在页面切换时使用RxJava持续更新UI界面

主要

(1) 使用异步任务和后台服务更新页面, 避免内存泄露.

(2) 使用RxJava的时间间隔\延迟发送\定制迭代, 处理后台任务, 保存发送状态.

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1. 基础

Gradle配置: Lambda表达式 + Butterknife + RxJava + LeakCanary.页面布局: Spinner选择使用模式, ProgressBar显示更新状态, 可选择启动LeakCanary.

主逻辑:(1) 使用Fragment存储页面信息, 包括异步任务, RxJava的观察者和主题.

        // 设置存储的Fragment          FragmentManager fm = getFragmentManager();          mRetainedFragment = (RetainedFragment) fm.findFragmentByTag(RETAINED_FRAGMENT);            if (mRetainedFragment == null) {              mRetainedFragment = new RetainedFragment();              fm.beginTransaction().add(mRetainedFragment, RETAINED_FRAGMENT).commit();          }

(2) 在页面重建时, 在onResume中恢复状态, 继续更新进度条.

    @Override protected void onResume() {          super.onResume();            // 是否包含内存泄露          if (mSTrackLeaks.isChecked()) {              LeakCanary.install(getApplication());          }            mMode = mRetainedFragment.getMode();          mCustomAsyncTask = mRetainedFragment.getCustomAsyncTask();            mObservable = mRetainedFragment.getObservable();          mSubject = mRetainedFragment.getSubject();          mSubscriber = createSubscriber();            switch (mMode) {              case ASYNC_TASK:                  if (mCustomAsyncTask != null) {                      if (!mCustomAsyncTask.isCompleted()) {                          mCustomAsyncTask.setActivity(this);                      } else {                          mRetainedFragment.setCustomAsyncTask(null);                      }                  }                  break;              case TIME_INTERVAL:                  if (mObservable != null) {                      mObservable.subscribeOn(Schedulers.io())                              .observeOn(AndroidSchedulers.mainThread())                              .take(MAX_PROGRESS)                              .map(x -> x + 1)                              .subscribe(mSubscriber);                  }                  break;              case DELAY_EMIT:                  if (mObservable != null) {                      mObservable.subscribeOn(Schedulers.io())                              .delay(1, TimeUnit.SECONDS)                              .observeOn(AndroidSchedulers.mainThread())                              .subscribe(mSubscriber);                  }                  break;              case CUSTOM_ITERATOR:                  if (mSubject != null) {                      mSubject.subscribe(mSubscriber);                  }              default:                  break;          }            setBusy(mRetainedFragment.isBusy());      }

2. 异步任务

启动异常任务AsyncTask, 在doInBackground中, 调用publishProgress显示进度, 触发onProgressUpdate回调, 从而更新进度条.

public class CustomAsyncTask extends AsyncTask<Void, Integer, Void> {        private WeakReference<MainActivity> mActivity; // 弱引用Activity, 防止内存泄露        private boolean mCompleted = false; // 是否完成        // 设置Activity控制ProgressBar      public void setActivity(MainActivity activity) {          mActivity = new WeakReference<>(activity);      }        // 判断是否完成      public boolean isCompleted() {          return mCompleted;      }        @Override      protected Void doInBackground(Void... params) {          for (int i = 1; i < MainActivity.MAX_PROGRESS + 1; i++) {              SystemClock.sleep(MainActivity.EMIT_DELAY_MS); // 暂停时间              publishProgress(i); // AsyncTask的方法, 调用onProgressUpdate, 表示完成状态          }          return null;      }        @Override      protected void onProgressUpdate(Integer... progress) {          mActivity.get().setProgressValue(progress[0]); // 更新ProgressBar的值          mActivity.get().setProgressPercentText(progress[0]); // 设置文字      }        @Override      protected void onPreExecute() {          mActivity.get().setProgressText("开始异步任务..."); // 准备开始          mCompleted = false;      }        @Override      protected void onPostExecute(Void result) {          mCompleted = true; // 结束          mActivity.get().setBusy(false);          mActivity.get().setProgressValue(0);      }  }

使用方式

    // 处理异步线程的点击      private void handleAsyncClick() {          // 获得异步线程          mCustomAsyncTask = new CustomAsyncTask();          mCustomAsyncTask.setActivity(this);            // 存储异步线程          mRetainedFragment.setCustomAsyncTask(mCustomAsyncTask);            // 执行异步线程          mCustomAsyncTask.execute();      }

2. 后台服务

通过LocalBroadcastManager的Intent传送当前状态, 更新页面.

