閱讀新版 Angular 6 HttpClient 快速入門
以前 激動人心的 Angular HttpClient 這篇文章已經介紹過 HttpClient ，今天看到 angular-university 博客中介紹 HttpClient 的文章，內容很詳細，我就簡單作了整理。有興趣的話，建議直接閱讀 原文。javascript
import {HttpClientModule} from '@angular/common/http';
@NgModule({
declarations: [
AppComponent
],
imports: [
BrowserModule,
HttpClientModule
],
providers: [],
bootstrap: [AppComponent]
})
export class AppModule {}
須要注意的是，如今 JSON 是默認的數據格式，咱們不須要再進行顯式的解析。即咱們不須要再使用如下代碼：java
http.get(url).map(res => res.json()).subscribe(...)
如今咱們能夠這樣寫：typescript
http.get(url).subscribe(...)
import {Component, OnInit} from '@angular/core';
import {Observable} from "rxjs/Observable";
import {HttpClient} from "@angular/common/http";
import * as _ from 'lodash';
interface Course {
description: string;
courseListIcon:string;
iconUrl:string;
longDescription:string;
url:string;
}
@Component({
selector: 'app-root',
template: `
<ul *ngIf="courses$ | async as courses else noData">
<li *ngFor="let course of courses">
{{course.description}}
</li>
</ul>
<ng-template #noData>No Data Available</ng-template>
`})
export class AppComponent implements OnInit {
courses$: Observable<any>;
constructor(private http:HttpClient) {}
ngOnInit() {
this.courses$ = this.http
.get("https://angular-http-guide.firebaseio.com/courses.json")
.map(data => _.values(data))
.do(console.log);
}
}
假設發送 Get 請求時，須要設置對應的查詢參數，預期的 URL 地址以下：shell
https://angular-http-guide.firebaseio.com/courses.json?orderBy="$key"&limitToFirst=1
import {HttpParams} from "@angular/common/http";
const params = new HttpParams()
.set('orderBy', '"$key"')
.set('limitToFirst', "1");
this.courses$ = this.http
.get("/courses.json", {params})
.do(console.log)
.map(data => _.values(data))
須要注意的是，咱們經過鏈式語法調用 set() 方法，構建 HttpParams 對象。這是由於 HttpParams 對象是不可變的，經過 set() 方法能夠防止該對象被修改。json
每當調用 set() 方法，將會返回包含新值的 HttpParams 對象，所以若是使用下面的方式，將不能正確的設置參數。bootstrap
const params = new HttpParams();
params.set('orderBy', '"$key"')
params.set('limitToFirst', "1");
fromString 語法const params = new HttpParams({fromString: 'orderBy="$key"&limitToFirst=1'});
request() APIconst params = new HttpParams({fromString: 'orderBy="$key"&limitToFirst=1'});
this.courses$ = this.http
.request(
"GET",
"/courses.json",
{
responseType:"json",
params
})
.do(console.log)
.map(data => _.values(data));
const headers = new HttpHeaders().set("X-CustomHeader", "custom header value");
this.courses$ = this.http
.get(
"/courses.json",
{headers})
.do(console.log)
.map(data => _.values(data));
httpPutExample() {
const headers = new HttpHeaders().set("Content-Type", "application/json");
this.http.put("/courses/-KgVwECOnlc-LHb_B0cQ.json",
{
"courseListIcon": ".../main-page-logo-small-hat.png",
"description": "Angular Tutorial For Beginners TEST",
"iconUrl": ".../angular2-for-beginners.jpg",
"longDescription": "...",
"url": "new-value-for-url"
},
{headers})
.subscribe(
val => {
console.log("PUT call successful value returned in body",
val);
},
response => {
console.log("PUT call in error", response);
},
() => {
console.log("The PUT observable is now completed.");
}
);
}
httpPatchExample() {
this.http.patch("/courses/-KgVwECOnlc-LHb_B0cQ.json",
{
"description": "Angular Tutorial For Beginners PATCH TEST",
})
.subscribe(
(val) => {
console.log("PATCH call successful value returned in body",
val);
},
response => {
console.log("PATCH call in error", response);
},
() => {
console.log("The PATCH observable is now completed.");
});
}
httpDeleteExample() {
this.http.delete("/courses/-KgVwECOnlc-LHb_B0cQ.json")
.subscribe(
(val) => {
console.log("DELETE call successful value returned in body",
val);
},
response => {
console.log("DELETE call in error", response);
},
() => {
console.log("The DELETE observable is now completed.");
});
}
httpPostExample() {
this.http.post("/courses/-KgVwECOnlc-LHb_B0cQ.json",
{
"courseListIcon": "...",
"description": "TEST",
"iconUrl": "..",
"longDescription": "...",
"url": "new-url"
})
.subscribe(
(val) => {
console.log("POST call successful value returned in body",
