自定义adapter问题

-_-_-_- 2013-01-23 10:09:06

碰到一个问题：当我按back键结束当前Activity后，用startActivity再启动该Activity时，onCreate方法里面自定义的adapter不为null，但是在Handler的handleMessage方法里却是null,这是为什么呢？

public class ChatActivity extends Activity implements OnClickListener,OnItemClickListener{

	private static final int UTFMSG = 0;	//文字信息

	private static final int PNGMSG = 1;	//图片信息

	EditText edt_myContent;

	ListView listView;

	Button btn_send, btn_quit;

	ImageButton imgbtn_expression;

	MyHandler myHandler;

	private SimpleChatAdapter adapter; //聊天记录listview适配器

	private boolean flag = true;

	private DataOutputStream dos;

	private DataInputStream dis;

	private Dialog dialog;	//表情对话框

	private static Integer[] imageIds = FaceDate.getFaceIds();//表情数据id

	private int clickId = -1;	//聊天list中的item位置

	

	private int from_ip,to_ip;	//发送者和接受者的ip

	

	@Override

	protected void onCreate(Bundle savedInstanceState) {

		// TODO Auto-generated method stub

		super.onCreate(savedInstanceState);

		setContentView(R.layout.activity_chat);

		init();

		if(adapter==null) {

			adapter = new SimpleChatAdapter(this);

			Log.i("info", "onCreate中adapter为："+adapter.toString());

		}

		listView.addHeaderView(LayoutInflater.from(this).inflate(R.layout.listview_title, null));

		listView.setAdapter(adapter);

		myHandler = new MyHandler();

		new Thread(new ReceiveThread()).start();		

		//为按钮添加点击事件

		btn_send.setOnClickListener(this);

		btn_quit.setOnClickListener(this);

		imgbtn_expression.setOnClickListener(this);

		//为listView添加点击事件

		listView.setOnItemClickListener(this);

	}

上面的代码为我的Activity，还有onCreate方法，其中SimpleChatAdapter为自定义适配器

	/**

	 * 接受服务器端数据的方法

	 */

	private void receiveMessage() {

		try {

			String receiveStr;

			receiveStr = dis.readUTF();

Log.i("info", "receiveStr的值为："+receiveStr);

			if(receiveStr == null)

				return;

			if(receiveStr.equals(Constants.SEND_PICTURE)) {	//指令为图片

				String date = dis.readUTF();

				int datalen = dis.readInt();

				byte[] inputBytes = new byte[datalen];

				int read = 0;

				while (read < datalen) {

					int result = dis.read(inputBytes, read, datalen - read);

					if (result == -1)

						break;

					read += result;

				}

				Message msg = new Message();

				msg.what = PNGMSG;

				Bundle b = new Bundle();// 存放数据

				b.putString("date", date);

				b.putByteArray("pic", inputBytes);

				msg.setData(b);

				myHandler.sendMessage(msg); // 向Handler发送消息,更新UI

			} else {	//指令不是图片则为文字信息

Log.i("info", "有信息接受到");

				Message msg = new Message();

				msg.what = UTFMSG;

				Bundle b = new Bundle();// 存放数据

				b.putString("message", receiveStr);

				msg.setData(b);

				myHandler.sendMessage(msg); // 向Handler发送消息,更新UI

			}

		} catch (IOException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}

	}

	/**

	 * 配合主线程更新UI

	 * @author Administrator

	 *

	 */

	class MyHandler extends Handler {

		@Override

		public void handleMessage(Message msg) {

			// TODO Auto-generated method stub

			Bundle b = msg.getData();

			switch (msg.what) {

			case PNGMSG:	//图片信息

				adapter.addMessage(b);

				break;

			case UTFMSG:	//表情和文字信息

				Log.i("info", "添加内容");

				Log.i("info", "myHandler为："+myHandler.toString());

				Log.i("info", "adapter为："+adapter);

				adapter.addMessage(b.getString("message"));

				break;

			default:

				break;

			}

		}

	}

上面为接收数据并用handler转发数据处理的代码。

	@Override

	public boolean onKeyDown(int keyCode, KeyEvent event) {

		// TODO Auto-generated method stub

		if(keyCode == KeyEvent.KEYCODE_BACK) {

			flag = false;

			Log.i("info", "ChatActivity退出");

			adapter = null;

			//adapter.clear();

			listView = null;

			finish();

		}

		return super.onKeyDown(keyCode, event);

	}

上面是back键代码。
以下是ChatActivity启动退出，再启动接收数据后的LOG和错误

01-23 10:05:43.459: I/info(29247): onCreate中adapter为：com.zhutj.adapter.SimpleChatAdapter@40757810

01-23 10:05:55.689: W/KeyCharacterMap(29247): Can't open keycharmap file

01-23 10:05:55.689: W/KeyCharacterMap(29247): Error loading keycharmap file '/system/usr/keychars/ft5206_input.kcm.bin'. hw.keyboards.131073.devname='ft5206_input'

01-23 10:05:55.689: W/KeyCharacterMap(29247): Using default keymap: /system/usr/keychars/qwerty.kcm.bin

01-23 10:05:55.689: I/info(29247): ChatActivity退出

01-23 10:05:57.069: I/info(29247): onCreate中adapter为：com.zhutj.adapter.SimpleChatAdapter@40769780

01-23 10:06:15.909: I/info(29247): receiveStr的值为：71	  [2013-01-23 10:05:33]splitf050

01-23 10:06:15.909: I/info(29247): 有信息接受到

01-23 10:06:15.909: I/info(29247): 添加内容

01-23 10:06:15.909: I/info(29247): myHandler为：Handler{4077f260}

01-23 10:06:15.909: I/info(29247): adapter为：null

01-23 10:06:15.909: W/dalvikvm(29247): threadid=1: thread exiting with uncaught exception (group=0x40248560)

01-23 10:06:15.919: E/AndroidRuntime(29247): FATAL EXCEPTION: main

01-23 10:06:15.919: E/AndroidRuntime(29247): java.lang.NullPointerException

01-23 10:06:15.919: E/AndroidRuntime(29247): 	at com.zhutj.chatclient.ChatActivity$MyHandler.handleMessage(ChatActivity.java:187)

01-23 10:06:15.919: E/AndroidRuntime(29247): 	at android.os.Handler.dispatchMessage(Handler.java:99)

01-23 10:06:15.919: E/AndroidRuntime(29247): 	at android.os.Looper.loop(Looper.java:130)

01-23 10:06:15.919: E/AndroidRuntime(29247): 	at android.app.ActivityThread.main(ActivityThread.java:3683)