Flutter GridView详解

GridView

GridView常用构造
- GridView
- - 构造函数
- GridView.count
- - 构造函数
  - 分析和使用
- GridView.extent
- - 构造函数
  - 分析和使用
- GridView.builder
- - 构造函数
  - 分析和使用
- GridView.custom
- - 构造函数
  - 分析和使用

GridView常用构造

GridView

构造函数

GridView({Key key, Axis scrollDirection: Axis.vertical, bool reverse: false,ScrollController controller, bool primary, ScrollPhysics physics, bool shrinkWrap: false,EdgeInsetsGeometry padding, @required SliverGridDelegate gridDelegate, bool addAutomaticKeepAlives: true,bool addRepaintBoundaries: true, bool addSemanticIndexes: true,double cacheExtent, List<Widget> children: const [], int semanticChildCount })Creates a scrollable, 2D array of widgets with a custom SliverGridDelegate. [...]

GridView.count

构造函数

GridView.count({Key key, Axis scrollDirection: Axis.vertical,
bool reverse: false, ScrollController controller,
bool primary, ScrollPhysics physics, bool shrinkWrap: false,
EdgeInsetsGeometry padding, @required int crossAxisCount,double mainAxisSpacing: 0.0, double crossAxisSpacing: 0.0, double childAspectRatio: 1.0, bool addAutomaticKeepAlives: true,bool addRepaintBoundaries: true, bool addSemanticIndexes: true,double cacheExtent, List<Widget> children: const [], int semanticChildCount })Creates a scrollable, 2D array of widgets with a fixed number of
tiles in the cross axis. [...]

分析和使用

 Widget gridViewDefaultCount(List<BaseBean> list) {return GridView.count(
//      padding: EdgeInsets.all(5.0),//一行多少个crossAxisCount: 5,//滚动方向scrollDirection: Axis.vertical,// 左右间隔crossAxisSpacing: 10.0,// 上下间隔mainAxisSpacing: 10.0,//宽高比childAspectRatio: 2 / 5,children: initListWidget(list),);}List<Widget> initListWidget(List<BaseBean> list) {List<Widget> lists = [];for (var item in list) {lists.add(new Container(height: 50.0,width: 50.0,color: Colors.yellow,child: new Center(child: new Text(item.age.toString(),)),));}return lists;}

GridView.extent

构造函数

GridView.extent({Key key, Axis scrollDirection: Axis.vertical,bool reverse: false, ScrollController controller,bool primary, ScrollPhysics physics, bool shrinkWrap: false, EdgeInsetsGeometry padding,@required double maxCrossAxisExtent,double mainAxisSpacing: 0.0, double crossAxisSpacing: 0.0,double childAspectRatio: 1.0, bool addAutomaticKeepAlives: true,bool addRepaintBoundaries: true, bool addSemanticIndexes: true,List<Widget> children: const [], int semanticChildCount })Creates a scrollable, 2D array of widgets with tiles that
each have a maximum cross-axis extent. [...]

分析和使用

 ///GridView.extent 允许您指定项的最大像素宽度Widget gridViewDefaultExtent(List<BaseBean> list) {return GridView.extent(///设置item的最大像素宽度  比如 130maxCrossAxisExtent: 130.0,///其他属性和count一样children: initListWidget(list),);}

GridView.builder

构造函数

GridView.builder({Key key, Axis scrollDirection: Axis.vertical,bool reverse: false, ScrollController controller, bool primary, ScrollPhysics physics,bool shrinkWrap: false, EdgeInsetsGeometry padding, @required SliverGridDelegate gridDelegate, @required IndexedWidgetBuilder itemBuilder,int itemCount, bool addAutomaticKeepAlives: true,bool addRepaintBoundaries: true, bool addSemanticIndexes: true, double cacheExtent, int semanticChildCount })Creates a scrollable, 2D array of widgets that are created on demand. [...]

分析和使用

 ///GridView.builder  可以定义gridDelegate的模式Widget gridViewDefaultBuilder(List<BaseBean> list) {return GridView.builder(gridDelegate: MyGridViewDefaultCustom(crossAxisCount: 2,mainAxisSpacing: 10.0,crossAxisSpacing: 10.0,childAspectRatio: 1.0,),itemBuilder: (context, i) => new Container(child: new Row(mainAxisAlignment: MainAxisAlignment.spaceEvenly,children: <Widget>[new Text("${list[i].name}",style: new TextStyle(fontSize: 18.0, color: Colors.red),),new Text("${list[i].age}",style: new TextStyle(fontSize: 18.0, color: Colors.green),),new Text("${list[i].content}",style: new TextStyle(fontSize: 18.0, color: Colors.blue),),],),));}

