Android RxJava使用介绍（四） RxJava的操作符
标签： android操作符2015-07-18 23:56 8794人阅读 评论(18)收藏举报 本文章已收录于：
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本篇文章继续介绍以下类型的操作符
- Combining Observables(Observable的组合操作符)
- Error Handling Operators(Observable的错误处理操作符)
Combining Observables(Observable的组合操作符)
combineLatest操作符
combineLatest操作符把两个Observable产生的结果进行合并，合并的结果组成一个新的Observable。这两个Observable中任意一个Observable产生的结果，都和另一个Observable最后产生的结果，按照一定的规则进行合并。流程图如下：
调用例子如下:
//产生0,5,10,15,20数列
Observable<Long> observable1 = Observable.timer(0, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<Long, Long>() {
@Override
public Long call(Long aLong) {
return aLong * 5;
}
}).take(5);
//产生0,10,20,30,40数列
Observable<Long> observable2 = Observable.timer(500, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<Long, Long>() {
@Override
public Long call(Long aLong) {
return aLong * 10;
}
}).take(5);
Observable.combineLatest(observable1, observable2, new Func2<Long, Long, Long>() {
@Override
public Long call(Long aLong, Long aLong2) {
return aLong+aLong2;
}
}).subscribe(new Subscriber<Long>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Long aLong) {
System.out.println("Next: " + aLong);
}
});
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运行结果如下：
Next: 0
Next: 5
Next: 15
Next: 20
Next: 30
Next: 35
Next: 45
Next: 50
Next: 60
Sequence complete.
join操作符
join操作符把类似于combineLatest操作符，也是两个Observable产生的结果进行合并，合并的结果组成一个新的Observable，但是join操作符可以控制每个Observable产生结果的生命周期，在每个结果的生命周期内，可以与另一个Observable产生的结果按照一定的规则进行合并，流程图如下：
join方法的用法如下：
observableA.join(observableB,
observableA产生结果生命周期控制函数，
observableB产生结果生命周期控制函数，
observableA产生的结果与observableB产生的结果的合并规则）
调用例子如下：
//产生0,5,10,15,20数列
Observable<Long> observable1 = Observable.timer(0, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<Long, Long>() {
@Override
public Long call(Long aLong) {
return aLong * 5;
}
}).take(5);
//产生0,10,20,30,40数列
Observable<Long> observable2 = Observable.timer(500, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<Long, Long>() {
@Override
public Long call(Long aLong) {
return aLong * 10;
}
}).take(5);
observable1.join(observable2, new Func1<Long, Observable<Long>>() {
@Override
public Observable<Long> call(Long aLong) {
//使Observable延迟600毫秒执行
return Observable.just(aLong).delay(600, TimeUnit.MILLISECONDS);
}
}, new Func1<Long, Observable<Long>>() {
@Override
public Observable<Long> call(Long aLong) {
//使Observable延迟600毫秒执行
return Observable.just(aLong).delay(600, TimeUnit.MILLISECONDS);
}
}, new Func2<Long, Long, Long>() {
@Override
public Long call(Long aLong, Long aLong2) {
return aLong + aLong2;
}
}).subscribe(new Subscriber<Long>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Long aLong) {
System.out.println("Next: " + aLong);
}
});
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运行结果如下：
Next: 0
Next: 5
Next: 15
Next: 20
Next: 30
Next: 35
Next: 45
Next: 50
Next: 60
Sequence complete.
groupJoin操作符
groupJoin操作符非常类似于join操作符，区别在于join操作符中第四个参数的传入函数不一致，其流程图如下： 
调用例子如下：
//产生0,5,10,15,20数列
Observable<Long> observable1 = Observable.timer(0, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<Long, Long>() {
@Override
public Long call(Long aLong) {
return aLong * 5;
}
}).take(5);
//产生0,10,20,30,40数列
Observable<Long> observable2 = Observable.timer(500, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<Long, Long>() {
@Override
public Long call(Long aLong) {
return aLong * 10;
}
}).take(5);
observable1.groupJoin(observable2, new Func1<Long, Observable<Long>>() {
@Override
public Observable<Long> call(Long aLong) {
return Observable.just(aLong).delay(1600, TimeUnit.MILLISECONDS);
}
}, new Func1<Long, Observable<Long>>() {
@Override
public Observable<Long> call(Long aLong) {
return Observable.just(aLong).delay(600, TimeUnit.MILLISECONDS);
}
}, new Func2<Long, Observable<Long>, Observable<Long>>() {
@Override
public Observable<Long> call(Long aLong, Observable<Long> observable) {
return observable.map(new Func1<Long, Long>() {
@Override
public Long call(Long aLong2) {
return aLong + aLong2;
}
});
}
}).subscribe(new Subscriber<Observable<Long>>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Observable<Long> observable) {
observable.subscribe(new Subscriber<Long>() {
@Override
public void onCompleted() {
}
@Override
public void onError(Throwable e) {
}
@Override
public void onNext(Long aLong) {
System.out.println("Next: " + aLong);
}
});
}
});
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运行结果如下：
Next: 0
Next: 5
Next: 10
Next: 15
Next: 20
Next: 25
Next: 30
Next: 35
Next: 40
Next: 45
Next: 50
Next: 60
Next: 55
Sequence complete.
merge操作符
merge操作符是按照两个Observable提交结果的时间顺序，对Observable进行合并，如ObservableA每隔500毫秒产生数据为0,5,10,15,20；而ObservableB每隔500毫秒产生数据0,10,20,30,40，其中第一个数据延迟500毫秒产生，最后合并结果为：0,0,5,10,10,20,15,30,20,40;其流程图如下：
调用例子如下：
//产生0,5,10,15,20数列
Observable<Long> observable1 = Observable.timer(0, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<Long, Long>() {
@Override
public Long call(Long aLong) {
return aLong * 5;
}
}).take(5);
//产生0,10,20,30,40数列
Observable<Long> observable2 = Observable.timer(500, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<Long, Long>() {
@Override
public Long call(Long aLong) {
return aLong * 10;
}
}).take(5);
Observable.merge(observable1, observable2)
.subscribe(new Subscriber<Long>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Long aLong) {
System.out.println("Next:" + aLong);
}
});
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运行结果如下：
Next:0
Next:0
Next:5
Next:10
Next:10
Next:20
Next:15
Next:30
Next:20
Next:40
Sequence complete.
mergeDelayError操作符
从merge操作符的流程图可以看出，一旦合并的某一个Observable中出现错误，就会马上停止合并，并对订阅者回调执行onError方法，而mergeDelayError操作符会把错误放到所有结果都合并完成之后才执行，其流程图如下：
调用例子如下：
//产生0,5,10数列,最后会产生一个错误
Observable<Long> errorObservable = Observable.error(new Exception("this is end!"));
Observable < Long > observable1 = Observable.timer(0, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<Long, Long>() {
@Override
public Long call(Long aLong) {
return aLong * 5;
}
}).take(3).mergeWith(errorObservable.delay(3500, TimeUnit.MILLISECONDS));
//产生0,10,20,30,40数列
Observable<Long> observable2 = Observable.timer(500, 1000, TimeUnit.MILLISECONDS)
.map(new Func1<Long, Long>() {
@Override
public Long call(Long aLong) {
return aLong * 10;
}
}).take(5);
Observable.mergeDelayError(observable1, observable2)
.subscribe(new Subscriber<Long>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Long aLong) {
System.out.println("Next:" + aLong);
}
});
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运行结果如下：
Next:0
Next:0
Next:5
Next:10
Next:10
Next:20
Next:30
Next:40
Error: this is end!
startWith操作符
startWith操作符是在源Observable提交结果之前，插入指定的某些数据，其流程图如下： 
调用例子如下：
Observable.just(10,20,30).startWith(2, 3, 4).subscribe(new Subscriber<Integer>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
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运行结果如下：
Next:2
Next:3
Next:4
Next:10
Next:20
Next:30
Sequence complete.
switchOnNext操作符
switchOnNext操作符是把一组Observable转换成一个Observable，转换规则为：对于这组Observable中的每一个Observable所产生的结果，如果在同一个时间内存在两个或多个Observable提交的结果，只取最后一个Observable提交的结果给订阅者，其流程图如下：
调用例子如下：
//每隔500毫秒产生一个observable
Observable<Observable<Long>> observable = Observable.timer(0, 500, TimeUnit.MILLISECONDS).map(new Func1<Long, Observable<Long>>() {
@Override
public Observable<Long> call(Long aLong) {
//每隔200毫秒产生一组数据（0,10,20,30,40)
return Observable.timer(0, 200, TimeUnit.MILLISECONDS).map(new Func1<Long, Long>() {
@Override
public Long call(Long aLong) {
return aLong * 10;
}
}).take(5);
}
}).take(2);
Observable.switchOnNext(observable).subscribe(new Subscriber<Long>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Long aLong) {
System.out.println("Next:" + aLong);
}
});
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运行结果如下：
Next:0
Next:10
Next:20
Next:0
Next:10
Next:20
Next:30
Next:40
Sequence complete.
