Android RxJava使用介绍(四) RxJava的操作符

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:
Android RxJava使用介绍(四) RxJava的操作符_第1张图片
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);
            }
        });

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);
            }
        });

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);
                    }
                });
            }
        });

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:
Android RxJava使用介绍(四) RxJava的操作符_第2张图片

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);
                    }
                });

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);
                    }
                });

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:
Android RxJava使用介绍(四) RxJava的操作符_第3张图片

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);
            }
        });

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:
Android RxJava使用介绍(四) RxJava的操作符_第4张图片

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);
            }
        });

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:
Android RxJava使用介绍(四) RxJava的操作符_第5张图片

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);
            }
        });

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:
Android RxJava使用介绍(四) RxJava的操作符_第6张图片
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);
            }
        });

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);
            }
        });

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、StackOverflowError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:
Android RxJava使用介绍(四) RxJava的操作符_第7张图片

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);
            }
        });

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:
Android RxJava使用介绍(四) RxJava的操作符_第8张图片

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);
            }
        });

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:
Android RxJava使用介绍(四) RxJava的操作符_第9张图片

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);
            }
        });

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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