Rxjava源碼——map操作符

作用:    將Observable所發送送的信息進行格式轉換或者處理，然後轉變爲另外一個類型，發送給Observer

思路：

一、ObservableCreate

二、ObservableMap

三、調用思路和源碼邏輯

四、生產環境代碼

五、畫圖總結

ps:

subscribe（） 是Observable中的的方法，因爲ObservableCreate和ObservableMap都繼承了Observable所以把該方法放到了這兩個類中

一、ObservableCreate

public final class ObservableCreate<T> extends Observable<T> {
    final ObservableOnSubscribe<T> source;

    public ObservableCreate(ObservableOnSubscribe<T> source) {
        this.source = source;
    }

   @Override
   void subscribe(Observer<? super T> observer) {
        subscribeActual(observer);
   }
   //

    @Override
    protected void subscribeActual(Observer<? super T> observer) {
        CreateEmitter<T> parent = new CreateEmitter<T>(observer);
        observer.onSubscribe(parent);

        source.subscribe(parent);
        
    }

    static final class CreateEmitter<T>
    extends AtomicReference<Disposable>
    implements ObservableEmitter<T>, Disposable {


        private static final long serialVersionUID = -3434801548987643227L;

        final Observer<? super T> observer;

        CreateEmitter(Observer<? super T> observer) {
            this.observer = observer;
        }

        @Override
        public void onNext(T t) {
            if (!isDisposed()) {
                observer.onNext(t);
            }
        }

        @Override
        public void onComplete() {
            observer.onComplete();
           
        }
    }
}

二、ObservableMap 

ObservableMap extends Observable{

   ObservableSource<T> source;  //指ObservableCreate
   
   public ObservableMap(ObservableSource<T> source, Function<? super T, ? extends U> function) {
    super(source);
    this.function = function;
  }

   @Override
   void subscribe(Observer<? super T> observer) {
        subscribeActual(observer);
   }
   //
@Override
public void subscribeActual(Observer<? super U> t) {
    source.subscribe(new MapObserver<T, U>(t, function));
}

static final class MapObserver<T, U> extends BasicFuseableObserver<T, U> {
    final Function<? super T, ? extends U> mapper;
    Observer<? super R> actual;

    MapObserver(Observer<? super U> actual, Function<? super T, ? extends U> mapper) {
        super(actual);
        this.mapper = mapper;
    }

    @Override
    public void onNext(T t) {
        U  v = ObjectHelper.requireNonNull(mapper.apply(t), "The mapper function returned a null value.");
        actual.onNext(v);
    }
}

---

三、分析調用流程 

1.第一塊

發起點：訂閱與map操作符操作

源碼中可以看到create() 創建了ObservableCreate

                         map() 創建了ObservableMap

                         map().subscribe(observer1) 其實是調用的 ObserbableMap的 subscribe() ——>subscribeActual()

ObserbableMap中的subscribeActual (Observer t ){

        source.subscribe(new MapObserver<T, U>(t, function));

}

發現：observer1已經被包裝成了MapObserver

source是誰？從哪裏來？？？ ：  source.subscribe(new MapObserver<T, U>(t, function)); 

---

2.第二塊

其實在ObserbableMap是調用的ObservableCreate的 map()方法創建的，代碼如下：

public final <R> Observable<R> map(Function<? super T, ? extends R> mapper) {

           return RxJavaPlugins.onAssembly(new ObservableMap<T, R>(this, mapper));

}

this : 指的是當前對象，當前對象就是ObservableCreate

ok那下一步就是調用ObservableCreate的subscribe()方法

---

3.第三塊：

ObservableCreate{

@Override
   void subscribe(Observer<? super T> observer) {
        subscribeActual(observer);
   }

@Override
    protected void subscribeActual(Observer<? super T> observer) {
        CreateEmitter<T> parent = new CreateEmitter<T>(observer);
        observer.onSubscribe(parent);

        source.subscribe(parent);
    }

}

source 是誰？ 是observableOnSubscribe1

parent 是誰？ parent是CreateEmitter的一個實例,包裹了MapObserver的對象

observableOnSubscribe1代碼：{

ObservableOnSubscribe observableOnSubscribe1 = new ObservableOnSubscribe<Integer>() {
            @Override
            public void subscribe(ObservableEmitter<Integer> emitter) throws Exception {
                emitter.onNext(1);
                emitter.onNext(2);
                emitter.onNext(3);
                emitter.onComplete();
            }
        };

      emitter.onNext(1);代碼如下：{

        public void onNext(T t) {

             observer.onNext(t); 

      }

     observer是MapObserver的一個實例被包裝在了CreateEmitter中

    observer.onNext(t); 代碼如下{     

        Observer<? super R> actual;
        public void onNext(T t) {
            U  v = ObjectHelper.requireNonNull(mapper.apply(t), "The mapper function returned a null value.");
            actual.onNext(v);
        }

       actual是實例observer1

    }

}

四、生產環境代碼

//創建一個下游 Observer
        Observer<Integer> observer1 = new Observer<Integer>() {
            @Override
            public void onSubscribe(Disposable d) {
                Log.d("donghe", "subscribe");
            }

            @Override
            public void onNext(Integer value) {
                Log.d("donghe", "" + value);
            }

            @Override
            public void onError(Throwable e) {
                Log.d("donghe", "error");
            }

            @Override
            public void onComplete() {
                Log.d("donghe", "complete");
            }
        };

        Function function1 = new Function<Integer, Object>() {

            @Override
            public Object apply(Integer integer) throws Exception {
                return null;
            }
        };

        ObservableOnSubscribe observableOnSubscribe1 = new ObservableOnSubscribe<Integer>() {
            @Override
            public void subscribe(ObservableEmitter<Integer> emitter) throws Exception {
                emitter.onNext(1);
                emitter.onNext(2);
                emitter.onNext(3);
                emitter.onComplete();
            }
        };

        //創建一個上游 Observable：
        Observable.create(observableOnSubscribe1).map(function1).subscribe(observer1);

五、調用邏輯順序