The Art of Rx

The Art of Rx
Матвей Мальков

Èñêóññòâî ðåàêòèâíîãî
ïðîãðàììèðîâàíèÿ

Èñêóññòâî – âûñîêàÿ ñòåïåíü
ìàñòåðñòâà â êàêîé-ëèáî
ñôåðå äåÿòåëüíîñòè.

Íàø ãëàâíûé íàâûê – óìåíèå
äóìàòü

9
Умение думать. Практика

• î ÷åì äóìàòü?
9

• î ÷åì äóìàòü?
• êàê äóìàòü?
9

10
О чем думать мобильному разработчику

• ýíåðãîïîòðåáëåíèå
10

• ïëàâíîñòü èíòåðôåéñà (60 fps)
10

• ôðàãìåíòàöèÿ óñòðîéñòâ
10

• ôðàãìåíòàöèÿ óñòðîéñòâ
• ïîòðåáëåíèå ïàìÿòè
10

11
Как думать мобильному разработчику?

• êàê ïîëüçîâàòåëü
11

• êàê äèçàéíåð
11

• êàê äèçàéíåð
• êàê ïðåäëàãàåò ôóíäàìåíòàëüíûé ôðåéìâîðê
11

12
Фундаментальный фреймворк

• äåëàåò ðàçðàáîòêó ïðîùå/ëó÷øå/áûñòðåå
12

• ïðèâíîñèò ÷òî-òî êîíöåïòóàëüíî íîâîå
12

• ïðîðàñòàåò âî âñå ïîäñèñòåìû
12

• ñëîæíî óáðàòü
12

• ñëîæíî óáðàòü
• òðåáóåò íàâûêîâ îáðàùåíèÿ
12

Íàø ëþáèìûé ôóíäàìåíòàëüíûé
ôðåéìâîðê – RxJava

Î ÷eì äóìàòü, èñïîëüçóÿ RxJava?

• ïðîáëåìû:
16
О контрактах

• ïîíèìàíèå
16

• ñîáëþäåíèå
16

• âàæíî:
16

• âàæíî:
• îñíîâû
16

• onNext – 0, n èëè inf
17
Нотификации

• onCompleted – 0 èëè 1
17

• onError – 0 èëè 1
17

• onError – 0 èëè 1
• onCompleted + onError <= 1
17

18
Подписка и отписка

• íå íóæíî îòïèñûâàòüñÿ ïîñëå çàâåðøåíèÿ
18

• íå íóæíî îòïèñûâàòüñÿ ïîñëå çàâåðøåíèÿ
• ïðè îòïèñêå çàâåðøåíèå íå ãàðàíòèðîâàíî
18

19
Observable<Response> obs = Observable 
.interval(1, TimeUnit.SECONDS) 
.map(this ::sendPing) 
.cache();

20
.cache();

21
.cache();

22
.cache();

23
.cache(); 
 
Subscription sub = obs.subscribe();

24
.cache(); 
 
Subscription sub = obs.subscribe(); 
 
//позже 
sub.unsubscribe();

25
.cache(); 
 
 
//позже 
sub.unsubscribe();
Note: You sacrifice the ability to
unsubscribe from the origin

26
.cache(); 
 
 
//позже 
sub.unsubscribe();
Note: You sacrifice the ability to
unsubscribe from the origin

• îòïðàâêà íîòèôèêàöèé
27

• çàâåðøåíèå ñ îøèáêîé
27

• çàâåðøåíèå ñ îøèáêîé
• ïîëíûé ñïèñîê : http://reactivex.io/documentation/contract.html
27

28
Состояние системы

• èçîëèðîâàííî
28

• îäèí èñòî÷íèê
28

• íåèçìåíÿåìî
28

• ïîä÷èíÿåòñÿ êîíòðàêòó Observable
28

29
nameEditTextChanges.subscribe(this ::updateName);

