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，如果用户未通过身份验证，该屏幕稍后将导航到Login 屏幕，如果用户通过身份验证，则导航到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Splash 的componentDidMount() 中打印来检查这一点。正因为如此，Login/Main画面进入了两次，看起来很不爽。有没有什么办法解决这一问题？ 另外，我想在屏幕从Splash 更改为Login 或Main 使用setTimeout() 时添加一些延迟。无论如何要这样做？ 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

解决方案

从render 中取出createStackNavigator。 在App 类上方包裹屏幕是更好的方法。

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

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

为什么？

render 的重复运行取决于各种条件，如状态变化、道具等。
您的代码看起来使用createStackNavigation 在render 中创建多个组件。拿出来:)

p.s 如果您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屏幕切换到主屏幕。因此，更好的方法是在SplashScreen 中加载字体并做你想做的事。