Null Pointer Exception - Custom Camera with Flash Light

Question

In my program i want to allow user to capture multiple Images back to back, but once i do tap on Capture button getting Null Pointer Exception (NPE). I have created a Custom Camera.

If i will remove the flash light code from my existing code, then it's working fine for me (yeah then i am able to capture multiple images back to back without facing any NPE), but whenever i use Flash Light code facing NPE

1. At line number : 324

   mediaFile = new File(mediaStorageDir.getPath() + File.separator
           + "IMG_" + timeStamp + ".jpg");
   

2. At line number : 301

       pictureFile = getOutputMediaFile();
   

3. Java Code

   @Override
   public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_camera);
   
       mCamera = getCameraInstance();
   
       mCameraPreview = new PreviewSurface(this, mCamera);
       FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
       preview.addView(mCameraPreview);
   
   
       Bundle extras = getIntent().getExtras();
       if (extras != null) {
           String value = extras.getString("folder_name");
           Log.d(CameraLauncherActivity.LOG_TAG, "folder_name :: " + value);    
       }
   
   
       Button captureButton = (Button) findViewById(R.id.btnCapture);
       Log.d(CameraLauncherActivity.LOG_TAG, "captureButton :: " + captureButton);
       captureButton.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View v) {
               mCamera.takePicture(null, null, mPicture);
               Log.d(CameraLauncherActivity.LOG_TAG, "mCamera.takePicture :: " + mCamera);                                         
           }
       });
   
       Button viewButton = (Button) findViewById(R.id.btnView);
       Log.d(CameraLauncherActivity.LOG_TAG, "SingleAngelActivityButton :: " + viewButton);
       viewButton.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View v) {             
   
               Intent intentNewEvent = new Intent(CameraLauncherActivity.this, UploadActivity.class);
               String event_id = customFolder;
               intentNewEvent.putExtra("event_id", event_id);
               startActivity(intentNewEvent);        
           }
       });
   
       cd = new ConnectionDetector(getApplicationContext());
   
       // Check if Internet present
       if (!cd.isConnectingToInternet()) {
           // Internet Connection is not present
           alert.showAlertDialog(CameraLauncherActivity.this, "Internet Connection Error",
                   "Please connect to working Internet connection", false);
           // stop executing code by return
           return;
       }
   
   
      hasFlash = getApplicationContext().getPackageManager()
               .hasSystemFeature(PackageManager.FEATURE_CAMERA_FLASH);
   
      // Check if Internet present
       if (!hasFlash) {
           // device doesn't support flash
           alert.showAlertDialog(CameraLauncherActivity.this, "Sorry",
                   "your Device doesn't support Flash Light !", false);
           // stop executing code by return
           return;
       }
   
        // displaying button image
      toggleButtonImage();
   
      // flash switch button
       btnSwitch = (ImageButton) findViewById(R.id.btnFlash);
   
       btnSwitch.setOnClickListener(new View.OnClickListener() {
   
           @Override
           public void onClick(View v) {
               if (isFlashOn) {
                   // turn off flash
                   turnOffFlash();
               } else {
                   // turn on flash
                   turnOnFlash();
               }
           }
       });              
   
   // Get event id, angel id
   Intent i = getIntent();
   event_id = i.getStringExtra("event_id");
   angel_id = i.getStringExtra("angel_id");
   
   // calling background thread
   new LoadSingleTrack().execute();
   }
   
    /**
    * Background Async Task to get single angel information
    * */
   class LoadSingleTrack extends AsyncTask<String, String, String> {
   
       /**
        * Before starting background thread Show Progress Dialog
        * */
       @Override
       protected void onPreExecute() {
           super.onPreExecute();
           pDialog = new ProgressDialog(CameraLauncherActivity.this);
           pDialog.setMessage("Initializing Camera...");
           pDialog.setIndeterminate(false);
           pDialog.setCancelable(false);
           pDialog.show();
       }
   
       /**
        * getting angel json and parsing
        * */
       protected String doInBackground(String... args) {
           // Building Parameters
           List<NameValuePair> params = new ArrayList<NameValuePair>();
   
