反应本地获取承诺.then()不会立即执行 [英] React Native fetch promise .then() not executing immediately

问题描述

我正在使用React Native为iOS和Android构建一个应用程序.在这里，只要轻按一下按钮，我就从外部函数中调用提取函数.fetch函数将POST请求发送到链接，并获取JSON响应(JSON是正确的，已通过Postman进行了各种测试).

I'm using React Native to build an app for iOS and Android. In there, I'm simply calling fetch function from an external function once a button is tapped. The fetch function sends a POST request to a link and gets back a JSON response (JSON is correct, tested with Postman in various ways).

问题在于.then()之后的代码不会立即执行，而是在我点击屏幕或使用导航返回或执行某种较小的操作之后执行.这是我使用的代码:

The issue is that the code after .then() is not executed immediately, but after I tap on the screen or go back using the navigation or perform some sort of minor actions. Here's the code that I used:

从功能中调用代码

verify() {
  this.setState({
    pressed: true
  });

  var self = this;
  var theURL = "<URL>"; //Removed for question

  fetch(theURL, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      uidOrEmail: this.state.email,
      code: this.state.value
    })
  })
.then(res => res.json())
.then(function(data) {
  console.log(data); //PROBLEM: This doesn't execute immediately
}

BINDING 我也像这样在构造函数中绑定此函数:

BINDING I'm also binding this function in the constructor like this:

constructor(props) {
  super(props);
  console.log(this.props.navigation.state.params.email);

  this.state = {
    email: props.navigation.state.params.email,
    value: '',
    pressed: false
  };

  this.verify = this.verify.bind(this);
}

从用户界面调用功能

<Button
  disabled={this.state.pressed}
  onPress={this.verify}
  >{!this.state.pressed ? 'Verify' : 'Verifying...'}</Button>

总结:提取功能无法立即解决promise.

To summarize: Fetch function not resolving promise immediately.

编辑

更多信息:

提取链接实际上是Firebase函数的链接.该函数如何返回:

The fetch link is actually a Firebase function's link. How that function is returning:

response.status(200).send({status: 200, token: "ABC"});

推荐答案

fetch 将返回一个 Promise 对象，由 then()添加的回调将在诺言成功之后被调用.如果承诺失败，则将调用 catch()添加的回调.

fetch will return a Promise object, the callbacks added by then() will be called after the promise is success. If the promise failed, the callback added by catch() will be called.

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