RxJava 转换操作符 flatMap

flatMap操作符是把Observable产生的结果转换成多个Observable,然后又直接把这些Observable转换一个Observable,并依次提交产生的结果给订阅者

规律:源Observable 传入flatMap对应参数，在flatMap中返回自定义的Observable

例子:扫描文件:

private void flatMap() {
        Observable.just(getApplicationContext().getExternalCacheDir()).flatMap(new Func1<File, Observable<File>>() {
            @Override
            public Observable<File> call(File file) {
                return listFiles(file);
            }
        }).subscribe(new Action1<File>() {
            @Override
            public void call(File file) {
                LogUtils.d("------>:" + file.getAbsolutePath());
            }
        });
    }

    private Observable<File> listFiles(File f) {
        if (f.isDirectory()) {
            return Observable.from(f.listFiles()).flatMap(new Func1<File, Observable<File>>() {
                @Override
                public Observable<File> call(File file) {
                    return listFiles(file);
                }
            });
        } else {
            return Observable.just(f);
        }
    }

扫描结果:

02-24 16:13:02.038 24715-24715/? D/----->: ------>:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/.text
02-24 16:13:02.038 24715-24715/? D/----->: ------>:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/0.text
02-24 16:13:02.038 24715-24715/? D/----->: ------>:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/1.text
02-24 16:13:02.038 24715-24715/? D/----->: ------>:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/2.text
02-24 16:13:02.038 24715-24715/? D/----->: ------>:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/3.text
02-24 16:13:02.038 24715-24715/? D/----->: ------>:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/4.text
02-24 16:13:02.048 24715-24715/? D/----->: ------>:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/5.text
02-24 16:13:02.048 24715-24715/? D/----->: ------>:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/6.text
02-24 16:13:02.048 24715-24715/? D/----->: ------>:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/7.text
02-24 16:13:02.048 24715-24715/? D/----->: ------>:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/8.text
02-24 16:13:02.048 24715-24715/? D/----->: ------>:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/9.text

flatMap和map的区别：map是将参数加工,flatMap是将源Observable变成多个Observable去处理并交给源Observable依次发送给订阅者

注意:这些新的Observable线程是默认伴随源Observable的:

private void flatMap() {
        Observable.just(getApplicationContext().getExternalCacheDir()).flatMap(new Func1<File, Observable<File>>() {
            @Override
            public Observable<File> call(File file) {
                LogUtils.d("------>Thread1:" + Thread.currentThread());
                return listFiles(file);
            }
        }).subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread()).subscribe(new Action1<File>() {
            @Override
            public void call(File file) {
                LogUtils.d("------>Thread3:" + Thread.currentThread().getName() + "   file:" + file.getAbsolutePath());
            }
        });
    }

    private Observable<File> listFiles(File f) {
        if (f.isDirectory()) {
            return Observable.from(f.listFiles()).flatMap(new Func1<File, Observable<File>>() {
                @Override
                public Observable<File> call(File file) {
                    LogUtils.d("------>Thread2:" + Thread.currentThread());
                    return listFiles(file);
                }
            });
        } else {
            return Observable.just(f);
        }
    }

线程关系:

02-24 16:27:42.118 25657-25835/? D/----->: ------>Thread1:Thread[RxCachedThreadScheduler-2,5,main]
02-24 16:27:42.118 25657-25835/? D/----->: ------>Thread2:Thread[RxCachedThreadScheduler-2,5,main]
02-24 16:27:42.118 25657-25835/? D/----->: ------>Thread2:Thread[RxCachedThreadScheduler-2,5,main]
02-24 16:27:42.118 25657-25835/? D/----->: ------>Thread2:Thread[RxCachedThreadScheduler-2,5,main]
02-24 16:27:42.128 25657-25835/? D/----->: ------>Thread2:Thread[RxCachedThreadScheduler-2,5,main]
02-24 16:27:42.128 25657-25835/? D/----->: ------>Thread2:Thread[RxCachedThreadScheduler-2,5,main]
02-24 16:27:42.128 25657-25835/? D/----->: ------>Thread2:Thread[RxCachedThreadScheduler-2,5,main]
02-24 16:27:42.128 25657-25835/? D/----->: ------>Thread2:Thread[RxCachedThreadScheduler-2,5,main]
02-24 16:27:42.128 25657-25835/? D/----->: ------>Thread2:Thread[RxCachedThreadScheduler-2,5,main]
02-24 16:27:42.138 25657-25835/? D/----->: ------>Thread2:Thread[RxCachedThreadScheduler-2,5,main]
02-24 16:27:42.138 25657-25835/? D/----->: ------>Thread2:Thread[RxCachedThreadScheduler-2,5,main]
02-24 16:27:42.138 25657-25835/? D/----->: ------>Thread2:Thread[RxCachedThreadScheduler-2,5,main]
02-24 16:27:42.138 25657-25657/? D/----->: ------>Thread3:main   file:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/.text
02-24 16:27:42.138 25657-25657/? D/----->: ------>Thread3:main   file:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/0.text
02-24 16:27:42.138 25657-25657/? D/----->: ------>Thread3:main   file:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/1.text
02-24 16:27:42.138 25657-25657/? D/----->: ------>Thread3:main   file:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/2.text
02-24 16:27:42.138 25657-25657/? D/----->: ------>Thread3:main   file:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/3.text
02-24 16:27:42.148 25657-25657/? D/----->: ------>Thread3:main   file:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/4.text
02-24 16:27:42.148 25657-25657/? D/----->: ------>Thread3:main   file:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/5.text
02-24 16:27:42.148 25657-25657/? D/----->: ------>Thread3:main   file:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/6.text
02-24 16:27:42.148 25657-25657/? D/----->: ------>Thread3:main   file:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/7.text
02-24 16:27:42.148 25657-25657/? D/----->: ------>Thread3:main   file:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/8.text
02-24 16:27:42.148 25657-25657/? D/----->: ------>Thread3:main   file:/storage/sdcard0/Android/data/com.rxandroid.test1/cache/9.text