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在應(yīng)用開(kāi)發(fā)中, 我們需要使用后臺(tái)任務(wù)更新前臺(tái)界面, 不因頁(yè)面切換而導(dǎo)致重新開(kāi)始, 或因某些任務(wù)阻塞界面刷新, 比如顯示下載或播放進(jìn)度等. 為了追求更優(yōu)質(zhì)的用戶(hù)體驗(yàn), 需要大量使用后臺(tái)任務(wù), 常見(jiàn)的就是異步任務(wù)(AsyncTask)和后臺(tái)服務(wù)(Service), 當(dāng)然還有RxJava. 我寫(xiě)了一個(gè)示例, 來(lái)講講如何使用這些常用的后臺(tái)方式.
主要
(1) 使用異步任務(wù)和后臺(tái)服務(wù)更新頁(yè)面, 避免內(nèi)存泄露.
(2) 使用RxJava的時(shí)間間隔\延遲發(fā)送\定制迭代, 處理后臺(tái)任務(wù), 保存發(fā)送狀態(tài).
示例: 旋轉(zhuǎn)屏幕更新進(jìn)度條, 在摧毀頁(yè)面和新建頁(yè)面時(shí), 保存和獲取頁(yè)面狀態(tài).
源碼的GitHub下載地址
1. 基礎(chǔ)
Gradle配置: Lambda表達(dá)式 + Butterknife + RxJava + LeakCanary.
頁(yè)面布局: Spinner選擇使用模式, ProgressBar顯示更新?tīng)顟B(tài), 可選擇啟動(dòng)LeakCanary.
主邏輯:
(1) 使用Fragment存儲(chǔ)頁(yè)面信息, 包括異步任務(wù), RxJava的觀察者和主題.
// 設(shè)置存儲(chǔ)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) 在頁(yè)面重建時(shí), 在onResume中恢復(fù)狀態(tài), 繼續(xù)更新進(jìn)度條.
@Override protected void onResume() {
super.onResume();
// 是否包含內(nèi)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());
}
生命周期: onCreate -> onRestoreInstanceState -> onResume.
在onResume中設(shè)置setActivity: 因?yàn)樵谛D(zhuǎn)頁(yè)面時(shí), 會(huì)執(zhí)行onRestoreInstanceState方法, 恢復(fù)旋轉(zhuǎn)屏幕之前保存的數(shù)據(jù), 即mPbProgressBar的值, 此時(shí)再恢復(fù)狀態(tài). 如果移到在onCreate時(shí)設(shè)置, 則會(huì)導(dǎo)致Progress值為0, 因?yàn)锳ctivity并沒(méi)有開(kāi)始恢復(fù)之前的數(shù)據(jù).
2. 異步任務(wù)
啟動(dòng)異常任務(wù)AsyncTask, 在doInBackground中, 調(diào)用publishProgress顯示進(jìn)度, 觸發(fā)onProgressUpdate回調(diào), 從而更新進(jìn)度條.
public class CustomAsyncTask extends AsyncTask<Void, Integer, Void> {
private WeakReference<MainActivity> mActivity; // 弱引用Activity, 防止內(nèi)存泄露
private boolean mCompleted = false; // 是否完成
// 設(shè)置Activity控制ProgressBar
public void setActivity(MainActivity activity) {
mActivity = new WeakReference<>(activity);
}
// 判斷是否完成
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); // 暫停時(shí)間
publishProgress(i); // AsyncTask的方法, 調(diào)用onProgressUpdate, 表示完成狀態(tài)
}
return null;
}
@Override
protected void onProgressUpdate(Integer... progress) {
mActivity.get().setProgressValue(progress[0]); // 更新ProgressBar的值
mActivity.get().setProgressPercentText(progress[0]); // 設(shè)置文字
}
@Override
protected void onPreExecute() {
mActivity.get().setProgressText("開(kāi)始異步任務(wù)..."); // 準(zhǔn)備開(kāi)始
mCompleted = false;
}
@Override
protected void onPostExecute(Void result) {
mCompleted = true; // 結(jié)束
mActivity.get().setBusy(false);
mActivity.get().setProgressValue(0);
}
}
注意使用WeakReference弱引用Activity, 因?yàn)榫€程的回收不太穩(wěn)定, 如果持有Activity, 會(huì)導(dǎo)致長(zhǎng)時(shí)間無(wú)法釋放, 導(dǎo)致內(nèi)存泄露.
