android rxJava:如何从缓存中获取数据,同时在后台进行更新?
我刚刚开始学习Android的rxJava,并希望实现常见用例:android rxJava:如何从缓存中获取数据,同时在后台进行更新?,android,rx-java,Android,Rx Java,我刚刚开始学习Android的rxJava,并希望实现常见用例: 从缓存请求数据并显示给用户 从web请求数据 服务器更新存储中的数据并自动向用户显示 传统上,最好的方案之一是使用CursorLoader从缓存中获取数据,在单独的线程中运行web请求,并通过内容提供程序将数据保存到磁盘,内容提供程序自动通知侦听器和CursorLoader自动更新UI 在rxJava中,我可以通过运行两个不同的观察者来实现这一点,正如您在下面的代码中所看到的,但我没有找到如何将这两个调用合并到一个调用中以达到
- 从缓存请求数据并显示给用户
- 从web请求数据
- 服务器更新存储中的数据并自动向用户显示
@Override
public Observable<SavingsGoals> getCachedSavingsGoal() {
return observableGoal.getSavingsGoals()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
@Override
public Observable<SavingsGoals> getRecentSavingsGoal() {
return api.getSavingsGoals()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
model.getCachedSavingsGoal().subscribe(new Observer<SavingsGoals>() {
@Override
public void onCompleted() {
// no op
}
@Override
public void onError(Throwable e) {
Log.e(App.TAG, "Failed to consume cached data");
view.showError();
}
@Override
public void onNext(SavingsGoals savingsGoals) {
Log.d(App.TAG, "Show the next item");
if (savingsGoals != null && !savingsGoals.getSavingsGoals().isEmpty()) {
view.showData(savingsGoals.getSavingsGoals());
} else {
view.showError();
}
}
});
model.getRecentSavingsGoal().subscribe(new Observer<SavingsGoals>() {
@Override
public void onCompleted() {
// no op
}
@Override
public void onError(Throwable e) {
Log.e(App.TAG, "Failed to consume data from the web", e);
view.showError();
}
@Override
public void onNext(SavingsGoals savingsGoals) {
if (savingsGoals != null && !savingsGoals.getSavingsGoals().isEmpty()) {
view.showData(savingsGoals.getSavingsGoals());
} else {
view.showError();
}
}
});
@覆盖
公共可观测getCachedSavingsGoal(){
return observegoal.getSavingsGoals()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
@凌驾
公共可观察getRecentSavingsGoal(){
返回api.getSavingsGoals()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
model.getCachedSavingsGoal().subscribe(新观察者(){
@凌驾
未完成的公共无效(){
//无操作
}
@凌驾
公共无效申报人(可丢弃的e){
Log.e(App.TAG,“无法使用缓存数据”);
view.ror();
}
@凌驾
公共无效onNext(储蓄利息储蓄利息){
Log.d(App.TAG,“显示下一项”);
if(savingsGoals!=null&!savingsGoals.getSavingsGoals().isEmpty()){
view.showData(savingsGoals.getSavingsGoals());
}否则{
view.ror();
}
}
});
model.getRecentSavingsGoal().subscribe(新观察者()){
@凌驾
未完成的公共无效(){
//无操作
}
@凌驾
公共无效申报人(可丢弃的e){
Log.e(App.TAG,“未能使用来自web的数据”,e);
view.ror();
}
@凌驾
公共无效onNext(储蓄利息储蓄利息){
if(savingsGoals!=null&!savingsGoals.getSavingsGoals().isEmpty()){
view.showData(savingsGoals.getSavingsGoals());
}否则{
view.ror();
}
}
});
此外,当前方法的一个问题是缓存和web数据不能保证连续运行。当过时的数据以最新的形式出现并覆盖来自web的最新数据时,这是可能的
为了解决这个问题,我实现了观测者合并和按时间戳过滤:它从缓存中获取数据,将数据传递给下一个观测者,如果缓存过时,则向web案例发出新的调用,以通过按时间戳过滤解决线程竞争问题。然而,这种方法的问题是我无法从这个可观察对象返回缓存数据——我需要等待两个请求完成它们的工作
代码片段
@Override
public Observable<Timestamped<SavingsGoals>> getSavingGoals() {
return observableGoal
.getTimestampedSavingsGoals()
.subscribeOn(Schedulers.io())
.flatMap(new Func1<Timestamped<SavingsGoals>, Observable<Timestamped<SavingsGoals>>>() {
@Override
public Observable<Timestamped<SavingsGoals>> call(Timestamped<SavingsGoals> cachedData) {
Log.d(App.FLOW, "getTimestampedSavingsGoals");
return getGoalsFromBothSources()
.filter(filterResponse(cachedData));
}
})
.subscribeOn(AndroidSchedulers.mainThread());
}
private Func1<Timestamped<SavingsGoals>, Boolean> filterResponse(Timestamped<SavingsGoals> cachedData) {
return new Func1<Timestamped<SavingsGoals>, Boolean>() {
@Override
public Boolean call(Timestamped<SavingsGoals> savingsGoals) {
return savingsGoals != null
