Android: Issue with newView and bindView in custom SimpleCursorAdapter

Question

I created a custom SimpleCursorAdapter from one of the only example I found.

When my ListActivity is called, newView and bindView are called for every of my DB entry, and called again for every entry. I've got a few questions:

-is the example right (if not, where can I find one)?

-if bindView call is always preceded by newView call, why doing the same in both functions?

-why is the sequence newView-bindView called twice for every item?

-why some CursorAdapter examples use getView instead of newView and bindView?

Basically, how should SimpleCursorAdapter be used, and what's wrong with my code?

Thanks

ListActivity

public class ContactSelection extends ListActivity {

    private WhipemDBAdapter mDbHelper;
    private FriendAdapter friendAdapter;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mDbHelper = new WhipemDBAdapter(this);
        mDbHelper.open();     

        setContentView(R.layout.contact_list);   

        Cursor c = mDbHelper.fetchAllFriends();
        startManagingCursor(c);     
        String[] from = new String[] {};
        int[] to = new int[] {};

        this.friendAdapter = new FriendAdapter(this, R.layout.contact_row, c, from, to);
        setListAdapter(this.friendAdapter);

        getListView().setItemsCanFocus(false);
        getListView().setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);
    }

    @Override
    protected void onResume() {
        super.onResume();
        mDbHelper.open();
    }

    @Override
    protected void onPause() {
        super.onPause();
        mDbHelper.close();
    }
}

Custom SimpleCursorAdapter

public class FriendAdapter extends SimpleCursorAdapter implements OnClickListener {

    private Context mContext;
    private int mLayout;

    public FriendAdapter(Context context, int layout, Cursor c, String[] from, int[] to) {
        super(context, layout, c, from, to);

        this.mContext = context;
        this.mLayout = layout;
    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup parent) {

        Cursor c = getCursor();

        final LayoutInflater inflater = LayoutInflater.from(context);
        View v = inflater.inflate(mLayout, parent, false);     

        String name = c.getString(c.getColumnIndex(WhipemDBAdapter.KEY_NAME));
        String fb_id = c.getString(c.getColumnIndex(WhipemDBAdapter.KEY_FB_ID));

        TextView name_text = (TextView) v.findViewById(R.id.contact_name);
        if (name_text != null) {
            name_text.setText(name);
        }

        ImageView im = (ImageView) v.findViewById(R.id.contact_pic);            
        Drawable drawable = LoadImageFromWebOperations("http://graph.facebook.com/"+fb_id+"/picture");
        if (im != null) {
            im.setImageDrawable(drawable);
        }

        CheckBox bCheck = (CheckBox) v.findViewById(R.id.checkbox);
        if (im != null) {
            bCheck.setTag(fb_id);
        }            

        if (((GlobalVars) mContext.getApplicationContext()).isFriendSelected(fb_id))
            bCheck.setChecked(true);

        bCheck.setOnClickListener(this);

        return v;
    }

    @Override
    public void bindView(View v, Context context, Cursor c) {

         String name = c.getString(c.getColumnIndex(WhipemDBAdapter.KEY_NAME));
         String fb_id = c.getString(c.getColumnIndex(WhipemDBAdapter.KEY_FB_ID));


         TextView name_text = (TextView) v.findViewById(R.id.contact_name);
         if (name_text != null) {
             name_text.setText(name);
         }

        ImageView im = (ImageView) v.findViewById(R.id.contact_pic);            
        Drawable drawable = LoadImageFromWebOperations("http://graph.facebook.com/"+fb_id+"/picture");
        if (im != null) {
            im.setImageDrawable(drawable);
        }

        CheckBox bCheck = (CheckBox) v.findViewById(R.id.checkbox);
        if (im != null) {
            bCheck.setTag(fb_id);
        }

        ArrayList<String> dude = ((GlobalVars) mContext.getApplicationContext()).getSelectedFriendList();

        if (((GlobalVars) mContext.getApplicationContext()).isFriendSelected(fb_id))
            bCheck.setChecked(true);

        bCheck.setOnClickListener(this);
    }


    @Override
    public void onClick(View v) {
        CheckBox cBox = (CheckBox) v;
        String fb_id = (String) cBox.getTag();

        if (cBox.isChecked()) {
            if (!((GlobalVars) mContext.getApplicationContext()).isFriendSelected(fb_id))
                ((GlobalVars) mContext.getApplicationContext()).addSelectedFriend(fb_id);
        } else {
            if (((GlobalVars) mContext.getApplicationContext()).isFriendSelected(fb_id))
                ((GlobalVars) mContext.getApplicationContext()).removeSelectedFriend(fb_id);
        }

    }

    private Drawable LoadImageFromWebOperations(String url)
    {
        try
        {
            InputStream is = (InputStream) new URL(url).getContent();
            Drawable d = Drawable.createFromStream(is, "src name");
            return d;
        }catch (Exception e) {
            System.out.println("Exc="+e);
            return null;
        }
    }

}

score 21 · Accepted Answer · answered Mar 03 '11 at 17:48

Overriding the getView() function gives you the possibility of "re-using" already inflated list items (the list items that are "scrolled out" from the current view port when you scroll your list back and forth).

