ViewHolder簡潔寫法

ViewHolder這麼寫（只提供一個靜態方法，其實能夠加一個私有構造函數防止外部實例化），代碼很簡單，看過就明白了

public class ViewHolder {

// I added a generic return type to reduce the casting noise in client code
@SuppressWarnings("unchecked")
public static <T extends View> T get(View view, int id) {
    SparseArray<View> viewHolder = (SparseArray<View>) view.getTag();
    if (viewHolder == null) {
        viewHolder = new SparseArray<View>();
        view.setTag(viewHolder);
    }
    View childView = viewHolder.get(id);
    if (childView == null) {
        childView = view.findViewById(id);
        viewHolder.put(id, childView);
    }
    return (T) childView;
}

}

在getView裏這樣寫

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

if (convertView == null) {
    convertView = LayoutInflater.from(context)
      .inflate(R.layout.banana_phone, parent, false);
}

ImageView bananaView = ViewHolder.get(convertView, R.id.banana);
TextView phoneView = ViewHolder.get(convertView, R.id.phone);

BananaPhone bananaPhone = getItem(position);
phoneView.setText(bananaPhone.getPhone());
bananaView.setImageResource(bananaPhone.getBanana());

return convertView;

}