Rx中的线程切换

初学者在使用RxJava的过程中，经常搞不清Observable的事件序列和每次操作应该怎样切换线程，切换哪个线程
首先需要搞懂在RxJava 中.subscribeOn() 和 observeOn() 之间的区别：
- .subscribeOn() 用来指定Observable应该操作的调度器(Scheduler)
- .observeOn() 指定 Observable在一个指定的调度器(Scheduler)上给观察者发送通知
- 默认情况下， 事件序列操作的线程与调用.subscribe()的线程一致

没理解？

英文原文: https://medium.com/@diolor/observe-in-the-correct-thread-1939bb9bb9d2#.nn1m7lrb8
翻译: hanks
注: 不是完全翻译,添加了具体例子

例子

1.主线程 / .subscribe() 线程

在 Activity的 onCreate()(主线程) 方法中添加以下代码：

Observable.just(1,2,3)  .subscribe();

调用情况如下：

实验:

Observable.just(1,2,3)            .doOnNext(new Action1<Integer>() {                @Override public void call(Integer integer) {                    Log.i("RxThread", "doOnNext:" + integer +", run In :" + Thread.currentThread().getName() );                }            })            .subscribe(new Action1<Integer>() {                @Override public void call(Integer integer) {                    Log.i("RxThread", "get result:" + integer +", run In :" + Thread.currentThread().getName() );                }            });

输出结果:

12-06 16:14:39.225 15603-15603/com.hanks.rxsearch I/RxThread: doOnNext:1, run In :main12-06 16:14:39.225 15603-15603/com.hanks.rxsearch I/RxThread: get result:1, run In :main12-06 16:14:39.225 15603-15603/com.hanks.rxsearch I/RxThread: doOnNext:2, run In :main12-06 16:14:39.225 15603-15603/com.hanks.rxsearch I/RxThread: get result:2, run In :main12-06 16:14:39.225 15603-15603/com.hanks.rxsearch I/RxThread: doOnNext:3, run In :main12-06 16:14:39.225 15603-15603/com.hanks.rxsearch I/RxThread: get result:3, run In :main

2. .subscribeOn()

即使你在主线程中添加下面的代码，但是整段代码将运行在 .subscribeOn()定义的线程上

Observable.just(1,2,3)  .subscribeOn(Schedulers.newThread())  .subscribe();

实验:

Observable.just(1,2,3)           .doOnNext(new Action1<Integer>() {               @Override public void call(Integer integer) {                   Log.i("RxThread", "doOnNext:" + integer +", run In :" + Thread.currentThread().getName() );               }           })           .subscribeOn(Schedulers.newThread())           .subscribe(new Action1<Integer>() {               @Override public void call(Integer integer) {                   Log.i("RxThread", "get result:" + integer +", run In :" + Thread.currentThread().getName() );               }           });

输出结果:

12-06 16:13:17.717 14294-14319/com.hanks.rxsearch I/RxThread: doOnNext:1, run In :RxNewThreadScheduler-112-06 16:13:17.717 14294-14319/com.hanks.rxsearch I/RxThread: get result:1, run In :RxNewThreadScheduler-112-06 16:13:17.717 14294-14319/com.hanks.rxsearch I/RxThread: doOnNext:2, run In :RxNewThreadScheduler-112-06 16:13:17.717 14294-14319/com.hanks.rxsearch I/RxThread: get result:2, run In :RxNewThreadScheduler-112-06 16:13:17.717 14294-14319/com.hanks.rxsearch I/RxThread: doOnNext:3, run In :RxNewThreadScheduler-112-06 16:13:17.717 14294-14319/com.hanks.rxsearch I/RxThread: get result:3, run In :RxNewThreadScheduler-1

3. .observeOn()

加入在主线程中添加下面的代码，首先 Observable 将在 .subscribe() 的线程上创建，但是 .observeOn()方法被调用之后，代码将运行在指定的线程上：

Observable.just(1,2,3)  .observeOn(Schedulers.newThread())  .subscribe();

实验:

new Thread() {           @Override public void run() {               Observable.just(1, 2, 3).doOnNext(new Action1<Integer>() {                   @Override public void call(Integer integer) {                       Log.i("RxThread", "doOnNext:" + integer + ", run In :" + Thread.currentThread()                               .getName());                   }               })               .observeOn(AndroidSchedulers.mainThread())               .subscribe(new Action1<Integer>() {                   @Override public void call(Integer integer) {                       Log.i("RxThread", "get result:" + integer + ", run In :" + Thread.currentThread()                               .getName());                   }               });           }       }.start();

输出结果:

12-06 16:18:06.493 18584-18606/com.hanks.rxsearch I/RxThread: doOnNext:1, run In :Thread-15512-06 16:18:06.493 18584-18606/com.hanks.rxsearch I/RxThread: doOnNext:2, run In :Thread-15512-06 16:18:06.493 18584-18606/com.hanks.rxsearch I/RxThread: doOnNext:3, run In :Thread-15512-06 16:18:06.521 18584-18584/com.hanks.rxsearch I/RxThread: get result:1, run In :main12-06 16:18:06.521 18584-18584/com.hanks.rxsearch I/RxThread: get result:2, run In :main12-06 16:18:06.521 18584-18584/com.hanks.rxsearch I/RxThread: get result:3, run In :main