zip操作符
zip操作符是把两个observable提交的结果，严格按照顺序进行合并，其流程图如下： 
调用例子如下：
Observable<Integer> observable1 = Observable.just(10,20,30);
Observable<Integer> observable2 = Observable.just(4, 8, 12, 16);
Observable.zip(observable1, observable2, new Func2<Integer, Integer, Integer>() {
@Override
public Integer call(Integer integer, Integer integer2) {
return integer + integer2;
}
}).subscribe(new Subscriber<Integer>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
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运行结果如下：
Next:14
Next:28
Next:42
Sequence complete.
Error Handling Operators(Observable的错误处理操作符)
onErrorReturn操作符
onErrorReturn操作符是在Observable发生错误或异常的时候（即将回调oError方法时），拦截错误并执行指定的逻辑，返回一个跟源Observable相同类型的结果，最后回调订阅者的onComplete方法，其流程图如下：
调用例子如下：
Observable<Integer> observable = Observable.create(new Observable.OnSubscribe<Integer>() {
@Override
public void call(Subscriber<? super Integer> subscriber) {
if (subscriber.isUnsubscribed()) return;
//循环输出数字
try {
for (int i = 0; i < 10; i++) {
if (i == 4) {
throw new Exception("this is number 4 error！");
}
subscriber.onNext(i);
}
subscriber.onCompleted();
} catch (Exception e) {
subscriber.onError(e);
}
}
});
observable.onErrorReturn(new Func1<Throwable, Integer>() {
@Override
public Integer call(Throwable throwable) {
return 1004;
}
}).subscribe(new Subscriber<Integer>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
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运行结果如下：
Next:0
Next:1
Next:2
Next:3
Next:1004
Sequence complete.
onErrorResumeNext操作符
onErrorResumeNext操作符跟onErrorReturn类似，只不过onErrorReturn只能在错误或异常发生时只返回一个和源Observable相同类型的结果，而onErrorResumeNext操作符是在错误或异常发生时返回一个Observable，也就是说可以返回多个和源Observable相同类型的结果，其流程图如下：
调用例子如下：
Observable<Integer> observable = Observable.create(new Observable.OnSubscribe<Integer>() {
@Override
public void call(Subscriber<? super Integer> subscriber) {
if (subscriber.isUnsubscribed()) return;
//循环输出数字
try {
for (int i = 0; i < 10; i++) {
if (i == 4) {
throw new Exception("this is number 4 error！");
}
subscriber.onNext(i);
}
subscriber.onCompleted();
} catch (Exception e) {
subscriber.onError(e);
}
}
});
observable.onErrorResumeNext(new Func1<Throwable, Observable<? extends Integer>>() {
@Override
public Observable<? extends Integer> call(Throwable throwable) {
return Observable.just(100,101, 102);
}
}).subscribe(new Subscriber<Integer>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
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运行结果如下：
Next:0
Next:1
Next:2
Next:3
Next:100
Next:101
Next:102
Sequence complete.
