在Android中的计时器内运行异步任务

我正在开发一个基本的聊天类型的应用程序,目前我正在运行代码,如下所示：

class GetMsgs extends AsyncTask<String, String, String> {


        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(MsgViewActivity.this);
            pDialog.setMessage("Fetching..");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }

        @Override
        protected String doInBackground(String... arg0) {
            Intent intent = getIntent();
            String tmp = intent.getStringExtra("Header");
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("Header", tmp));
            // getting JSON Object
            // Note that create product url accepts POST method
            json = jsonParser.makeHttpRequest(url,
                        "POST", params); 

            return null;
        }

        protected void onPostExecute(String file_url) {
            pDialog.dismiss();
            ListView listView_msg = (ListView)findViewById(R.id.MsgView);
            int j = 0;
            String Msgs[];
            try{
                msgs = json.getJSONArray("Messages");
                auths = json.getJSONArray("Authors");
                id = json.getString("ID");
                Msgs = new String[msgs.length()];
                for(int i = 0; i < msgs.length(); i++){
                    if ((msgs.getString(i) != "")&&(auths.getString(i) != "")){
                        Msgs[j++] = auths.getString(i) + " : " + msgs.getString(i);
                    }
                }
                msg_adapter = new ArrayAdapter<String>(MsgViewActivity.this,
                        android.R.layout.simple_list_item_1, Msgs);
                listView_msg.setChoiceMode(ListView.CHOICE_MODE_SINGLE);
                listView_msg.setAdapter(msg_adapter);
            }       
            catch(JSONException e){
                e.printStackTrace();
            }
        }

    }

如下：

new GetMsgs().execute();

当我在Android的事件开始时运行它,甚至点击按钮时,它的工作和完美表现.但是当我尝试以给定间隔运行它来刷新消息屏幕时,应用程序崩溃了.

我试过我在这里找到的方法：
i)How to set a timer in android
ii)Android timer? How-to?

但我不断收到应用程序崩溃.

由于某种原因,是否无法以特定的时间间隔运行代码,或者是某些实现问题.

一些帮助将不胜感激.

