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async_pipe.ts
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async_pipe.ts
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/**
* @license
* Copyright Google Inc. All Rights Reserved.
*
* Use of this source code is governed by an MIT-style license that can be
* found in the LICENSE file at https://angular.io/license
*/
import {ChangeDetectorRef, EventEmitter, Injectable, OnDestroy, Pipe, PipeTransform, WrappedValue, ɵisObservable, ɵisPromise, ɵlooseIdentical} from '@angular/core';
import {Observable, SubscriptionLike} from 'rxjs';
import {invalidPipeArgumentError} from './invalid_pipe_argument_error';
interface SubscriptionStrategy {
createSubscription(async: Observable<any>|Promise<any>, updateLatestValue: any): SubscriptionLike
|Promise<any>;
dispose(subscription: SubscriptionLike|Promise<any>): void;
onDestroy(subscription: SubscriptionLike|Promise<any>): void;
}
class ObservableStrategy implements SubscriptionStrategy {
createSubscription(async: Observable<any>, updateLatestValue: any): SubscriptionLike {
return async.subscribe({next: updateLatestValue, error: (e: any) => { throw e; }});
}
dispose(subscription: SubscriptionLike): void { subscription.unsubscribe(); }
onDestroy(subscription: SubscriptionLike): void { subscription.unsubscribe(); }
}
class PromiseStrategy implements SubscriptionStrategy {
createSubscription(async: Promise<any>, updateLatestValue: (v: any) => any): Promise<any> {
return async.then(updateLatestValue, e => { throw e; });
}
dispose(subscription: Promise<any>): void {}
onDestroy(subscription: Promise<any>): void {}
}
const _promiseStrategy = new PromiseStrategy();
const _observableStrategy = new ObservableStrategy();
/**
* @ngModule CommonModule
* @description
*
* Unwraps a value from an asynchronous primitive.
*
* The `async` pipe subscribes to an `Observable` or `Promise` and returns the latest value it has
* emitted. When a new value is emitted, the `async` pipe marks the component to be checked for
* changes. When the component gets destroyed, the `async` pipe unsubscribes automatically to avoid
* potential memory leaks.
*
* @usageNotes
*
* ### Examples
*
* This example binds a `Promise` to the view. Clicking the `Resolve` button resolves the
* promise.
*
* {@example common/pipes/ts/async_pipe.ts region='AsyncPipePromise'}
*
* It's also possible to use `async` with Observables. The example below binds the `time` Observable
* to the view. The Observable continuously updates the view with the current time.
*
* {@example common/pipes/ts/async_pipe.ts region='AsyncPipeObservable'}
*
* @publicApi
*/
@Injectable()
@Pipe({name: 'async', pure: false})
export class AsyncPipe implements OnDestroy, PipeTransform {
private _latestValue: any = null;
private _latestReturnedValue: any = null;
private _subscription: SubscriptionLike|Promise<any>|null = null;
private _obj: Observable<any>|Promise<any>|EventEmitter<any>|null = null;
private _strategy: SubscriptionStrategy = null !;
constructor(private _ref: ChangeDetectorRef) {}
ngOnDestroy(): void {
if (this._subscription) {
this._dispose();
}
}
transform<T>(obj: null): null;
transform<T>(obj: undefined): undefined;
transform<T>(obj: Observable<T>|null|undefined): T|null;
transform<T>(obj: Promise<T>|null|undefined): T|null;
transform(obj: Observable<any>|Promise<any>|null|undefined): any {
if (!this._obj) {
if (obj) {
this._subscribe(obj);
}
this._latestReturnedValue = this._latestValue;
return this._latestValue;
}
if (obj !== this._obj) {
this._dispose();
return this.transform(obj as any);
}
if (ɵlooseIdentical(this._latestValue, this._latestReturnedValue)) {
return this._latestReturnedValue;
}
this._latestReturnedValue = this._latestValue;
return WrappedValue.wrap(this._latestValue);
}
private _subscribe(obj: Observable<any>|Promise<any>|EventEmitter<any>): void {
this._obj = obj;
this._strategy = this._selectStrategy(obj);
this._subscription = this._strategy.createSubscription(
obj, (value: Object) => this._updateLatestValue(obj, value));
}
private _selectStrategy(obj: Observable<any>|Promise<any>|EventEmitter<any>): any {
if (ɵisPromise(obj)) {
return _promiseStrategy;
}
if (ɵisObservable(obj)) {
return _observableStrategy;
}
throw invalidPipeArgumentError(AsyncPipe, obj);
}
private _dispose(): void {
this._strategy.dispose(this._subscription !);
this._latestValue = null;
this._latestReturnedValue = null;
this._subscription = null;
this._obj = null;
}
private _updateLatestValue(async: any, value: Object): void {
if (async === this._obj) {
this._latestValue = value;
this._ref.markForCheck();
}
}
}