[flutter_local_notifications] Throw ArgumentError when trying to initialize LocalNotification without per Platform settings

[talamaska]

change: throw ArgumentError when trying to initialize LocalNotification without per Platform settings
add: tests
add: inline docs

[talamaska]

The solution is not using asserts, because they are not flexible enough and also they force us to not use const constructors, which is undesirable. Throwing and ArgumentError is the right thing to do. The check will happen before the null check operator used on null value exception throws. Added more Readme and inline docs for the devs to make clearer.

[MaikuB]

Thanks for the PR. I left some comments on the changes but also wanted to ask if you could clarify the following point

The solution is not using asserts, because they are not flexible enough and also they force us to not use const constructors, which is undesirable.

Whilst I don't have an issue with using ArgumentError, the point of const constructors doesn't apply to this PR. I assume you're referring to have code in the body of the constructor, if so wouldn't that happen for ArgumentErrors too? In actual fact, assertions are the one that do allow for const constructors. There a lot widgets within Flutter with const constructors and assertions. Perhaps you're not familiar with how this can be done but there's also an example within the repository

flutter_local_notifications/flutter_local_notifications/lib/src/types.dart

Line 42 in 3b5f61d

]) : assert(hour >= 0 && hour < 24),

[talamaska]

Thanks for the PR. I left some comments on the changes but also wanted to ask if you could clarify the following point

The solution is not using asserts, because they are not flexible enough and also they force us to not use const constructors, which is undesirable.

Whilst I don't have an issue with using ArgumentError, the point of const constructors doesn't apply to this PR. I assume you're referring to have code in the body of the constructor, if so wouldn't that happen for ArgumentErrors too? In actual fact, assertions are the one that do allow for const constructors. There a lot widgets within Flutter with const constructors and assertions. Perhaps you're not familiar with how this can be done but there's also an example within the repository

flutter_local_notifications/flutter_local_notifications/lib/src/types.dart

Line 42 in 3b5f61d

]) : assert(hour >= 0 && hour < 24),

yes, but they do not refer to Platform.

[MaikuB]

yes, but they do not refer to Platform.

Not sure what you were trying to answer with this one but if it's to do with assertions then given my comments on the PR where the platform checks you added aren't needed as they already exist, suppose assertions were added then they would be done within the various if blocks for each platform to check to see if the corresponding settings isn't null.

[MaikuB]

Thanks for making the changes. Been really busy so haven't been able to revisit this until now and I just noticed a minor formatting thing for API docs so I made the change directly here so this can go out soon