简介

我们在React Native中使用flexBox规则来指定某个组件的子元素的布局。FlexBox可以在不同屏幕尺寸上提供一致的布局结构。相对于Native开发的布局更加快捷方便。

FlexBox使用flexDirection、alignItems和 justifyContent三个样式属性就已经能满足大多数布局需求

flexDirection

flexDirection可以决定zu jian组件布局的主轴，子元素会沿着主轴排列，或水平或垂直。

flexDirection的默认值是竖直轴（column）方向

column（默认）

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{flex: 1}}> <View style={{width: 50,height: 50,backgroundColor: 'red'}} /> <View style={{width: 50,backgroundColor: 'green'}} /> <View style={{width: 50,backgroundColor: 'blue'}} /> </View> ); } } AppRegistry.registerComponent('AsomeProject',() => AsomeProject);

column-reverse

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{flex: 1,flexDirection: 'column-reverse'}}> <View style={{width: 50,() => AsomeProject);

row

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{flex: 1,flexDirection: 'row'}}> <View style={{width: 50,() => AsomeProject); 

row-reverse

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{flex: 1,flexDirection: 'row-reverse'}}> <View style={{width: 50,() => AsomeProject); 

justifyContent

在组件的style中指定justifyContent可以决定其子元素沿着主轴的排列方式。子元素是应该靠近主轴的起始端还是末尾段分布呢？亦或应该均匀分布？对应的这些可选项有：flex-start、center、flex-end、space-around以及space-between。

flex-start

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{ flex: 1,flexDirection: 'column',justifyContent: 'flex-start'}}> <View style={{width: 50,() => AsomeProject);

center

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{ flex: 1,justifyContent: 'center'}}> <View style={{width: 50,() => AsomeProject);

flex-end

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{ flex: 1,justifyContent: 'flex-end'}}> <View style={{width: 50,() => AsomeProject);

space-around

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{ flex: 1,justifyContent: 'space-around'}}> <View style={{width: 50,() => AsomeProject);

space-between

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{ flex: 1,justifyContent: 'space-between'}}> <View style={{width: 50,() => AsomeProject);

alignItems

在组件的style中指定alignItems可以决定其子元素沿着次轴（与主轴垂直的轴，比如若主轴方向为row，则次轴方向为column）的排列方式。子元素是应该靠近次轴的起始端还是末尾段分布呢？亦或应该均匀分布？对应的这些可选项有：flex-start、center、flex-end以及stretch。

flex-start

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{ flex: 1,justifyContent: 'center',alignItems: 'flex-start'}}> <View style={{width: 50,() => AsomeProject);

center

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{ flex: 1,alignItems: 'center'}}> <View style={{width: 50,() => AsomeProject);

flex-end

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{ flex: 1,alignItems: 'flex-end'}}> <View style={{width: 50,() => AsomeProject);

stretch

注意：

要使stretch选项生效的话，子元素在次轴方向上不能有固定的尺寸。以下面的代码为例：只有将子元素样式中的width: 50去掉之后，alignItems: ‘stretch’才能生效。

export default class AsomeProject extends Component { constructor(props) { super(props); } render() { return ( <View style={{ flex: 1,alignItems: 'stretch'}}> <View style={{height: 50,backgroundColor: 'red'}} /> <View style={{height: 150,backgroundColor: 'green'}} /> <View style={{height: 100,() => AsomeProject);