           // post event id, angel id as GET parameters
           params.add(new BasicNameValuePair("event", event_id));
           params.add(new BasicNameValuePair("angel", angel_id));
   
           // getting JSON string from URL
           String json = jsonParser.makeHttpRequest(URL_angel, "GET",
                   params);
   
           // Check your log cat for JSON reponse
           Log.d("Single Track JSON: ", json);
   
           try {
               JSONObject jObj = new JSONObject(json);
               if(jObj != null){
                   angel_name = jObj.getString(TAG_ANGEL);
                   event_name = jObj.getString(TAG_EVENT);
               }           
   
           } catch (JSONException e) {
               e.printStackTrace();
           }
   
           return null;
       }
   
       /**
        * After completing background task Dismiss the progress dialog
        * **/
       protected void onPostExecute(String file_url) {
           // dismiss the dialog after getting angel information
           pDialog.dismiss();
   
           // updating UI from Background Thread
           runOnUiThread(new Runnable() {
               public void run() {
   
                   TextView txt_angel_name = (TextView) findViewById(R.id.angel_title);
                   String timeStamp = new SimpleDateFormat("dd-MM-yyyy").format(new Date());
   
                   txt_angel_name.setText(event_name + " Event_"+ angel_name + "-" + timeStamp);
                   customFolder = txt_angel_name.getText().toString();
   
                   // Change Activity Title with angel title
                   setTitle(angel_name);
   
                   // folder name
                   mediaStorageDir = new File(
                           Environment
                                   .getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),
                                   "/CaptureImages/"+ customFolder + "/");
   
                   if (!mediaStorageDir.exists()) {
                       if (!mediaStorageDir.mkdirs()) {
                           Log.d("App", "failed to create directory");                  
                       }
                   }                   
               }
           });
       }
   }
   

   }

Logcat:-

12-04 23:23:04.610: E/AndroidRuntime(798): FATAL EXCEPTION: main
12-04 23:23:04.610: E/AndroidRuntime(798): java.lang.NullPointerException
12-04 23:23:04.610: E/AndroidRuntime(798):  at com.example.camera.CameraLauncherActivity.getOutputMediaFile(CameraLauncherActivity.java:324)
12-04 23:23:04.610: E/AndroidRuntime(798):  at com.example.camera.CameraLauncherActivity$1.onPictureTaken(CameraLauncherActivity.java:301)
12-04 23:23:04.610: E/AndroidRuntime(798):  at android.hardware.Camera$EventHandler.handleMessage(Camera.java:773)
12-04 23:23:04.610: E/AndroidRuntime(798):  at android.os.Handler.dispatchMessage(Handler.java:99)
12-04 23:23:04.610: E/AndroidRuntime(798):  at android.os.Looper.loop(Looper.java:137)
12-04 23:23:04.610: E/AndroidRuntime(798):  at android.app.ActivityThread.main(ActivityThread.java:5103)
12-04 23:23:04.610: E/AndroidRuntime(798):  at java.lang.reflect.Method.invokeNative(Native Method)
12-04 23:23:04.610: E/AndroidRuntime(798):  at java.lang.reflect.Method.invoke(Method.java:525)
12-04 23:23:04.610: E/AndroidRuntime(798):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
12-04 23:23:04.610: E/AndroidRuntime(798):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
12-04 23:23:04.610: E/AndroidRuntime(798):  at dalvik.system.NativeStart.main(Native Method)
12-04 23:23:07.570: I/Process(798): Sending signal. PID: 798 SIG: 9

Answer 1

I can't figure out the exact sequence of execution for various parts of your code, but the only thing on that line that can generate a NPE is that mediaStorageDir is null. Since you initialize mediaStorageDir after an instance of LoadSingleTrack asynchronously executes, I can only assume that it is executing after line 324 executes. Resolve this out-of-order sequencing of code execution and the problem should disappear.

Just as a side note: there is no point in calling runOnUiThread from onPostExecute of an AsyncTask; you are already on the UI thread when onPostExecute is called.