1. Flutter Flex layout model

1. What is Flex Layout

Flex是Flexible Box的缩写, 译为"弹性布局",用来为盒状模型提供最大的灵活性

Flutter支持Flex的Widget
Row
Column
Expanded 
Flexible

2. Basic Concepts

采购Flex布局的Widget,称为Flex容器(flex container),它的所有子元素自动成为容器成员

Flex默认有两根轴,水平方向主轴(main axis),和垂直的交叉轴(cross axis)
主轴的开始位置(起点)叫做main start 结束位置叫做(main end);交叉轴的开始位置叫做(cross start),
结束位置叫做(cross end)

Third, the properties of the container

• MainAxisAlignment
• MainAxisSize (stretch size)
• CrossAxisAlignment (horizontal axis alignment)
• Text Direction
• VerticalDirection (layout direction)
• TextBaseline (text alignment)

- Four, a login interface