angular 5 POST 请求出错。发送 header 参数无效

angular 5 Getting an error on POST request. Sending header param not works

我正在尝试发送 POST 请求,例如:

public getAppData(countryPath) : Observable<any> {
    const headers = new Headers();
    headers.append('Content-Type', 'application/json');
    let options = new RequestOptions({ headers: headers });
    return this.http.post(this.retailApi, JSON.stringify(this.postParam), {headers: options } );
}

但是我得到一个错误:

这里有什么问题?谁能帮我解决一下?

在我尝试其他选项后,出现了这个错误:

试试这个:

请像这样导入 HttpClientHttpHeaders

import { HttpClient, HttpHeaders } from '@angular/common/http';

并注入你的 class:

constructor(private http: HttpClient) {
}

你的方法是这样的:

 public getAppData(countryPath):Observable<any>{
      let headers: HttpHeaders = new HttpHeaders();
      headers.set('Content-Type', 'application/json');
      return this.http.post(this.retailApi, JSON.stringify(this.postParam), { headers: headers });
    }