About NotifyDataSetChanged

Question

I've been working on adapter and tried to update it with notifydatasetchanged. But the problem I face is that after i successfully update the adapter where I can see the changes have been made in the listview, it will then change back to previous data after I return from other fragment. I've heard that adapter will reuse the convert view with same data which cause the problem, but I don't know how to fix this. I've searched for the answer but couldn't find anything similar as most of the answers were all about declaring a new adapter. Below is part of my code:

1.refresh method in fragment

public void toggleRefreshInBackground(ArrayList<HashMap<String, Object>> list) {
    dialog_list.clear();
    dialog_list.addAll(list);
    adapter.update(list);
}

2.getView() of my adapter

public class DialogListAdapter extends BaseAdapter {
Context context;
private ImageLoader imageLoader;
private static LayoutInflater inflater;
private ArrayList<HashMap<String, Object>> member_list;
private ArrayList<HashMap<String, Object>> member_list2;
private SparseBooleanArray mSelectedItemsIds;
private ArrayList<Integer> selectedItemPosition;
//private static final int droidGreen = Color.parseColor("#A4C639");
//private BadgeView badge;
Resources res;
String sorting;

public DialogListAdapter(Context c,
                         ArrayList<HashMap<String, Object>>content, String temp_sorting) {

    inflater=(LayoutInflater)c.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    this.context=c;
    this.member_list = content;

    this.member_list2 = new ArrayList<>();
    this.member_list2.addAll(this.member_list);

    res=c.getResources();

    this.sorting = temp_sorting;
    mSelectedItemsIds = new SparseBooleanArray();
    selectedItemPosition = new ArrayList<>();

}

@Override
public int getCount() {
    // TODO Auto-generated method stub
    return member_list.size();
}

@Override
public HashMap<String, Object> getItem(int position) {
    // TODO Auto-generated method stub
    return member_list.get(position);
}

@Override
public long getItemId(int position) {
    // TODO Auto-generated method stub
    return position;
}

public void update(ArrayList<HashMap<String,Object>> obj) {
    member_list2.clear();
    member_list2.addAll(obj);
    notifyDataSetChanged();
}

public final class DialogListItem{ // view holder
    public TextView read_count;
    public TextView nameView;
    public TextView numberView;
    public TextView statusView;
    public ImageView thumb_image;
    public TextView timeView;
    public TextView senderView;
    public ImageView tick;
    //public BadgeView badge;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    int index;

    if(sorting.equals("D")){
        index = member_list.size()-position-1;
    }else{
        index = position;
    }

    View row = convertView;
    DialogListItem dialogItem=null;
    String textbuff_time = null;
    String textbuff_mess = null;
    String textbuff_sender = null;
    if (convertView==null){
        row=inflater.inflate(R.layout.dialog_list_single, null);
        dialogItem=new DialogListItem();
        dialogItem.read_count=(TextView)row.findViewById(R.id.readcount);
        dialogItem.nameView=(TextView)row.findViewById(R.id.member_name);
        dialogItem.numberView=(TextView)row.findViewById(R.id.tab2number);
        dialogItem.statusView=(TextView)row.findViewById(R.id.tab2status);
        dialogItem.thumb_image=(ImageView)row.findViewById(R.id.tab2image);
        dialogItem.timeView=(TextView) row.findViewById(R.id.tab2date);
        dialogItem.senderView=(TextView) row.findViewById(R.id.tab2sender);
        dialogItem.tick = (ImageView) row.findViewById(R.id.tick);
        row.setTag(dialogItem);
    }
    else{
        dialogItem=(DialogListItem) row.getTag();
    }

    if (mSelectedItemsIds.get(position)) {
        row.setBackgroundColor(context.getResources().getColor(R.color.item_selected));
    } else {
        row.setBackgroundColor(context.getResources().getColor(R.color.item_unselected));
    }

