typescript 使用 observables 检测 Angular 2 变化
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Angular 2 change detection with observables
提问by FacelessPanda
I usually manage to find what I'm doing wrong just browsing existing questions, but here, nothing has helped.
我通常通过浏览现有问题来设法找到我做错了什么，但在这里，没有任何帮助。
I'm working with a simple Ng2 module that attempts to list and update the contents of a NeDB store.
我正在使用一个简单的 Ng2 模块，该模块尝试列出和更新 NeDB 存储的内容。
Mind you, I have no issues with the NeDB store, I have confirmed that it gets updated correctly, and correctly loaded initially, so the problems I have lie elsewhere.
请注意，我对 NeDB 商店没有任何问题，我已确认它已正确更新，并且最初已正确加载，因此我遇到的问题在别处。
The problems I have are the following:
我遇到的问题如下：
"the async pipe doesn't work".
“异步管道不起作用”。
I have this module.
我有这个模块。
@NgModule({
imports: [CommonModule],
exports: [],
declarations: [WikiComponent],
providers: [WikiDbService],
})
export class WikiModule { }
I have this component.
我有这个组件。
@Component({
selector: 'wiki',
templateUrl: './wiki.component.html'
})
export class WikiComponent implements OnInit {
items: Observable<WikiItem[]>;
constructor(private _db : WikiDbService) { }
ngOnInit() {
this.items = this._db.items;
this.items.subscribe({
next: x => console.log("got value", x),
error: e => console.error("observable error", e),
complete: () => console.log("done")
});
}
}
I have this template.
我有这个模板。
<p>{{items | async | json}}</p>
<ul>
<li *ngFor="let item of (items | async)">{{item.name}}</li>
</ul>
<input #newName (keyup)="0">
<button (click)="_db.addByName(newName.value)">ADD</button>
And I have this service.
我有这项服务。
@Injectable()
export class WikiDbService {
private sub: BehaviorSubject<WikiItem[]> = new BehaviorSubject<WikiItem[]>([]);
private db: DataStore;
public items: Observable<WikiItem[]> = this.sub.asObservable();
constructor() {
console.log("BehaviorSubject", this.sub);
console.log("Observable", this.items);
this.db = new DataStore(
{
filename: path.join(app.getAppPath(),"wiki.db"),
autoload: true,
onload:
(err)=>{
if(!err) {
this.db.find<WikiItem>({},
(e,docs) => {
if(!e) {
this.sub.next(docs);
}
})
}
}
});
}
public add(v: WikiItem) {
this.db.insert(
v,
(e, nDoc) =>
{
if(!e) {
this.sub.next([...this.sub.getValue(),nDoc]);
}
}
)
}
public addByName(str:string) {
this.add({name: str, _id: undefined});
}
}
When routing to my component with a non-empty persistent store I get the following console log (corresponding to the logging in the OnInit method of the component):
当使用非空持久存储路由到我的组件时，我得到以下控制台日志（对应于组件的 OnInit 方法中的日志记录）：
got value > [] (wiki.component.ts:20)
got value > [Object, Object, Object, Object] (wiki.component.ts:20)
However my DOM stays as this:
但是我的 DOM 保持如下：
<wiki>
<p>[]</p>
<ul>
<!--template bindings={
"ng-reflect-ng-for-of": ""
}-->
</ul>
<input>
<button>ADD</button>
</wiki>
So a manual subscription to my observable does work and gets me the values. But the async pipe doesn't get them.
因此，手动订阅我的 observable 确实有效并为我提供了值。但是异步管道没有得到它们。
Am I doing something wrong here, or is this a bug?
我在这里做错了什么，还是这是一个错误？
EDITS
编辑
12/19/16 3:45pm
16 年 12 月 19 日下午 3:45
The
ngFordirective was "let item of items | async" before, and I thought maybe the async pipe was scoped to the item and not my observable so I added brackets, but results were unchanged. This is not relevant for the issue.
该
ngFor指令之前是“let item of items | async”，我想也许异步管道的范围是项目而不是我的可观察对象，所以我添加了括号，但结果没有改变。这与问题无关。
12/20/16 3.06pm
16 年 12 月 20 日下午 3.06
As per @olsn's advice, Initialized the component's itemsproperty with an auto-log, to check if the template subscribed to the Observable.
根据@olsn 的建议，使用items自动日志初始化组件的属性，以检查模板是否订阅了 Observable。
It does. So it comes down to detecting the changes, I guess. Amending the title.
确实如此。所以归结为检测变化，我猜。修改标题。
Adding this bit of information : My Component is now as such (commented changes)
添加这一点信息：我的组件现在是这样（评论更改）
@Component({
selector: 'wiki',
templateUrl: './wiki.component.html',
changeDetection: ChangeDetectionStrategy.OnPush // <=== I've read this might help. It doesn't.
})
export class WikiComponent implements OnInit {
items: Observable<WikiItem[]> = this._db.items //
.do(x => console.log("got value", x)) // <== new initialization, with a stream
.publishReplay().refCount(); //
constructor(private _db : WikiDbService, private _cd: ChangeDetectorRef) { }
ngOnInit() {
// <=== moved items initialization
}
reload() : void {
this._cd.markForCheck(); // <== added a button to force the change detector to react. Does not do anything.
}
}
with this addition in the template :
在模板中添加此内容：
<button (click)="reload()">REFRESH</button>
SOLUTION
解决方案
@osln gave a correct answer.
@osln 给出了正确答案。
The problem wasn't fundamentally about subscription or detecting changes, it was because my sub.nextcall were in callbacks given to an external library, which concretely meant that I was doing them outside of Angular territory.
问题根本不在于订阅或检测更改，而是因为我的sub.next调用是在给外部库的回调中进行的，这具体意味着我是在 Angular 领域之外执行这些操作。
Forcing them back onto Angular soil with NgZone calls was the way to fix this issue.
通过 NgZone 调用迫使它们回到 Angular 土壤是解决这个问题的方法。
Thanks @osln.
谢谢@osln。
回答by olsn
Try to initialize your item-object beforengInit and add a temporary log directly into the stream, that way you know if the template really subscribes to the stream, because your current log is done on a completely separate stream.
尝试在ngInit之前初始化您的 item-object并将临时日志直接添加到流中，这样您就知道模板是否真的订阅了流，因为您当前的日志是在完全独立的流上完成的。
@Component({
selector: 'wiki',
templateUrl: './wiki.component.html'
})
export class WikiComponent implements OnInit {
items: Observable<WikiItem[]> = this._db.items
.do(x => console.log("got value", x)
// if items is not a Behavior- or ReplaySubject or ReplayObservable, also add the following:
.publishReplay()
.refCount();
constructor(private _db : WikiDbService) { }
ngOnInit() {
// ..nothing to do here
}
}
Additionally you might try to wrap your data-retrieval in an NgZone.run:
此外，您可能会尝试将数据检索包装在NgZone.run：
First inject this in your DbService: private ngZone: NgZone(from @angular/core) and then instead of just using this.sub.next(docs);, use:
首先将它注入到您的 DbService: private ngZone: NgZone(from @angular/core) 中，然后this.sub.next(docs);使用：
this.ngZone.run(() => this.sub.next(docs));
(also for the add-call)
（也用于添加呼叫）
