Question

我有一个像这样的全局变量usersSerivce.js：

let user = null;
let loadedScreens = {};

/**
 * Return user information and the number of times this screen gets user information
 * @param {string} The screen name
 * @returns Promise<{user:any,loadCount:number}>
 */
export function getUser(screenName) {
  return Promis.resolve(user).then(_usr => {
    if (!_usr) {
      return ajax.get("get user api"); // a Promise
    } else {
      return _usr;
    }
  }).then(_usr => {
    //Here, I have user information.
    user = _usr;
    //Record the screen load user count.
    loadedScreens[screenName] = (loadedScreens[screenName] || 0) + 1;
    return {
      loadCount: loadedScreens[screenName],
      user
    };
  });
}

和HomeScreen.js

中

import { getUser } from "./usersService";
import { NavigationEvents } from 'react-navigation';

export default class HomeScreen extend Component {
  screenFocus(e) {
    getUser(this.props.navigation.state.routeName).then(({user,loadCount})=>{
      this.setState({user});
      if (loadCount === 1) { //The problem appears in this line
        //Here, in order to prevent the user from loading the page data each time the Home page is entered,
        //the loading is performed only when the user information is read for the first time.
        ajax.get("get current user tasks list API").then(tasks=>{
          this.setState({tasks});
        })
      }
    })
  }
  render(){
    return (
      <View>
        <NavigationEvents onDidFocus={(e)=>this.screenFocus(e)}/>
        {/*other components*/}
      </View>
    )
  }
}

这似乎没有任何问题。

但是在Android中，我单击了hardware [return]按钮以退出该应用程序。当我再次打开应用程序时，由loadCount返回的getUser不是不是 1，而{中的state.tasks和state.user {1}}都是HomeScreen（undefined已重新安装），当我阅读用户信息之后，无法再次加载任务信息。

为什么退出应用程序时全局变量HomeScreen不能循环使用，导致再次打开应用程序时此变量仍然存在？退出应用程序后如何重置loadScreens？

PS：如果我打开Android的应用程序列表并在退出应用程序后完全退出应用程序，则不会出现此类问题。

在React Native中退出应用程序时如何清除全局变量

0 个答案: