javascript - native react : render function not being called after state change

Question

我有一个应用程序，我试图在其中理解 AsyncStorage。我正在使用这个Amazing library这简化了实际AsyncStorage实现。

应用程序的流程是-

1. 我设置初始状态arr:[]，

2. 在 componentDidMount() 中，我调用 userTest() 并获得 promise 。

3. 我正在尝试在 stateSetting()

   中设置状态

我的观察-

1. 在 stateSetting() 中，我不确定 setState 是否已设置(请参阅下面的日志)。

2. render() 函数在 setState 之后不会执行。

[如果你想执行代码，它位于 Github ，克隆它来调试，或者拉请求，那就太好了]

代码-

'use strict';

var React = require('react-native');
var reactNativeStore = require('react-native-store');
var {
  AsyncStorage,
  PickerIOS,
  Text,
  AppRegistry,
  View
} = React;

var reactNativeStore = require('react-native-store');

var RNStorage = require('./RNStorage');

var userArr = 
[
    { name: 'j', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 3, location: { name: 'USA', coords: { lat: 123, lng: 123 }  } },
    { name: 'a', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 4, location: { name: 'USA', coords: { lat: 123, lng: 123 }  } },
    { name: 'v', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 1, location: { name: 'USA', coords: { lat: 123, lng: 123 }  } },
    { name: 'a', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 2, location: { name: 'USA', coords: { lat: 123, lng: 123 }  } },
    { name: 's', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 1, location: { name: 'EU', coords: { lat: 423, lng: 123 }  } },
    { name: 'c', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 1, location: { name: 'EU', coords: { lat: 423, lng: 123 }  } },
    { name: 'r', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 7, location: { name: 'EU', coords: { lat: 423, lng: 123 }  } },
    { name: 'i', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 9, location: { name: 'Outer Space', coords: { lat: 999, lng: 999 }  } },
    { name: 'p', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 4, location: { name: 'InterGalatic Space', coords: { lat: 9001, lng: 42 }  } },
    { name: 't', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 999, location: { name: 'Outside', coords: { lat: -1, lng: 0 }  } },
];

var differentArr = 
[
    { name: 'j', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 1, location: { name: 'USA', coords: { lat: 101, lng: 101 }  } },
    { name: 'a', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 2, location: { name: 'USA', coords: { lat: 101, lng: 101 }  } },
    { name: 'v', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 3, location: { name: 'USA', coords: { lat: 101, lng: 101 }  } },
    { name: 'a', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 4, location: { name: 'USA', coords: { lat: 101, lng: 101 }  } },
    { name: 's', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 5, location: { name: 'EU', coords: { lat: 423, lng: 101 }  } },
    { name: 'c', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 6, location: { name: 'EU', coords: { lat: 423, lng: 101 }  } },
    { name: 'r', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 7, location: { name: 'EU', coords: { lat: 423, lng: 101 }  } },
    { name: 'i', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 8, location: { name: 'Outer Space', coords: { lat: 999, lng: 999 }  } },
    { name: 'p', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 9, location: { name: 'InterGalatic Space', coords: { lat: 9001, lng: 42 }  } },
    { name: 't', img: 'https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png', price: 10, location: { name: 'Outside', coords: { lat: -1, lng: 0 }  } },
];

var user = new RNStorage(userArr);
var diff = new RNStorage(differentArr);


async function userTest () {
    console.info('=== start react-native-store USER test! ===')
    await user.destroyModel();
    await user.init();
    await user.findTest();
    await user.findByIdTest();
    var returnVal = await user.updateTest();
    console.log("returnVal = "+JSON.stringify(returnVal));
    await user.updateByIdTest();
    await user.removeTest();
    await user.removeByIdTest();
    console.info('=== react-native-store USER test complete! ===')
    return returnVal;
}

async function diffTest () {
    console.info('=== start react-native-store DIFF test! ===')
    await diff.destroyModel();
    await diff.init();
    await diff.findTest();
    await diff.findByIdTest();
    var returnVal = await diff.updateTest();
    console.log("returnVal = "+JSON.stringify(returnVal));
    await diff.updateByIdTest();
    await diff.removeTest();
    await diff.removeByIdTest();
    console.info('=== react-native-store DIFF test complete! ===')
}

