Angular 5 Promise返回undefined

Question

我试图在HTTP请求之后返回一个promise但是当我在我的组件上打印返回时我得到了未定义。

服务：

getPlace() {
let promise = new Promise((resolve, reject) => {

  this.http.get('http://localhost:3000/api/place/')
      .toPromise()
      .then(
          res => { // Success
            this.results = res.results.map(item => {
              var place = new Place();
              place.place_id = item.place_id;
              place.name=item.name;
              place.vicinity=item.vicinity;
              place.coordinates = new Coordinates();
              place.coordinates.latitude = item.geometry.location.lat;
              place.coordinates.longitude = item.geometry.location.lng;
              return place;
            });

            resolve();
            console.log(  this.results);
          },
          msg => { // Error
            reject(msg);
          }
      );
});
return promise;
}

这是我的组件调用：

getPlace(): void{
 this.cityService.getPlace().then( (res) => {console.log(res);
   });
}

Answer 1

无论你传递给.then()，resolve()中的参数函数都将作为参数。

因此，当你做resolve('stuff')然后最终.then(r => console.log(r))将打印'stuff'。

你正在获得undefined，因为现在你的resolve被调用而没有参数：

      res => { // Success
        this.results = res.results.map(item => {
          var place = new Place();
          place.place_id = item.place_id;
          place.name=item.name;
          place.vicinity=item.vicinity;
          place.coordinates = new Coordinates();
          place.coordinates.latitude = item.geometry.location.lat;
          place.coordinates.longitude = item.geometry.location.lng;
          return place;
        });

        resolve();                              // <==== resolve without arguments here
        console.log(  this.results);
      },

既然你想让.then()获得results，请将它添加到resolve。上面的代码应该是：

      res => { // Success
        this.results = res.results.map(item => {
          var place = new Place();
          place.place_id = item.place_id;
          place.name=item.name;
          place.vicinity=item.vicinity;
          place.coordinates = new Coordinates();
          place.coordinates.latitude = item.geometry.location.lat;
          place.coordinates.longitude = item.geometry.location.lng;
          return place;
        });

        resolve(this.results);                  // <===== changed this line
        console.log(  this.results);
      },

Answer 2

您将返回undefined，因为您没有使用Promise解析。

this.http.get('http://localhost:3000/api/place/')
      .toPromise()
      .then(
          res => { // Success
            this.results = res.results.map(item => {
              var place = new Place();
              place.place_id = item.place_id;
              place.name=item.name;
              place.vicinity=item.vicinity;
              place.coordinates = new Coordinates();
              place.coordinates.latitude = item.geometry.location.lat;
              place.coordinates.longitude = item.geometry.location.lng;
              //return place; Remove this
            });

        resolve(this.results);
        console.log(  this.results);
      },
      msg => { // Error
        reject(msg);
      }
  );