Container详解

Container是一个拥有绘制、定位、调整大小的widget。

padding和margin

padding和margin分别设置Container的内边距和外边距。可取值包括下面四个：

• EdgeInsets.all(50)：设置所有的padding为同一个值50。
• EdgeInsets.only(left: 50,right: 50)：只设置左边和右边。
• EdgeInsets.fromLTRB(50,10,50,10)：分别设置左上右下的值为50、10。
• EdgeInsets.symmetric(vertical: 10,horizontal: 50)：如果上下或者左右的padding值一样可以指定vertical的值为上下的padding值。horizontal指定左右的padding值。

Scaffold(
    appBar: AppBar(title: Text('Container')),
    body: Center(
    child: Column(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: <Widget>[
        Container(
            padding: EdgeInsets.all(50),
            decoration: BoxDecoration(
                border: Border.all(color: Colors.red, width: 1),
                borderRadius: BorderRadius.all(Radius.circular(20))),
            child: Text(
            "确定",
            style: TextStyle(color: Colors.red),
            ),
        ),
        Container(
            padding: EdgeInsets.only(left: 50,right: 50),
            decoration: BoxDecoration(
                border: Border.all(color: Colors.red, width: 1),
                borderRadius: BorderRadius.all(Radius.circular(20))),
            child: Text(
            "确定",
            style: TextStyle(color: Colors.red),
            ),
        ),
        Container(
            padding: EdgeInsets.fromLTRB(50, 10, 50, 10),
            decoration: BoxDecoration(
                border: Border.all(color: Colors.red, width: 1),
                borderRadius: BorderRadius.all(Radius.circular(20))),
            child: Text(
            "确定",
            style: TextStyle(color: Colors.red),
            ),
        ),
        Container(
            padding: EdgeInsets.symmetric(vertical: 10, horizontal: 50),
            decoration: BoxDecoration(
                border: Border.all(color: Colors.red, width: 1),
                borderRadius: BorderRadius.all(Radius.circular(20))),
            child: Text(
            "确定",
            style: TextStyle(color: Colors.red),
            ),
        ),
        ],
    ),
)),

width和height

width和height指定宽高，如果不指定则为子widget的宽高。如果想要完全撑满父容器，可以将width和height设置为double.infinity。

decoration

decoration经常被用来改变一个Container的展示效果。其概念类似与android中的shape。一般实际场景中会使用他的子类BoxDecoration。BoxDecoration提供了对背景色，边框，圆角，阴影和渐变等功能的定制能力。

• image: DecorationImage设置一张图片作为背景。
• border: Border设置边界。
• borderRadius: BorderRadius设置边界圆角。当shape是BoxShape.circle设置borderRadius将不起作用
• shape: BoxShape设置形状。
• gradient设置渐变。可选值包括三种类型的渐变LinearGradient、RadialGradient、SweepGradient。

Scaffold(
    appBar: AppBar(title: Text('BorderRadius')),
    body: Center(
        child: Column(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: <Widget>[
            Container(
            height: 200,
            width: 200,
            decoration: BoxDecoration(
                color: Colors.yellow,
                //设置图片
                image: DecorationImage(
                    fit: BoxFit.fitWidth,
                    image: NetworkImage(
                    'https://flutter.io/images/catalog-widget-placeholder.png',
                    ),
                ),
                //设置边界
                border: Border.all(color: Colors.deepOrange, width: 3),
                //设置阴影
                boxShadow: const [
                    BoxShadow(blurRadius: 10),
                ],
                //设置边界圆角
                borderRadius: BorderRadius.all(Radius.circular(18))),
            ),
            Container(
            height: 200,
            width: 200,
            decoration: BoxDecoration(
                gradient: RadialGradient(
                //渐变
                colors: const [
                    Colors.green,
                    Colors.deepOrange,
                    Colors.pinkAccent,
                    Colors.deepPurple
                ],
                ),
                //设置边界圆角
                shape: BoxShape.circle,
            ),
            )
        ],
        ),
    ),
),

2.Column和Row

MainAxisAlignment

Scaffold(
    appBar: AppBar(title: Text('Flutter')),
    body: Column(
        children: <Widget>[
        Text("MainAxisAlignment.start",style:TextStyle(
            color: Colors.blueAccent,
            fontSize: 18
        )),
        Row(
            mainAxisAlignment: MainAxisAlignment.start,
            children: <Widget>[
            Icon(Icons.star,color: Colors.yellow, size: 50),
            Icon(Icons.star,color: Colors.yellow, size: 50),
            Icon(Icons.star,color: Colors.yellow, size: 50),
            ],
        ),
        Text("MainAxisAlignment.center",style:TextStyle(
            color: Colors.blueAccent,
            fontSize: 18
        )),
        Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
            Icon(Icons.star,color: Colors.yellow, size: 50),
            Icon(Icons.star,color: Colors.yellow, size: 50),
            Icon(Icons.star,color: Colors.yellow, size: 50),
            ],
        ),
        Text("MainAxisAlignment.spaceAround",style:TextStyle(
            color: Colors.blueAccent,
            fontSize: 18
        )),
        Row(
            mainAxisAlignment: MainAxisAlignment.spaceAround,
            children: <Widget>[
            Icon(Icons.star,color: Colors.yellow, size: 50),
            Icon(Icons.star,color: Colors.yellow, size: 50),
            Icon(Icons.star,color: Colors.yellow, size: 50),
            ],
        ),
        Text("MainAxisAlignment.spaceBetween",style:TextStyle(
            color: Colors.blueAccent,
            fontSize: 18
        )),
        Row(
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: <Widget>[
            Icon(Icons.star,color: Colors.yellow, size: 50),
            Icon(Icons.star,color: Colors.yellow, size: 50),
            Icon(Icons.star,color: Colors.yellow, size: 50),
            ],
        ),
        Text("MainAxisAlignment.spaceEvenly",style:TextStyle(
            color: Colors.blueAccent,
            fontSize: 18
        )),
        Row(
            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
            children: <Widget>[
            Icon(Icons.star,color: Colors.yellow, size: 50),
            Icon(Icons.star,color: Colors.yellow, size: 50),
            Icon(Icons.star,color: Colors.yellow, size: 50),
            ],
        ),
        Text("MainAxisAlignment.end",style:TextStyle(
            color: Colors.blueAccent,
            fontSize: 18
        )),
        Row(
            mainAxisAlignment: MainAxisAlignment.end,
            children: <Widget>[
            Icon(Icons.star,color: Colors.yellow, size: 50),
            Icon(Icons.star,color: Colors.yellow, size: 50),
            Icon(Icons.star,color: Colors.yellow, size: 50),
            ],
        )
        ],
    ),
),

crossAxisAlignment

Scaffold(
    appBar: AppBar(title: Text('Flutter')),
    body: Column(
        children: <Widget>[
        Text("CrossAxisAlignment.start",style:TextStyle(
            color: Colors.blueAccent,
            fontSize: 18
        )),
        Row(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
            Icon(Icons.star,color: Colors.yellow, size: 30),
            Icon(Icons.star,color: Colors.yellow, size: 60),
            Icon(Icons.star,color: Colors.yellow, size: 30),
            ],
        ),
        Text("CrossAxisAlignment.center",style:TextStyle(
            color: Colors.blueAccent,
            fontSize: 18
        )),
        Row(
            crossAxisAlignment: CrossAxisAlignment.center,
            children: <Widget>[
            Icon(Icons.star,color: Colors.yellow, size: 30),
            Icon(Icons.star,color: Colors.yellow, size: 60),
            Icon(Icons.star,color: Colors.yellow, size: 30),
            ],
        ),

        Text(" CrossAxisAlignment.end",style:TextStyle(
            color: Colors.blueAccent,
            fontSize: 18
        )),
        Row(
            crossAxisAlignment: CrossAxisAlignment.end,
            children: <Widget>[
            Icon(Icons.star,color: Colors.yellow, size: 30),
            Icon(Icons.star,color: Colors.yellow, size: 60),
            Icon(Icons.star,color: Colors.yellow, size: 30),
            ],
        )
        ],
    ),
),

参考

• Flutter Layout Cheat Sheet
• Flutter快速上车之Widget