角度6：无法正确设置HTTP标头的内容类型

我正在尝试使用Angular 6中的HttpHeader进行发布呼叫，并将Content-Type设置为application / json。
但是服务器获取的Content-Type是x-www-form-urlencoded而不是application / json。

I'm trying to make a post call using HttpHeader in angular 6 And I set Content-Type to application/json. But the server get x-www-form-urlencoded instead of application/json for Content-Type.

service.ts

service.ts

   
myFunction(id: string, name: string, fields: string[]) {
  const body = {
    id: id,
    name: name,
    fields: fields
  };
  let headers = new HttpHeaders();
  headers= headers.set('content-type', 'application/json');
  return this.http.post(this.URL , body, {headers});
}

component.ts

component.ts

submit(){
  this.myService.myFunction(this.id, this.form.value.name,  
  this.form.value.fields).subscribe((res:any) => {
    console.log(this.form);
  }, error => {
    console.log(JSON.parse(error.error).errors);
  })
}