1，信息数据的查询，删除使用AsycnQueryHandler处理
AsycnQueryHandler继承了Handler
public abstract class AsyncQueryHandler extends Handler
内部使用HandleThread来实现异步线程处理数据，成员变量也有一个Handler并拥有HandleThread的looper。
private Handler mWorkerThreadHandler; public AsyncQueryHandler(ContentResolver cr) { super(); mResolver = new WeakReference<ContentResolver>(cr); synchronized (AsyncQueryHandler.class) { if (sLooper == null) { HandlerThread thread = new HandlerThread("AsyncQueryWorker"); thread.start(); sLooper = thread.getLooper(); } } mWorkerThreadHandler = createHandler(sLooper); }
主线程调用AsycnQueryHandler的startQuery方法，成员变量mWorkerThreadHandler传递Message给HandleThread处理，查询参数使用对象WorkerArgs封装。
public void startQuery(int token, Object cookie, Uri uri, String[] projection, String selection, String[] selectionArgs, String orderBy) { // Use the token as what so cancelOperations works properly Message msg = mWorkerThreadHandler.obtainMessage(token); msg.arg1 = EVENT_ARG_QUERY; WorkerArgs args = new WorkerArgs(); args.handler = this; args.uri = uri; args.projection = projection; args.selection = selection; args.selectionArgs = selectionArgs; args.orderBy = orderBy; args.cookie = cookie; msg.obj = args; mWorkerThreadHandler.sendMessage(msg); }
protected class WorkerHandler extends Handler { public WorkerHandler(Looper looper) { super(looper); } @Override public void handleMessage(Message msg) { final ContentResolver resolver = mResolver.get(); if (resolver == null) return; WorkerArgs args = (WorkerArgs) msg.obj; int token = msg.what; int event = msg.arg1; switch (event) { case EVENT_ARG_QUERY: Cursor cursor; try { cursor = resolver.query(args.uri, args.projection, args.selection, args.selectionArgs, args.orderBy); // Calling getCount() causes the cursor window to be filled, // which will make the first access on the main thread a lot faster. if (cursor != null) { cursor.getCount(); } } catch (Exception e) { Log.w(TAG, "Exception thrown during handling EVENT_ARG_QUERY", e); cursor = null; } args.result = cursor; break;
HandleThread将处理结果result封装到WorkerArgs中，再通过Message传递给AsycnQueryHandler, AsycnQueryHandler调用handleMessage就是主线程中处理了。
public void handleMessage(Message msg) { WorkerArgs args = (WorkerArgs) msg.obj; if (localLOGV) { Log.d(TAG, "AsyncQueryHandler.handleMessage: msg.what=" + msg.what + ", msg.arg1=" + msg.arg1); } int token = msg.what; int event = msg.arg1; // pass token back to caller on each callback. switch (event) { case EVENT_ARG_QUERY: onQueryComplete(token, args.cookie, (Cursor) args.result); break;
2，对于信息数据加载后在UI中展现处理。
ConversationList中ConversationListItem布局时在XML中写好的，只需根据Conversation数据来显示或隐藏对应的view即可。
ComposeMessageActivity中的MessageListItem需要处理彩信附件，彩信附件有多种格式，且UI布局是从数据库中读取解析，所以无法直接在XML中写好，需要在代码中动态加载。也就是说对于彩信，需要同时处理UI加载(MessageListItem)和数据加载(MessageItem)。
MessageItem中使用了异步处理加载MMS数据。
private ItemLoadedFuture mItemLoadedFuture;
mItemLoadedFuture = MmsApp.getApplication().getPduLoaderManager() .getPdu(mMessageUri, loadSlideshow, new PduLoadedMessageItemCallback());
PduLoadManager是MMS源码中定义的异步处理类，使用了ThreadPoolExecutor来实现异步处理。getPdu方法中将处理结果封装为PduLoaded类通过PduLoadedMessageItemCallback接口回调将结果在主线程处理。
ItemLoadedFuture也是使用了接口回调的设计，回调方法setIsDone是在 PduLoadedMessageItemCallback中触发，但实现是在PduLoadManager中，所以主线程可以通过ItemLoadedFuture取消PduLoadManager中的Executor运行。
public class PduLoaderManager extends BackgroundLoaderManager BackgroundLoaderManager(Context context) { mPendingTaskUris = new HashSet<Uri>(); mCallbacks = new HashMap<Uri, Set<ItemLoadedCallback>>(); final LinkedBlockingQueue<Runnable> queue = new LinkedBlockingQueue<Runnable>(); final int poolSize = MAX_THREADS; mExecutor = new ThreadPoolExecutor( poolSize, poolSize, 5, TimeUnit.SECONDS, queue, new BackgroundLoaderThreadFactory(getTag())); mCallbackHandler = new Handler(); }
