android Handler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;
		}
	}

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。

以后的路还很长，我要静下心来，写出比较好的代码~~~~~~~~~~~~~~~~~~~~