onExceptionResumeNext操作符
onExceptionResumeNext操作符和onErrorResumeNext操作符类似，不同的地方在于onErrorResumeNext操作符是当Observable发生错误或异常时触发，而onExceptionResumeNext是当Observable发生异常时才触发。
这里要普及一个概念就是，Java的异常分为错误（error）和异常（exception）两种，它们都是继承于Throwable类。
错误（error）一般是比较严重的系统问题，比如我们经常遇到的OutOfMemoryError、*Error等都是错误。错误一般继承于Error类，而Error类又继承于Throwable类，如果需要捕获错误，需要使用try..catch(Error e)或者try..catch(Throwable e)句式。使用try..catch(Exception e)句式无法捕获错误
异常（Exception）也是继承于Throwable类，一般是根据实际处理业务抛出的异常，分为运行时异常（RuntimeException）和普通异常。普通异常直接继承于Exception类，如果方法内部没有通过try..catch句式进行处理，必须通过throws关键字把异常抛出外部进行处理（即checked异常）；而运行时异常继承于RuntimeException类，如果方法内部没有通过try..catch句式进行处理，不需要显式通过throws关键字抛出外部，如IndexOutOfBoundsException、NullPointerException、ClassCastException等都是运行时异常，当然RuntimeException也是继承于Exception类，因此是可以通过try..catch(Exception e)句式进行捕获处理的。
onExceptionResumeNext流程图如下： 
调用例子如下：
Observable<Integer> observable = Observable.create(new Observable.OnSubscribe<Integer>() {
@Override
public void call(Subscriber<? super Integer> subscriber) {
if (subscriber.isUnsubscribed()) return;
//循环输出数字
try {
for (int i = 0; i < 10; i++) {
if (i == 4) {
throw new Exception("this is number 4 error！");
}
subscriber.onNext(i);
}
subscriber.onCompleted();
} catch (Throwable e) {
subscriber.onError(e);
}
}
});
observable.onExceptionResumeNext(Observable.just(100, 101, 102)).subscribe(new Subscriber<Integer>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
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运行结果如下：
Next:0
Next:1
Next:2
Next:3
Next:100
Next:101
Next:102
Sequence complete.
retry操作符
retry操作符是当Observable发生错误或者异常时，重新尝试执行Observable的逻辑，如果经过n次重新尝试执行后仍然出现错误或者异常，则最后回调执行onError方法；当然如果源Observable没有错误或者异常出现，则按照正常流程执行。其流程图如下：
调用例子如下：
Observable<Integer> observable = Observable.create(new Observable.OnSubscribe<Integer>() {
@Override
public void call(Subscriber<? super Integer> subscriber) {
if (subscriber.isUnsubscribed()) return;
//循环输出数字
try {
for (int i = 0; i < 10; i++) {
if (i == 4) {
throw new Exception("this is number 4 error！");
}
subscriber.onNext(i);
}
subscriber.onCompleted();
} catch (Throwable e) {
subscriber.onError(e);
}
}
});
observable.retry(2).subscribe(new Subscriber<Integer>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
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运行结果如下：
Next:0
Next:1
Next:2
Next:3
Next:0
Next:1
Next:2
Next:3
Next:0
Next:1
Next:2
Next:3
Error: this is number 4 error！
retryWhen操作符
retryWhen操作符类似于retry操作符，都是在源observable出现错误或者异常时，重新尝试执行源observable的逻辑，不同在于retryWhen操作符是在源Observable出现错误或者异常时，通过回调第二个Observable来判断是否重新尝试执行源Observable的逻辑，如果第二个Observable没有错误或者异常出现，则就会重新尝试执行源Observable的逻辑，否则就会直接回调执行订阅者的onError方法。其流程图如下：
调用例子如下：
Observable<Integer> observable = Observable.create(new Observable.OnSubscribe<Integer>() {
@Override
public void call(Subscriber<? super Integer> subscriber) {
System.out.println("subscribing");
subscriber.onError(new RuntimeException("always fails"));
}
});
observable.retryWhen(new Func1<Observable<? extends Throwable>, Observable<?>>() {
@Override
public Observable<?> call(Observable<? extends Throwable> observable) {
return observable.zipWith(Observable.range(1, 3), new Func2<Throwable, Integer, Integer>() {
@Override
public Integer call(Throwable throwable, Integer integer) {
return integer;
}
}).flatMap(new Func1<Integer, Observable<?>>() {
@Override
public Observable<?> call(Integer integer) {
System.out.println("delay retry by " + integer + " second(s)");
//每一秒中执行一次
return Observable.timer(integer, TimeUnit.SECONDS);
}
});
}
}).subscribe(new Subscriber<Integer>() {
@Override
public void onCompleted() {
System.out.println("Sequence complete.");
}
@Override
public void onError(Throwable e) {
System.err.println("Error: " + e.getMessage());
}
@Override
public void onNext(Integer value) {
System.out.println("Next:" + value);
}
});
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运行结果如下：
subscribing
delay retry by 1 second(s)
subscribing
delay retry by 2 second(s)
subscribing
delay retry by 3 second(s)
subscribing
Sequence complete.
好了，先介绍这么多，下回继续介绍其他的操作符，敬请期待！
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