    HashMap<String,Object>items;
    items=member_list.get(index);
    dialogItem.nameView.setText((String)items.get(DBhelper.MEMBER_NAME));
    dialogItem.nameView.setTypeface(null,Typeface.BOLD);
    dialogItem.nameView.setSingleLine(true);
    dialogItem.nameView.setMaxLines(1);
    dialogItem.nameView.setEms(13);
    dialogItem.nameView.setEllipsize(TruncateAt.END);
    dialogItem.numberView.setText((String)items.get(DBhelper.MEMBER_NUMBER));
    String textbuff=(String)items.get(DBhelper.MEMBER_LMESSAGE);
    if (!TextUtils.isEmpty(textbuff)){
        textbuff_time=textbuff.substring(0, 19);
        textbuff_mess=textbuff.substring(20);
        int bound=textbuff_mess.indexOf("½");
        if(bound!=-1){
            textbuff_sender=textbuff_mess.substring(0,bound);
            textbuff_mess=textbuff_mess.substring(bound+2);
        }
        else
            textbuff_sender="";

        dialogItem.statusView.setText(textbuff_mess);

        if (textbuff_sender.equals(context.getResources().getString(R.string.myself))) {
            dialogItem.senderView.setVisibility(View.GONE);
            dialogItem.tick.setVisibility(View.VISIBLE);
        } else {
            textbuff_sender = textbuff_sender + ": ";
            dialogItem.senderView.setVisibility(View.VISIBLE);
            dialogItem.senderView.setText(textbuff_sender);
            dialogItem.tick.setVisibility(View.GONE);
        }

        try {
            dialogItem.timeView.setText(Utility.relativeTime(row.getContext(), textbuff_time));
        } catch (ParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
    else{
        dialogItem.statusView.setText("");
        dialogItem.senderView.setText("");
        dialogItem.timeView.setText("---");
    }

    dialogItem.statusView.setTextColor(Color.GRAY);
    dialogItem.statusView.setTypeface(null,Typeface.NORMAL);
    dialogItem.timeView.setTextColor(Color.GRAY);
    dialogItem.timeView.setTypeface(null,Typeface.NORMAL);
    dialogItem.senderView.setTextColor(Color.GRAY);
    dialogItem.senderView.setTypeface(null,Typeface.NORMAL);
    dialogItem.senderView.getPaint().setTextSkewX(-0.25f);

    String sformat=" "+String.valueOf(items.get(DBhelper.MEMBER_SIZE))+" ";
    dialogItem.read_count.setText(sformat);
    int badge_number=(Integer)items.get(DBhelper.MEMBER_SIZE);
    if(badge_number>0){

        dialogItem.read_count.setVisibility(View.VISIBLE);
        dialogItem.statusView.setTextColor(Color.BLACK);
        dialogItem.statusView.setTypeface(null,Typeface.BOLD);
        dialogItem.timeView.setTextColor(Color.BLACK);
        dialogItem.timeView.setTypeface(null,Typeface.BOLD);
        dialogItem.senderView.setTextColor(Color.BLACK);
        dialogItem.senderView.setTypeface(null,Typeface.BOLD);
        dialogItem.senderView.getPaint().setTextSkewX(-0.25f);
    }
    else{
        dialogItem.read_count.setVisibility(View.GONE);
    }

    StringBuffer link=new StringBuffer(Register.get_current_server_address());
    if(items.get(DBhelper.MEMBER_TYPE).equals(res.getString(R.string.broadcast_chat))){
        dialogItem.nameView.setTextColor(row.getResources().getColor(R.color.tab4_title));
        link.append("uniappSystemFile.asp");
        link.append("?file=").append("broadcast.png");
        //imageLoader.DisplayImage(link.toString(), dialogItem.thumb_image);
        Picasso.with(context).load(link.toString()).transform(new CircleTransform()).resize(200,200).into(dialogItem.thumb_image);
        dialogItem.read_count.setVisibility(View.GONE); // disable broadcast badge
    }
            Picasso.with(context).load(R.drawable.ic_contact).resize(200,200).into(dialogItem.thumb_image);
            Picasso.with(context).load(R.drawable.ic_notif).resize(200, 200).into(dialogItem.thumb_image);
        }else{
            link2 = new IMService(context.getApplicationContext()).group_image_thumb_get(tab2.myphone, (String) items.get(DBhelper.MEMBER_NUMBER));
            dialogItem.nameView.setTextColor(row.getResources().getColor(R.color.tab3_title));
            //imageLoader.DisplayImage(link2, dialogItem.thumb_image);
            Picasso.with(context).load(link2).transform(new CircleTransform()).resize(200, 200).placeholder(R.drawable.ic_group_circle_black_48dp).error(R.drawable.ic_group_circle_black_48dp).into(dialogItem.thumb_image);
        }
    }