3. Combined logic

由于操作可以被组合使用,于是有了下面的代码：

Observable.just(1,2,3)  .subscribeOn(Schedulers.newThread())  .observeOn(Schedulers.newThread())  .subscribe();

实验:

new Thread() {     @Override public void run() {         Observable.just(1, 2, 3).doOnNext(new Action1<Integer>() {             @Override public void call(Integer integer) {                 Log.i("RxThread", "doOnNext:" + integer + ", run In :" + Thread.currentThread()                         .getName());             }         })         .subscribeOn(Schedulers.newThread())         .observeOn(AndroidSchedulers.mainThread())         .subscribe(new Action1<Integer>() {             @Override public void call(Integer integer) {                 Log.i("RxThread", "get result:" + integer + ", run In :" + Thread.currentThread()                         .getName());             }         });     } }.start();

输出结果:

12-06 16:19:53.066 20247-20274/com.hanks.rxsearch I/RxThread: doOnNext:1, run In :RxNewThreadScheduler-112-06 16:19:53.066 20247-20274/com.hanks.rxsearch I/RxThread: doOnNext:2, run In :RxNewThreadScheduler-112-06 16:19:53.066 20247-20274/com.hanks.rxsearch I/RxThread: doOnNext:3, run In :RxNewThreadScheduler-112-06 16:19:53.077 20247-20247/com.hanks.rxsearch I/RxThread: get result:1, run In :main12-06 16:19:53.077 20247-20247/com.hanks.rxsearch I/RxThread: get result:2, run In :main12-06 16:19:53.077 20247-20247/com.hanks.rxsearch I/RxThread: get result:3, run In :main

Tips / Gotchas:

1. “UI线程运行异常”

Observable.just(1,2,3)  .subscribeOn(Schedulers.newThread())  .subscribe(/** logic which touches ui **//); //在newThread中调用

obviously.

2. 逻辑处理放在后台(newThread)

错误姿势：

Observable.just(1,2,3)  .subscribeOn(Schedulers.newThread())  .observeOn(AndroidSchedulers.mainThread())  .flatMap(/** logic which doesn't touch ui **//)  .subscribe();

实验:

new Thread() {       @Override public void run() {           Observable.just("Android-Picasso", "Android-Glide", "Android-Fresco").doOnNext(new Action1<String>() {               @Override public void call(String str) {                   Log.i("RxThread", "doOnNext:" + str + ", run In :" + Thread.currentThread()                           .getName());               }           })           .subscribeOn(Schedulers.newThread())           .observeOn(AndroidSchedulers.mainThread())           .flatMap(new Func1<String, Observable<String>>() {               @Override public Observable<String> call(String str) {                   Log.i("RxThread", "flatMap:" + str + ", run In :" + Thread.currentThread());                   return Observable.from(str.split("-") ); // 返回平方               }           })           .subscribe(new Action1<String>() {               @Override public void call(String str) {                   Log.i("RxThread", "get result:" + str + ", run In :" + Thread.currentThread()                           .getName());               }           });       }   }.start();

输出结果:

12-06 16:43:00.181 8161-8190/com.hanks.rxsearch I/RxThread: doOnNext:Android-Picasso, run In :RxNewThreadScheduler-112-06 16:43:00.181 8161-8190/com.hanks.rxsearch I/RxThread: doOnNext:Android-Glide, run In :RxNewThreadScheduler-112-06 16:43:00.181 8161-8190/com.hanks.rxsearch I/RxThread: doOnNext:Android-Fresco, run In :RxNewThreadScheduler-112-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: flatMap:Android-Picasso, run In :Thread[main,5,main]12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Android, run In :main12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Picasso, run In :main12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: flatMap:Android-Glide, run In :Thread[main,5,main]12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Android, run In :main12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Glide, run In :main12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: flatMap:Android-Fresco, run In :Thread[main,5,main]12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Android, run In :main12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Fresco, run In :main

正确姿势:

Observable.just(1,2,3)  .subscribeOn(Schedulers.newThread())  .flatMap(/** logic which doesn't touch ui **//)  .observeOn(AndroidSchedulers.mainThread())  .subscribe();

第二段代码中 flatMap (或者其他逻辑处理)将运行在后台线程， 如果是在Android中，这样做不会阻塞UI，阻塞UI的话有可能导致ANR之类的异常。这跟 AsyncTask中的 doInBackground()类似，在 doInBackground()中做耗时操作

