React Native:可能未处理的承诺拒绝 [英] React Native: Possible unhandled promise rejection

问题描述

我收到以下错误:可能未处理的承诺拒绝(id:0:网络请求失败

这是承诺代码，我看不出这里有什么问题，有什么想法吗?

Here's the promise code, I don't see what's wrong here, any ideas?

  return fetch(url)
    .then(function(response){
      return response.json();
    })
    .then(function(json){
      return {
        city: json.name,
        temperature: kelvinToF(json.main.temp),
        description: _.capitalize(json.weather[0].description)
      }
    })
    .catch(function(error) {
    console.log('There has been a problem with your fetch operation: ' + error.message);
    });
}

**Edit: 我添加了一个 catch 函数并得到了一个更好的错误 你传递了一个未定义或空的状态对象；相反，使用 forceUpdate().index.ios.js:64 未定义

** I added a catch function and got a better error You passed an undefined or null state object; instead, use forceUpdate(). index.ios.js:64 undefined

这是 index.ios.js 代码.网址很好，并为我提供了正确的 json 数据.我可以通过控制台日志看到 region.latitude 和 region.longitude 在 Api(region.latitude, region.longitude) 中都可用.但是 data 是未定义的.我仍然不确定发生了什么，为什么 data 有问题以及为什么它没有定义.

Here's the index.ios.js code. The url is fine and giving me the correct json data. I can see with console log that both region.latitude and region.longitude are available in Api(region.latitude, region.longitude). But data is undefined. I'm still not sure what's going on, why there's a problem with data and why it's undefined.

// var React = require('react-native'); --deprecated

// updated
import React from 'react';

// updated
import {
  AppRegistry,
  MapView,
  View,
  Text,
  StyleSheet,
} from 'react-native';

/*
var {
  AppRegistry,
  MapView,
  View,
  Text,
  StyleSheet
} = React;
*/ // -- depreciated 


var Api = require('./src/api');

var Weather = React.createClass({
  getInitialState: function() {
    return {
      pin: {
        latitude: 0,
        longitude: 0
      },
      city: '',
      temperature: '',
      description: ''
    };
  },
  render: function() {
    return <View style={styles.container}>
      <MapView
        annotations={[this.state.pin]}
        onRegionChangeComplete={this.onRegionChangeComplete}
        style={styles.map}>
      </MapView>
      <View style={styles.textWrapper}>
        <Text style={styles.text}>{this.state.city}</Text>
        <Text style={styles.text}>{this.state.temperature}</Text>
        <Text style={styles.text}>{this.state.description}</Text>
      </View>
    </View>
  },
  onRegionChangeComplete: function(region) {
    this.setState({
      pin: {
        longitude: region.longitude,
        latitude: region.latitude
      }
    });

    Api(region.latitude, region.longitude)
      .then((data) => {
        console.log(data);
        this.setState(data);
      });
  }
});




var styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'stretch',
    backgroundColor: '#F5FCFF'
  },
  map: {
    flex: 2,
    marginTop: 30
  },
  textWrapper: {
    flex: 1,
    alignItems: 'center'
  },
  text: {
    fontSize: 30
  }
});

AppRegistry.registerComponent('weather', () => Weather);

推荐答案

api 中的 catch 函数应该返回一些可以由 React 类中的 Api 调用处理的数据，或者抛出应该使用 catch 函数在 React 类中捕获的新错误你的 React 类代码.后一种方法应该类似于:

catch function in your api should either return some data which could be handled by Api call in React class or throw new error which should be caught using a catch function in your React class code. Latter approach should be something like:

return fetch(url)
.then(function(response){
  return response.json();
})
.then(function(json){
  return {
    city: json.name,
    temperature: kelvinToF(json.main.temp),
    description: _.capitalize(json.weather[0].description)
  }
})
.catch(function(error) {
console.log('There has been a problem with your fetch operation: ' + error.message);
 // ADD THIS THROW error
  throw error;
});

然后在你的 React 类中:

Then in your React Class:

Api(region.latitude, region.longitude)
  .then((data) => {
    console.log(data);
    this.setState(data);
  }).catch((error)=>{
     console.log("Api call error");
     alert(error.message);
  });

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