ViewHolder模式超簡潔寫法

以前都是這樣一遍遍的 new ViewHolder

private class LvAdapter extends BaseAdapter{
        private ViewHolder holder;

        @Override
        public int getCount() {
            return list.size();
        }

        @Override
        public Object getItem(int position) {
            return list.get(position);
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            if(convertView == null){
                holder = new ViewHolder();
                convertView = LayoutInflater.from(MainActivity.this).inflate(R.layout.activity_main_item,null);
                holder.txt = (TextView)convertView.findViewById(R.id.txt);
                convertView.setTag(holder);
            }
            else{
                holder = (ViewHolder) convertView.getTag();
            }
            //TextView txt = ViewHolder.get(convertView,R.id.txt);
            holder.txt.setText(list.get(position));
            return convertView;
        }

        private class ViewHolder{
            TextView txt;
        }
    }

因此，有這麼一種簡潔的寫法分享給你們，先聲明，從國外網站上看的，不是本身原創的，但確實很喜歡這個簡潔的設計。

public class ViewHolder {
    public static <T extends View> T get(View view, int id) {
        SparseArray viewHolder = (SparseArray) view.getTag();
        if (viewHolder == null) {
            viewHolder = new SparseArray();
            view.setTag(viewHolder);
        }
        View childView = (View) viewHolder.get(id);
        if (childView == null) {
            childView = view.findViewById(id);
            viewHolder.put(id, childView);
        }
        return (T) childView;
    }
}

private class LvAdapter extends BaseAdapter{

        @Override
        public int getCount() {
            return list.size();
        }

        @Override
        public Object getItem(int position) {
            return list.get(position);
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            if(convertView == null){
                convertView = LayoutInflater.from(MainActivity.this).inflate(R.layout.activity_main_item,null);
            }
            TextView txt = ViewHolder.get(convertView,R.id.txt);
            txt.setText(list.get(position));
            return convertView;
        }
    }

值得注意的是SparseArray這個知識點，優化過的存儲integer和object鍵值對的HashMap