Question

In my Android app I have a grid showing images as items. When I click a button the items should be change their positions. I am populating this grid through a cursor adapter. Previously it was working fine but was taking some time to change the positions of the images and refresh the grid once again. So for that i implemented a progress dialog, so that user could understand that something is going on.

Here is my code so far.

My Handler

public void handleMessage(Message msg) {
switch (msg.what) {
    case PROGRESS_DIALOG_HANDLER_ID:
        progressDialog.dismiss(); //ProgressDialog
        DBAdapter adapter = new DBAdapter(SplittedImageActivity.this);
        adapter.open();
        Cursor cursor = adapter.getAllImages();
        adapter.close();
        startManagingCursor(cursor);
        cursorAdapter.changeCursor(cursor); //My cursor adapter
        gridView.setAdapter(cursorAdapter);
        cursor.close();

My onclick method

progressDialog = ProgressDialog.show(SplittedImageActivity.this, "", "Please wait...");
new Thread(){
        public void run() {
        Random random = new Random();
        DBAdapter adapter = new DBAdapter(getApplicationContext());
        adapter.open();
        int childs = gridView.getChildCount(), oldPosition, newPotision;
        newPotision = childs-1;
        for(int i=0 ; i<childs ; i++){
            oldPosition = random.nextInt(m_cGridView.getChildCount());
            adapter.updatePosition(oldPosition, newPotision); //updates the position of the images in database
            newPotision = oldPosition;
        }
        adapter.close();
        handler.sendEmptyMessage(PROGRESS_DIALOG_HANDLER_ID);
    };
}.start();

Problems:

The progress dialog is showing eprfectly, the positions are also changed in the database. but the gridview is not refreshing. I mean after all works done the progress dialog disappears and the screen becomes blank.

Please help me where i am doing wrong?

Answer 1

I think the problem is that you are assigning a new adapter on the handler, but not calling to NotifyDataSetChanged() on the main thread, that’s maybe why is not updating the grid.

Also, why not use AsyncTasks?

public class LoadAsyncTask extends AsyncTask<Void, Void, Boolean> {
    Context context;

    public LoadAsyncTask(Context context) {
        this.context = context;         
    }

    protected void onPreExecute() {
    }

    protected Boolean doInBackground(Void... v) {
        DBAdapter adapter = new DBAdapter(context);
        adapter.open();
        int childs = gridView.getChildCount(), oldPosition, newPotision;
        newPotision = childs-1;
        for(int i=0 ; i<childs ; i++){
                    oldPosition = random.nextInt(m_cGridView.getChildCount());
                    adapter.updatePosition(oldPosition, newPotision); //updates the position of the images in database
                    newPotision = oldPosition;
        }
        adapter.close();

        DBAdapter adapter = new DBAdapter(context);
        adapter.open();
        Cursor cursor = adapter.getAllImages();
        adapter.close();
        startManagingCursor(cursor);
        cursorAdapter.changeCursor(cursor); //My cursor adapter
        gridView.setAdapter(cursorAdapter);
        cursor.close();                
        return true;
    }

    protected void onPostExecute(Boolean success) {
        if (success) {
            //This will be executed on the main activity thread
            cursorAdapter.notifyDataSetChanged();
        } else {
            showError();
        }
    }

}