table的cell是可以复用的，滚动起来的时候， 需要用到的cell都已经生成了，需要做的只是把内容填写到将要显示的cell上去， 如果这个内容（图片，文字）也都已经加载到内存里了，有什么是能够导致不流畅的因素呢？除非你在“填写”cell这个操作里做了什么阻塞的事情。。。

• 重用 cell
• 避免重复布局 cell 的内容
• 保持 cell 内容为非透明

Cells and Table View Performance

The proper use of table view cells, whether off-the-shelf or custom
cell objects, is a major factor in the performance of table views.
Ensure that your application does the following three things:

Reuse cells. Object allocation has a performance cost, especially if
the allocation has to happen repeatedly over a short period—say, when
the user scrolls a table view. If you reuse cells instead of
allocating new ones, you greatly enhance table view performance.

Avoid relayout of content. When reusing cells with custom subviews, refrain
from laying out those subviews each time the table view requests a
cell. Lay out the subviews once, when the cell is created.

Use opaque subviews. When customizing table view cells, make the subviews of the > cell opaque, not
transparent.

Ref：https://developer.apple.com/library/ios/documentation/userexperience/conceptual/tableview_iphone/TableViewCells/TableViewCells.html