Question

我想向DollarView组件发送道具但由于未知原因，它失败了。为了测试这个问题，我使用Alert来显示DollarView组件的dollarValue道具（我在DollarView组件中使用了这行代码：Alert.alert(this.props.dollarValue.toString());），但是在应用程序刷新时，整个应用程序停止并且我收到此错误：< / p>

TypeError: undefined is not an object (evaluating '_this.props.dollarValue.toString')

这是我的代码：

export default class App extends Component {

  constructor(props) {
    super(props);
    this.updateDollar = this.updateDollar.bind(this);
    this.state = {
      value: 0,
      date: 0,
      isReady: 'need to update'
    };
  }

  componentWillMount() {
    var savedData = (async function init() {
      var value = await AsyncStorage.getItem('value');
      if (!value) {
        value = 0;
      } else {
        value = parseInt(value);
      }
      var date = Date.parse(await AsyncStorage.getItem('date'));
      return [value, date];
    }());
    this.setState({
      value: savedData[0],
      date: savedData[1]
    });
  }

  updateDollar() {
    this.setState({
      isReady: false
    });
    axios.get('https://digiarz.com/webservice/api/')
      .then(async (response) => {
        var dollarRate = response.data.BTC.rates.USD.rate;
        var tomanRate = response.data.BTC.rates.TMN.rate;
        var dollar = Math.round(tomanRate / dollarRate) * 10;
        var newDate = new Date();
        await AsyncStorage.setItem('value', dollar.toString());
        await AsyncStorage.setItem('date', newDate.toString());
        this.setState({
          value: dollar,
          date: newDate,
          isReady: true
        });
      })
      .catch((error) => {
        Alert.alert('خطا', 'خطا در دسترسی به اطلاعات. لطفا اتصال اینترنت خود را بررسی نمایید.');
        this.setState({
          isReady: 'failed'
        });
      });
  }

  render() {
    var {value, date, isReady} = this.state;
    return (
      <View style={styles.container}>
        <DollarView isReady={isReady} dollarValue={value} date={date} />
        <DollarCalculator onUpdate={this.updateDollar} dollarValue={value} />
      </View>
    );
  }
}

和DollarView组件：

class DollarView extends Component {

        constructor(props) {
            super(props);
            this.state = {
                dollarValue: 0,
                value: 0,
                date: 0,
                isReady: true
            };
        }

        componentWillReceiveProps(nextProps) {
            var {dollarValue, value, date, isReady} = nextProps;
            this.setState({
                dollarValue: dollarValue,
                value: value,
                date: date,
                isReady: isReady
            });
        }

        render() {
            var {dollarValue, date, isReady} = this.state;
            if (isReady == 'failed') {
                var indicator = <Text style={styles.failed}>{dollarValue}</Text>;
            } else if (isReady) {
                var indicator = <Text style={styles.success}>{dollarValue}</Text>;
            } else {
                var indicator = <ActivityIndicator size={75} color="#0000ff" />;
            }
            return (
                <View>
                    {indicator}
                </View>
            );
        }
    }

同样的事情也发生在DollarCalculator组件上。

Answer 1

代码中的async await对无效。

saveData是一个承诺，因此saveData[0]未定义，这就是您收到错误的原因。

您可以这样做：

async componentWillMount() {
  var value = await AsyncStorage.getItem('value');
  if (!value) {
    value = 0;
  } else {
    value = parseInt(value);
  }
  var date = Date.parse(await AsyncStorage.getItem('date'));
  this.setState({
    value,
    date,
  });
}

无法在React Native中向子组件发送道具

1 个答案: