iOS 8: UITableViewCell.contentView doesn't resize subviews in it - ios

Question

I put an CustomView in UITableViewCell.contentView, setting the autoresize mask of the custom view as W+H.
But when running, the CustomView gets a larger height than the ContentView, the ContentView is 60pt in height(which is the same as setting in UITableViewDelegate), but the CustomView inside contentView is 76pt in height.
By Xcode6's view debugging, I see some strange constraints on my custom view, they are:
self.height = superview.height + 16
self.midY = superview.midY + 8
Where are these constraints come from and how to modify them? I've never set anything with a value 8 or 16.
UPDATE:
I've made a test project, which is simply a tableview in storyboard with a CustomView loaded from a nib file, and this test project replicated the problem, when running, the CustomView which is a subview of TableViewCell.contentView becomes larger in height than the TableViewCell.contentView.
The test project is here:
https://drive.google.com/file/d/0B5y_NrRbhGlSb1dlbVZNb19vNjQ/view?usp=sharing

Answer 1

At last I understand, auto layout can only form relations in the same xib or storyboard, my CustomView is in a separated xib and is loaded at runtime, so the super view and CustomView don't have any auto layout constraints between them.
If I set translatesAutoresizingMaskIntoConstraints to YES, then there goes the problem, I still don't know why using W+H as auto resizing mask makes CustomView taller than its super view(cell.contentView), but I found a way around:
I manually add constraints between superview and CustomView, and turn off customView. translatesAutoresizingMaskIntoConstraints, there the code goes:
customView.translatesAutoresizingMaskIntoConstraints = NO;
NSLayoutConstraint *top = [NSLayoutConstraint constraintWithItem:customView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:cell.contentView attribute:NSLayoutAttributeTop multiplier:1 constant:0];
NSLayoutConstraint *bottom = [NSLayoutConstraint constraintWithItem:customView attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:cell.contentView attribute:NSLayoutAttributeBottom multiplier:1 constant:0];
NSLayoutConstraint *left = [NSLayoutConstraint constraintWithItem:customView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:cell.contentView attribute:NSLayoutAttributeLeft multiplier:1 constant:0];
NSLayoutConstraint *right = [NSLayoutConstraint constraintWithItem:customView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:cell.contentView attribute:NSLayoutAttributeRight multiplier:1 constant:0];
[cell.contentView addConstraints:#[top, bottom, left, right]];