public ItemLoadedFuture getPdu(Uri uri, boolean requestSlideshow, final ItemLoadedCallback<PduLoaded> callback) { if (uri == null) { throw new NullPointerException(); } //……此处省略掉一些源码 //……为了显示不太长，便于查看 if (pduExists && slideshowExists) { if (callbackRequired) { PduLoaded pduLoaded = new PduLoaded(cacheEntry.getPdu(), slideshow); callback.onItemLoaded(pduLoaded, null); }//这几从缓存中返回数据 return new NullItemLoadedFuture(); } if (callbackRequired) { addCallback(uri, callback); } if (newTaskRequired) { mPendingTaskUris.add(uri); Runnable task = new PduTask(uri, requestSlideshow); mExecutor.execute(task);//后台线程执行加载数据 } return new ItemLoadedFuture() {//返回接口实现 private boolean mIsDone; public void cancel(Uri uri) { cancelCallback(callback); removePdu(uri); // the pdu and/or slideshow might be half loaded. Make sure // we load fresh the next time this uri is requested. } public void setIsDone(boolean done) { cancelCallback(callback); mIsDone = done; } public boolean isDone() { return mIsDone; } }; }
ItemLoadedFuture接口在MessageItem中声明，但在处理后台线程的类PduLoadManager中实现，可以实现主线程管理后台线程（如取消后台任务）
PduLoadedMessageItemCallback接口在MessageItem中实现，作为参数传递给PduLoadManager，将后台线程处理的结果result通过方法onItemLoaded(Object result, Throwable exception)返回到主线程处理。
MessageListItem中加载彩信附件
private void bindCommonMessage(final boolean sameItem) { …… …… if (mMessageItem.mSlideshow == null) {//如果附件数据还未加载完成 final int mCurrentAttachmentType = mMessageItem.mAttachmentType; mMessageItem.setOnPduLoaded(new MessageItem.PduLoadedCallback() {//这里又是接口回调实现 public void onPduLoaded(MessageItem messageItem) { if (DEBUG) { Log.v(TAG, "PduLoadedCallback in MessageListItem for item: " + mPosition + " " + (mMessageItem == null ? "NULL" : mMessageItem.toString()) + " passed in item: " + (messageItem == null ? "NULL" : messageItem.toString())); } if (messageItem != null && mMessageItem != null && messageItem.getMessageId() == mMessageItem.getMessageId()) { mMessageItem.setCachedFormattedMessage(null); bindCommonMessage(//继续调用此方法，直到mMessageItem.mSlideshow加载完成 mCurrentAttachmentType == messageItem.mAttachmentType); } } }); } else { if (mPresenter == null) { mPresenter = PresenterFactory.getPresenter( "MmsThumbnailPresenter", mContext, this, mMessageItem.mSlideshow); } else { mPresenter.setModel(mMessageItem.mSlideshow); mPresenter.setView(this); } if (mImageLoadedCallback == null) { mImageLoadedCallback = new ImageLoadedCallback(this); } else { mImageLoadedCallback.reset(this); } mPresenter.present(mImageLoadedCallback); } …… …… requestLayout(); }
3, 幻灯片编辑列表界面(SlideshowEditActivity)，幻灯片中视频缩略图加载处理。
SlideListAdapter的getView方法加载幻灯片缩略图
private View createViewFromResource(int position, View convertView, int resource) { SlideListItemView slideListItemView; slideListItemView = (SlideListItemView) mInflater.inflate( resource, null); // Show slide number. TextView text; text = (TextView) slideListItemView.findViewById(R.id.slide_number_text); text.setText(mContext.getString(R.string.slide_number, position + 1)); SlideModel slide = getItem(position); int dur = slide.getDuration() / 1000; text = (TextView) slideListItemView.findViewById(R.id.duration_text); text.setText(mContext.getResources(). getQuantityString(R.plurals.slide_duration, dur, dur)); if (mPresenter == null) { mPresenter = PresenterFactory.getPresenter( "SlideshowPresenter", mContext, slideListItemView, mSlideshow); } else { mPresenter.setModel(mSlideshow); mPresenter.setView(slideListItemView); } ((SlideshowPresenter) mPresenter).setLocation(position); mPresenter.present(null); return slideListItemView; }
SlideshowPresenter中调用present(..)方法，针对视频类型使用了异步线程处理，避免耗时阻塞UI。也是用接口回调设计，
mItemLoadedFuture = video.loadThumbnailBitmap(mItemLoadedCallback, mLocation, mAdapterHandler);
mItemLoadedFuture的实现在ThumbnailManager中实现，ThumbnailManager也继承了BackgroundLoaderManager，还是使用Executor实现后台线程。
mItemLoadedCallback在SlideshowPresenter中实现，并传递给ThumbnailManager，用来将后台线程处理的结果返回到主线程处理。mItemLoadedCallback的回调方法处理返回的缩略图时，需要根据幻灯片的postion确定显示位置。但源码中，直接在SlideListAdapter的getView方法中设置positon,这样等视频缩率图返回时，position的值已经被修改了（因为getView在主线程中处理position, 而视频缩略图在异步线程中处理，当异步线程比主线程慢时，postion已经给后续处理改变了。）对于这个问题，可以将positon直接传给异步线程处理，缩率图显示时直接读取传递下去的postion，就不会被主线程的position影响。
