函数式编程--响应式编程 ---android应用例子
RxJava implements this operator as create
.
It is good practice to check the observer’s isUnsubscribed
state from within the function you pass tocreate
so that your Observable can stop emitting items or doing expensive calculations when there is no longer an interested observer.
Observable.create(xxxx),返回一个流
Observable.create(new Observable.OnSubscribe<Integer>() {
@Override
public void call(Subscriber<? super Integer> observer) {
try {
if (!observer.isUnsubscribed()) {
for (int i = 1; i < 5; i++) {
observer.onNext(i);
}
observer.onCompleted();
}
} catch (Exception e) {
observer.onError(e);
}
}
} ).subscribe(new Subscriber<Integer>() {
@Override
public void onNext(Integer item) {
System.out.println("Next: " + item);
} @Override
public void onError(Throwable error) {
System.err.println("Error: " + error.getMessage());
} @Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
});
结果:
Next: 1
Next: 2
Next: 3
Next: 4
Sequence complete.
Scheduler
onNext
, onError
, and onCompleted
methods on a particular Scheduler; SubscribeOn takes this a step further and instructs the Observable to do all of its processing (including the sending of items and notifications to observers) on a particular Scheduler.Varieties of Scheduler
You obtain a Scheduler from the factory methods described in the Schedulers
class. The following table shows the varieties of Scheduler that are available to you by means of these methods in RxJava:
Scheduler | purpose |
---|---|
Schedulers.computation( ) |
meant for computational work such as event-loops and callback processing; do not use this scheduler for I/O (use Schedulers.io( ) instead); the number of threads, by default, is equal to the number of processors |
Schedulers.from(executor) |
uses the specified Executor as a Scheduler |
Schedulers.immediate( ) |
schedules work to begin immediately in the current thread |
Schedulers.io( ) |
meant for I/O-bound work such as asynchronous performance of blocking I/O, this scheduler is backed by a thread-pool that will grow as needed; for ordinary computational work, switch toSchedulers.computation( ) |
Schedulers.newThread( ) |
creates a new thread for each unit of work |
Schedulers.trampoline( ) |
queues work to begin on the current thread after any already-queued work |
public class ConcurrencyWithSchedulersDemoFragment extends BaseFragment { @InjectView(R.id.progress_operation_running) ProgressBar _progress;
@InjectView(R.id.list_threading_log) ListView _logsList; private LogAdapter _adapter;
private List<String> _logs;
private Subscription _subscription; @Override
public void onDestroy() {
super.onDestroy();
if (_subscription != null) {
_subscription.unsubscribe();
}
} @Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
_setupLogger();
} @Override
public View onCreateView(LayoutInflater inflater,
@Nullable ViewGroup container,
@Nullable Bundle savedInstanceState) {
View layout = inflater.inflate(R.layout.fragment_concurrency_schedulers, container, false);
ButterKnife.inject(this, layout);
return layout;
} @OnClick(R.id.btn_start_operation)
public void startLongOperation() { _progress.setVisibility(View.VISIBLE);
_log("Button Clicked"); _subscription = AppObservable.bindFragment(this, _getObservable()) // Observable,相当于是stream,流
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(_getObserver()); // Observer
} private Observable<Boolean> _getObservable() {
return Observable.create(new Observable.OnSubscribe<Boolean>() { @Override
public void call(Subscriber<? super Boolean> observer) { if(!observer.isUnsubscribed())
{
_log("Within Observable"); _doSomeLongOperation_thatBlocksCurrentThread();
observer.onNext(true);
observer.onCompleted();
} }
});
} /**
* Observer that handles the result List<Integer> from Observable
* through the 3 important actions:
*
* 1. onCompleted
* 2. onError
* 3. onNext
*/
private Observer<Boolean> _getObserver() {
return new Observer<Boolean>() { @Override
public void onCompleted() {
_log("On complete");
_progress.setVisibility(View.INVISIBLE);
} @Override
public void onError(Throwable e) {
Timber.e(e, "Error in RxJava Demo concurrency");
_log(String.format("Boo Error %s", e.getMessage()));
_progress.setVisibility(View.INVISIBLE);
} @Override
public void onNext(Boolean aBoolean) {
_log(String.format("onNext with return value \"%b\"", aBoolean));
}
};
} // -----------------------------------------------------------------------------------
// Method that help wiring up the example (irrelevant to RxJava) private void _doSomeLongOperation_thatBlocksCurrentThread() {
_log("performing long operation"); try {
Thread.sleep(3000); } catch (InterruptedException e) {
Timber.d("Operation was interrupted");
}
} private void _log(String logMsg) { if (_isCurrentlyOnMainThread()) {
_logs.add(0, logMsg + " (main thread) ");
_adapter.clear();
_adapter.addAll(_logs);
} else {
_logs.add(0, logMsg + " (NOT main thread) "); // You can only do below stuff on main thread.
new Handler(Looper.getMainLooper()).post(new Runnable() { @Override
public void run() {
_adapter.clear();
_adapter.addAll(_logs);
}
});
}
} private void _setupLogger() {
_logs = new ArrayList<String>();
_adapter = new LogAdapter(getActivity(), new ArrayList<String>());
_logsList.setAdapter(_adapter);
} private boolean _isCurrentlyOnMainThread() {
return Looper.myLooper() == Looper.getMainLooper();
} private class LogAdapter
extends ArrayAdapter<String> { public LogAdapter(Context context, List<String> logs) {
super(context, R.layout.item_log, R.id.item_log, logs);
}
}
}
参考资料:http://reactivex.io/documentation/operators/create.html
https://github.com/ReactiveX/RxJava/wiki/The-RxJava-Android-Module
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