///自定义SliverGridDelegate
class MyGridViewDefaultCustom extends SliverGridDelegate {///横轴上的子节点数。  一行多少个childfinal int crossAxisCount;///沿主轴的每个子节点之间的逻辑像素数。 默认垂直方向的子child间距  这里的是主轴方向 当你改变 scrollDirection: Axis.vertical,就是改变了主轴发方向final double mainAxisSpacing;///沿横轴的每个子节点之间的逻辑像素数。默认水平方向的子child间距final double crossAxisSpacing;///每个孩子的横轴与主轴范围的比率。 child的宽高比  常用来处理child的适配final double childAspectRatio;bool _debugAssertIsValid() {assert(mainAxisSpacing >= 0.0);assert(crossAxisSpacing >= 0.0);assert(childAspectRatio > 0.0);return true;}const MyGridViewDefaultCustom({@required this.crossAxisCount,this.mainAxisSpacing = 0.0,this.crossAxisSpacing = 0.0,this.childAspectRatio = 1.0,})  : assert(crossAxisCount != null && crossAxisCount > 0),assert(mainAxisSpacing != null && mainAxisSpacing >= 0),assert(crossAxisSpacing != null && crossAxisSpacing >= 0),assert(childAspectRatio != null && childAspectRatio > 0);///  返回值有关网格中图块大小和位置的信息。这里就是处理怎么摆放 我们可以自己定义///   SliverGridLayout是抽象类  SliverGridRegularTileLayout继承于SliverGridLayout是抽象类@overrideSliverGridLayout getLayout(SliverConstraints constraints) {// TODO: implement getLayoutassert(_debugAssertIsValid());///对参数的修饰 自定义final double usableCrossAxisExtent =constraints.crossAxisExtent - crossAxisSpacing * (crossAxisCount - 1);final double childCrossAxisExtent = usableCrossAxisExtent / crossAxisCount;final double childMainAxisExtent = childCrossAxisExtent / childAspectRatio;return MySliverGridLayout(crossAxisCount: crossAxisCount,mainAxisStride: childMainAxisExtent + mainAxisSpacing,crossAxisStride: childCrossAxisExtent + crossAxisSpacing,childMainAxisExtent: childMainAxisExtent,childCrossAxisExtent: childCrossAxisExtent,reverseCrossAxis: axisDirectionIsReversed(constraints.crossAxisDirection),);}/// 和ListView的 shouldRebuild 作用一样   之前的实例和新进来的实例是相同的就返回true@overridebool shouldRelayout(SliverGridDelegate oldDelegate) {// TODO: implement shouldRelayoutreturn true;}
}

GridView.custom

构造函数

GridView.custom({Key key, Axis scrollDirection: Axis.vertical,bool reverse: false, ScrollController controller, bool primary, ScrollPhysics physics, bool shrinkWrap: false, EdgeInsetsGeometry padding,@required SliverGridDelegate gridDelegate,@required SliverChildDelegate childrenDelegate, double cacheExtent,int semanticChildCount })Creates a scrollable, 2D array of widgets with both a customSliverGridDelegate and a custom SliverChildDelegate. [...]

分析和使用

 ///GridView.custom 就是自己定制规则/// 这里说一下 GridView.count gridDelegate 其实就是内部实现 SliverGridDelegateWithFixedCrossAxisCount/// GridView.extent gridDelegate 其实就是内部实现 SliverGridDelegateWithMaxCrossAxisExtentWidget gridViewDefaultCustom(List<BaseBean> list) {return GridView.custom(gridDelegate: MyGridViewDefaultCustom(crossAxisCount: 2,mainAxisSpacing: 10.0,crossAxisSpacing: 10.0,childAspectRatio: 1.0,),childrenDelegate: MyGridChildrenDelegate((BuildContext context, int i) {return new Container(child: new Row(mainAxisAlignment: MainAxisAlignment.spaceEvenly,children: <Widget>[new Text("${list[i].name}",style: new TextStyle(fontSize: 18.0, color: Colors.red),),new Text("${list[i].age}",style: new TextStyle(fontSize: 18.0, color: Colors.green),),new Text("${list[i].content}",style: new TextStyle(fontSize: 18.0, color: Colors.blue),),],));},childCount: list.length,),);}

/*** 继承SliverChildBuilderDelegate  可以对列表的监听*/
class MyGridChildrenDelegate extends SliverChildBuilderDelegate {MyGridChildrenDelegate(Widget Function(BuildContext, int) builder, {int childCount,bool addAutomaticKeepAlive = true,bool addRepaintBoundaries = true,}) : super(builder,childCount: childCount,addAutomaticKeepAlives: addAutomaticKeepAlive,addRepaintBoundaries: addRepaintBoundaries);///监听 在可见的列表中 显示的第一个位置和最后一个位置@overridevoid didFinishLayout(int firstIndex, int lastIndex) {print('firstIndex: $firstIndex, lastIndex: $lastIndex');}///可不重写 重写不能为null  默认是true  添加进来的实例与之前的实例是否相同 相同返回true 反之false///listView 暂时没有看到应用场景 源码中使用在 SliverFillViewport 中@overridebool shouldRebuild(SliverChildBuilderDelegate oldDelegate) {// TODO: implement shouldRebuildprint("oldDelegate$oldDelegate");return super.shouldRebuild(oldDelegate);}
}

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Flutter GridView详解

GridView

GridView常用构造

GridView

构造函数

GridView.count

构造函数

分析和使用

GridView.extent

构造函数

分析和使用

GridView.builder

构造函数

分析和使用

GridView.custom

构造函数

分析和使用

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