当我按下后退按钮时应用程序没有响应

Question

在我的应用程序中，我只有一个从数据库获取数据到列表视图的异步任务，但如果没有数据，则什么也不会显示，当我按下后退按钮时，应用程序没有响应问题是甚至没有错误我的日志甚至没有一个错误。当我按下后退按钮时，它开始滞后，然后它说应用程序没有响应，但如果我的数据库中有数据，应用程序运行正常。有什么想法吗？

  private class SyncData extends AsyncTask<String, String, String> {
        String msg;


        @Override
        protected void onPreExecute() //Starts the progress dailog
        {

            System.out.println("Start");

            //lottieAnimationView.playAnimation();
            customProgress.showProgress(supervisor_specialty.this, "Loading..."
                    , false);
        }

        @Override
        protected String doInBackground(String... strings)  // Connect to the database, write query and add items to array list
        {


            try {
                Connection conn = connectionClass.CONN(); //Connection Object
                if (conn == null) {
                    success = false;
                    msg = "Sorry something went wrong,Please check your internet connection";
                } else {
                    // Change below query according to your own database.

                    Statement stmt = conn.createStatement();
                    ResultSet rs = stmt.executeQuery(query);


                    if (rs != null) // if resultset not null, I add items to itemArraylist using class created
                    {
                        while (rs.next()) {

                            try {
                                Blob rsBlob = rs.getBlob("Store_Picture");
                                Boolean active = rs.getBoolean("Active");
                                itemArrayList.add(new ClassLista(rs.getString("StoreArabicName"),active,rsBlob));

                                //Picasso.with(agzakhana_mainAr.this).load(rs.getString("SpecialityIcon")).into(specialityicon);

                            } catch (Exception ex) {
                                ex.printStackTrace();
                            }
                        }

                        msg = "تم";
                        success = true;
                    } else {
                        msg = "No Data found!";
                        success = false;
                    }


                }
            } catch (Exception e) {
                e.printStackTrace();
                Writer writer = new StringWriter();
                e.printStackTrace(new PrintWriter(writer));
                msg = writer.toString();
                Log.d("Error", writer.toString());
                success = false;
            }


            return msg;
        }


        @Override
        protected void onPostExecute(String msg) // disimissing progress dialoge, showing error and setting up my listview
        {
            //progress2.hideProgress();
            customProgress.hideProgress();
            System.out.println("End");
            if (msg != null) {
                Toast.makeText(supervisor_specialty.this, msg + "", Toast.LENGTH_LONG).show();
            }

            if (!success) {
            } else {
                try {
                    myAppAdapter = new MyAppAdapter(itemArrayList, supervisor_specialty.this);
                    while (myAppAdapter.getCount() == 0) {
                    }
                    listView21.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);
                    listView21.setAdapter(myAppAdapter);
                } catch (Exception ex) {

                }

            }
        }
    }

    public class MyAppAdapter extends BaseAdapter//has a class viewholder which holds
    {


        public class ViewHolder {

            TextView StoreName;
            ImageView active;
            ImageView StoreIcon;

        }

        public List<ClassLista> parkingList;

        public Context context;
        ArrayList<ClassLista> arraylist;


        private MyAppAdapter(List<ClassLista> apps, Context context) {
            this.parkingList = apps;
            this.context = context;
            arraylist = new ArrayList<ClassLista>();
            arraylist.addAll(parkingList);
        }

        @Override
        public int getCount() {
            return parkingList.size();
        }

        @Override
        public Object getItem(int position) {
            return position;
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(final int position, View convertView, ViewGroup parent) // inflating the layout and initializing widgets
        {

            View rowView = convertView;
            MyAppAdapter.ViewHolder viewHolder = null;
            if (rowView == null) {
                LayoutInflater inflater = getLayoutInflater();
                rowView = inflater.inflate(R.layout.listitems2, parent, false);
                viewHolder = new MyAppAdapter.ViewHolder();
                viewHolder.StoreName = rowView.findViewById(R.id.store_name);
                viewHolder.active = rowView.findViewById(R.id.active);
                viewHolder.StoreIcon = rowView.findViewById(R.id.store_pic);
                rowView.setTag(viewHolder);
            } else {
                viewHolder = (MyAppAdapter.ViewHolder) convertView.getTag();
            }
            // here setting up names and images
            if (parkingList.get(position).getName() != null){
                viewHolder.StoreName.setText(parkingList.get(position).getName() + "");
            }



            if(parkingList.get(position).getActive()){
                viewHolder.active.setImageResource(R.drawable.checkk);
            }else {
                viewHolder.active.setImageResource(R.drawable.timer);
            }

            Blob blob = parkingList.get(position).getStoreicon();
            if (blob!= null){
                byte[] decodedString = new byte[0];
                try {
                    decodedString = Base64.decode(blob.getBytes(1,(int) blob.length()), Base64.NO_WRAP);
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                Bitmap decodedByte = BitmapFactory.decodeByteArray(decodedString, 0, decodedString.length);
                viewHolder.StoreIcon.setImageBitmap(decodedByte);
            }else {
                viewHolder.StoreIcon.setImageResource(R.drawable.agzakahana);
            }

            // Picasso.with(context).load(parkingList.get(position).getDiscountimage()).into(viewHolder.imagediscount);


            listView21.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                    //What happens when you click on a place!
//                    Intent intent = new Intent(LoggedIn.this,MapsActivity.class);
//                    startActivity(intent);


                }
            });
            //LayoutAnimationController lac = new LayoutAnimationController(AnimationUtils.loadAnimation(context, R.anim.thelistanim), 0.3f); //0.5f == time between appearance of listview items.
            //listView21.setLayoutAnimation(lac);
            //listView21.startLayoutAnimation();
            return rowView;
        }

    }

Answer 1

执行这段代码时：

 ResultSet rs = stmt.executeQuery(query);

如果没有数据，这并不意味着它应该为空！所以当你检查

if (rs != null) 
  while (rs.next())

因此 while 循环会导致无限循环，导致应用程序出现滞后而不是崩溃。

当我按下后退按钮时应用程序没有响应

Application not responding when i press the back button

java

android

android-asynctask