UITableview Cells重用须知

1、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.