使用方式
// 處理異步線程的點(diǎn)擊
private void handleAsyncClick() {
// 獲得異步線程
mCustomAsyncTask = new CustomAsyncTask();
mCustomAsyncTask.setActivity(this);
// 存儲(chǔ)異步線程
mRetainedFragment.setCustomAsyncTask(mCustomAsyncTask);
// 執(zhí)行異步線程
mCustomAsyncTask.execute();
}
存儲(chǔ)異步任務(wù), 在旋轉(zhuǎn)屏幕時(shí), 頁(yè)面重建, 可以讀取當(dāng)前進(jìn)度, 繼續(xù)更新.
2. 后臺(tái)服務(wù)
通過(guò)LocalBroadcastManager的Intent傳送當(dāng)前狀態(tài), 更新頁(yè)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, 先判斷進(jìn)度, 后判斷狀態(tài).
private void handleIntentServiceClick() {
mTvProgressText.setText("開(kāi)始消息服務(wù)...");
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更新進(jìn)度條的方法有很多種, 可以使用時(shí)間間隔, 延遲發(fā)送, 和定制迭代器, 但是如果需要處理頁(yè)面重建的連續(xù)更新, 需要存儲(chǔ)PublishSubject, 使用定制迭代器即可完成.
時(shí)間間隔: 在旋轉(zhuǎn)頁(yè)面時(shí), 會(huì)刷新數(shù)據(jù), 重新開(kāi)始.
延遲發(fā)送: 在旋轉(zhuǎn)頁(yè)面時(shí), 會(huì)完成前一個(gè)發(fā)送后, 重新開(kāi)始.
定制迭代: 在旋轉(zhuǎn)頁(yè)面時(shí), 可以正常完成連續(xù)更新.
時(shí)間間隔
private void handleTimeIntervalClick() {
mTvProgressText.setText("開(kāi)始時(shí)間間隔...");
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);
}
Observable.interval觀察者, take終止條件, map數(shù)據(jù)加工.
延遲發(fā)送
private void handleDelayEmitClick() {
mTvProgressText.setText("開(kāi)始延遲發(fā)射...");
mSubscriber = createSubscriber();
mObservable = createObservable();
mObservable.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(mSubscriber);
mRetainedFragment.setObservable(mObservable);
}
觀察者發(fā)送數(shù)據(jù)時(shí), 會(huì)延遲一秒, 即SystemClock.sleep.
// 創(chuàng)建延遲觀察者
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中存儲(chǔ)PublishSubject.
private void handleCustomIteratorClick() {
mTvProgressText.setText("開(kāi)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, 重寫(xiě)next方法, 返回?cái)?shù)據(jù).
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++);
}
// 不允許使用
@Override public void remove() {
throw new UnsupportedOperationException();
}
};
}
}
效果動(dòng)畫(huà)
比較而言, 使用異步任務(wù)容易造成內(nèi)存泄露, 并且可擴(kuò)展性比較小, 適合簡(jiǎn)單的更新; 使用后臺(tái)服務(wù)比較重, 需要另起進(jìn)程, 適合復(fù)雜的數(shù)據(jù)處理, 不適合更新頁(yè)面; 使用RxJava, 容易擴(kuò)展, 可以控制釋放時(shí)機(jī), 是比較不錯(cuò)的選擇.
That's all! Enjoy it!
