UITableViewCell在IOS6下分割線是預設頂頭的,在IOS7以後左邊會有一定的間距（15）。

網上有一些解決辦法，分享我找到的最簡單的一種：在資料來源方法tableView：cellForRowAtIndexPath：中加入如下三行

        cell.preservesSuperviewLayoutMargins = NO;
        cell.separatorInset = UIEdgeInsetsZero;
        cell.layoutMargins = UIEdgeInsetsZero;

需要注意的是preservesSuperviewLayoutMargins

至於原因如下：

Setting the separatorInset of tableView to UIEdgeInsetsZero is not going to work. It will only effect the extra separators, not the cells that you created.
iOS8 introduces layoutMargins property on UIView, along with another property called preservesSuperviewLayoutMargins indicating whether superview’s layoutMargins is preserved (Think of it as an override) which is YES by default. layoutMargins property is a set of insets from the edge of the view’s bounds that denote a default spacing for laying out content.
The default separatorInset of tableView and tableViewCell is (top = 0, left = 15, bottom = 0, right = 0)
The default layoutMargins of tableView and tableViewCell is (top = 8, left = 8, bottom = 8, right = 8)
These 3 properties are defining the behaviour of separator indentation.
However, setting tableView’s layoutMargins is not going to effect tableViewCell. Because tableViewCell’s superview is not tableView. It’s tableView’s subView, an instance of UITableViewWrapperView whose superClass is UIScrollView and whose layoutMargins is (top = 8, left = 15, bottom = 8, right = 15) and preservesSuperviewLayoutMargins is YES.
You have to set separatorInset and layoutMargins of tableViewCell directly:
tableViewCell.preservesSuperviewLayoutMargins = NO;
tableViewCell.separatorInset = UIEdgeInsetsZero;
tableViewCell.layoutMargins = UIEdgeInsetsZero;
You can put those code in cell’s init method or awakeFromNib or tableView’s delegate tableView:willDisplayCell:fromRowAtIndexPath, etc.

大致的意思是說iOS7只有separatorInset的概念,在IOS7下tableView的分割線左邊有15畫素的間距。

iOS8中還有layoutMargins，用來表示子view和父view的間距，有8畫素的間距。preservesSuperviewLayoutMargins預設為true表示開啟子view與父view的間距。