//diffTest();



var AsyncStorageExample = React.createClass({

    getInitialState: function () {
        console.log("getInitialState");
        return {
            arr : [],
        }
    },

    componentDidMount: function () {
        console.log("componentDidMount");

        var retval = userTest();
        console.log("componentDidMount retval"+retval);
        retval.then(function (argument) {
            console.log("argument"+JSON.stringify(argument));
            this.stateSetting(argument);
        });
    },

    stateSetting: function(arrval) {
        console.log("stateSetting");
        this.setState({
            arr : arrval,
        });
        console.log("value = "+this.state.arr);
    },

    render : function() {
        console.log("render");
        console.log("render - value of this.state.arr"+JSON.stringify(this.state.arr));
        return (
          <View>
            {this.state.arr.map(arr =>
              <Text key={arr.name}>
                &bull; {arr.name}
              </Text>
            )}
          </View>
        );
  },

});

AppRegistry.registerComponent('AsyncStorageExample', () => AsyncStorageExample);

完整代码 - 关于 GITHUB

日志-

12-24 18:29:06.516 18964-7584/com.asyncstorageexample I/ReactNativeJS: Running application "AsyncStorageExample" with appParams: {"initialProps":{},"rootTag":1}. __DEV__ === true, development-level warning are ON, performance optimizations are OFF
12-24 18:29:06.541 18964-7584/com.asyncstorageexample I/ReactNativeJS: getInitialState
12-24 18:29:06.546 18964-7584/com.asyncstorageexample I/ReactNativeJS: render
12-24 18:29:06.546 18964-7584/com.asyncstorageexample I/ReactNativeJS: render - value of this.state.arr[]
12-24 18:29:06.551 18964-7584/com.asyncstorageexample I/ReactNativeJS: componentDidMount
12-24 18:29:06.556 18964-7584/com.asyncstorageexample I/ReactNativeJS: === start react-native-store USER test! ===
12-24 18:29:06.556 18964-7584/com.asyncstorageexample I/ReactNativeJS: componentDidMount retval[object Object]
12-24 18:29:06.606 18964-7584/com.asyncstorageexample I/ReactNativeJS: 0. init data
12-24 18:29:06.886 18964-7584/com.asyncstorageexample I/ReactNativeJS: 1. find method:

ALL ASYNCSTORAGE METHODS GET EXECUTED - CROPPING LOGS

12-24 18:29:07.176 18964-7584/com.asyncstorageexample I/ReactNativeJS: === react-native-store USER test complete! ===
12-24 18:29:07.176 18964-7584/com.asyncstorageexample I/ReactNativeJS: argument[{"name":"a","img":"https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png","price":0,"location":{"name":"USA","coords":{"lat":123,"lng":123}},"_id":2},{"name":"a","img":"https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png","price":0,"location":{"name":"USA","coords":{"lat":123,"lng":123}},"_id":4},{"name":"c","img":"https://cdn4.iconfinder.com/data/icons/48x48-free-object-icons/48/House.png","price":0,"location":{"name":"EU","coords":{"lat":423,"lng":123}},"_id":6}]

我做错了什么？请指导/帮助我。

Answer 1

问题在于范围

retval.then(function (argument) {
    console.log("argument"+JSON.stringify(argument));
    this.stateSetting(argument);
});

promise 中的 this 值不再是组件。您需要绑定(bind)该函数，或者使用闭包。

retval.then(function (argument) {
    console.log("argument"+JSON.stringify(argument));
    this.stateSetting(argument);
}.bind(this));

或者

var self = this;
retval.then(function (argument) {
   console.log("argument"+JSON.stringify(argument));
   self.stateSetting(argument);
});