30
PublishSubject<Integer> nameEditTextChanges = 
PublishSubject.create();

31
PublishSubject<Integer> nameEditTextChanges = 
PublishSubject.create();
nameEditTextChanges.onNext("хаха, обманул!");

Subject – âîçìîæíîå íàðóøåíèå
êîíòðàêòà

• ïîä÷èíÿåòñÿ êîíòðàêòó Observable
34

• ñîåäèíåíèå èìïåðàòèâíîãî è ðåàêòèâíîãî ìèðà
35
Subjects

• êîãäà íåâîçìîæíî ñäåëàòü ïî äðóãîìó
35
Subjects

• ýòî âàø ñëó÷àé? ÍÅÒ!
35
Subjects

• âñå òàêè âàø? Íåò, ýòî íå òàê!
35
Subjects

• âñå òàêè âàø? Íåò, ýòî íå òàê!
• ìåíüøå – ëó÷øå
35
Subjects

• ïðîáëåìû
37
О тредах

• íåò ïîíèìàÿ ðàáîòû
37
О тредах

• ñóþò subscribeOn è observeOn âåçäå ïîäðÿä
37
О тредах

• âàæíî :
37
О тредах

• âàæíî :
• ðàçáèðàòüñÿ
37
О тредах

• ïëàíèðîâêà çàäà÷
38
Scheduler

• ðàáîòà ñ òðåäàìè
38
Scheduler

• subscribeOn
38
Scheduler

• subscribeOn
• observeOn
38
Scheduler

Äîãìû
observeOn
subscribeOn

1. observeOn ìåíÿåò Scheduler äëÿ
âñåãî, ÷òî íèæå ïî êîäó

2. subscribeOn ìåíÿåò Scheduler ñ
ñàìîãî âåðõà öåïî÷êè

3. Êàæäûé ñëåäóþùèé observeOn
çàìåíÿåò ïðåäûäóùèé

4. subscribeOn àêòóàëåí äî
ïåðâîãî observeOn

Âñåãäà äóìàéòå î òîì,
â êàêîì òðåäå âûïîëíÿåòñÿ ôóíêöèÿ

45
Observable<Response> requestObs = userDbChanges 
.filter(u -> u.age < 18) 
.map(this ::toRequestModel) 
.map(this ::doRequest) 
.onErrorReturn(this ::doRecoverReq) 
.map(this ::cacheAndModify); 
//ui thread 
requestObs.subscribe(this ::showOnUi);

46
.filter(u -> u.age < 18) 
.map(this ::cacheAndModify); 
//ui thread 

47
.filter(u -> u.age < 18)
.observeOn(networkScheduler) 
.subscribeOn(Schedulers.computation()) 
.observeOn(mainThread) 
.map(this ::toUiModel); 
//ui thread 

48
//ui thread 

49
//ui thread 

50
//ui thread 

51
//ui thread 

52
//ui thread 

53
//ui thread 

Âåëèêîëåïíûé subscribeOn

55
subscribeOn
public final Observable<T> subscribeOn(Scheduler scheduler) {
 
//какой-то неважный код
 
return nest().lift(new OperatorSubscribeOn<T>(scheduler)); 
}

56
subscribeOn
 
 
}

57
public final Observable<Observable<T >> nest() { 
return just(this); 
}

61
subscribeOn
 
 
}

62
subscribeOn
 
 
}

63
subscribeOn
 
 
}

64
public class OperatorSubscribeOn<T> implements Operator<T, Observable<T >> { 
 
private final Scheduler scheduler; 
 
public OperatorSubscribeOn(Scheduler scheduler) { 
this.scheduler = scheduler; 
} 
 
@Override 
public Subscriber<? super Observable<T >> call(final Subscriber<? super T> subscriber) {
… 
}

65
 
 
} 
 
@Override 
… 
}
принимаетвозвращает

66
 
 
} 
 
@Override 
… 
}

67
@Override 
public Subscriber<? super Observable<T >> call(final Subscriber<? super T> subscriber) { 
final Worker inner = scheduler.createWorker(); 
subscriber.add(inner); 
return new Subscriber<Observable<T >>(subscriber) { 
 
@Override 
public void onNext(final Observable<T> o) { 
inner.schedule(new Action0() { 
 
@Override 
public void call() { 
final Thread t = Thread.currentThread(); 
o.unsafeSubscribe(new Subscriber<T>(subscriber) {
//обычный inner subscribe
} 
 
