Question

我已经设置了一个简单的服务来从数据库中提取数据，该服务工作正常，但是当我尝试通过 aysnc 函数从服务中获取数据并放入组件时，我似乎无法通过通过使用“this”来定义函数的作用域。

有什么想法吗？因为我是开发新手，所以我一定是在做一些明显错误的事情。

这是工作正常的服务代码；

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Injectable({
  providedIn: 'root'
})
export class VenueserviceService {

  constructor(private http: HttpClient) { }

  httpGetFeatures() {
    console.log("inFeatures")
    this.http.post("http://******************",
  {
         "command": "get_feature",
         "classes":"F,G"
  })

  .subscribe(
         (val) => {
        console.log("inSubscribe")
        console.log(val)
          return(val)
          //this.parseFeatures(val)
         },
         response => {
         console.log("POST call in error", response);
         },
                 () => {
  });
  }



  parseFeatures (val: any) {
    console.log("in parse Features")
    console.log(val)
  }



}

这里是组件 TS，问题是“this”抛出错误，因为它未定义，因为我相信 this 的范围没有被传递。它是底部的最终异步函数。

import { Component, OnInit } from '@angular/core';
import * as data from "./testfile.json";
import * as catdata from "../categories/cattestfile.json";
import {VenueserviceService} from "../../services/venueservice.service"


@Component({
  selector: 'app-homepage',
  templateUrl: './homepage.component.html',
  styleUrls: ['./homepage.component.css']
})
export class HomepageComponent implements OnInit {

  constructor(private venueService: VenueserviceService) { }

  panelOpenState = false;
  title = 'Cotswolds Destinations';

  venues: any = (data as any).default;

  categories: any = (catdata as any).default;

  formatLabel(value: number) {
    if (value >= 1000) {
      return Math.round(value / 1000) + 'm';
    }

    return value;
  }

  value = 'Clear me!';

  ngOnInit(): void {
    console.log("Homepage Start");
    console.log(this.categories);
    console.log(this.venues);
    console.log(data);
    console.log(this.venues.name);
    for(var i=0; i < this.venues.length; i++){
    console.log(this.venues[i]);
    }
    console.log("Homepage End");
    let categories = this.venueService.httpGetFeatures()

    console.log(categories)

  }
}



const getData =  async () => {
  const data  = await this.venueService.httpGetFeatures()
  console.log(data)
}

Answer 1

我建议你这样做

服务文件

    httpGetFeatures() {
        console.log("inFeatures")
        return this.http.post("http://cotswoldsdestinations.co.uk:8443",
        {
            "command": "get_feature",
            "classes":"F,G"
        })
    }

组件文件

fetchedData:any;
const getData =  async () => {
  this.venueService.httpGetFeatures()
    .subscribe( data => { this.fetchedData = data });
}

Answer 2

1st，你在 VenueserviceService.httpGetFeatures 中没有返回任何东西，它的返回类型是 void。

第二，因为您使用的是 asyc-await 语法，所以您希望在您的 getData lambda 函数中得到一个承诺。要么这样做：

httpGetFeatures() {
  return this.http.post("http://cotswoldsdestinations.co.uk:8443",
  {
    "command": "get_feature",
    "classes":"F,G"
  }).toPromise();
}

或者直接订阅返回的 observable 而无需等待：

httpGetFeatures() {
  return this.http.post("http://cotswoldsdestinations.co.uk:8443",
  {
    "command": "get_feature",
    "classes":"F,G"
  });
}
const getData = () => {
  this.venueService.httpGetFeatures().subscribe(data =>
    console.log(data);
  );
}

如果您在某个组件中定义了 getData，该组件的构造函数中通过 DI 传递了 venueService: VenueserviceService，那么这一切都没有问题。

为了使其正常工作，将 getData 定义为主页组件类的成员，例如：

export component HomePageComponent {
  constructor(private venueService: VenueserviceService) {}

  getData() {
    this.venueService.httpGetFeatures().subscribe(data =>
      console.log(data);
    );
  }
}

打字稿异步和此范围

2 个答案: