Why does using headerReferenceSize with self-sizing cells in a collection view cause a crash in iOS 8?

问题

I managed to figure out the approach for self-sizing collection view cells under iOS 8.

I want to do this as a part of a accessory view.

I get a crash ... the interesting part of the stacktrace is as follows:

** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil'
*** First throw call stack:
(
  0   CoreFoundation    __exceptionPreprocess + 165
  1   libobjc.A.dylib   objc_exception_throw + 45
  2   CoreFoundation    -[__NSArrayM insertObject:atIndex:] + 954
  3   UIKit             -[UICollectionViewFlowLayout layoutAttributesForElementsInRect:] + 384
  4   UIKit             __45-[UICollectionViewData validateLayoutInRect:]_block_invoke + 144
  5   UIKit             -[UICollectionViewData validateLayoutInRect:] + 1396
  6   UIKit             -[UICollectionView layoutSubviews] + 170
  7   UIKit             -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 521
  8   QuartzCore        -[CALayer layoutSublayers] + 150
  9   QuartzCore        _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 380
  10  UIKit             -[UIView(Hierarchy) layoutBelowIfNeeded] + 611
  11  UIKit             -[UIInputSetHostView layoutIfNeeded] + 105
  12  UIKit             __43-[UIInputWindowController setInputViewSet:]_block_invoke + 112
  13  UIKit             +[UIView(Animation) performWithoutAnimation:] + 65
  14  UIKit             -[UIInputWindowController setInputViewSet:] + 291
  15  UIKit             -[UIInputWindowController performOperations:withAnimationStyle:] + 50
  16  UIKit             -[UIPeripheralHost(UIKitInternal) setInputViews:animationStyle:] + 1054
  17  UIKit             -[UIResponder becomeFirstResponder] + 468
  18  UIKit             -[UIView(Hierarchy) becomeFirstResponder] + 99
  19  UIKit             -[UITextView becomeFirstResponder] + 75
  ...

This looks like an Apple bug. Why does the layout seem to return an empty layout attribute?

回答1:

The best idea I have so far is based on this repository: https://github.com/algal/SelfSizingCellsDemo

On line 50 of ViewController.swift we have label.preferredMaxLayoutWidth = 320 which produces a cell that fills the whole screen and wraps the lines if there is enough text. This would need to be changed to fit whatever size screen you are working with. Then after each section you would need to add enough text to fill that label like is done on line 20 let items = smallitems.componentsSeparatedByString(" ") + [onelongitem]

The problem with this approach is that I don't yet know how I would put different views in that cell, besides text. This might work enough for your situation though.

来源：https://stackoverflow.com/questions/25460323/why-does-using-headerreferencesize-with-self-sizing-cells-in-a-collection-view-c