 
//тут еще оооочень много закрывающихся скобочек 
}

68
@Override 
 
@Override 
 
@Override 
} 
 
 
}

69
@Override 
 
@Override 
 
@Override 
} 
 
 
}

70
@Override 
 
@Override 
 
@Override 
} 
 
 
}

71
@Override 
 
@Override 
 
@Override 
} 
 
 
}
Наш Observable

72
@Override 
 
@Override 
 
@Override 
} 
 
 
}

73
@Override 
 
@Override 
 
@Override 
} 
 
 
}

75
OperatorSubscribeOn(Scheduler)

76
OperatorSubscribeOn(Scheduler)

78
Observable.just(1) 
.subscribeOn(scheduler1)
.subscribeOn(scheduler2) 
.subscribe();

79
Observable.just(1) 
.subscribeOn(scheduler1)
.subscribeOn(scheduler2) 
.subscribe(); //scheduler1

2. Ïåðâûé subscribeOn ìåíÿåò
Scheduler ñ ñàìîãî âåðõà öåïî÷êè

82
//computation 
Observable<Long> o1 = Observable.interval(1, TimeUnit.SECONDS); 
//network 
Observable<Integer> o2 = Observable.just(1) 
.observeOn(networkScheduler); 
 
Observable.zip(o1, o2, o3, (r1, r2) -> r1 * r2);

83
//computation 
//network 
 

84
//computation 
//network 
 
//computation or network

85
final class InnerSubscriber extends Subscriber { 
 
@Override 
public void onNext(Object t) { 
try { 
items.onNext(t); 
} catch (MissingBackpressureException e) { 
onError(e); 
} 
tick(); 
} 
};

86
final class InnerSubscriber extends Subscriber { 
 
@Override 
public void onNext(Object t) { 
try { 
items.onNext(t); 
} catch (MissingBackpressureException e) { 
onError(e); 
} 
tick(); 
} 
};

87
void tick() { 
//тут много кода, не имеющего сейчас значения
 
if (requested.get() > 0 && allHaveValues) { 
try { 
// всем потокам есть что zip’ать 
child.onNext(zipFunction.call(vs));
}
// еще много кода и скобочки

88
void tick() { 
 
try { 
}

89
void tick() { 
 
try { 
}

О количестве элементов

92
Количество элементов

92

• áîëüøå ýëåìåíòîâ – áîëüøå ìóñîðà
92

• RxJava ïîñòîÿííî âñå êîïèðóåò
92

• âàæíî:
92

• âàæíî:
• íå ïàíèêîâàòü
92

• âàæíî:
• íå ïàíèêîâàòü
• çàáîòèòüñÿ î GC
92

• «×òî ñ GC?» : ñàìûé æàðêèé âîïðîñ
93
Не паниковать

• êîïèðîâàíèå òîëüêî ïðè íîòèôèêàöèÿõ
93

• êîïèðîâàíèå òîëüêî ïðè íîòèôèêàöèÿõ
• âñå îïòèìèçèðîâàííî
93

94
locationUpdates() 
.distinctUntilChanged() 
.subscribe();

95
.subscribe();

96
.subscribe();
touchEvents(view) 
.filter(e -> e.x > minWidth && e.y > minHeight) 
.doOnNext(this ::processEvents) 
.subscribe();

97
.subscribe();
.filter(e -> e.x > minWidth && e.y > minHeight) 
.doOnNext(this ::processEvents) 
.subscribe();

98
nameEditTextChanges 
.map(this ::prepareForSending) 
.map(this ::sendName) 
.map(this ::cacheAndModify);

99
.map(this ::prepareForSending) //раз 

100
.map(this ::sendName) // два 

101
.map(this ::sendName) // два 
.map(this ::cacheAndModify); // три

102
.debounce(500, TimeUnit.MILLISECONDS) 

• áåðåæåò GC
103
debounce

• áåðåæåò òðàôèê ïîëüçîâàòåëÿ
103
debounce

• áåðåæåò òðàôèê ïîëüçîâàòåëÿ
• áåðåæåò íàñ îò BackPressure
103
debounce

• îòäàþùèé òðåä äàåò ìíîãî
104
Backpressure

• ïðèíèìàþùèé òðåä íå óñïåâàåò
104
Backpressure

• â ìíîãîïîòî÷íîé ñðåäå ìíîãîâåðîÿòíî
104
Backpressure

• â ìíîãîïîòî÷íîé ñðåäå ìíîãîâåðîÿòíî
• ïåðâûé ïðèçíàê – observeOn
104
Backpressure

106
events ﬁlter
.filter(e -> e.x > minWidth)

107
events ﬁlter map
.filter(e -> e.x > minWidth) 
.map(this ::normalize)

108
events ﬁlter map observeOn
.map(this ::normalize) 
.observeOn(networkScheduler)

109
 
map

110
.map(this ::doMotionRequest) 
map map

111
.subscribe()
map map subscriber

112
.subscribe()
map map subscriber

113
.subscribe()
map map subscriber

114
.subscribe()
map map subscriber

115
map map subscriber
.subscribe()

116
map map subscriber
.subscribe()

117
map map subscriber
.subscribe()

118
map map subscriber
.subscribe()

119
map map subscriber
.subscribe()

120
map map subscriber
.subscribe()

121
map map subscriber
.subscribe()

122
map map subscriber
.subscribe()

123
map map subscriber
.subscribe()

124
map map subscriber
.subscribe()

125
map map subscriber
2
.subscribe()

126
map map subscriber
2
.subscribe()

127
map map subscriber
2
.subscribe()

128
map map subscriber
2
.subscribe()

129
map map subscriber
3
.subscribe()

130
map map subscriber
3
.subscribe()

131
map map subscriber
3
Устал
.subscribe()

132
map map subscriber
3
Устал
.subscribe()

133
map map subscriber
4
rx.exceptions.MissingBackpressureException

134
Observable.zip( 
Observable.interval(10, TimeUnit.MILLISECONDS), 
(r1, r2) -> r1 * r2 
).subscribe();

135
Observable.zip( 
(r1, r2) -> r1 * r2 
).subscribe();

136
Observable.zip( 
(r1, r2) -> r1 * r2 
).subscribe();

137
Observable.zip( 
(r1, r2) -> r1 * r2 
).subscribe();

138
Observable.zip( 
(r1, r2) -> r1 * r2 
).subscribe();
rx.exceptions.MissingBackpressureException

139
Борьба с Backpressure

• debounce, throttle
139

• window, buffer
139

• window, buffer
• onBackpressureBuffer
139

• window, buffer
• onBackpressureBuffer
• onBackpressureDrop
139

Âñåãäà äóìàéòå î òîì,
ñêîëüêî ýëåìåíòîâ âàì íóæíî
îò Observable

Êàê äóìàòü, èñïîëüçóÿ RxJava?

• íå áîéñÿ ðàñøèðÿòü ôðåéìâîðê
145
Как инженер

• íå áîéñÿ ðàñøèðÿòü ôðåéìâîðê
• ïîíèìàé, êàê îí ðàáîòàåò âíóòðè
145
Как инженер

• doOnNext == ñàéä ýôôåêò
146
DoOnNextAsync

• íå áëîêèðîâàòü âûïîëíåíèå ðîäèòåëÿ
146
DoOnNextAsync

• áûë ïðèâÿçàí ê æèçíåííîìó öèêëó ðîäèòåëÿ
146
DoOnNextAsync

• áûë ïðèâÿçàí ê æèçíåííîìó öèêëó ðîäèòåëÿ
• íå ÷åðåç Subjects
146
DoOnNextAsync

147
userDbChanges 
.doOnNext(resp -> { 
globalSubscription = createCacheObs(resp)
.subscribe(); 
}) 
.map(this ::doAnotherRequest);

148
userDbChanges 
.doOnNext(resp -> { 
globalSubscription = createCacheObs(resp)
.subscribe(); 
}) 

149
userDbChanges 
.lift(new DoOnNextAsync <>(this ::cacheObs)) 

150
userDbChanges 
.lift(new DoOnNextAsync <>(this ::cacheObs)) 

151
class DoOnNextAsync<F, T> implements Observable.Operator<F, F> { 
private final Func1<F, Observable<T >> nested; 
 
public DoOnNextAsync(Func1<F, Observable<T >> func) { 
this.nested = func; 
} 
//больше кода дальше

152
 
} 

153
 
} 

154
@Override 
public Subscriber<? super F> call(Subscriber<? super F> subscriber) { 
return new Subscriber<F>() { 
 
@Override 
public void onNext(F next) { 
if (!subscriber.isUnsubscribed()) {
Subscription s = nested.call(next).subscribe(); 
subscriber.add(s); 
} 
}
//тривиальные onError и onCompleted здесь 
}; 
}

155
@Override 
 
@Override 
} 
}
}; 
}

156
@Override 
 
@Override 
} 
}
}; 
}

157
@Override 
 
@Override 
} 
}
}; 
}

158
@Override 
 
@Override 
} 
}
}; 
}

• Operator, lift,
• subscribeOn, observeOn
• nest, defer, create
159
Понимай, как работает внутри

