从异步函数react-native获取未定义

Posted 2021-04-12

我有一系列异步函数，这些函数必须返回true或false，但是我从一个函数中得到的未定义比获得位置要多。

这里是返回未定义的函数：

async getGeoLoc(trigger = 'cDidMount') {
   return navigator.geolocation.getCurrentPosition(
      async position => {
        const isDataReady = await this.setCityFromCoordinate(
          trigger,
          position.coords.latitude,
          position.coords.longitude,
        );
        console.log('isDataReady getGeoLoc', isDataReady); // this gives true in console
        return isDataReady
          },

我在这里称呼它：

async getLocationPermission(trigger) {
    if (Platform.OS == 'android') {
      const response = await PermissionsAndroid.request(
        PermissionsAndroid.PERMISSIONS.ACCESS_FINE_LOCATION,
      );
      if (
        response == PermissionsAndroid.RESULTS.DENIED ||
        response == PermissionsAndroid.RESULTS.NEVER_ASK_AGAIN
      ) {
        Alert.alert(
          i18n.t('search:geolocation_disabled'),
          i18n.t('search:need_location'),
        );
        return false;
      } else {


        return await this.getGeoLoc(trigger);
      }
    } else {
      return await this.getGeoLoc(trigger);
      // for ios go directly here
    }
  },

谢谢！

答案

将导航呼叫置于Promise中

  function  getGeoLoc(trigger = 'cDidMount') {
 return new Promise((resolve, reject) => {
       navigator.geolocation.getCurrentPosition(
          async position => {
            const isDataReady = await this.setCityFromCoordinate(
              trigger,
              position.coords.latitude,
              position.coords.longitude,
            );
            console.log('isDataReady getGeoLoc', isDataReady); // this gives true in console
            return isDataReady
              },

另一答案

getCurrentPosition使用回调。如果您想使用一个单独的功能来接收头寸，则可以创建一个Promise像这样>

    const myCoord = () =>
  new Promise((resolve, reject) => {
    const geoSuccess = position => resolve(position);
    const geoFailure = error => reject(error);

    navigator.geolocation.getCurrentPosition(
      geoSuccess,
      geoFailure,
      geoOptions
    );

    const geoOptions = {
      timeout: 5000,
      maximumAge: 5000,
      enableHighAccuracy: false
    };

  });
然后您可以通过异步/等待方式调用它：

const getLocation = async () => {
      const response = await myCoord();
      console.log(response);
    };

    getLocation();