Android App开发学习第十四天：BaseAdapter的一些优化

重用ConvertView

一般我们在重写BaseAdapter里的getView()中，有多少条数据就要inflate多少次布局文件，比较浪费资源。未优化前的代码

 @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        convertView = LayoutInflater.from(mContext).inflate(R.layout.item_demo,parent,false);
       
        TextView textView = convertView.findViewById(R.id.tv_item);
        textView.setText(list.get(position));
        return convertView;
    }

实际上，convertView是系统提供给我们的可复用的View的缓存对象，只需加一个判断即可实现复用。

   @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView ==null){
            convertView = LayoutInflater.from(mContext).inflate(R.layout.item_demo,parent,false);
        }
        TextView textView = convertView.findViewById(R.id.tv_item);
        textView.setText(list.get(position));
        return convertView;
    }

ViewHolder重用组件
getView()会被调用多次，则findViewById也一样会被调用多次。未修改前

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView ==null){
            convertView = LayoutInflater.from(mContext).inflate(R.layout.item_demo,parent,false);
        }
       TextView textView = convertView.findViewById(R.id.tv_item);
        textView.setText(list.get(position));
        return convertView;
    }

可以自定义ViewHolder来绑定控件

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView ==null){
            convertView = LayoutInflater.from(mContext).inflate(R.layout.item_demo,parent,false);
            viewHolder = new ViewHolder();
            viewHolder.textView = convertView.findViewById(R.id.tv_item);
            convertView.setTag(viewHolder); //将viewHolder存储到convertView中
        }else {
            viewHolder = (ViewHolder) convertView.getTag();
        }
        viewHolder.textView.setText(list.get(position));
        return convertView;
    }

    static class ViewHolder{
        TextView textView;
    }
    }