161
Думать реактивно

• ñîåäèíÿòü èìïåðàòèâíûé è ðåàêòèâíûé ìèð
161

• íå èñïîëüçîâàòü ñàáäæåêòû
161

• íå èñïîëüçîâàòü ñàáäæåêòû
• îïèñûâàòü, «êàê äåëàòü», à íå «÷òî äåëàòü»
161

• íàó÷èòü RecycerView àâòîïîäãðóçêå
162
AutoLoadingRecyclerView

• ñäåëàòü ñ ïîìîùüþ RxJava
162

• ñäåëàòü ñ ïîìîùüþ RxJava
• â ðåàêòèâíîì ñòèëå
162

163
public class AutoLoadingRecyclerView<T> extends RecyclerView { 
 
protected PublishSubject<Pair<Integer, Integer >> scrollLoadingChannel = 
PublishSubject.create(); 
 
protected void startScrollingChannel() { 
addOnScrollListener(new RecyclerView.OnScrollListener() { 
@Override 
public void onScrolled(RecyclerView recyclerView, int dx, int dy) { 
if (shouldLoad()) { 
int offset = getAdapter().getItemCount(); 
scrollLoadingChannel.onNext(new Pair(offset, limit)); 
} 
} 
}); 
}

164
 
 
@Override 
} 
} 
}); 
}

165
 
 
@Override 
} 
} 
}); 
}

166
 
 
@Override 
} 
} 
}); 
}

167
 
 
@Override 
} 
} 
}); 
}

168
 
protected PublishSubject<OffsetAndLimit> scrollLoadingChannel = 
protected Subscription loadNewItemsSubscription; 
protected Subscription subscribeToLoadingChannelSubscription;

169
 

170
 

171
private static Observable<Integer> 
getScrollObservable(RecyclerView recyclerView, int limit) {
 
return Observable.create(subscriber -> { 
final RecyclerView.OnScrollListener sl = new RecyclerView.OnScrollListener() { 
@Override 
if (!subscriber.isUnsubscribed() && shouldLoad()) { 
subscriber.onNext(recyclerView.getAdapter().getItemCount()); 
} 
} 
}; 
recyclerView.addOnScrollListener(sl); 
subscriber.add(Subscriptions.create(() -> recyclerView.removeOnScrollListener(sl))); 
}); 
}

172
 
@Override 
} 
} 
}; 
}); 
}

173
 
@Override 
} 
} 
}; 
}); 
}

174
 
@Override 
} 
} 
}; 
}); 
}

175
 
@Override 
} 
} 
}; 
}); 
}

176
 
@Override 
} 
} 
}; 
}); 
}

177
getScrollObservable() 
.switchMap(offset -> getLoadingObservable(offset)) 
.subscribeOn(Schedulers 
.from(BackgroundExecutor.getSafeBackgroundExecutor()) 
) 
.observeOn(AndroidSchedulers.mainThread()) 
.subscribe(loadNewItemsSubscriber);

178
) 

179
) 

180
) 

181
) 

182
) 

183

• èñïîëüçîâàòü ñòàíäàðòíûå ñðåäñòâà RxJava
183

• íî íå ñàáäæåêòû
183

• ïðè íåîáõîäèìîñòè – ïèñàòü ñâîå
183

• îáîðà÷èâàòü ñîñòîÿíèå â Observable
183

• îáîðà÷èâàòü ñîñòîÿíèå â Observable
• ñòàðàòüñÿ è íå ñäàâàòüñÿ
183

• äóìàòü î
184
The Art of Rx

• äóìàòü î
• î êîíòðàêòàõ
184
The Art of Rx

• äóìàòü î
• î òðåäàõ
184
The Art of Rx

• äóìàòü î
• î òðåäàõ
• î êîëè÷åñòâå ýëåìåíòîâ
184
The Art of Rx

• äóìàòü î
• î òðåäàõ
• äóìàòü êàê
184
The Art of Rx

• äóìàòü î
• î òðåäàõ
• èíæåíåð
184
The Art of Rx

• äóìàòü î
• î òðåäàõ
• èíæåíåð
• ðåàêòèâíî
184
The Art of Rx

Ñòàòü ïðîôåññèîíàëîì – íåïðîñòî

Äóìàéòå ìíîãî
Î âàæíûõ âåùàõ

189
Ìàëüêîâ Ìàòâåé
Ñïàñèáî
matveyka_jj

The Art of Rx

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