val);
},
response => {
console.log("POST call in error", response);
},
() => {
console.log("The POST observable is now completed.");
});
}
duplicateRequestsExample() {
const httpGet$ = this.http
.get("/courses.json")
.map(data => _.values(data));
httpGet$.subscribe(
(val) => console.log("logging GET value", val)
);
this.courses$ = httpGet$;
}
在上面例子中，咱們正在建立了一個 HTTP observable 對象 httpGet$，接着咱們直接訂閱該對象。而後，咱們把 httpGet$ 對象賦值給 courses$ 成員變量，最後在模板中使用 async 管道訂閱該對象。segmentfault
這將致使發送兩個 HTTP 請求，在這種狀況下，請求顯然是重複的，由於咱們只但願從後端查詢一次數據。爲了不發送冗餘的請求，咱們可使用 RxJS 提供的 shareReplay 操做符：後端
// put this next to the other RxJs operator imports
import 'rxjs/add/operator/shareReplay';
const httpGet$ = this.http
.get("/courses.json")
.map(data => _.values(data))
.shareReplay();
並行發送 HTTP 請求的一種方法是使用 RxJs 中的 forkjoin 操做符：api
import 'rxjs/add/observable/forkJoin';
parallelRequests() {
const parallel$ = Observable.forkJoin(
this.http.get('/courses/-KgVwEBq5wbFnjj7O8Fp.json'),
this.http.get('/courses/-KgVwECOnlc-LHb_B0cQ.json')
);
parallel$.subscribe(
values => {
console.log("all values", values)
}
);
}
sequentialRequests() {
const sequence$ = this.http.get<Course>('/courses/-KgVwEBq5wbFnjj7O8Fp.json')
.switchMap(course => {
course.description+= ' - TEST ';
return this.http.put('/courses/-KgVwEBq5wbFnjj7O8Fp.json', course)
});
sequence$.subscribe();
}
sequentialRequests() {
const sequence$ = this.http.get<Course>('/courses/-KgVwEBq5wbFnjj7O8Fp.json')
.switchMap(course => {
course.description+= ' - TEST ';
return this.http.put('/courses/-KgVwEBq5wbFnjj7O8Fp.json', course)
},
(firstHTTPResult, secondHTTPResult) => [firstHTTPResult, secondHTTPResult]);
sequence$.subscribe(values => console.log("result observable ", values) );
}
throwError() {
this.http
.get("/api/simulate-error")
.catch( error => {
// here we can show an error message to the user,
// for example via a service
console.error("error catched", error);
return Observable.of({description: "Error Value Emitted"});
})
.subscribe(
val => console.log('Value emitted successfully', val),
error => {
console.error("This line is never called ",error);
},
() => console.log("HTTP Observable completed...")
);
}
當發生異常時，控制檯的輸出結果：angular2
Error catched
HttpErrorResponse {headers: HttpHeaders, status: 404, statusText: "Not Found", url: "http://localhost:4200/api/simulate-error", ok: false, … }
Value emitted successfully {description: "Error Value Emitted"}
HTTP Observable completed...
import {Injectable} from "@angular/core";
import {HttpEvent, HttpHandler, HttpInterceptor} from "@angular/common/http";
import {HttpRequest} from "@angular/common/http";
import {Observable} from "rxjs/Observable";
@Injectable()
export class AuthInterceptor implements HttpInterceptor {
constructor(private authService: AuthService) {
}
intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
const clonedRequest = req.clone({
headers: req.headers.set('X-CustomAuthHeader', authService.getToken())
});
console.log("new headers", clonedRequest.headers.keys());
return next.handle(clonedRequest);
}
}
@NgModule({
declarations: [
AppComponent
],
imports: [
BrowserModule,
HttpClientModule
],
providers: [
[ { provide: HTTP_INTERCEPTORS, useClass: AuthInterceptor, multi: true } ]
],
bootstrap: [AppComponent]
})
export class AppModule { }
longRequest() {
const request = new HttpRequest(
"POST", "/api/test-request", {},
{reportProgress: true});
this.http.request(request)
.subscribe(
event => {
if (event.type === HttpEventType.DownloadProgress) {
console.log("Download progress event", event);
}
if (event.type === HttpEventType.UploadProgress) {
console.log("Upload progress event", event);
}
if (event.type === HttpEventType.Response) {
console.log("response received...", event.body);
}
}
);
}
上面示例運行後，控制檯的可能的輸出結果：
Upload progress event Object {type: 1, loaded: 2, total: 2}
Download progress event Object {type: 3, loaded: 31, total: 31}
Response Received... Object {description: "POST Response"}