Android應用程序崩潰與對話框

Question

我正在獲取AsyncTask類中的設備的GPS協調（通過getLocation方法），但是，如果GPS被禁用，我會打開一個對話框，讓用戶能夠轉移到「設置」區域並將GPS打開或取消。在用戶甚至按下其中一個按鈕之前，每當對話警報打開時，應用程序崩潰。我該如何解決它？

public class StarTask extends AsyncTask<Void,Void,ArrayList<Song>>{ 

    final int k_ThreadSleepTime = 3000; 
    final int k_MaxThreadTries = 7; 
    double latitude = 0; 
    double longitude = 0; 
    GPSTracker gps; 
    TestMain client; 

    @Override 
    protected void onPreExecute() { 
     super.onPreExecute(); 
     gps = new GPSTracker(getApplication()); 
    } 

    @Override 
    protected ArrayList<Song> doInBackground(Void... params) { 
     ArrayList<Song> list = new ArrayList(); 
     client = new TestMain(); 
     int tries = 0; 
     String o; 
     getLocation(); 
     String url = builtURL(); 
     try { 
      String jsonPageStr = client.doGetRequest(url); 
      JSONObject obj = new JSONObject(jsonPageStr); 
      userId = obj.getJSONObject("info").getInt("user_id"); 
      isWait = (wait.equals("true")); 

      while (isWait && tries < k_MaxThreadTries) { 
       url = builtURL(); 
       jsonPageStr = client.doGetRequest(url); 
       obj = new JSONObject(jsonPageStr); 
       if (!(obj.equals("") || obj.equals(null))) { 
        isWait = (wait.equals("true")); 
       } 
       tries++; 
       try { 
        Thread.sleep(k_ThreadSleepTime); 
       } catch (InterruptedException e) { 
        e.printStackTrace(); 
       } 
      } 

      if(tries == k_MaxThreadTries) { 
       //exit the App 
       onMyDestroy(); 
      } 
    } 

    private String builtURL() {} 

    private void getLocation() { 
     if (gps.canGetLocation()) { 
      latitude = gps.getLatitude(); 
      longitude = gps.getLongitude(); 

     } else { 
      // can't get location 
      // GPS or Network is not enabled 
      // Ask user to enable GPS/network in settings 

      //gps.showSettingsAlert(); 

      showSettingsAlert(); 
     } 
     gps.stopUsingGPS(); 
    } 

    public void showSettingsAlert(){ 

     runOnUiThread(new Runnable() { 
      @Override 
      public void run() { 
       final AlertDialog.Builder alertDialog = new AlertDialog.Builder(MainActivity.this); 

       // Setting Dialog Title 
       alertDialog.setTitle("GPS is settings"); 

       // Setting Dialog Message 
       alertDialog.setMessage("GPS is not enabled. Do you want to go to settings menu?"); 

       // On pressing Settings button 
       alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() { 
        public void onClick(DialogInterface dialog,int which) { 
         Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS); 
         MainActivity.this.startActivity(intent); 
         hasBeenNoGps = true; 
        } 
       }); 

       // on pressing cancel button 
       alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() { 
        public void onClick(DialogInterface dialog, int which) { 
         dialog.cancel(); 
         hasBeenNoGps = true; 
         onMyDestroy(); 
        } 
       }); 

       // Showing Alert Message 
       alertDialog.show(); 
      } 
     }); 
    } 

    @Override 
    protected void onPostExecute(ArrayList<Song> aVoid) { 
     super.onPostExecute(aVoid); 

Answer 1

你在showSettingsAlert()這期間你AsyncTask的doInBackground()稱爲做UI操作。允許的方法是將涉及UI的所有操作保持在doInBackground()之外。在這裏，您可以從getLocation()中刪除其他條件，而將其實施爲onPreExecute()。與此類似，

public class StarTask extends AsyncTask<Void,Void,ArrayList<Song>>{ 

    final int k_ThreadSleepTime = 3000; 
    final int k_MaxThreadTries = 7; 
    double latitude = 0; 
    double longitude = 0; 
    GPSTracker gps; 
    TestMain client; 

    @Override 
    protected void onPreExecute() { 
     super.onPreExecute(); 
     gps = new GPSTracker(getApplication()); 
     if (!gps.canGetLocation()) { 
      showSettingsAlert(); 
     } 
    } 

    @Override 
    protected ArrayList<Song> doInBackground(Void... params) { 
     ArrayList<Song> list = new ArrayList(); 
     client = new TestMain(); 
     int tries = 0; 
     String o; 
     getLocation(); 
     String url = builtURL(); 
     try { 
      String jsonPageStr = client.doGetRequest(url); 
      JSONObject obj = new JSONObject(jsonPageStr); 
      userId = obj.getJSONObject("info").getInt("user_id"); 
      isWait = (wait.equals("true")); 

      while (isWait && tries < k_MaxThreadTries) { 
       url = builtURL(); 
       jsonPageStr = client.doGetRequest(url); 
       obj = new JSONObject(jsonPageStr); 
       if (!(obj.equals("") || obj.equals(null))) { 
        isWait = (wait.equals("true")); 
       } 
       tries++; 
       try { 
        Thread.sleep(k_ThreadSleepTime); 
       } catch (InterruptedException e) { 
        e.printStackTrace(); 
       } 
      } 

      if(tries == k_MaxThreadTries) { 
       //exit the App 
       onMyDestroy(); 
      } 
    } 

    private void getLocation() { 
     if (gps.canGetLocation()) { 
      latitude = gps.getLatitude(); 
      longitude = gps.getLongitude(); 

     } 
     gps.stopUsingGPS(); 
    } 

Answer 2

您正在嘗試運行在後臺線程UI線程（你的AsyncTask內），你所能做的就是在你的AsyncTask類中創建一個全球性的對話，並顯示在 doInBackground方法然後關閉它 onPostExecute（）。您的對話需要上下文。