React Native之didFocus和didBlur

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.

文章来源: chenyu.blog.csdn.net，作者：chen.yu，版权归原作者所有，如需转载，请联系作者。

原文链接：chenyu.blog.csdn.net/article/details/83218639