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"/> <Button title="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> <Button title="Go to Details... again" onPress={() => this.props.navigation.push('Details', { itemId: Math.floor(Math.random() * 100), })} /> <Button title="Go to Home" onPress={() => this.props.navigation.navigate('Home')} /> <Button title="Go back" onPress={() => this.props.navigation.goBack()} /> <Button title="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 ReactNativeJS
1) 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.