public class CustomService extends IntentService {        public static final String KEY_EXTRA_BUSY = "busy";      public static final String KEY_EXTRA_PROGRESS = "progress";        private LocalBroadcastManager mLbm;        public CustomService() {          super(CustomService.class.getSimpleName());      }        @Override protected void onHandleIntent(Intent intent) {          mLbm = LocalBroadcastManager.getInstance(getApplicationContext());            Intent broadcastIntent = new Intent(MainActivity.UPDATE_PROGRESS_FILTER);          broadcastIntent.putExtra(KEY_EXTRA_BUSY, true);          mLbm.sendBroadcast(broadcastIntent);            for (int i = 1; i < MainActivity.MAX_PROGRESS + 1; ++i) {              broadcastIntent = new Intent(MainActivity.UPDATE_PROGRESS_FILTER);              broadcastIntent.putExtra(KEY_EXTRA_PROGRESS, i);              mLbm.sendBroadcast(broadcastIntent);              SystemClock.sleep(MainActivity.EMIT_DELAY_MS);          }            broadcastIntent = new Intent(MainActivity.UPDATE_PROGRESS_FILTER);          broadcastIntent.putExtra(KEY_EXTRA_BUSY, false);          broadcastIntent.putExtra(KEY_EXTRA_PROGRESS, 0);          mLbm.sendBroadcast(broadcastIntent);      }  }

使用方式, 先判断进度, 后判断状态.

    private void handleIntentServiceClick() {          mTvProgressText.setText("开始消息服务...");            Intent intent = new Intent(this, CustomService.class);          startService(intent);      }    ...        private BroadcastReceiver mUpdateProgressReceiver = new BroadcastReceiver() {          @Override public void onReceive(Context context, Intent intent) {              if (intent.hasExtra(CustomService.KEY_EXTRA_PROGRESS)) {                  int progress = intent.getIntExtra(CustomService.KEY_EXTRA_PROGRESS, 0);                  mPbProgressBar.setProgress(progress);                  setProgressPercentText(progress);              }                if (intent.hasExtra(CustomService.KEY_EXTRA_BUSY)) {                  setBusy(intent.getBooleanExtra(CustomService.KEY_EXTRA_BUSY, false));              }          }      };

3. RxJava

RxJava更新进度条的方法有很多种, 可以使用时间间隔, 延迟发送, 和定制迭代器, 但是如果需要处理页面重建的连续更新, 需要存储PublishSubject, 使用定制迭代器即可完成.

时间间隔

    private void handleTimeIntervalClick() {          mTvProgressText.setText("开始时间间隔...");            mSubscriber = createSubscriber();          mObservable = Observable.interval(1, TimeUnit.SECONDS);            mObservable.subscribeOn(Schedulers.io())                  .observeOn(AndroidSchedulers.mainThread())                  .take(MAX_PROGRESS)                  .map(x -> x + 1)                  .subscribe(mSubscriber);            mRetainedFragment.setObservable(mObservable);      }

延迟发送

    private void handleDelayEmitClick() {          mTvProgressText.setText("开始延迟发射...");            mSubscriber = createSubscriber();          mObservable = createObservable();            mObservable.subscribeOn(Schedulers.io())                  .observeOn(AndroidSchedulers.mainThread())                  .subscribe(mSubscriber);            mRetainedFragment.setObservable(mObservable);      }

观察者发送数据时, 会延迟一秒, 即SystemClock.sleep.

    // 创建延迟观察者      private Observable<Long> createObservable() {          return Observable.create(new Observable.OnSubscribe<Long>() {              @Override public void call(Subscriber<? super Long> subscriber) {                  for (long i = 1; i < MAX_PROGRESS + 1; i++) {                      SystemClock.sleep(EMIT_DELAY_MS);                      subscriber.onNext(i);                  }                  subscriber.onCompleted();              }          });      }

定制迭代器, 在RetainedFragment中存储PublishSubject.

    private void handleCustomIteratorClick() {          mTvProgressText.setText("开始定制迭代器...");            mObservable = Observable.from(new CustomIterator());          mSubscriber = createSubscriber();          mSubject = PublishSubject.create();            mObservable.subscribeOn(Schedulers.io())                  .observeOn(AndroidSchedulers.mainThread())                  .subscribe(mSubject);            mSubject.subscribe(mSubscriber);            mRetainedFragment.setObservable(mObservable);          mRetainedFragment.setSubject(mSubject);      }

定制迭代器, 重写next方法, 返回数据.

public class CustomIterator implements Iterable<Long> {        private List<Long> mNumberList = new ArrayList<>();        public CustomIterator() {          for (long i = 0; i < MainActivity.MAX_PROGRESS; i++) {              mNumberList.add(i + 1);          }      }        @Override public Iterator<Long> iterator() {          return new Iterator<Long>() {              private int mCurrentIndex = 0;                @Override public boolean hasNext() {                  return mCurrentIndex < mNumberList.size() && mNumberList.get(mCurrentIndex) != null;              }                @Override public Long next() {                  SystemClock.sleep(MainActivity.EMIT_DELAY_MS);                  return mNumberList.get(mCurrentIndex++);              }                // 不允许使用              @Override public void remove() {                  throw new UnsupportedOperationException();              }          };      }  }

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