By doing so you'll save a lot of memory resources and processor run time, since inflating is a quite time consuming operation. For each and every convertView you re-use you also save GC run-time (since the garbage collector doesn't have to collect that specific list item).

You can also create a "view collection" class (the ViewHolder class in the below example) which will hold the references for each view in your inflated list item. This way you don't have to find them each and every time you update a list item with new values (typically whan you scroll the list). findViewById() is also a rather time consuming operation.

Also I think you can cache more variables, like the layout inflater, and the column indices. Everything to save time :-)

private final Context mContext;
private final int mLayout;
private final Cursor mCursor;
private final int mNameIndex;
private final int mIdIndex;
private final LayoutInflater mLayoutInflater;

private final class ViewHolder {
    public TextView name;
    public ImageView image;
    public CheckBox checkBox;
}

public FriendAdapter(Context context, int layout, Cursor c, String[] from, int[] to) {
    super(context, layout, c, from, to);

    this.mContext = context;
    this.mLayout = layout;
    this.mCursor = c;
    this.mNameIndex = mCursor.getColumnIndex(WhipemDBAdapter.KEY_NAME);
    this.mIdIndex = mCursor.getColumnIndex(WhipemDBAdapter.KEY_FB_ID);
    this.mLayoutInflater = LayoutInflater.from(mContext);
}

public View getView(int position, View convertView, ViewGroup parent) {
    if (mCursor.moveToPosition(position)) {
        ViewHolder viewHolder;

        if (convertView == null) {
            convertView = mLayoutInflater.inflate(mLayout, null);

            viewHolder = new ViewHolder();
            viewHolder.name = (TextView) convertView.findViewById(R.id.contact_name);
            viewHolder.image = (ImageView) convertView.findViewById(R.id.contact_pic);
            viewHolder.checkBox = (CheckBox) convertView.findViewById(R.id.checkbox);

            convertView.setTag(viewHolder);
        }
        else {
            viewHolder = (ViewHolder) convertView.getTag();
        }

        String name = mCursor.getString(mNameIndex);
        String fb_id = mCursor.getString(mIdIndex);
        Drawable drawable = LoadImageFromWebOperations("http://graph.facebook.com/"+fb_id+"/picture");
        boolean isChecked = ((GlobalVars) mContext.getApplicationContext()).isFriendSelected(fb_id);

        viewHolder.name.setText(name);
        viewHolder.image.setImageDrawable(drawable);
        viewHolder.checkBox.setTag(fb_id);
        viewHolder.checkBox.setChecked(isChecked);
    }

    return convertView;
}

This is very useful. Thank you for your time. I'm now investigating why getVBiew is called twice for every item in my DB. — jul, Mar 04 '11 at 08:59
Excellent answer, thanks. But what we should do if we want to add an onClick Listener to the ImageView? I added an onClick(View v) method on my custom adapter, but it didn't work. Any hints? — Antonis, Dec 02 '11 at 13:43
I'm not really sure how to add a click listener to a specific view in the list item. I'm not even sure if that is a good idea. I would guess that you somehow would need to "deactivate" the click listener of the list, or at least consume the onClick event before it reaches the list, and instantiate your own onClickListener (create it in the Activity perhaps) and pass it in to your custom list adapter (perhaps in the constructor), which in turn would assign it to all your images. I haven't done such a maneuver before, though, and I have no idea which evil caveats are lurking in the dark :-) — dbm, Dec 03 '11 at 13:04
I can only guess; but are any of your member fields `static`? — dbm, Mar 19 '14 at 12:22

score 13 · Answer 2 · edited Aug 22 '17 at 15:24

13

The example is almost right. You don't need to do the binding in newView(), since like you mentioned, bindView() will be called. If you see the sequence newView/bindView called twice per item, you are probably using ListView with its height set to wrap_content, which is always a bad idea. Finally, newView() and bindView() are specific to CursorAdapter: it implements getView() and calls either newView() or bindView() for you. However, overriding getView() is perfectly valid as well. This is how other adapters work.

Note that getView() (and therefore bindView/newView) are only invoked for each item that will be displayed on the screen.

edited Aug 22 '17 at 15:24

Muthukrishnan Rajendran

11,122
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answered Mar 03 '11 at 17:13

Romain Guy

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1

Thanks a lot for your clarification. Height of ListView is not set to wrap_content thought. – jul Mar 04 '11 at 08:28
I've just found the video of your talk "Make your Android UI Fast and Efficient". I wish I found it earlier! – jul Mar 04 '11 at 09:17
So while I use newView BindView, I still have to go for the getView? Also that I am using the Tag pattern rather than the holder pattern. I still get duplicate values. – Skynet Dec 19 '13 at 09:02

Android: Issue with newView and bindView in custom SimpleCursorAdapter

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