&& cachedData != null
&& cachedData.getTimestampMillis() < savingsGoals.getTimestampMillis()
&& savingsGoals.getValue().getSavingsGoals().size() != 0;
}
};
}
private Observable<Timestamped<SavingsGoals>> getGoalsFromBothSources() {
Log.d(App.FLOW, "getGoalsFromBothSources:explicit");
return Observable.merge(
observableGoal.getTimestampedSavingsGoals().subscribeOn(Schedulers.io()),
api.getSavingsGoals()
.timestamp()
.flatMap(new Func1<Timestamped<SavingsGoals>, Observable<Timestamped<SavingsGoals>>>() {
@Override
public Observable<Timestamped<SavingsGoals>> call(Timestamped<SavingsGoals> savingsGoals) {
Log.d(App.FLOW, "getGoalsFromBothSources:implicit");
return observableGoal.saveAllWithTimestamp(savingsGoals.getTimestampMillis(), savingsGoals.getValue().getSavingsGoals());
}
}))
.subscribeOn(Schedulers.io());
}
@覆盖
公众可观察的getSavingGoals(){
回归自我
.getTimestampedSavingsGoals()
.subscribeOn(Schedulers.io())
.flatMap(新函数1(){
@凌驾
公共可观察调用(带时间戳的cachedData){
Log.d(App.FLOW,“getTimestampedSavingsGoals”);
返回getGoalsFromBothSources()
.filter(filterResponse(cachedData));
}
})
.subscribeOn(AndroidSchedulers.mainThread());
}
private Func1 filterResponse(带时间戳的cachedData){
返回新的Func1(){
@凌驾
公共布尔调用(带时间戳的savingsGoals){
返回savingsGoals!=null
&&cachedData!=null
&&cachedData.getTimestampMillis()
你知道在一个观察者身上做这件事的方法吗
潜在解决方案:
@Override
public Observable<SavingsGoals> getSavingGoals() {
return api.getSavingsGoals()
.publish(network ->
Observable.mergeDelayError(
observableGoal.getSavingsGoals().takeUntil(network),
network.flatMap(new Func1<SavingsGoals, Observable<SavingsGoals>>() {
@Override
public Observable<SavingsGoals> call(SavingsGoals savingsGoals) {
return observableGoal.saveAll(savingsGoals.getSavingsGoals());
}
})
)
)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
@覆盖
公众可观察的getSavingGoals(){
返回api.getSavingsGoals()
.发布(网络->
可观测误差(
observegegoal.getSavingsGoals().takeUntil(网络),
network.flatMap(新的Func1(){
@凌驾
公共可观察呼叫(SavingsGoals SavingsGoals){
返回observegoal.saveAll(savingsGoals.getSavingsGoals());
}
})
)
)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
- 抱歉,ID中的热替换
public Observable<NetworkResponse> getDataFromNetwork( final Request request) { return networkCall.doOnNext(networkResponse -> saveToStorage(networkResponse); }
public Observable<Response> getData(final Request request) { return dataService.getDataFromNetwork(request) .publish(networkResponse -> Observable.merge(networkResponse, dataService.getDataFromStorage(request).takeUntil(networkResponse))); }
public Observable<Response> getData(final Request request) { return dataService.getDataFromNetwork(request) .publish(networkResponse -> Observable.merge(networkResponse, dataService.getDataFromStorage(request).takeUntil(networkResponse))) .onErrorResumeNext(dataService.getDataFromStorage(request); }
@Nonnull public Observable<SomeData> getSomeDataObservable() { return Observable .defer(new Func0<Observable<SomeData>>() { @Override public Observable<SomeData> call() { return Observable.just(getSomeData()); } }); }
@Nonnull public Observable<SomeData> getSomeDataObservableRefreshable() { return refreshSubject.startWith((Object)null).switchMap(new Func1() { public Observable<T> call(Object o) { return getSomeDataObservable(); } } }
@Nonnull public Observable<SomeData> getSomeDataObservable() { return Observable .defer(new Func0<Observable<SomeData>>() { @Override public Observable<SomeData> call() { return Observable.just(getSomeData()); } }) .compose(MoreOperators.<SomeData>refresh(refreshSubject)); }