What about multithreading in Android SQLite?

Question

In my app I\'ve got to implement some UI and Sync service. It runs in the background and updates data. Sync service is not very simple, it uses multithreading.

So, here

Answer 1

Ciaoo: Here the solution:

I tried to explain everything in the code .

import android.app.Activity;
import android.content.Context;
import android.database.Cursor;
import android.os.AsyncTask;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewTreeObserver;
import android.widget.ScrollView;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

class HelpUI {

   final static class GetDataFromDBInAsyncMode extends AsyncTask {

      private Context context;
      private String SQL;
      private final int xMin = -X_App.ScreenHeight; // put here your screen height (get it from code)
      private final int xMax = X_App.ScreenHeight * 2; // put here your screen height (get it from code)

      // this is the main view witch go to have all views
      // Use this in onProgressUpdate to add other vies you get in runtime when you get data from database
      private ViewGroup view_container;

      // if you have a scrollview hide views witch isnot visible to user
      private ScrollView scroll_view_container;

      // this workaround make free processors in measureaments, your UI is more fluent
      final ViewTreeObserver.OnScrollChangedListener onScrollChangedListener = () -> {

         if (view_container == null || view_container.getChildCount() == 0) { return; }

         int scrollY = scroll_view_container.getScrollY();

         for (int i = 0; i < view_container.getChildCount(); i++) {

            final View current = view_container.getChildAt(i);
            final int topView = current.getTop(); //container_views.getChildAt(i).getTop();
            final int diffTop = topView - scrollY;

            if ((diffTop > xMin) && (diffTop < xMax)) {
               current.setVisibility(View.VISIBLE);
            } else {

               current.setVisibility(View.INVISIBLE);
            }

         }

      };

      // constructor
      GetDataFromDBInAsyncMode(Context ctx, String mSQL) {
         this.context = ctx;
         this.SQL = mSQL;

         // put here the id of scrollViewContainer
         scroll_view_container = X_App.getRootV().findViewById(R.id.scroll_view_container);
         if (scroll_view_container != null) {
            // add listener on scroll
            scroll_view_container.getViewTreeObserver().addOnScrollChangedListener(onScrollChangedListener);
         }

      }


      @Override
      protected Object doInBackground(Object... objects) {


         // All dirty things go to being in background
         // Your cursor
         final Cursor cursor = X_SqLite.get(X_App.getContext()).GeDataAsCursor(SQL);

         if (cursor != null && cursor.getCount() > 0 && cursor.moveToFirst()) {

            // The magic part
            ScheduledExecutorService giveMeAsync = Executors.newSingleThreadScheduledExecutor();

            // Give time to processor to do her tasks and do you dirty task here
            // 50 millisec is enough per a single task
            giveMeAsync.scheduleAtFixedRate(() -> {
               ViewGroup viewInflated = ((Activity) this.context).findViewById(R.id.icon_view);

               // Give your data from Database
               // Do here all your things but take care some of these need to be done on UI thread (like adding view etc, you can do that on onProgressUpdate)
               final String data1 = cursor.getString(cursor.getColumnIndex("data1"));
               viewInflated.setTag(data1);

               // Send this to UI thread
               publishProgress(viewInflated, false);

               // Here test to cursor if is finish or not
               if (!cursor.moveToNext()) {
                  giveMeAsync.shutdownNow();
                  cursor.close();
                  publishProgress(null, true);
               }

            }, 1, 50, TimeUnit.MILLISECONDS);


         }

         // otherwise if cursor is emty close them
         if (cursor != null && cursor.getCount() == 0) {
            cursor.close();
            publishProgress(null, true);
         }


         return null;

      }


      @Override
      protected void onProgressUpdate(Object... values) {
         final View viewInflated = (View) values[0];
         final boolean isCursorEnded = (Boolean) values[0];

         // Here you is in main thread
         // You can do all what you do with the viewInflated


         if (isCursorEnded) {
            //raise your event to tell to your app reading data is finished
         }

      }


   }


}

Usage:

import android.app.Activity;
import android.os.Bundle;

class MyActivity extends Activity {
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      new HelpUI.GetDataFromDBInAsyncMode(this, "Select * FROM YourTable").execute();
   }
} 

Change variables with your variables/objects