反应原生导航 - componentDidMount（）触发两次

Question

我是React Native的新手。我正在尝试构建一个具有Splash屏幕的应用程序，如果用户未经过身份验证后将导航到Login屏幕，如果用户经过身份验证，则会导航到Main屏幕。这是使用this.props.navigation.navigate()完成的问题是Splash组件将被安装两次。我通过在componentDidMount()的Splash内打印来检查这个。因此，登录/主屏幕进入两次，看起来非常不愉快。有没有什么办法解决这一问题？此外，当屏幕使用Splash从Login更改为Main或setTimeout()时，我想添加一些延迟。无论如何要去做这个？这是我的代码：

index.js

import React from 'react';
import { createStore, applyMiddleware, compose } from 'redux';
import { Provider } from 'react-redux';
import { persistStore } from 'redux-persist';
import reduxThunk from 'redux-thunk';
import reducers from './src/reducers';

import { StyleSheet } from 'react-native';
import LoginScreen from './src/components/Login/LoginScreen';
import Splash from './src/components/Login/Splash';
import Navigation from './src/components/Navigation/Navigation';
import { Font } from 'expo';
import {
  createStackNavigator
} from 'react-navigation';

const createStoreWithMiddleware = applyMiddleware(reduxThunk)(createStore);
const store = createStoreWithMiddleware(reducers);
const persistor = persistStore(store);

export default class App extends React.Component {
  constructor(props){
    super(props);
    this.state = {
      fontLoaded: false,
      currentScreen: 'Splash',
    };
    setTimeout(() => this.setState({currentScreen: 'Login'}), 2000);
  }

  async componentDidMount() {
    await Font.loadAsync({
      'Quicksand': require('./assets/fonts/Quicksand-Regular.ttf'),
      'Quicksand-Medium': require('./assets/fonts/Quicksand-Medium.ttf'),
      'Quicksand-Bold': require('./assets/fonts/Quicksand-Bold.ttf'),
    });
    this.setState({ fontLoaded: true });
  }

  render() {
    const MainNavigator = createStackNavigator({
      Splash: { screen: Splash },
      Main: { screen: Navigation },
      Login: { screen: LoginScreen },
    })
    if (this.state.fontLoaded)
      return (
        <Provider store={store}>
          <MainNavigator></MainNavigator>
        </Provider>
      )
    else return null;
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#fff',
    alignItems: 'center',
    justifyContent: 'center',
  },
});

Splash.js

import React from 'react';
import { StyleSheet, Text, View, ImageBackground, Image, Button } from 'react-native';
import bgImage from '../../../assets/images/login-background2.png';
import logo from '../../../assets/images/app-logo.png';

import { connect } from 'react-redux';
import { checkAuth } from '../../actions/auth.actions';

class Splash extends React.Component {
  static navigationOptions ={
    header: null
  }
  constructor(props){
    super(props);
    this.state = {
      stillLoading: true,
    }
  }

  componentDidMount() {
    this.props.checkAuth();
  }

  render() {
    if (this.props.authState.isLoginPending)
      return (
        <ImageBackground source={bgImage} style={styles.backgroundContainer}>
              <View style={styles.logoContainer}>
                  <Image source={logo} style={styles.logo}></Image>
                  <Text style={styles.logoText}> Welcome to HealthScout</Text>
              </View>
        </ImageBackground>
      );
    else if (this.props.authState.isLoginSuccess){
      setTimeout(() => this.props.navigation.navigate('Main'));
      return null;
    }
    else{
      setTimeout(() => this.props.navigation.navigate('Login'));
      return null;
    }
  }
}

const mapStateToProps = state => {
  return {
    authState: state.authState
  }
}

const mapDispatchToProps = dispatch => {
  return {
    checkAuth: () => dispatch(checkAuth()),
  }
}

export default connect(mapStateToProps, mapDispatchToProps)(Splash);

const styles = StyleSheet.create({
  backgroundContainer: {
    flex: 1,
    alignItems: 'center',
    width: null,
    height: null,
    justifyContent: 'center',
  },
  logoContainer: {
    alignItems: 'center',
  },
  logo: {
    width: 110,
    height: 149,
  },
  logoText: {
    color: '#fff',
    fontSize: 40,
    fontFamily: 'Quicksand',
    opacity: 0.7,
    marginTop: 20,
    marginBottom: 10,
    textAlign: 'center',
  },
});

Answer 1

Solution

从createStackNavigator取出render。在App类以上包装屏幕是更好的方法。

const MainNavigator = createStackNavigator({
  Splash: { screen: Splash },
  Main: { screen: Navigation },
  Login: { screen: LoginScreen },
})

export default class App extends React.Component {
...

Why?

render反复运行取决于各种条件，如改变状态，道具等。 你的代码看起来在createStackNavigation中用render制作了多个组件。取出 ：）

p.s如果你想在显示主屏幕之前等待加载字体，只需在加载字体后从启动画面切换到主屏幕。因此，更好的方法是在SplashScreen中加载字体并做你想要的。