UITableView got lag when scroll to larger row number

I have a UITableView that each of its cell has a same-size UIImageView as contentView's subView.

When I scroll it, at the beginning, it was quite smooth,but when it comes to larger row number, almost 50 开发者_开发问答row or more, the FPS become lower than 30,and the larger the row is ,the lower fps become.

I checked that there is no memory leak.

I‘m wondering if this is a common phenomenon?

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Most likely, you are doing something like [cellView addSubview:mySubview]; in your cellForRowAtIndexPath: method, irrespective of whether that cell was just created or re-used. The subviews are being stacked up leading to the problem that you are seeing.