Dont pass around BuildContext for making snackbars

[JAicewizard]

What

Use a GlobalKey<ScaffoldMessengerState> instead of passing around a BuildContext

Why

BuildContext can expire, and although it is possible to avoid using an expired BuildContext we don't know if the scaffold is still alive at the time of calling a snackbar.

How

https://github.com/flutter/flutter/blob/master/examples/api/lib/material/scaffold/scaffold_messenger.of.1.dart

[DeD1rk]

That solution actually requires passing down the globalkey all over the widget tree, or lookign it up using another context. So it doesn't really help when compared to looking up from context synchronously.

[JAicewizard]

Yeah but in most cases its just in the widget itself, when its available its probably better to do this as its also faster