MMS源码中异步处理简析

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。