public void setSearchPattern(String pattern) {
    filterListByPattern(pattern.trim());
    this.notifyDataSetChanged();
}

private void filterListByPattern(String searchPattern) {

    member_list.clear();
    for (HashMap<String,Object> info : member_list2) {
        boolean add = true;
        do {
            if (searchPattern == null || searchPattern.equals("")) {
                break;
            }
            if (info.get(DBhelper.MEMBER_NAME).toString().toLowerCase().contains(searchPattern)) {
                break;
            }
            add = false;
        } while (false);
        if (add) {
            member_list.add(info);
        }
    }
}

public void resetList() {
    this.member_list2 = new ArrayList<HashMap<String,Object>>();
    this.member_list2.addAll(this.member_list);
    this.notifyDataSetChanged();
}

public void remove(Object object) {
    member_list.remove(object);
    notifyDataSetChanged();
}

public void toggleSelection(int position) {
    selectView(position, !mSelectedItemsIds.get(position));
}

public void removeSelection() {
    mSelectedItemsIds = new SparseBooleanArray();
    selectedItemPosition = new ArrayList<>();
    notifyDataSetChanged();
}

public void selectView(int position, boolean value) {
    if (value) {
        mSelectedItemsIds.put(position, value);
        selectedItemPosition.add(position);
    } else {
        mSelectedItemsIds.delete(position);
        selectedItemPosition.remove(selectedItemPosition.indexOf(position));
    }
    notifyDataSetChanged();
}

public int getSelectedCount() {
    return mSelectedItemsIds.size();
}

public SparseBooleanArray getSelectedIds() {
    return mSelectedItemsIds;
}

public ArrayList<Integer> getItemPosition() {
    return selectedItemPosition;
}

}

So, my question is why would my adapter and listview show the old data after I return from other fragment to this fragment, and how to fix this?

P.S. please don't tell me to declare a new adapter like this

adapter = new MyAdapter(list);
adapter.notifyDataSetChanged();

I know it works, but it's not a good and appropriate approach since it's a heavy operation and you don't even need to use notifyDataSetChanged after declaring a new adapter.

Many thanks

@Anonymous but what's the difference between recyclerview and list view?? I still need an adapter and make changes on it — Harris.C, Sep 08 '17 at 05:12
View holder in recyclerview is a major enhancement over list-view i think.Any ways post your entire adapter no.It will be easy to analyse the code — Sharath kumar, Sep 08 '17 at 05:14
@Anonymous I'm afk right now. I'll post the entire adapter about half an hour later. — Harris.C, Sep 08 '17 at 05:24
@IntelliJAmiya Recyclerview can handle the problem like this?? but my adapter is too big for me to do migration, is it possible to stick to listview and fix this problem? thanks — Harris.C, Sep 08 '17 at 06:37

score 0 · Answer 1 · answered Sep 08 '17 at 07:39

Try putting setRetainInstance(true); inside your fragment.

If above does not work then try with onSaveInstanceState() as below -

Declare at top, Parcelable state;

Save listview state, state = listview.onSaveInstanceState(); inside onpause() of fragment or manually while changing fragment. Then inside onCreateView check state is null or not. If null then set adapter / get data, if not then set

listview.onRestoreInstanceState(state);

On the other hand, Each time you load fragment, ArrayList will start off empty. So you need to be careful to save data.

About NotifyDataSetChanged

1 Answers1