logcat的：

04-06 11:45:40.396: V/Provider/Setting(5644): invalidate [system]: current 286 != cached 0
04-06 11:45:40.406: V/Provider/Setting(5644): from db cache, name = sound_effects_enabled value = 1
04-06 11:45:40.407: V/InputMethodManager(5644): focusOut: android.widget.EditText@41c27350 mServedView=android.widget.EditText@41c27350 winFocus=true
04-06 11:45:40.456: D/dalvikvm(5644): create interp thread : stack size=32KB
04-06 11:45:40.456: D/dalvikvm(5644): create new thread
04-06 11:45:40.456: D/dalvikvm(5644): new thread created
04-06 11:45:40.456: D/dalvikvm(5644): update thread list
04-06 11:45:40.456: D/dalvikvm(5644): threadid=11: interp stack at 0x52af2000
04-06 11:45:40.457: D/dalvikvm(5644): threadid=11: created from interp
04-06 11:45:40.457: D/dalvikvm(5644): start new thread
04-06 11:45:40.457: D/dalvikvm(5644): threadid=11: notify debugger
04-06 11:45:40.457: D/dalvikvm(5644): threadid=11 (AsyncTask #1): calling run()
04-06 11:45:40.529: V/InputMethodManager(5644): Starting input: view=android.widget.TabHost@41c23ab0
04-06 11:45:40.529: V/InputMethodManager(5644): Starting input: tba=android.view.inputmethod.EditorInfo@41c68d80 ic=null
04-06 11:45:40.529: V/InputMethodManager(5644): START INPUT: android.widget.TabHost@41c23ab0 ic=null tba=android.view.inputmethod.EditorInfo@41c68d80 controlFlags=#100
04-06 11:45:40.531: V/InputMethodManager(5644): Starting input: Bind result=InputBindResult{com.android.internal.view.IInputMethodSession$Stub$Proxy@41c698a0 com.touchtype.swiftkey/com.touchtype.KeyboardService #4807}
04-06 11:45:40.534: V/InputMethodManager(5644): onWindowFocus: null softInputMode=288 first=true flags=#1820002
04-06 11:45:40.534: V/InputMethodManager(5644): Not IME target window, ignoring
04-06 11:45:40.540: D/dalvikvm(5644): threadid=12: interp stack at 0x537ff000
04-06 11:45:40.542: D/libc-netbsd(5644): getaddrinfo: myphptestsite.bugs3.com get result from proxy >>
04-06 11:45:40.549: I/System.out(5644): propertyValue:true
04-06 11:45:40.550: I/System.out(5644): [socket][0] connection /93.188.160.82:80;LocalPort=45152(0)
04-06 11:45:40.551: I/System.out(5644): [CDS]connect[/93.188.160.82:80] tm:90
04-06 11:45:40.552: D/Posix(5644): [Posix_connect Debug]Process com.example.groupchat :80 
04-06 11:45:40.925: I/SurfaceTextureClient(5644): [STC::queueBuffer] (this:0x51247728) fps:11.83, dur:1014.51, max:391.89, min:15.83
04-06 11:45:41.562: I/SurfaceTextureClient(5644): [STC::queueBuffer] (this:0x52afe8e0) fps:54.92, dur:1001.41, max:60.19, min:7.67
04-06 11:45:41.912: I/System.out(5644): [socket][/100.69.10.243:45152] connected
04-06 11:45:41.913: I/System.out(5644): [CDS]rx timeout:0
04-06 11:45:41.922: I/System.out(5644): >doSendRequest
04-06 11:45:41.930: I/System.out(5644): <doSendRequest
04-06 11:45:42.573: I/SurfaceTextureClient(5644): [STC::queueBuffer] (this:0x52afe8e0) fps:56.37, dur:1011.19, max:23.49, min:12.03
04-06 11:45:43.365: D/dalvikvm(5644): GC_CONCURRENT freed 211K, 12% free 13462K/15171K, paused 2ms+2ms, total 17ms
04-06 11:45:43.372: D/OpenGLRenderer(5644): Flushing caches (mode 0)
04-06 11:45:43.439: I/SurfaceTextureClient(5644): [STC::queueBuffer] (this:0x51247728) fps:5.57, dur:2514.10, max:2279.30, min:12.11
04-06 11:45:43.455: V/InputMethodManager(5644): onWindowFocus: android.widget.ListView@41c2fd98 softInputMode=16 first=false flags=#1810100
04-06 11:45:43.456: V/InputMethodManager(5644): Starting input: view=android.widget.ListView@41c2fd98
04-06 11:45:43.456: V/InputMethodManager(5644): Starting input: tba=android.view.inputmethod.EditorInfo@41bf0db8 ic=null
04-06 11:45:43.456: V/InputMethodManager(5644): START INPUT: android.widget.ListView@41c2fd98 ic=null tba=android.view.inputmethod.EditorInfo@41bf0db8 controlFlags=#101
04-06 11:45:43.458: V/InputMethodManager(5644): Starting input: Bind result=InputBindResult{com.android.internal.view.IInputMethodSession$Stub$Proxy@41c0ada8 com.touchtype.swiftkey/com.touchtype.KeyboardService #4808}
04-06 11:45:45.101: D/VelocityTracker(5644): Couldn't open '/dev/touch' (No such file or directory)
04-06 11:45:45.101: D/VelocityTracker(5644): tpd read x fail: Bad file number
04-06 11:45:45.101: D/VelocityTracker(5644): tpd read y fail: Bad file number
04-06 11:45:45.260: I/SurfaceTextureClient(5644): [STC::queueBuffer] (this:0x51247728) fps:1.65, dur:1821.68, max:1796.98, min:9.99
04-06 11:45:46.205: V/Provider/Setting(5644): from settings cache , name = sound_effects_enabled value = 1
04-06 11:45:46.262: I/SurfaceTextureClient(5644): [STC::queueBuffer] (this:0x51247728) fps:3.00, dur:1001.27, max:782.15, min:67.85
04-06 11:45:46.464: D/AbsListView(5644): checkAbsListViewlLogProperty get invalid command
04-06 11:45:46.468: D/dalvikvm(5644): create interp thread : stack size=32KB
04-06 11:45:46.468: D/dalvikvm(5644): create new thread
04-06 11:45:46.469: D/dalvikvm(5644): new thread created
04-06 11:45:46.469: D/dalvikvm(5644): update thread list
04-06 11:45:46.469: D/dalvikvm(5644): threadid=13: interp stack at 0x51cc3000
04-06 11:45:46.469: D/dalvikvm(5644): threadid=13: created from interp
04-06 11:45:46.469: D/dalvikvm(5644): start new thread
04-06 11:45:46.470: D/dalvikvm(5644): threadid=13: notify debugger
04-06 11:45:46.470: D/dalvikvm(5644): threadid=13 (Timer-0): calling run()
04-06 11:45:46.470: D/dalvikvm(5644): threadid=13: exiting
04-06 11:45:46.471: W/dalvikvm(5644): threadid=13: thread exiting with uncaught exception (group=0x40f1e908)
04-06 11:45:46.473: E/AndroidRuntime(5644): FATAL EXCEPTION: Timer-0
04-06 11:45:46.473: E/AndroidRuntime(5644): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
04-06 11:45:46.473: E/AndroidRuntime(5644):     at android.os.Handler.<init>(Handler.java:121)
04-06 11:45:46.473: E/AndroidRuntime(5644):     at android.app.Dialog.<init>(Dialog.java:107)
04-06 11:45:46.473: E/AndroidRuntime(5644):     at android.app.AlertDialog.<init>(AlertDialog.java:114)
04-06 11:45:46.473: E/AndroidRuntime(5644):     at android.app.AlertDialog.<init>(AlertDialog.java:98)
04-06 11:45:46.473: E/AndroidRuntime(5644):     at android.app.ProgressDialog.<init>(ProgressDialog.java:77)
04-06 11:45:46.473: E/AndroidRuntime(5644):     at com.example.groupchat.MsgViewActivity$GetMsgs.onPreExecute(MsgViewActivity.java:100)
04-06 11:45:46.473: E/AndroidRuntime(5644):     at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
04-06 11:45:46.473: E/AndroidRuntime(5644):     at android.os.AsyncTask.execute(AsyncTask.java:534)
04-06 11:45:46.473: E/AndroidRuntime(5644):     at com.example.groupchat.MsgViewActivity$1.run(MsgViewActivity.java:57)
04-06 11:45:46.473: E/AndroidRuntime(5644):     at java.util.Timer$TimerImpl.run(Timer.java:284)
04-06 11:45:46.482: V/InputMethodManager(5644): focusOut: android.widget.ListView@41c2fd98 mServedView=android.widget.ListView@41c2fd98 winFocus=false
04-06 11:45:46.493: V/InputMethodManager(5644): Not IME target window, ignoring
04-06 11:45:46.675: D/OpenGLRenderer(5644): Flushing caches (mode 0)
04-06 11:45:46.838: D/OpenGLRenderer(5644): Flushing caches (mode 0)
04-06 11:45:48.058: D/OpenGLRenderer(5644): Flushing caches (mode 0)
04-06 11:45:48.071: D/OpenGLRenderer(5644): Flushing caches (mode 0)
04-06 11:45:48.074: D/OpenGLRenderer(5644): Flushing caches (mode 1)

