1 didFocus和didBlur解释
didFocus - the screen focused (if there was a transition, the transition completed)didBlur - the screen unfocused (if there was a transition, the transition completed)
didFocus是指当前页面第一次加载的时候会调用一次
didBlur是指当前页面离开的时候会调用一次(前提是当前页面没有被销毁既没有执行componentWillUnmount()函数)
2 测试代码
import React from 'react';
import { View, Text, Button} from 'react-native';
import { createStackNavigator } from 'react-navigation';class HomeScreen extends React.Component {constructor(props) {super(props);console.log("HomeScreen constructor start");this.didFocusListener = this.props.navigation.addListener('didFocus',(obj) => {console.log("HomeScreen didFocus start")});this.didBlurListener = this.props.navigation.addListener('didBlur',(obj) => {console.log('HomeScreen didBlur start')});}static navigationOptions = {title : 'HomeScreen',}componentDidMount = () => {console.log("HomeScreen componentDidMount start")}componentWillUnmount() {console.log("HomeScreen componentWillUnmount start")this.didFocusListener.remove();this.didBlurListener.remove();}render() {return (<View style={{flex: 1, alignItems: 'center', justifyContent: 'center'}}><Text>Home Screen</Text><Button onPress={() => this.props.navigation.navigate('Details', {itemId:100,otherParam:'chenyu',})} title = "go to Details"/><Buttontitle="Go back"onPress={() => this.props.navigation.goBack()}/></View>);}
}class DetailsScreen extends React.Component {constructor(props) {super(props);console.log("DetailsScreen constructor start");this.didFocusListener = this.props.navigation.addListener('didFocus',(obj) => {console.log("DetailsScreen didFocus start")});this.didBlurListener = this.props.navigation.addListener('didBlur',(obj) => {console.log('DetailsScreen didBlur start')});}static navigationOptions = ({navigation}) => {return {title : navigation.getParam('otherParam', 'no-values'),};};componentDidMount = () => {console.log("DetailsScreen componentDidMount start")}componentWillUnmount() {console.log("DetailsScreen componentWillUnmount start")this.didFocusListener.remove();this.didBlurListener.remove();}render() {const {navigation} = this.props;const itemId = navigation.getParam('itemId', 'no-values');const otherParam = navigation.getParam('otherParam', 'no-values');return (<View style={{ flex: 1, alignItems: 'center', justifyContent: 'center' }}><Text>Details Screen</Text><Text>itemId:{JSON.stringify(itemId)}</Text><Text>otherParam:{JSON.stringify(otherParam)}</Text><Buttontitle="Go to Details... again"onPress={() => this.props.navigation.push('Details', {itemId: Math.floor(Math.random() * 100),})}/><Buttontitle="Go to Home"onPress={() => this.props.navigation.navigate('Home')}/> <Buttontitle="Go back"onPress={() => this.props.navigation.goBack()}/><Buttontitle="Go popToTop"onPress={() => this.props.navigation.popToTop()}/></View>);}
}const RootStack = createStackNavigator({Home: HomeScreen,Details: DetailsScreen,},{initialRouteName: 'Home',}
);export default class App extends React.Component {constructor(props) {super(props);}render() {return <RootStack/>;}}
3 运行结果
2个页面分别如下
在控制台过来React Native命令
adb logcat | grep ReactNativeJS1) 程序起来打印日志如下
I/ReactNativeJS(21233): HomeScreen constructor start
I/ReactNativeJS(21233): HomeScreen componentDidMount start
I/ReactNativeJS(21233): HomeScreen didFocus start
这里的didFocus start是在componentDidMount后面执行
2 ) 然后点击go to DETAILS按钮日志如下
I/ReactNativeJS(21233): DetailsScreen constructor start
I/ReactNativeJS(21233): DetailsScreen componentDidMount start
I/ReactNativeJS(21233): HomeScreen didBlur start
I/ReactNativeJS(21233): DetailsScreen didFocus start
然后执行了HomeScreen didBlur start,但是并没有执行HomeScreen componentWillUnmount start,因为页面还没有销毁,所以执行了HomeScreen didBlur start.
3 )然后在在第二个页面点击"GO BACK"或者按下返回键,日志打印如下
I/ReactNativeJS(21233): DetailsScreen componentWillUnmount start
I/ReactNativeJS(21233): HomeScreen didFocus start
发现没有,既然执行了componentWillUnmount函数,说明页面已经销毁,既然销毁了,就没有执行DetailsScreen didBlur start,因为前面的页面没有死,所以不会重新加载再次调用首页的constructor和componentDidMount方法.从前面日志打印
I/ReactNativeJS(21233): DetailsScreen constructor start
I/ReactNativeJS(21233): DetailsScreen componentDidMount start
I/ReactNativeJS(21233): HomeScreen didBlur start
I/ReactNativeJS(21233): DetailsScreen didFocus start
可以看出,另外一个页面执行新页面的constructor函数和componentDidMount函数才执行之前页面的didBlur start,所以估计这里是来不及执行页面就销毁了,所以没有打印DetailsScreen didBlur start.
4 )然后再次点击返回物理键日志如下
I/ReactNativeJS(23183): HomeScreen componentWillUnmount start
只调用了componentWillUnmount函数,所以页面销毁了,HomeScreen didBlur start来不及打印.
4 总结
didFocus只会在当前页面的constructor函数和componentDidMount函数后面执行
didBlur只会在当前页面没有调用componentWillUnmount函数,然后离开当前页面才执行,也意味着,这个页面没有死但是去了另外一个页面才会调用,如果自己页面死了,就不会调用到这里.
