FC 3.5.3提升listview的執行效率
阿新 • • 發佈:2018-11-24
- convertView
- ViewHolder
在普通的listview中,自定義的adapter裡的getview方法,每次都會將佈局重新載入了一遍,其實沒有必要,使用convertView對載入好的佈局進行快取,以後的進行重用即可。
使用ViewHolder,用於對控制元件的例項進行快取。當convertView為null時,建立一個ViewHolder物件,將控制元件的例項存放在ViewHolder裡,然後呼叫view的settag方法,將ViewHolder存放在view中。當convertView不為null時,呼叫ViewHolder的gettag方法,將ViewHolder重新取出。
public class FruitAdapter extends ArrayAdapter<Fruit> { private int resourceId; public FruitAdapter(Context context, int textViewResourceId, List<Fruit> objects) { super(context, textViewResourceId, objects); resourceId = textViewResourceId; } @Override public View getView(int position, View convertView, ViewGroup parent) { Fruit fruit = getItem(position); // 獲取當前項的Fruit例項 View view; ViewHolder viewHolder; if (convertView == null) { view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false); viewHolder = new ViewHolder(); viewHolder.fruitImage = (ImageView) view.findViewById (R.id.fruit_image); viewHolder.fruitName = (TextView) view.findViewById (R.id.fruit_name); view.setTag(viewHolder); // 將ViewHolder儲存在View中 } else { view = convertView; viewHolder = (ViewHolder) view.getTag(); // 重新獲取ViewHolder } viewHolder.fruitImage.setImageResource(fruit.getImageId()); viewHolder.fruitName.setText(fruit.getName()); return view; } class ViewHolder { ImageView fruitImage; TextView fruitName; } }