如何检测 react-native 中的首次启动

Question

检测 react-native 应用的首次启动和初始启动以显示入门/介绍屏幕的好方法是什么？

Answer 1

你的逻辑应该遵循这个：

class MyStartingComponent extends React.Component {
    constructor(){
        super();
        this.state = {firstLaunch: null};
    }
    componentDidMount(){
        AsyncStorage.getItem("alreadyLaunched").then(value => {
            if(value == null){
                 AsyncStorage.setItem('alreadyLaunched', true); // No need to wait for `setItem` to finish, although you might want to handle errors
                 this.setState({firstLaunch: true});
            }
            else{
                 this.setState({firstLaunch: false});
            }}) // Add some error handling, also you can simply do this.setState({fistLaunch: value == null})
    }
    render(){
       if(this.state.firstLaunch === null){
           return null; // This is the 'tricky' part: The query to AsyncStorage is not finished, but we have to present something to the user. Null will just render nothing, so you can also put a placeholder of some sort, but effectively the interval between the first mount and AsyncStorage retrieving your data won't be noticeable to the user.
       }else if(this.state.firstLaunch == true){
           return <FirstLaunchComponent/>
       }else{
           return <NotFirstLaunchComponent/>
       }
}

希望对你有帮助

Answer 2

我对martinarroyo 的建议做了一些调整。 AsyncStorage.setItem 应该设置一个字符串值而不是布尔值。

import { AsyncStorage } from 'react-native';
    
const HAS_LAUNCHED = 'hasLaunched';

function setAppLaunched() {
  AsyncStorage.setItem(HAS_LAUNCHED, 'true');
}

export default async function checkIfFirstLaunch() {
  try {
    const hasLaunched = await AsyncStorage.getItem(HAS_LAUNCHED);
    if (hasLaunched === null) {
      setAppLaunched();
      return true;
    }
    return false;
  } catch (error) {
    return false;
  }
}

然后可以将这个函数导入到任何你需要的地方。请注意，您应该在等待异步函数检查 AsyncStorage 时呈现 null（或其他巧妙的东西）。

import React from 'react';
import { Text } from 'react-native';
import checkIfFirstLaunch from './utils/checkIfFirstLaunch';

export default class App extends React.Component {
  constructor(props) {
    super(props);

    this.state = {
      isFirstLaunch: false,
      hasCheckedAsyncStorage: false,
    };
  }

  async componentWillMount() {
    const isFirstLaunch = await checkIfFirstLaunch();
    this.setState({ isFirstLaunch, hasCheckedAsyncStorage: true });
  }

  render() {
    const { hasCheckedAsyncStorage, isFirstLaunch } = this.state;

    if (!hasCheckedAsyncStorage) {
      return null;
    }

    return isFirstLaunch ?
      <Text>This is the first launch</Text> :
      <Text>Has launched before</Text>
    ;
  }
}