react-native-lifecycle

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开发过程中发现对React Native生命周期的理解还不够完整，导致渲染的时候性能出现问题，所以写了个例子观察了一下。

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/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 * @flow
 */

import React, { Component } from 'react';
import {
  AppRegistry,
  StyleSheet,
  Text,
  View
} from 'react-native';
import ChildComponent from './child';
export default class Parent extends Component {
  constructor(props) {
    super(props);
    this.state = {
    	content:'content'
    };
  }

  componentDidMount(){
  	console.log('Parent====componentDidMount')
  }

  render() {
  	console.log('Parent====render')
    return (
      <View style={styles.container}>
        <Text style={styles.welcome}>
         {this.state.content}
        </Text>
         <ChildComponent content={this.state.content}/>
         <Text style={{margin:20}} onPress={()=>{this.onPress()}}>Press Me!</Text>
         <Text style={{margin:20}} onPress={()=>{this.onPressME()}}>Press!</Text>
      </View>
    );
  }

  onPress(){
  	this.setState({content:'React Native Props'});
  } 

  onPressME(){
  	this.setState({content:'React Native'});
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#F5FCFF',
  },
  welcome: {
    fontSize: 20,
    textAlign: 'center',
    margin: 10,
  },
  instructions: {
    textAlign: 'center',
    color: '#333333',
    marginBottom: 5,
  },
});
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/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 * @flow
 */

import React, { Component } from 'react';
import {
  AppRegistry,
  StyleSheet,
  Text,
  View
} from 'react-native';

export default class Child extends Component {
  constructor(props) {
    super(props);
    this.state = {
    	content:this.props.content
    };
  }
  
  componentWillMount(){
  	console.log('child====componentWillMount')
  }

  //先调用子组件的 componentDidMount()，然后调用父组件的函数
  componentDidMount(){
  	console.log('child====componentDidMount')
  }
	
	//1.父组件触发render后触发子组件该方法，不管属性是否改变；
	//2.这里setState不会触发额外的render()
	componentWillReceiveProps(nextProps){
			console.log(this.props.content+'===='+'componentWillReceiveProps'+'====='+nextProps.content)
			this.setState({content:'componentWillReceiveProps'});


	}

	shouldComponentUpdate(nextProps,nextState){
		console.log('shouldComponentUpdate')
		return true
	}

	// 这个函数调用之后，就会把 nextProps 和 nextState 分别设置到 this.props 和 this.state 中
	componentWillUpdate(nextProps,nextState){
		console.log('componentWillUpdate')
	}

  render() {
  	console.log('child render')
    return (
      <View style={styles.container}>
        <Text style={styles.welcome}>
         {this.props.content}
        </Text>
        <Text style={styles.instructions}>
          To get started, edit index.android.js
        </Text>
      </View>
    );
  }

  componentDidUpdate(prevProps,prevState){
  	console.log(prevProps.content+'===='+'componentDidUpdate'+'====='+this.props.content)
  }
}

const styles = StyleSheet.create({
  container: {
    
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#F5FCFF',
  },
  welcome: {
    fontSize: 20,
    textAlign: 'center',
    margin: 10,
  },
  instructions: {
    textAlign: 'center',
    color: '#333333',
    marginBottom: 5,
  },
});
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第一次加载：
parent.js:28 Parent====render
child.js:24 child====componentWillMount
child.js:52 child render
child.js:29 child====componentDidMount
parent.js:24 Parent====componentDidMount

点击Press Me!:
parent.js:28 Parent====render
child.js:35 content====componentWillReceiveProps=====React Native Props
child.js:42 shouldComponentUpdate
child.js:48 componentWillUpdate
child.js:52 child render
child.js:66 content====componentDidUpdate=====React Native Props

再次点击Press Me:
parent.js:28 Parent====render
child.js:35 React Native Props====componentWillReceiveProps=====React Native Props
child.js:42 shouldComponentUpdate
child.js:48 componentWillUpdate
child.js:52 child render
child.js:66 React Native Props====componentDidUpdate=====React Native Props

点击Press!:
parent.js:28 Parent====render
child.js:35 React Native Props====componentWillReceiveProps=====React Native
child.js:42 shouldComponentUpdate
child.js:48 componentWillUpdate
child.js:52 child render
child.js:66 React Native Props====componentDidUpdate=====React Native