我如何等待 AsyncStorage 的结果？答案

【问题标题】：How i can await the result of the AsyncStorage?我如何等待 AsyncStorage 的结果？
【发布时间】：2020-08-21 15:24:09
【问题描述】：

我需要在运行其他函数之前先运行 AsyncStorage，但是 AsyncStorage 需要一些时间才能运行，它会在代码末尾给出结果

 constructor(props) {
   super(props);
  
  AsyncStorage.getItem(TOKEN).then((r) => {
    console.log("AsyncStorage Function")
  })

  this.state = { token: null } 
  console.log("The last Function")

}

【问题讨论】：

标签： reactjs react-native

【解决方案1】：

假设这是一个反应类组件，理想情况下你不应该在构造函数中执行任何异步任务。

因此，如果您希望执行任何异步任务，您可以使用组件生命周期方法中的componentDidMount。

但一般来说，如果你想等待异步操作，那么这可以通过不同的方式实现

使用承诺

const promiseFun = () => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve("Success")
    }, 1000)
  })
}

promiseFun().then((res) => {
  //here res will be what is returned from the promise function
  console.log(res);

  //All the required things that needed to be perfomed after the async operation should be placed here.
});


//Whatever the actions/statements written here will be executed before the async operation is finished
console.log("Before Promise Returned");

使用异步/等待

const promiseFun = () => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve("Success")
    }, 1000)
  })
}

const execFun = async() => {
  let res = await promiseFun();
  //All the statments from here will be executed only after the promise/async function returned. 
  console.log(res);
  
}

execFun();
//All the statements here will be executed without waiting for the promise/async function gets executed 
console.log("Before Promise Returned");

【讨论】：