Container
是有多个widget组成的(LimitedBox->ConstrainedBox->Align->Padding->DecoratedBox->ConstrainedBox->Padding->Transform)
constraints：添加到child上额外的约束条件 最大最小值
current = ConstrainedBox(constraints: constraints, child: current);
alignment：控制child的对齐方式，
current = Align(alignment: alignment, child: current);
padding：文本区域和widget之间
current = Padding(padding: effectivePadding, child: current);
margin ：widget和widget之间
current = Padding(padding: margin, child: current);
decoration
decoration： 背景装饰 类似android中的shape 边框 圆角，背景色，背景图片等
current = DecoratedBox(decoration: decoration, child: current); const BoxDecoration({ this.color, this.image, this.border, this.borderRadius, this.boxShadow, this.gradient, this.backgroundBlendMode, this.shape = BoxShape.rectangle, }) : assert(shape != null), assert( backgroundBlendMode == null || color != null || gradient != null, 'backgroundBlendMode applies to BoxDecoration\'s background color or ' 'gradient, but no color or gradient was provided.' );
color：背景色，最后也会设置到decoration这个widget上面 所以不可同时设置color和decoration
//断言不能同时存在 assert(color == null || decoration == null) //用color生成BoxDecoration decoration = decoration ?? (color != null ? BoxDecoration(color: color) : null),
foregroundDecoration 前景色 DecoratedBox 底部颜色即背景色，中间内容，顶部颜色即前景色 会遮挡中间内容
current = DecoratedBox( decoration: foregroundDecoration, position: DecorationPosition.foreground, child: current,);
width height 最后要作用到BoxConstraints，由BoxConstraints限制范围
constraints = (width != null || height != null) ? constraints?.tighten(width: width, height: height) ?? BoxConstraints.tightFor(width: width, height: height) : constraints,
dart 语法学习
三元表达式 ?:
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