Bug 43444 - NSDimension.BaseUnit static method causes NSInvalidArgumentException
Summary: NSDimension.BaseUnit static method causes NSInvalidArgumentException
Alias: None
Product: iOS
Classification: Xamarin
Component: Xamarin.iOS.dll ()
Version: XI 9.99 (iOS 10 previews)
Hardware: PC Mac OS
: Normal normal
Target Milestone: Xcode8 (iOS10)
Assignee: Sebastien Pouliot
Depends on:
Reported: 2016-08-17 00:37 UTC by Larry O'Brien
Modified: 2016-08-25 09:07 UTC (History)
3 users (show)

Is this bug a regression?: ---
Last known good build:

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Description Larry O'Brien 2016-08-17 00:37:56 UTC
OK, so I'm still using the previous binding where NSUnit/NSDimension/NSUnit{Foo} instead of Unit/Dimension/Unit{Foo} but putting that aside:

The new NSUnit/NSDimension/NSUnit{Foo} hierarchy has a method `BaseUnit` that is supposed to return: "An NSDimension subclass object from which all other units provided by the subclass are defined." and "The default implementation returns nil to indicate that the NSDimension class should not be used directly.

When implementing a subclass, you should return a unit converter that returns the inputted value for both the baseUnitValueFromValue: and valueFromBaseUnitValue: methods." 

So, for instance, in Swift you have:

   var au = UnitAcceleration.baseUnit()

And that gives you an instance of UnitAcceleration. 

We bind it as a static method, but when you run

   var au = NSUnitAcceleration.BaseUnit;

You get:

NSInvalidArgumentException "You must override baseUnit in your class NSDimension to define its base unit." 

(The issue is not unique to NSUnitAcceleration, of course...)
Comment 1 Sebastien Pouliot 2016-08-17 19:55:12 UTC
> where  NSUnit/NSDimension/NSUnit{Foo} instead of Unit/Dimension/Unit{Foo}

I'm not sure what you mean by the above, it seems you're comparing the ObjC vs the Swift API.

> BaseUnit

I'll check that. In ObjC you can override static "methods" which is not something you can do in C# and it requires a bit of extra code.
Comment 2 Sebastien Pouliot 2016-08-18 02:06:41 UTC
I got a local fix for NSUnitAcceleration - but it needs to be duplicated for other types (since it's _unnatural_ for C# to override static methods).

It's nice that you spotted this as it will need to be documented, i.e. how to handle `baseUnit` when subclassing `NSUnit` for your own types.

Also note that `NSDimension` will become `abstract` based on the comment

> NSDimension is an abstract subclass of NSUnit

from https://developer.apple.com/reference/foundation/nsdimension?language=objc
Comment 3 Sebastien Pouliot 2016-08-18 13:55:41 UTC
Comment 4 Sebastien Pouliot 2016-08-19 14:05:43 UTC
Fixed in xamarin-macios/xcode8 c7abd28f2c07407602080527b6b9486743af995b