[英]Observable of Component Attribute Changes in Angular2
當在angular 2中創建一個通過@Input具有輸入屬性的組件時,如何從對該屬性@Input所做的更改中獲得一個可觀察到的信息(不要與用戶表單輸入相混淆)。
export class ExampleComponent implement OnChanges{
@Input() userObject: User;
ngOnChanges(changes: any): void{
// Validate that its the 'userObject' property first
this.doStuff()
}
}
在實踐中,我想將userObject的Observable更改與其他事物的Observable更改合並,以形成流暢的更改反應模式。
export class ExampleComponent implement OnChanges{
@Input() userObject: User;
constructor():{
userObject.valueChanges.subscribe(x=>{ this.doStuff() });
}
}
我發現BehaviorSubject類可以最好地實現此方案。 您可以使用BehaviorSubject的getValue
函數在當前值達到峰值,而不是創建單獨的后端字段。 然后,使用后盾BehaviorSubject將其視為可觀察到的更改。
export class ExampleComponent{
private _userObject: BehaviorSubject<User> = new BehaviorSubject<User>(null);
@Input()
set userObject(value: User): { this._userObject.next(value); }
get userObject(): User { return this._userObject.getValue(); }
}
嘗試使用get和set,下面的valueChanges()將在設置時觸發。
private _userObject: User;
@Input()
set userObject(userObject: User) {
this._userObject = userObject;
this.valueChanges();
}
get userObject(): User {
return this._userObject;
}
具有可觀察的:
private userObjectChange = new Subject<User>();
userObjectChange$ = this.userObjectChange.asObservable();
private _userObject: User;
@Input()
set userObject(userObject: User) {
this.userObjectChange.next(userObject);
this._userObject = userObject;
}
get userObject(): User {
return this._userObject;
}
認購:
this.newQuote.subscribe(user => {...})
您可以為此使用主題:
export class ExampleComponent {
@Input() set userObject(userObject: User) {
this.userObject$.next(userObject);
}
private userObject$ = new Subject<User>();
constructor():{
this.userObject$.subscribe(x=>{ this.doStuff() });
}
}
檢查輸入更改的最佳方法實際上是使用ngOnChanges
生命周期。
ngOnChanges(changes: { [propertyName: string]: SimpleChange }) {
const changedInputs = Object.keys(changes);
// Only update the userObject if the inputs changed, to avoid unnecessary DOM operations.
if (changedInputs.indexOf('userObject') != -1) {
// do something
}
}
參考: https : //github.com/angular/material2/blob/master/src/lib/icon/icon.ts#L143
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