当我按下返回按钮时应用程序没有响应

Posted 2023-05-07

【中文标题】当我按下返回按钮时应用程序没有响应

【英文标题】：Application not responding when i press the back button

【发布时间】：2020-10-12 11:03:23

【问题描述】：

在我的应用程序中，我只有一个将数据从数据库获取到列表视图的异步任务，但如果没有数据，则没有任何显示，当我按下后退按钮时，应用程序没有响应问题是我的日志中甚至没有错误甚至没有一个错误。 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，但是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;
        

    

【参考方案1】：

执行此代码时：

 ResultSet rs = stmt.executeQuery(query);
      

如果没有数据，这并不意味着它应该为空！ 所以当你检查时

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

因此，while 循环会导致无限循环，导致延迟而不是应用崩溃。

【讨论】：

我尝试将其更改为 if 而不是 while。但错误仍然存​​在