Very slow listview on scroll bar

Question

I have a problem I don’t know how to solve, I have a ListView customized with images and the scroll bar keeps crashing, even with the list loaded. It slows down the list to scroll.

Adapter:

public class AdapterSegmento extends BaseAdapter {

private LayoutInflater mInflater;
private ArrayList<Categoria> itens;

public AdapterListView(Context context, ArrayList<Categoria> itens) {
    //Itens que preencheram o listview
    this.itens = itens;
    //responsavel por pegar o Layout do item.
    mInflater = LayoutInflater.from(context);
}

/**
 * Retorna a quantidade de itens
 *
 * @return
 */
public int getCount() {
    return itens.size();
}

/**
 * Retorna o item de acordo com a posicao dele na tela.
 *
 * @param position
 * @return
 */
public Categoria getItem(int position) {
    return itens.get(position);
}

/**
 * Sem implementação
 *
 * @param position
 * @return
 */
public long getItemId(int position) {
    return position;
}

public View getView(int position, View view, ViewGroup parent) {
    //Pega o item de acordo com a posção.
    Categoria item = itens.get(position);
    //infla o layout para podermos preencher os dados
    view = mInflater.inflate(R.layout.item_list, null);

    //atravez do layout pego pelo LayoutInflater, pegamos cada id relacionado
    //ao item e definimos as informações.
    ((TextView) view.findViewById(R.id.text)).setText(item.getTexto());
    ((ImageView) view.findViewById(R.id.imagemview)).setImageResource(item.getIconeRid());
  //  ((TextView) view.findViewById(R.id.subtitulo)).setText(item.getSubtitulo());

    return view;
}

Class filling the list:

private void gerarLista() {

    itens = new ArrayList<Categoria>();

    String[] categorias = getResources().getStringArray(R.array.categorias);
    String[] drawableCategorias = getResources().getStringArray(
            R.array.categorias_drawable);

    listView.setScrollingCacheEnabled(false);

    // Vai recuperar os dois array's la do strings.xml e iterar sobre eles e criar os itens
    for (int i = 0; i < categorias.length; ++i) {
        itens.add(new Categoria(categorias[i], getResources()
                .getIdentifier(drawableCategorias[i], "drawable",
                        this.getPackageName())));
    }

    // Criamos uma lista que preenchera o ListView
    /*
     * itens = new ArrayList<Categoria>(); Categoria item1 = new
     * Categoria("Alimentação", R.drawable.alimentacao); Categoria item2 =
     * new Categoria("Esporte", R.drawable.esporte);
     * 
     * itens.add(item1); itens.add(item2);
     */
    // Cria o adapter
    adapterListView = new AdapterListView(this, itens);

    // Define o Adapter
    listView.setAdapter(adapterListView);
    // Cor quando a lista é selecionada para ralagem.
    listView.setCacheColorHint(Color.TRANSPARENT);
}

How to solve this?

Answer 1

The problem lies in the architecture of your algorithm. With each iteration in the method getView() of Adapter you are inflating to view you want. This is bad practice!

You need to use the design standard Holder, which will store the references statically from your Views and will improve performance. Also, if you notice, the method getView() receives as parameter a View (view) that is nothing more than the View that you return in this method itself, that is, they use the recursive methodology.

A very basic example of the Holder pattern would be:

public static class ViewHolder {
  TextView hTextViewName;
}

public View getView(int position, View view, ViewGroup parent) {
  ViewHolder holder;
  if (view == null) {
    holder = new ViewHolder();
    view = LayoutInflater.from(context).inflate(R.layout.view_to_inflate, parent, false);
    holder.hTextViewName = (TextView) view.findViewById(R.id.textView_name);
    view.setTag(holder);
  } else {
    holder = (ViewHolder) view.getTag();
  }

  String name = getItem(position);
  holder.hTextViewName.setText(name);

  return view;
}

You can tell the difference! This way you will have much more performance.

In short, from the above case you just need to adapt it to your context! :-)