如何将 Observable 转换为 BehaviorSubject?
How to convert an Observable into a BehaviorSubject?
我正在尝试将 Observable 转换为 BehaviorSubject。像这样:
a$ = new Observable()
b$ = BehaviorSubject.create(new BehaviorSubject(123), a$)
//
我也试过:
a$ = new Observable()
b$ = new BehaviorSubject(a$, 123)
//
并且:
a$ = new Observable()
b$ = a$.asBehaviorSubject(123)
//
并且:
a$ = new Observable()
b$ = a$.pipe(
toBehaviorSubject(123)
)
//
但是 none 这些作品。现在我必须这样实现:
a$ = new Observable()
b$ = new BehaviorSubject(123)
a$.subscribe(b$)
//
这在 class:
中会有点难看
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可以在不使用 class 构造函数的情况下将 Observable 转换为 BehaviorSubject?
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$.value]
// do something with `item`
}
}
我也很担心用例。但这里有一个解决方案,只要您也留下反馈,就可以随意投反对票。由于 BehaviourSubject
和任何其他 Subject
是 Observables
,
import { BehaviorSubject, from } from 'rxjs';
import { map, mergeMap } from 'rxjs/operators';
const source$ = from([1,2,3,4,5,6,7,8,9]);
const bs = new BehaviorSubject('start')
.pipe(
mergeMap(() => source$)
);
bs.subscribe(console.log);
这就是我将 Observables 转换为 BehaviorSubjects 的方式:
import { Observable, BehaviorSubject } from 'rxjs';
export function convertObservableToBehaviorSubject<T>(observable: Observable<T>, initValue: T): BehaviorSubject<T> {
const subject = new BehaviorSubject(initValue);
observable.subscribe(subject);
return subject;
}
无需转换。
只需创建一个主题并将可观察对象附加到它:obs.subscribe(sub)
示例:
var obs = new rxjs.Observable((s) => {setTimeout(()=>{s.next([1])} , 500)}) //observable
var sub = new rxjs.BehaviorSubject([0]) //create subject
obs.subscribe(sub) //<----- HERE ----- attach observable to subject
setTimeout(() => {sub.next([2, 3])}, 1500) //subject updated
sub.subscribe(a => console.log(a)) //subscribe to subject
注意:obs.subscribe(sub)
等同于:
obs.subscribe({
next: v => sub.next(v),
error: v => sub.error(v),
complete: () => sub.complete()
})
我正在尝试将 Observable 转换为 BehaviorSubject。像这样:
a$ = new Observable()
b$ = BehaviorSubject.create(new BehaviorSubject(123), a$)
//
我也试过:
a$ = new Observable()
b$ = new BehaviorSubject(a$, 123)
//
并且:
a$ = new Observable()
b$ = a$.asBehaviorSubject(123)
//
并且:
a$ = new Observable()
b$ = a$.pipe(
toBehaviorSubject(123)
)
//
但是 none 这些作品。现在我必须这样实现:
a$ = new Observable()
b$ = new BehaviorSubject(123)
a$.subscribe(b$)
//
这在 class:
中会有点难看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可以在不使用 class 构造函数的情况下将 Observable 转换为 BehaviorSubject?
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$.value]
// do something with `item`
}
}
我也很担心用例。但这里有一个解决方案,只要您也留下反馈,就可以随意投反对票。由于 BehaviourSubject
和任何其他 Subject
是 Observables
,
import { BehaviorSubject, from } from 'rxjs';
import { map, mergeMap } from 'rxjs/operators';
const source$ = from([1,2,3,4,5,6,7,8,9]);
const bs = new BehaviorSubject('start')
.pipe(
mergeMap(() => source$)
);
bs.subscribe(console.log);
这就是我将 Observables 转换为 BehaviorSubjects 的方式:
import { Observable, BehaviorSubject } from 'rxjs';
export function convertObservableToBehaviorSubject<T>(observable: Observable<T>, initValue: T): BehaviorSubject<T> {
const subject = new BehaviorSubject(initValue);
observable.subscribe(subject);
return subject;
}
无需转换。
只需创建一个主题并将可观察对象附加到它: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)
等同于:
obs.subscribe({
next: v => sub.next(v),
error: v => sub.error(v),
complete: () => sub.complete()
})