问题描述
我正在通过互联网寻找随机 Angular 问题的解决方案,并遇到以下示例:
export class AppModule {
constructor(private router: Router,private viewportScroller: ViewportScroller) {
this.router.events.pipe(
filter((e: Event): e is Scroll => e instanceof Scroll),pairwise()
).subscribe((e: Scroll[]) => {
const prevIoUs = e[0];
const current = e[1];
if (current.position) {
this.viewportScroller.scrollToPosition(current.position);
} else if (current.anchor) {
this.viewportScroller.scrollToAnchor(current.anchor);
} else ...
...
ViewportScroller 是一个抽象类。我试图了解 Angular 中的依赖注入。如何使抽象类可注入?
解决方法
将注入的是扩展 ViewportScroller
的实际类。 Interfacets 也可以作为注入令牌。将注入的是某些(如果有)provider
您可以注入具有具体实现的抽象类。
以下是在 Angular source code 中定义的 ViewportScroller
:
/**
* Defines a scroll position manager. Implemented by `BrowserViewportScroller`.
*/
export abstract class ViewportScroller {
// De-sugared tree-shakable injection
// See #23917
/** @nocollapse */
static ɵprov = ɵɵdefineInjectable({
token: ViewportScroller,providedIn: 'root',factory: () => new BrowserViewportScroller(ɵɵinject(DOCUMENT),window)
});
...
然后,它由BrowserViewportScroller
实现:
/**
* Manages the scroll position for a browser window.
*/
export class BrowserViewportScroller implements ViewportScroller {
private offset: () => [number,number] = () => [0,0];
constructor(private document: Document,private window: Window) {}
...