门户网站注意事项,网站注册需要什么,docker 搭建wordpress,05网伴你学1 ConstrainedBox、SizedBox、UnconstrainedBox介绍
1)、ConstrainedBox用于对子组件添加额外的约束。例如#xff0c;如果你想让子组件的最小高度是80像素 ConstrainedBox({Key key,required this.constraints,Widget child,})
我们可以看到这里有个constraints final BoxC…1 ConstrainedBox、SizedBox、UnconstrainedBox介绍
1)、ConstrainedBox用于对子组件添加额外的约束。例如如果你想让子组件的最小高度是80像素 ConstrainedBox({Key key,required this.constraints,Widget child,})
我们可以看到这里有个constraints final BoxConstraints constraints;
class BoxConstraints extends Constraints {/// Creates box constraints with the given constraints.const BoxConstraints({this.minWidth 0.0,this.maxWidth double.infinity,this.minHeight 0.0,this.maxHeight double.infinity,}) : assert (minWidth ! null),assert (maxWidth ! null),assert (minHeight ! null),assert (maxHeight ! null);
我们可以看到BoxConstraints继承Constraints然后一些属性设置。
有多重ConstrainedBox限制时对于minWidth和minHeight来说是取父子中相应数值较大的 2)、SizedBox用于给子元素指定固定的宽高
3)、UnconstrainedBox不会对子组件产生任何限制它允许其子组件按照其本身大小绘制
一般用来去掉父约束 2 测试代码
测试1、 overrideWidget build(BuildContext context) {return MaterialApp(title: open url,home: Scaffold(appBar: AppBar(// Here we take the value from the MyHomePage object that was created by// the App.build method, and use it to set our appbar title.title: Text(hello flutter),),body: Center(child: ConstrainedBox(constraints: BoxConstraints(minWidth: double.infinity,minHeight: 100),child: Container(width: 50,height: 50,color: Colors.green,),),),),);}
}
测试2、 overrideWidget build(BuildContext context) {return MaterialApp(title: open url,home: Scaffold(appBar: AppBar(title: Text(hello flutter),),body: Center(child: ConstrainedBox(constraints: BoxConstraints(minWidth: 200,minHeight: 100),child: ConstrainedBox(constraints: BoxConstraints(minWidth: 100,minHeight: 200),child: Container(width: 50,height: 50,color: Colors.green,),),),),),);}
} 测试3、
overrideWidget build(BuildContext context) {return MaterialApp(title: open url,home: Scaffold(appBar: AppBar(title: Text(hello flutter),),body: Center(child: ConstrainedBox(constraints: BoxConstraints(minWidth: 200,minHeight: 100),child: UnconstrainedBox(child: ConstrainedBox(constraints: BoxConstraints(minWidth: 50,minHeight: 50),child: Container(width: 10,height: 15,color: Colors.red,),),),),),),);}
}3 运行效果
