view.setTag

无意中注意到了view.setTag（Object tag)方法.

Tag在View中是很有作用的属性，API中这样描述的：

Unlike IDs, tags are not used to identify views. Tags are essentially an extra piece of information that can be associated with a view. They are most often used as a convenience to store data related to views in the views themselves rather than by putting them in a separate structure.

Tag不像ID是用标示view的。Tag从本质上来讲是就是相关联的view的额外的信息。它们经常用来存储一些view的数据，这样做非常方便而不用存入另外的单独结构。

其实，我们在优化listview的getView()方法中就用到了setTag()和getTag（）。

摘取代码段如下：

ViewHolder viewHolder;
			if (convertView == null) {
				convertView = LayoutInflater.from(SongsActivity.this).inflate(
						R.layout.music_item, null);
				ImageView pImageView = (ImageView) convertView
						.findViewById(R.id.albumPhoto);
				viewHolder = new ViewHolder(pImageView, pTitle, pDuration,
						pArtist);
				convertView.setTag(viewHolder);
			} else {
				viewHolder = (ViewHolder) convertView.getTag();
			}

 setTag还有带2个参数的形式，setTag（key, tag），暂时不做讨论。