Programatically scrolling UICollectionView when estimated item size is set causes crash.

Originator:dillan.laughlin
Number:rdar://22936683 Date Originated:10-01-2015
Status:Open Resolved:
Product:iOS SDK Product Version:
Classification:Crash Reproducible:Always
 
Summary:
Programatically scrolling a collection view after setting the estimated item size crash if the user has not already scrolled to the destination position.

From the attached backtrace it appears to be a divide by zero issue while calculating layout attributes.

Steps to Reproduce:
1. Run the attached sample project.
2. Without manually scrolling, tap the "Scroll to Index Path..." toolbar button to initiate a programatic scroll.

Expected Results:
Collection view scrolls to specified index path.

Actual Results:
App crashes with apparent divide by zero layout calculation exception.

Version:
iOS 9.0.1

Notes:
If you comment out the estimated item size code in -[ViewController viewDidLoad], the app will not crash when attempting programatic scrolling.

Configuration:
iPad Air 2

Attachments:
'collection_view_backtrace.txt' and 'CollectionViewScroll.zip' were successfully uploaded.

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