addListeners 有时不起作用 - 反应本机选项卡导航

Question

我使用了 react-navigation 的标签导航。每次按下选项卡时，我都需要在 componentDidMount 中调用 loadData 函数。所以我在其中使用了 addListener 。但问题是显示数据花费的时间太长。有时它可以无缝运行，有时它一直只显示“正在加载数据......”。 我是否正确使用了 addListener？提前致谢。

Home.js

state = {
  storageCheck: true
};

componentDidMount() {
    this._unsubscribe = this.props.navigation.addListener('willFocus', () => {
      this.loadData();
    });
}

componentWillUnmount() {
    this._unsubscribe.remove();
}

loadData = () => {
    this.setState({
        storageCheck: false
    })
}

render() {
if (this.state.storageCheck) {
  return <View>
    <Text>Loading Data...</Text>
  </View>
}
return (
    <View>
        <Text>Data</Text>
    </View>
)}

标签导航

const TabNavigator = createBottomTabNavigator({
  Home: {
    screen: Home
  },
  Profile: {
    screen: Profile,
    navigationOptions: ({ navigation }) => ({
      // title: 'Profile',
    })
  },
  Setting: {
    screen: Setting,
  }
},
  {
    defaultNavigationOptions: ({ navigation }) => ({
      tabBarIcon: ({ focused, tintColor }) => {
        const { routeName } = navigation.state;
        let iconName;
        if (routeName === 'Home') {
          iconName = 'home';
        } else if (routeName === 'Profile') {
          iconName = 'account-circle';
        } else if (routeName === 'Setting') {
          iconName = 'settings';
        }

        return <MaterialIcons name={iconName} size={28} color={tintColor} />;
      },
    })
  }
);

export default createAppContainer(TabNavigator);

Answer 1

在反应导航 v4 中。

您可以使用 await-async 函数。

state = {
  storageCheck: true,
  loader: true,
  someData: null
};

componentDidMount() {
    this._unsubscribe = this.props.navigation.addListener('willFocus', () => {
      this.loadData();
    });
}

componentWillUnmount() {
    this._unsubscribe.remove();
}

loadData = async() => {
    this.setState({
        someData: await AsyncStorage.getItem("SOME_KEY"),
        storageCheck: false,
        loader: false
    })
}

render() {
  return (
      <View>
       {this.state.someData ? (
        <Text>data is loaded</Text>
       ) : (
        <Text> loading ... </Text>
       )}
      </View>
  )
}

干杯！

Answer 2

这是一个明确的解决方案。我认为你可以使用 hooks 和 function component。 我使用与此相关的解决方案

import React, { useState, useEffect } from "react";
import { 
    View,
    Text,
    ActivityIndicator
} from "react-native";
import { useIsFocused } from "@react-navigation/native";

const TestComp = () => {

    const [storageCheck, setStorageCheck] = useState(false);
    const [isLoaded, setIsLoaded] = useState(false);
    const isFocused = useIsFocused();

    useEffect(() => {
        const loadData = async() => {
            setStorageCheck(true);
            setIsLoaded(true);
        }
        loadData();
    }, [isFocused])


    return(
        <>
            {isLoaded ? (
                <View>
                    <Text>some data or texts..</Text>
                </View>
            ) : (
                <ActivityIndicator />
            )}
        </>
    )
}
export default TestComp;

干杯！