#2922 RotatorTile _nextElement null exception

[SoundersFan]

Guard against dereferencing null _nextElement

Issue: #2922

PR Type

What kind of change does this PR introduce?

• Bugfix

What is the current behavior?

When RotatorTile is initially Collapsed the OnApplyTemplate() method is not called before the control starts it's background timer to auto-advance the items. In advancing the _nextElement is dereferenced but since OnApplyTemplate has not run, it is still null and, kaboom.

What is the new behavior?

The null reference is avoided and no kaboom

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Pull Request has been submitted to the documentation repository instructions. Link:
• Sample in sample app has been added / updated (for bug fixes / features)
  • Icon has been created (if new sample) following the Thumbnail Style Guide and templates
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Header has been added to all new source files (run build/UpdateHeaders.bat)
• Contains NO breaking changes

Other information

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All CLA requirements met.

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[michael-hawker]

Thanks @SoundersFan, it looks like we try and start the timer in both the OnApplyTemplate and when the control has Loaded. However, we should probably not start the timer on Load if the control is collapsed? I'm wondering if trying to mitigate the scenario where this occurs would be better than trying to just add null checks everywhere?

[michael-hawker]

We discussed, we can address the timer question separately. Will test quick later so we can merge this.

[michael-hawker]

Thanks @SoundersFan, tested it out and it looks good!

[Kyaa-dost]

Tested on my end and seems to be performing as expected. All clear!