Question

I have a ListView which extends BaseAdapter. I have a data[] array. The ListView inflates and populates correctly. What I am trying to do is make a ImageView visible on the list item (basically a check image on the right side of the inflated view) when the user selects the item and if there was a previous item selected, I just hide that ImageView. This works fine too.

But after I select a new item and scroll back and forth I see weird behavior, the check image is sometimes visible in multiple list items or is hidden in the actual item that is currently selected. Could someone please help and explain what I am doing wrong?

I have these two lines in the onCreate method:

    adap = new EfficientAdapter(this);
    lstview.setAdapter(adap);

and the adapter code:

public static class EfficientAdapter extends BaseAdapter implements Filterable {
  private LayoutInflater mInflater;
  private Context context;
  private ImageView CurrentSelectedImageView;
  private Integer CurrentPosition = 14;


  public EfficientAdapter(Context context) {
    mInflater = LayoutInflater.from(context);
    this.context = context;
  }


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

    ViewHolder holder;

    //Log.e("TAG",String.valueOf(position));

    if (convertView == null) {
      convertView = mInflater.inflate(R.layout.adaptor_content, null);

      holder = new ViewHolder();
      holder.textLine = (TextView) convertView.findViewById(R.id.txtCategoryCaption);
      holder.iconLine = (ImageView) convertView.findViewById(R.id.iconLine);
      holder.imgCheckbox = (ImageView) convertView.findViewById(R.id.imgCheck);


      //If the CurrentPosition == position then make the checkbox visible else dont.
      if (CurrentPosition == position){

        holder.imgCheckbox.setVisibility(View.VISIBLE);
      }else{
        holder.imgCheckbox.setVisibility(View.INVISIBLE);
      }


      final ImageView Checkbox = holder.imgCheckbox;

      //Now if the list item is clicked then set the position as the current item and make the checkbox visible.

      convertView.setOnClickListener(new OnClickListener() {
        private int pos = position;

        @Override
        public void onClick(View v) {
            if (CurrentSelectedImageView!=null){
                CurrentSelectedImageView.setVisibility(View.INVISIBLE);
            }
            Checkbox.setVisibility(View.VISIBLE);
            CurrentSelectedImageView = Checkbox;
            CurrentPosition = pos;

        }
      });

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


        int id = context.getResources().getIdentifier("nodeinsert", "drawable", context.getString(R.string.package_str));
        if (id != 0x0) {
          mIcon1 = BitmapFactory.decodeResource(context.getResources(), id);
        }

        holder.iconLine.setImageBitmap(mIcon1);
        holder.textLine.setText(String.valueOf(data[position]));


    if (CurrentPosition == position){
        Log.e("TAG",CurrentPosition + "---" + String.valueOf(position));
        holder.imgCheckbox.setVisibility(View.VISIBLE);
    }else{
        holder.imgCheckbox.setVisibility(View.INVISIBLE);
    }


    return convertView;
  }



  static class ViewHolder {
    TextView textLine;
    ImageView iconLine;
    ImageView imgCheckbox;
  }

  @Override
  public Filter getFilter() {
    // TODO Auto-generated method stub
    return null;
  }

  @Override
  public long getItemId(int position) {
    // TODO Auto-generated method stub
    return 0;
  }

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

  @Override
  public Object getItem(int position) {
    // TODO Auto-generated method stub
    return data[position];
  }

}

Answer 1

But after I select a new item and scroll back and forth I see wierd
behavior, the check image is sometimes visible in multiple list items
or is hidden in the actual item that is currently selected.

That’s most likely happening because of the way you set the click listener for convertView. You set the OnCLickListener only for the case when convertView is null but as you scroll the ListView up and down, rows will get recycled and you would end up with the same listener as other rows.

Anyway if you just want to have only one row with the image visible there is a much simpler way to do it. First of all you should drop the OnCLickListener on the convertView and use the OnItemClickListener on your ListView element. From this listener callback you’ll modify the rows:

lstview.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> l, View v, int position,
                    long id) {
                View oldView = l.getChildAt(adap.getSelectedPosition());
                ImageView img;
                if (oldView != null && adap.getSelectedPosition() != -1) {
                    img = (ImageView) oldView.findViewById(R.id.imageView1);
                    img.setVisibility(View.INVISIBLE);
                }
                img = (ImageView) v.findViewById(R.id.imageView1);
                img.setVisibility(View.VISIBLE);
                adap.setSelectedPosition(position);
            }
        });

Then modify the adapter like this:

// a field in the adapter
private int mSelectedPosition = -1;

// getter and setter methods for the field above
public void setSelectedPosition(int selectedPosition) {
    mSelectedPosition = selectedPosition;
    notifyDataSetChanged();
}

public int getSelectedPosition() {
    return mSelectedPosition;
}

// and finally your getView() method
public View getView(final int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    if (convertView == null) {
      convertView = mInflater.inflate(R.layout.adaptor_content, parent, false);
      holder = new ViewHolder();
      holder.textLine = (TextView) convertView.findViewById(R.id.txtCategoryCaption);
      holder.iconLine = (ImageView) convertView.findViewById(R.id.iconLine);
      holder.imgCheckbox = (ImageView) convertView.findViewById(R.id.imgCheck);
      convertView.setTag(holder);
    } else {
      holder = (ViewHolder) convertView.getTag();
    }
    if (mSelectedPosition == position) {
    holder.imgCheckbox.setVisibility(View.VISIBLE);
    } else {
    holder.imgCheckbox.setVisibility(View.INVISIBLE);
    }     
      // what is the point of this call?!
      // you should move this to another place(like the adapter's constructor), the getIdentifier()
      // method is a bit slow and you call it each time the adapter calls getView()
      // you should never use it in the getView() method(), especially as all you do is get the id of the same drawable again and again
      int id = context.getResources().getIdentifier("nodeinsert", "drawable", context.getString(R.string.package_str));
      // ?!?
      if (id != 0x0) {
          mIcon1 = BitmapFactory.decodeResource(context.getResources(), id);
      }
      holder.iconLine.setImageBitmap(mIcon1);
      holder.textLine.setText(String.valueOf(data[position]));
      return convertView;
}