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Editorial Team
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Asked: 2026-06-17T16:06:03+00:00

I am new to Android development and reading through some example code. I have

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I am new to Android development and reading through some example code. I have copied one method from the sample code in an Adapter class (derived from ArrayAdapter), the derived class has a checkbox in addition to the text view:

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

  View listItem = super.getView(position, convertView, parent);

  CheckedTextView checkMark = null;
  ViewHolder holder = (ViewHolder) listItem.getTag();
  if (holder != null) {
    checkMark = holder.checkMark;
  } else {
    checkMark = (CheckedTextView) listItem.findViewById(android.R.id.text1);
    holder = new ViewHolder(checkMark);
    listItem.setTag(holder);
  }

  checkMark.setChecked(isInCollection(position));
  return listItem;
}

private class ViewHolder {
  protected final CheckedTextView checkMark;

  public ViewHolder(CheckedTextView checkMark) {
     this.checkMark = checkMark;
  }
}

The sample code is to optimize the getView by caching the View within a ViewHolder object.

Where I am confused is I thought the convertView, if not null, would be re-purposed and then the View data is populated into it and returned.

If this is the case, then how could the setTag / getTag methods called in the code be relied upon? It would seem that the same object would have to be retrieved in order for it to work?

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1 Answer

  1. Editorial Team

    perhaps view returned from getTag on a subsequent call is for a different list item, and returns the wrong view

    Adapters use a RecycleBin. This class allows the ListView to only create as many row layouts as will fit on the screen, plus one or two for scrolling and pre-loading. So if you have a ListView with 1000 rows and a screen that only displays 7 rows, odds are the ListViiew will only have 8 unique Views.

    Now to your question using my example above: only eight row layouts and 8 subsequent ViewHolders are ever created. When the users scrolls no new row layouts are ever created; only the content of the row layout changes. So getTag() will always have a valid ViewHolder that references the appropriate View(s).

    (Does that help?)

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