实验:

new Thread() {       @Override public void run() {           Observable.just("Android-Picasso", "Android-Glide", "Android-Fresco").doOnNext(new Action1<String>() {               @Override public void call(String str) {                   Log.i("RxThread", "doOnNext:" + str + ", run In :" + Thread.currentThread()                           .getName());               }           })           .subscribeOn(Schedulers.newThread())           .flatMap(new Func1<String, Observable<String>>() {               @Override public Observable<String> call(String str) {                   Log.i("RxThread", "flatMap:" + str + ", run In :" + Thread.currentThread());                   return Observable.from(str.split("-") ); // 返回平方               }           })           .observeOn(AndroidSchedulers.mainThread())           .subscribe(new Action1<String>() {               @Override public void call(String str) {                   Log.i("RxThread", "get result:" + str + ", run In :" + Thread.currentThread()                           .getName());               }           });       }   }.start();

输出结果:

12-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: doOnNext:Android-Picasso, run In :RxNewThreadScheduler-112-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: flatMap:Android-Picasso, run In :Thread[RxNewThreadScheduler-1,5,main]12-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: doOnNext:Android-Glide, run In :RxNewThreadScheduler-112-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: flatMap:Android-Glide, run In :Thread[RxNewThreadScheduler-1,5,main]12-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: doOnNext:Android-Fresco, run In :RxNewThreadScheduler-112-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: flatMap:Android-Fresco, run In :Thread[RxNewThreadScheduler-1,5,main]12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Android, run In :main12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Picasso, run In :main12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Android, run In :main12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Glide, run In :main12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Android, run In :main12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Fresco, run In :main

3. 最早的 .subscribeOn() 生效

看下面的代码：

Observable.just(1,2,3)  .subscribeOn(thread1)  .subscribeOn(thread2)  .subscribe();

Observable 的创建和 .subscribeOn() 的调用都将在 thread1 上面执行，所以没有必要多次调用 .subscribeOn(),因为只有第一次的是有用的。

实验:

new Thread() {      @Override public void run() {          Observable.just("Android-Picasso", "Android-Glide", "Android-Fresco").doOnNext(new Action1<String>() {              @Override public void call(String str) {                  Log.i("RxThread", "doOnNext:" + str + ", run In :" + Thread.currentThread()                          .getName());              }          })          .subscribeOn(Schedulers.newThread())          .subscribeOn(Schedulers.io())          .subscribeOn(Schedulers.computation())          .subscribe(new Action1<String>() {              @Override public void call(String str) {                  Log.i("RxThread", "get result:" + str + ", run In :" + Thread.currentThread()                          .getName());              }          });      }  }.start();

输出结果

12-06 16:51:17.581 15622-15652/com.hanks.rxsearch I/RxThread: doOnNext:Android-Picasso, run In :RxNewThreadScheduler-112-06 16:51:17.581 15622-15652/com.hanks.rxsearch I/RxThread: get result:Android-Picasso, run In :RxNewThreadScheduler-112-06 16:51:17.581 15622-15652/com.hanks.rxsearch I/RxThread: doOnNext:Android-Glide, run In :RxNewThreadScheduler-112-06 16:51:17.581 15622-15652/com.hanks.rxsearch I/RxThread: get result:Android-Glide, run In :RxNewThreadScheduler-112-06 16:51:17.581 15622-15652/com.hanks.rxsearch I/RxThread: doOnNext:Android-Fresco, run In :RxNewThreadScheduler-112-06 16:51:17.581 15622-15652/com.hanks.rxsearch I/RxThread: get result:Android-Fresco, run In :RxNewThreadScheduler-1

实验

new Thread() {       @Override public void run() {           Observable.just("Android-Picasso", "Android-Glide", "Android-Fresco").doOnNext(new Action1<String>() {               @Override public void call(String str) {                   Log.i("RxThread", "doOnNext:" + str + ", run In :" + Thread.currentThread()                           .getName());               }           })           .subscribeOn(Schedulers.io())           .subscribeOn(Schedulers.newThread())           .subscribeOn(Schedulers.computation())           .subscribe(new Action1<String>() {               @Override public void call(String str) {                   Log.i("RxThread", "get result:" + str + ", run In :" + Thread.currentThread()                           .getName());               }           });       }   }.start();

输出结果

12-06 16:52:13.378 16424-16454/com.hanks.rxsearch I/RxThread: doOnNext:Android-Picasso, run In :RxCachedThreadScheduler-212-06 16:52:13.379 16424-16454/com.hanks.rxsearch I/RxThread: get result:Android-Picasso, run In :RxCachedThreadScheduler-212-06 16:52:13.379 16424-16454/com.hanks.rxsearch I/RxThread: doOnNext:Android-Glide, run In :RxCachedThreadScheduler-212-06 16:52:13.379 16424-16454/com.hanks.rxsearch I/RxThread: get result:Android-Glide, run In :RxCachedThreadScheduler-212-06 16:52:13.379 16424-16454/com.hanks.rxsearch I/RxThread: doOnNext:Android-Fresco, run In :RxCachedThreadScheduler-212-06 16:52:13.379 16424-16454/com.hanks.rxsearch I/RxThread: get result:Android-Fresco, run In :RxCachedThreadScheduler-2

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