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RxJava操作符源碼傳送門

• https://github.com/xiehui999/fuseProgram

在上篇文章RxJava操作符系列一我們介紹的操作符幾乎都是創(chuàng)建被觀察者的操作符，那么今天的這篇文章就介紹一下經(jīng)常用到的轉(zhuǎn)換操作符。話不多說，開始上車。

Map

該操作符是對原始Observable發(fā)射的每一項數(shù)據(jù)運用一個函數(shù)，然后返回一個發(fā)射這些結果的Observable。

例如我們有一個整形數(shù)組的數(shù)據(jù)，當大于5時輸出為true，則代碼實現(xiàn)

Integer[] integers = {0, 9, 6, 4, 8}; 
        Observable.from(integers).map(new Func1() { 
            @Override 
            public Boolean call(Integer integer) { 
                Log.e(TAG, "call: "+integer); 
                return (integer > 5); 
            } 
        }).subscribe(new Subscriber() { 
            @Override 
            public void onCompleted() { 
                Log.e(TAG, "onCompleted: "); 
            } 
  
            @Override 
            public void onError(Throwable e) { 
                Log.e(TAG, "onError: "); 
            } 
  
            @Override 
            public void onNext(Boolean aBoolean) { 
                Log.e(TAG, "onNext: "+aBoolean); 
            } 
        });  

日志輸出信息

call: 0 
onNext: false 
call: 9 
onNext: true 
call: 6 
onNext: true 
call: 4 
onNext: false 
call: 8 
onNext: true 
onCompleted:  

對于map,他可以將將數(shù)據(jù)源變換為你想要的類型，比如，你想獲取有一個Student對象(里面age，name屬性)那么我們可以通過map只獲取name。接下來。我們再舉個例子，我們根據(jù)一個圖片路徑獲取圖片并將圖片設置到ImageView,然后將ImageView加的我們的布局中。 

String path = Environment.getExternalStorageDirectory()+ File.separator+"aaa.jpg"; 
        Observable.just(path) 
                .subscribeOn(Schedulers.io()) 
                .map(new Func1() { 
                    @Override 
                    public Bitmap call(String s) { 
                        Bitmap bitmap = BitmapFactory.decodeFile(s); 
                        Log.e(TAG, "call: Bitmap"+bitmap); 
                        return bitmap; 
                    } 
                }).map(new Func1() { 
            @Override 
            public ImageView call(Bitmap bitmap) { 
                Log.e(TAG, "call: ImageView"); 
                ImageView imageView = new ImageView(getActivity()); 
                LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT); 
                imageView.setLayoutParams(params); 
                imageView.setImageBitmap(bitmap); 
                return imageView; 
            } 
        }).observeOn(AndroidSchedulers.mainThread()) 
                .subscribe(new Subscriber() { 
                    @Override 
                    public void onCompleted() { 
                        Log.e(TAG, "onCompleted: "); 
                    } 
                    @Override 
                    public void onError(Throwable e) { 
                        Log.e(TAG, "onError: "); 
                    } 
  
                    @Override 
                    public void onNext(ImageView imageView) { 
                        Log.e(TAG, "onNext: "); 
                        layout.addView(imageView); 
                    } 
                });  

Cast

該操作符就是做一些強制類型轉(zhuǎn)換操作的。例如，當我們在頁面跳轉(zhuǎn)時數(shù)據(jù)對象往往是序列化的，當我們在新的頁面收到數(shù)據(jù)后就要強制轉(zhuǎn)換為我們想要的類型。cast操作符也可以實現(xiàn)這樣的功能。如下

Observable.just(serializable).cast(FileInfo.class).subscribe(new Subscriber() { 
            @Override 
            public void onCompleted() { 
                Log.e(TAG, "onCompleted: " ); 
            } 
  
            @Override 
            public void onError(Throwable e) { 
                Log.e(TAG, "onError: " ); 
            } 
  
            @Override 
            public void onNext(FileInfo fileInfo) { 
                Log.e(TAG, "onNext: "+fileInfo.toString()); 
                tv1.append("\n"+fileInfo.toString()); 
            } 
        });  

不過在該操作符實際用途并沒有那么的廣泛，很少用到，當然這個操作符也可以達到java 中instanceof相同的作用，用于類型檢查，當不是該類型就會執(zhí)行onError()方法。

FlatMap

該操作符與map操作符的區(qū)別是它將一個發(fā)射數(shù)據(jù)的Observable變換為多個Observables，然后將它們發(fā)射的數(shù)據(jù)合并后放進一個單獨的Observable.

Integer[] integers = {1, 2, 3}; 
        Observable.from(integers).flatMap(new Func1>() { 
            @Override 
            public Observable call(final Integer integer) { 
                return Observable.create(new Observable.OnSubscribe() { 
                    @Override 
                    public void call(Subscriber super String> subscriber) { 
                        Log.e(TAG, "call: FlatMap " + Thread.currentThread().getName()); 
                        try { 
                            Thread.sleep(200); 
                            subscriber.onNext(integer + 100 + " FlatMap"); 
                            subscriber.onCompleted(); 
                        } catch (InterruptedException e) { 
                            e.printStackTrace(); 
                            subscriber.onError(e); 
                        } 
                    } 
                }).subscribeOn(Schedulers.newThread()); 
            } 
        }).observeOn(AndroidSchedulers.mainThread()) 
                .subscribe(new Subscriber() { 
                    @Override 
                    public void onCompleted() { 
                        Log.e(TAG, "onCompleted: FlatMap"); 
                    } 
  
                    @Override 
                    public void onError(Throwable e) { 
                        Log.e(TAG, "onError: FlatMap"); 
                    } 
  
                    @Override 
                    public void onNext(String s) { 
                        Log.e(TAG, "onNext: FlatMap " + s); 
                    } 
                });  

打印日志信息 

call: FlatMap RxNewThreadScheduler-2 
call: FlatMap RxNewThreadScheduler-3 
call: FlatMap RxNewThreadScheduler-4 
onNext: FlatMap 101 FlatMap 
onNext: FlatMap 102 FlatMap 
onNext: FlatMap 103 FlatMap 
onCompleted: FlatMap  

ConcatMap

該操作符是類似于最簡單版本的flatMap，但是它按次序連接而不是合并那些生成的Observables，然后產(chǎn)生自己的數(shù)據(jù)序列.將上述flatMap代碼更改如下 

Integer[] integers = {1, 2, 3}; 
        Observable.from(integers).concatMap(new Func1>() { 
            @Override 
            public Observable call(final Integer integer) { 
                return Observable.create(new Observable.OnSubscribe() { 
                    @Override 
                    public void call(Subscriber super String> subscriber) { 
                        Log.e(TAG, "call:2 ConcatMap " + Thread.currentThread().getName()); 
                        try { 
                            Thread.sleep(200); 
                            subscriber.onNext(integer + 100 + " ConcatMap"); 
                            subscriber.onCompleted(); 
                        } catch (InterruptedException e) { 
                            e.printStackTrace(); 
                            subscriber.onError(e); 
                        } 
                    } 
                }).subscribeOn(Schedulers.newThread()); 
            } 
        }).observeOn(AndroidSchedulers.mainThread()) 
                .subscribe(new Subscriber() { 
                    @Override 
                    public void onCompleted() { 
                        Log.e(TAG, "onCompleted: ConcatMap"); 
                    } 
  
                    @Override 
                    public void onError(Throwable e) { 
                        Log.e(TAG, "onError: ConcatMap"); 
                    } 
  
                    @Override 
                    public void onNext(String s) { 
                        Log.e(TAG, "onNext: ConcatMap " +s); 
                    } 
                });  

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