How to pass URLSearchParams in the HttpClient “get

问题:

I used Angular 4.2 with the Http service and I used the get method like this where params is a URLSearchParams object:

this.http.get(url, {headers: this.setHeaders(), search: params})

I want to migrate to Angular 5. http is now a HttpClient object like recommended by the angular team. I got an error with the 'search' key.

Do you know how to migrate Http to HttpClient service in my case?

Thank you.

回答1:

Since Angular 4.3 you can use HttpClient like this :

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

   constructor(private httpClient: HttpClient) { }    

   getData(){
        let headers = new HttpHeaders();
        headers  = headers.append('header-1', 'value-1');
        headers  = headers.append('header-2', 'value-2');

       let params = new HttpParams();
       params = params.append('param-1', 'value-1');
       params = params.append('param-2', 'value-2');

       this.httpClient.get("/data", {headers , params })
   }

HttpParams and HttpHeaders are immutable classes so after each call of set or append methods they return a new instance that's why you should do this : params = params.append(...)

回答2:

Angular 4 Way:

this.http.get(url, {headers: this.setHeaders(), search: params})

Angular 5 Way:

import { HttpClient, HttpParams } from '@angular/common/http';
let params = new HttpParams().set('paramName', paramValue);
this.http.get(url,  { params: params })

Multiple Params:

// Initialize Params Object
let Params = new HttpParams();

// Begin assigning parameters
Params = Params.append('firstParameter', firstVal);
Params = Params.append('secondParameter', secondVal);

回答3:

Following will be the changes, you need to do:

• Replace Older Http import with:

  import { HttpClient } from "@angular/common/http";

• Create HttpClient object as below:

  constructor( protected httpClient: HttpClient, ) {}

  Now there are ways to achieve search parameter namely as below:

  public get(searchParam: string): Observable { return this.httpClient.get(${this.URL}/${searchParam}); }

or:

public get(searchParam: string): Observable<object> {
let headers = new Headers({ 'Content-Type': 'application/json' });
    let myParams = HttpParams().set("id", searchParam);

    let options = new RequestOptions({ headers: headers, method: 'get', params: myParams });

return this.http.get("this.url",options)
         .map((res: Response) => res.json())
         .catch(this.handleError);
}

回答4:

I had a situation when there were multiple parameters that needed to be passed to the api. The only thing that worked for me is when calling set() method in the same line chained together during HttpParams object intialization:

public get(userid: string, username: string): Observable<object> {
    let headers = new Headers({ 'Content-Type': 'application/json' });
    let myParams = HttpParams().set("id", userid).set("username", username);
    let options = new RequestOptions({ headers: headers, method: 'get', params: 
myParams });