给tableview cell添加阴影：

cell.layer.shadowOffset =CGSizeMake(0, 1);

cell.layer.shadowColor = [UIColorgrayColor].CGColor;

cell.layer.shadowRadius = 1;

cell.layer.shadowOpacity = .5f;

CGRect shadowFrame = cell.layer.bounds;

CGPathRef shadowPath = [UIBezierPath bezierPathWithRect:shadowFrame].CGPath; cell.layer.shadowPath
= shadowPath;

注意：不要给section footer 或 section header设置背景色，否则无效果。