Implement ITransactionHistoryExtensions

[jsteinich]

ITransactionHistoryExtensions is useful for determining more information about why a purchase failed.
Currently trying to access results in an exception:

ArgumentException: No binding for type UnityEngine.Purchasing.ITransactionHistoryExtensions
      at UnityEngine.Purchasing.PurchasingFactory.GetExtension[T]

Ideally it would have the error code and debug message that gets logged on failure.

[Qing451800]

Thanks for letting us know. We add this to our backlog.

[RaulGMR]

Any updates on this? I also have the same issue, when I try to retrieve extra info from a failed purchase ...

[Qing451800]

It turns out to be not that straightforward since this interface is not in Purchasing.dll but in Stores.dll. We're still investigating it. It's not our top priority but it's definitely on our list.

[jsteinich]

I've gotten a version of this at least partially working here.

I'm relying on the fact that our project includes unity purchasing and therefore Stores.dll, but I imagine that won't work for the published package.

[Qing451800]

The implementation looks good to me. If that serves your purpose, then feel free to use it.

We're holding a similar fix because we don't want to create a dependency on Unity's Stores.dll. Once the Unity IAP is fully migrated to use the Package Manager, the dependency issue will not happen.