Nullable is Inconsistent

[gmck]

Android application type

Android for .NET (net6.0-android, etc.)

Affected platform version

VS 2022 17.5.0 Prev 1

Description

After getting my latest test app built and running in release mode, I then went back and enabled Nullable.
I’m now getting inconsistent results regarding replacing code such as if (Build.VERSION.SdkInt >= BuildVersionCodes.S)) with if (OperatingSystem.IsAndroidVersionAtLeast(31)).

See issue #7586 now closed and @jonathanpeppers reply.

As I progressed through all the .cs files modifying code for nullable, I was replacing code such as the above with OperatingSystem.IsAndroidVersionAtLeast(xx) as I went and the squiggles would go away etc. and I finished up one night with everything corrected except for one file SettingsFragment, which I knew had a number of these to be fixed.

So the next day I started to fix the SettingsFragment which needed other nullable type corrections as well. So I fixed all the other stuff leaving the OperatingSystem.IsAndroidVersionAtLeast(xx) to last.

As I started to fix them, I noticed that a number of them weren’t showing the usual squiggles and they were also building without any warnings.

So now I have a number of them where the new code is commented out, the old code is in play, and I still don’t have any warnings. I’ve tried cleaning and deleting the obj and bin folders, but I can’t make the warnings return using the old code.

Another example that resulted in a crash at runtime. (HelperExplanationDialogFragment)

BottomSheetBehavior? bottomSheetBehavior = BottomSheetBehavior.From((View)view!.Parent!); //OK
BottomSheetBehavior? bottomSheetBehavior = BottomSheetBehavior.From(view!.Parent is View);// Crashed at runtime

The last line was the suggested fix by the IDE.

Error from the log:

attempt to pass an instance of java.lang.Boolean as argument 1 to com.google.android.material.bottomsheet.BottomSheetBehavior com.google.android.material.bottomsheet.BottomSheetBehavior.from(android.view.View)

A final example is probably more of a how-to question.

How to correct the following?

Toast.MakeText(Activity, Resources.GetString(Resource.String.toast_message), ToastLength.Long).Show();

You can do the following, but would you want to?

Toast? toast = Toast.MakeText(Activity!, Resources.GetString(Resource.String.toast_message), ToastLength.Long);
 toast!.Show();

Test app https://github.com/gmck/NavigationGraph7Net7

Steps to Reproduce

See above.

Did you find any workaround?

No

Relevant log output

See above

[dellis1972]

@gmck I'm not sure, I'm gonna ask someone with a bit more experience on Nullables to take a look at this

[jonpryor]

@gmck: regarding your runtime crash, it is the result of a combination of factors:

1. generator has a bug wherein generic type parameters are bound as Java.Lang.Object and not the closest matching type constraint on the type parameter; see Use Java generic type parameters constraints java-interop#669
   Because of this, static <V extends View> BottomSheetBehavior<V> BottomSheetBehavior.from(V) is bound as BottomSheetBehavior.From(Java.Lang.Object), not as BottomSheetBehavior.From(Android.Views.View).

2. Java.Lang.Object has an implicit conversion from bool, which "boxes" boolean values into Java.Lang.Boolean values.

3. The fix suggested by the IDE is either wrong, or mis-interpreted. I have not tried to repro this.

In particular, the type of the expression e is T is of type bool. What your "IDE-suggested" code is actually doing is equivalent to:

bool v1 = view!.Parent is View;
var  v2 = new Java.Lang.Boolean(v1); // via "bool to Java.Lang.Object" implicit conversion
BottomSheetBehavior? bottomSheetBehavior = BottomSheetBehavior.From(v2);

What would work is if you used the as operator, e as T, which returns an expression of type T:

BottomSheetBehavior? bottomSheetBehavior = BottomSheetBehavior.From(view!.Parent as View);

Regarding your Toast.MakeText() question, I don't think there's a better way, unless you want to really ensure than Activity isn't null:

Toast toast = Toast.MakeText(
    Activity ?? throw new InvalidOperationException("Activity is null!"),
    Resources.GetString(Resource.String.toast_message),
    ToastLength.Long
) ?? throw new InvalidOperationException("Toast.MakeText returned null!");
toast.Show();

Hi @gmck. We have added the "need-info" label to this issue, which indicates that we have an open question for you before we can take further action. This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.

[jonpryor]

@gmck: are there any remaining questions or issues to address? Thanks!

[gmck]

@jonpryor

What would work is if you used the as operator, e as T, which returns an expression of type T:
BottomSheetBehavior? bottomSheetBehavior = BottomSheetBehavior.From(view!.Parent as View);

My original code (xamarin.android version) was From(view.Parent as View) therefore my first effort was as you have written, but that turned green.

If I paste your code example from here - it still turns green.

However, casting it is ok.
BottomSheetBehavior? bottomSheetBehavior = BottomSheetBehavior.From((View)view!.Parent!); //OK

Isn't (View) the equivalent of "as View"?

are there any remaining questions or issues to address? Thanks!

if (Build.VERSION.SdkInt >= BuildVersionCodes.S)) with if (OperatingSystem.IsAndroidVersionAtLeast(31))
My question re the above in this thread.

Also, issues raised in #7570 re Animations changes between Xamarin.AndroidX.Navigation.Ui from 2.5.1 to 2.5.2 and menu deprecations in #611 in AndroidX