如何将可观察对象转换为行为主体? [英] How to convert an Observable into a BehaviorSubject?
本文介绍了如何将可观察对象转换为行为主体?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我正在尝试将可观察对象转换为BehaviorSubject。如下所示:
a$ = new Observable()
b$ = BehaviorSubject.create(new BehaviorSubject(123), a$)
// 🔴
我也尝试过:
a$ = new Observable()
b$ = new BehaviorSubject(a$, 123)
// 🔴
和:
a$ = new Observable()
b$ = a$.asBehaviorSubject(123)
// 🔴
和:
a$ = new Observable()
b$ = a$.pipe(
toBehaviorSubject(123)
)
// 🔴
但这些都不管用。目前,我必须这样实现:
a$ = new Observable()
b$ = new BehaviorSubject(123)
a$.subscribe(b$)
// 🔵
这在类中可能有点难看:
class Foo() {
a$ = new Observable() // Actually, a$ is more complicated than this.
b$ = new BehaviorSubject(123)
constructor() {
this.a$.subscribe(this.b$)
}
}
那么,有没有更简单的方法将可观测对象转换为BehaviorSubject而不使用类构造函数?
这是我的真实案例:
export class Foo {
autoCompleteItems$ = new BehaviorSubject<string[]>(null)
autoCompleteSelected$ = new BehaviorSubject<number>(-1)
autoCompleteSelectedChange$ = new Subject<'up'|'down'>()
constructor() {
this.autoCompleteItems$.pipe(
switchMap((items) => {
if (!items) return EMPTY
return this.autoCompleteSelectedChange$.pipe(
startWith('down'),
scan<any, number>((acc, value) => {
if (value === 'up') {
if (acc <= 0) {
return items.length - 1
} else {
return acc - 1
}
} else {
if (acc >= items.length - 1) {
return 0
} else {
return acc + 1
}
}
}, -1)
)
})
).subscribe(this.autoCompleteSelected$)
}
doAutoComplete = () => {
const item = this.autoCompleteItems$.value[this.autoCompleteSelected$.value]
// do something with `item`
}
}
推荐答案
无需转换。
只需创建一个主题并使用obs.subscribe(sub)
示例:
var obs = new rxjs.Observable((s) => {setTimeout(()=>{s.next([1])} , 500)}) //observable
var sub = new rxjs.BehaviorSubject([0]) //create subject
obs.subscribe(sub) //<----- HERE ----- attach observable to subject
setTimeout(() => {sub.next([2, 3])}, 1500) //subject updated
sub.subscribe(a => console.log(a)) //subscribe to subject
注意:obs.subscribe(sub)
相当于:
obs.subscribe({
next: v => sub.next(v),
error: v => sub.error(v),
complete: () => sub.complete()
})
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