Android Hander机制的理解

总以为自己对Handler比较了解，但今天发现还是不了解，以后写代码得好好的看看android doc了，这样才能理解的更深。
一直以为Handler.post(Runnable)为开启一个线程，所以出现了一下问题。
我定义了一个Runnable用来实现短信的分段读取：

private class SubSectionRunnable implements Runnable{  
        private Cursor mCursor;  
        private final int RECIPIENT_IDS = 3;  
        private final int SNIPPET = 4;  
        private String mRecipient;  
        private String mSnippet;  
        private String mNumber;  
        private Long mSnippetCS;  
        private String mName;  
        private String mThreadId;  
        private final int mFirstQueryStep = 20;  
        private final int mOtherQueryStep = 80;  
        private Long mDate = 0l;  
        private boolean mIsFirstQuery = true;  
        private TestSpeed mTestSpeed1 = new TestSpeed();  
        private TestSpeed mTestSpeed2 = new TestSpeed();  
        @Override  
        public void run() {  
            mTestSpeed1.loadBeginTime();  
            mCursor = getContentResolver().query(THREADS_URI,  
                    ALL_THREADS_PROJECTION, null, null, "date DESC limit " + mFirstQueryStep);  
            while(mCursor != null && mCursor.getCount() > 0){  
                Log.i("xiao", "onPostExecute new " + mCursor.getCount());  
                ConversationInfo conver = new ConversationInfo();  
                mConversationInfoPreviousList.add(conver);  
                while(mCursor.moveToNext()){  
                    mThreadId = mCursor.getString(ID);  
                    mDate = mCursor.getLong(DATE);  
                    mRecipient = mCursor.getString(RECIPIENT_IDS);  
                    mSnippetCS = mCursor.getLong(SNIPPET_CS);  
                    if(mSnippetCS ==0){  
                        mSnippet = mCursor.getString(SNIPPET);  
                    }  
                    else{  
                        try {  
                            mSnippet = new String(  
                                    mCursor.getString(SNIPPET).getBytes("ISO8859_1"), "utf-8");  
                        } catch (UnsupportedEncodingException e) {  
                            // TODO Auto-generated catch block  
                            e.printStackTrace();  
                        }  
                    }  
                    Cursor cr = getContentResolver().query(  
                            Uri.parse("content://mms-sms/canonical-addresses"),  
                            new String[] { "_id", "address" }, "_id=?",  
                            new String[] { mRecipient }, null);  
                    if(cr != null && cr.moveToFirst()){  
                        mNumber = cr.getString(1);  
                        mName = getContactNameByPhone(cr.getString(1));  
                    }  
                    else{  
                        mNumber = "";  
                        mName = null;  
                    }  
                    ConversationInfo conversation = new ConversationInfo(mRecipient, mSnippet, mNumber, mSnippetCS, mName, mThreadId);  
                    mConversationInfoPreviousList.add(conversation);  
                }  
                for( int i = 0; i < mConversationInfoPreviousList.size(); i++){  
                    try {  
                        mConversationInfoAdapterList.add(mConversationInfoPreviousList.get(i).clone());  
                    } catch (CloneNotSupportedException e) {  
                        // TODO Auto-generated catch block  
                        e.printStackTrace();  
                    }  
                }  
                mCursor.close();  
                if(mIsFirstQuery){  
                    Message message = new Message();  
                    message.what = 1;  
                    boolean flag1 = mGetMmsHandler.sendMessage(message);  
                    Log.i("xiao", "flag1 = " + flag1);  
                    mIsFirstQuery = !mIsFirstQuery;  
                    mTestSpeed1.loadEndTime();  
                    mTestSpeed1.printDuration();  
                }  
                Message message = new Message();  
                message.what = 2;  
                boolean flag2 = mGetMmsHandler.sendMessage(message);  
                Log.i("xiao", "flag2 = " + flag2);  
                mTestSpeed2.loadEndTime();  
                mTestSpeed2.printDuration();  
                mCursor = null;  
                mTestSpeed2.loadBeginTime();  
                mCursor = getContentResolver().query(THREADS_URI,  
                        ALL_THREADS_PROJECTION, "date < " + mDate, null, "date DESC limit " + mOtherQueryStep);  
                }  
        }  

        public String getContactNameByPhone(String number) {  
            String name = "";  
            Uri personUri = Uri.withAppendedPath(  
                    ContactsContract.PhoneLookup.CONTENT_FILTER_URI, number);  

            try{  
                Cursor cur = getContentResolver().query(personUri,  

                    new String[] { PhoneLookup.DISPLAY_NAME },  
                    null, null, null );  
            if(cur != null){  
                if( cur.moveToFirst() ) {  
                    int nameIdx = cur.getColumnIndex(PhoneLookup.DISPLAY_NAME);  

                    name = cur.getString(nameIdx);  

                }  
                cur.close();  
            }  
            }  
            catch(Exception e){  
                Log.i("xiao", "" + e.getMessage());  
            }  
            return name;  
        }  
    }  

然后定义了一个Handler用来更新界面：

private class GetMmsHandler extends Handler{  

        @Override  
        public void handleMessage(Message msg) {  
            // TODO Auto-generated method stub  
            super.handleMessage(msg);  
            int what = msg.what;  
            switch(what){  
            case 0:  
                showProgress();  
                mGetMmsThread.start();  
                break;  
            case 1:  
                hideProgress();  
                break;  
            case 2:  
                Log.i("xiao", "handleMessage 22222222222222");  
                mConversationAdapter.notifyDataSetChanged();  
                break;  
            }  

        }  
    }  

但我发现每次都是等所有的短信读取完毕后才会打印几次handlerMessage 222222222222信息，所以界面更本没有出现先显示一些，然后陆续加载的过程，我就很奇怪，为什么会会是这样呢，我在mGetMmsHandler.sendMessage后加了判断，看这个消息是否发送成功，验证后是发送成功了，我就查看Handler的doc，原来post(Runnable)是把这个Runnable加到当前的消息队列中，所以等这个Runnable处理完毕后才会处理接受到的多次what为2的消息。