java RxJava - 当返回可能为空时使用 flatmap
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RxJava - Using flatmap when return could be null
提问by Sree
Let's use this class for the example:
让我们以这个类为例：
public static class CurrentUser{
public static Observable<User> get(){
//code basically returns the currently logged in User object
//but sometimes there may not be a logged in user
}
public static Observable<PutResult> logOut(){
return get()
//I only want to execute the following if user != null
.flatMap(new Func1<User, Observable<PutResult>>() {
@Override
public Observable<PutResult> call(User user) {
//delete the session token and save
user.removeSessionToken();
return DatabaseModule.getStorIOSQLite()
.put()
.object(user)
.prepare()
.asRxObservable();
}
});
}
}
Should I just return null inside the flatmap? Are there any repercussions to this since it's expecting an Observable?
我应该在平面图中返回 null 吗？因为它期待一个 Observable，所以对此有任何影响吗？
回答by knutwalker
You should not return nullbut Observable.empty()instead.
你不应该返回，null而是Observable.empty()相反。
.flatMap(new Func1<User, Observable<PutResult>>() {
@Override
public Observable<PutResult> call(User user) {
if (user == null) return Observable.empty();
//delete the session token and save
user.removeSessionToken();
return DatabaseModule.getStorIOSQLite()
.put()
.object(user)
.prepare()
.asRxObservable();
}
});
回答by Malt
It isn't clear what nullyou're talking about.
不清楚null你在说什么。
If you're asking whether the Observable<PutResult>can emit a PutResultthat's null, then yes. This would result in a nullbeing emitted by the outer observable.
如果你问是否Observable<PutResult>可以发出PutResultthat's null，那么是的。这将导致null外部 observable 发出a 。
If you're asking whether the Observable<PutResult>returned by the Func1can be null, then no. Return Observable.empty()instead, (or Observable.just(null)or similar if you need to keep track of the number of emitted items).
如果您要问Observable<PutResult>返回的是否Func1可以为空，则否。返回Observable.empty()，（或Observable.just(null)类似，如果您需要跟踪发出的项目数量）。
回答by rana
In RxJava 2 null is considered to be an invalid value. You can use Maybe component in those cases , some thing like the below
在 RxJava 2 中，null 被认为是无效值。您可以在这些情况下使用 Maybe 组件，如下所示
Maybe<Result>
or
You can use flatMapMaybe<Result>