工作代码：

public void callAsynchronousTask() {
        final Handler handler = new Handler();
        Timer timer = new Timer();
        TimerTask doAsynchronousTask = new TimerTask() {       
            @Override
            public void run() {
                handler.post(new Runnable() {
                    public void run() {       
                        try {
                            GetMsgs performBackgroundTask = new GetMsgs();
                            // PerformBackgroundTask this class is the class that extends AsynchTask 
                            performBackgroundTask.execute();
                        } catch (Exception e) {
                            // TODO Auto-generated catch block
                        }
                    }
                });
            }
        };
        timer.schedule(doAsynchronousTask, 0, 1000*10); //execute in every 50000 ms
    }

重要的删除代码
 new GetMsgs().execute();
 从Timer中启动并在您的活动的onCreate方法中启动它,并在您的活动的Destroy方法上停止您的异步任务

class GetMsgs extends AsyncTask<String, String, String> {

   boolean flag = false;
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        flag = true;
  }

    @Override
    protected String doInBackground(String... arg0) {
        while(flag)
        {
            publishProgress("start");

            //Your Code what you are doing in the Do inBackground

            try 
            {
                Thread.sleep(3000);//Your Interval after which you want to refresh the screen
            }
            catch (InterruptedException e) 
            {
            }
            publishProgress("stop");

        }
        return null;
    }
    @Override
    protected void onProgressUpdate(String... values) 
    {
        super.onProgressUpdate(values);
        if(values[0].equalsIgnoreCase("start"))
        {
            //Create Your Dialog in it
            //Do here what you are doing in the onPreExecute    
        }
        else if(values[0].equalsIgnoreCase("stop"))
        {
            //Code you are doing in the onPostExecute
        }

    }
   @Override
    protected void onCancelled() {
        // TODO Auto-generated method stub
        super.onCancelled();
        flag = false;
    }
}