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：

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

调用情况如下：

图片

实验:

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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:

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

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

图片

实验:

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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:

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

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

图片

实验:

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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:

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12-06 16:18:06.493 18584-18606/com.hanks.rxsearch I/RxThread: doOnNext:1, run In :Thread-155
12-06 16:18:06.493 18584-18606/com.hanks.rxsearch I/RxThread: doOnNext:2, run In :Thread-155
12-06 16:18:06.493 18584-18606/com.hanks.rxsearch I/RxThread: doOnNext:3, run In :Thread-155
12-06 16:18:06.521 18584-18584/com.hanks.rxsearch I/RxThread: get result:1, run In :main
12-06 16:18:06.521 18584-18584/com.hanks.rxsearch I/RxThread: get result:2, run In :main
12-06 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：

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

图片

实验:

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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:

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

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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：

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

实验:

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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:

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12-06 16:43:00.181 8161-8190/com.hanks.rxsearch I/RxThread: doOnNext:Android-Picasso, run In :RxNewThreadScheduler-1
12-06 16:43:00.181 8161-8190/com.hanks.rxsearch I/RxThread: doOnNext:Android-Glide, run In :RxNewThreadScheduler-1
12-06 16:43:00.181 8161-8190/com.hanks.rxsearch I/RxThread: doOnNext:Android-Fresco, run In :RxNewThreadScheduler-1
12-06 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 :main
12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Picasso, run In :main
12-06 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 :main
12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Glide, run In :main
12-06 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 :main
12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Fresco, run In :main

正确姿势:

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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:

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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:

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12-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: doOnNext:Android-Picasso, run In :RxNewThreadScheduler-1
12-06 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-1
12-06 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-1
12-06 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 :main
12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Picasso, run In :main
12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Android, run In :main
12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Glide, run In :main
12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Android, run In :main
12-06 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：

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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:

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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

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

实验

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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

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

Android Rxjava Rxandroid

文章出处 (https://hanks.xyz)