130 图解 DraggableScrollableSheet 可手势滑动的菜单栏

发布于: 54 分钟前
【Flutter 专题】130 图解 DraggableScrollableSheet 可手势滑动的菜单栏

    小菜发现在长期未登陆小米应用市场时,再次登陆会有可滑动的半屏底部菜单,供用户方便下载和推广;而在 Flutter 中这个半屏底部菜单并不是一个简单的 BottomSheet 完成的,可以通过 DraggableScrollableSheet 根据手势操作滑动固定位的菜单栏完成;小菜简单学习一下;



DraggableScrollableSheet

源码分析

const DraggableScrollableSheet({    Key key,    this.initialChildSize = 0.5,    // 初始比例    this.minChildSize = 0.25,       // 最小比例    this.maxChildSize = 1.0,        // 最大比例    this.expand = true,             // 是否填充满    @required this.builder,})
@overridepWidget build(BuildContext context) { return LayoutBuilder( builder: (BuildContext context, BoxConstraints constraints) { _extent.availablePixels = widget.maxChildSize * constraints.biggest.height; final Widget sheet = FractionallySizedBox( heightFactor: _extent.currentExtent, child: widget.builder(context, _scrollController), alignment: Alignment.bottomCenter, ); return widget.expand ? SizedBox.expand(child: sheet) : sheet; }, );}
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    简单分析源码 DraggableScrollableSheet 作为一个有状态的 StatefulWidget 小组件,通过 FractionallySizedBox 以父 Widget 为基数,可设置宽高比例的容器构建子内容;

案例尝试

1. builder

    ScrollableWidgetBuilder 构造器作为必选字段,用于在 DraggableScrollableSheet 中显示可滑动的子内容;其中返回内容需为可滑动的 ScrollableWidget,例如 ListView / GridView / SingleChildScrollView 等;


_listWid(controller) => SingleChildScrollView(    controller: controller,    child: Column(children: [      Container(          height: 5.0, width: 25.0,          decoration: BoxDecoration(color: Colors.blue.withOpacity(0.8), borderRadius: BorderRadius.all(Radius.circular(16.0))),          margin: EdgeInsets.symmetric(vertical: 12.0)),      Padding(          padding: EdgeInsets.symmetric(horizontal: 12.0),          child: GridView.builder(              physics: ScrollPhysics(),              primary: false, shrinkWrap: true,              gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(                  crossAxisCount: 5, mainAxisSpacing: 8.0, crossAxisSpacing: 12.0, childAspectRatio: 0.7),              itemCount: 12,              itemBuilder: (context, index) => GestureDetector(                  child: Column(children: <Widget>[                    PhysicalModel(                        color: Colors.transparent, shape: BoxShape.circle,                        clipBehavior: Clip.antiAlias, child: Image.asset('images/icon_hzw01.jpg')),                    SizedBox(height: 4), Text('海贼王')                  ]),                  onTap: () {}))),      ListView.builder(          physics: NeverScrollableScrollPhysics(),          shrinkWrap: true,          itemCount: 15,          itemBuilder: (BuildContext context, index) => ListTile(title: Text('Current Item = ${(index + 1)}')))    ]));
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2. initialChildSize

    initialChildSize 用于显示初始子 Widgets 所占父 Widget 比例;同时,若返回的子 Widget 未提供 ScrollController,则 DraggableScrollableSheet 不会随手势进行滑动,小菜理解为 initialChildSize = minChildSize = maxChildSize


_sheetWid02() => DraggableScrollableSheet(    initialChildSize: 0.66,    builder: (BuildContext context, ScrollController scrollController) =>        Container(            decoration: BoxDecoration(                color: Colors.grey.withOpacity(0.4),                borderRadius: BorderRadius.only(topLeft: Radius.circular(16.0), topRight: Radius.circular(16.0))),            child: _listWid(null)));
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3. minChildSize & maxChildSize

    minChildSize & maxChildSize 分别对应子 Widgets 占整体的最大最小比例,其中 initialChildSize 需要在两者之间;


_sheetWid03() => DraggableScrollableSheet(    initialChildSize: 0.6,    minChildSize: 0.3,    maxChildSize: 0.9,    expand: true,    builder: (BuildContext context, ScrollController scrollController) =>        Container(            decoration: BoxDecoration(                color: Colors.grey.withOpacity(0.4),                borderRadius: BorderRadius.only(topLeft: Radius.circular(16.0), topRight: Radius.circular(16.0))),            child: _listWid(scrollController)));
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4. expand

    expand 用于是否填充满父 Widget,若 DraggableScrollableSheet 外层固定高度则不影响;若外层未对高度进行固定,expand 作用于是否填充满父 Widget;构造的源码也是通过 SizedBox.expand 对父 Widget 进行填充判断的;


return widget.expand ? SizedBox.expand(child: sheet) : sheet;
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小扩展

    之前在分析 DraggableScrollableSheet 时其源码采用了 FractionallySizedBox 比例容器,小菜简单了解一下,其源码非常简单,通过设置 heightFactor & widthFactor 占父 Widget 的比例即可,通过 alignment 设置所在父 widget 的对齐方式;


SizedBox.expand(child: _sizedBox())
_sizedBox() => FractionallySizedBox( heightFactor: 0.5, widthFactor: 0.5, alignment: Alignment.center, child: Container( color: Colors.deepOrange.withOpacity(0.4), child: ListView.builder( itemCount: 15, itemBuilder: (BuildContext context, index) => ListTile(title: Text('Current Item = ${(index + 1)}')))));
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    案例源码


    小菜对 DraggableScrollableSheet 的手势滑动过程还不够熟悉,之后会对手势进行进一步学习;如有错误,请多多指导!


来源: 阿策小和尚

发布于: 54 分钟前阅读数: 2
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【Flutter 专题】130 图解 DraggableScrollableSheet 可手势滑动的菜单栏