[Mono.Android] JNIEnv.FindClass() uses JniEnvironment.Types.FindClass() (#9769)

Context: xamarin/monodroid@ed984a3
Context: dotnet/java-interop#23

Update `JNIEnv.FindClass()` to use `JniEnvironment.Types.FindClass()`.

This avoids the problem of `JNIEnvInit.mid_Class_forName` being
`null` in a NativeAOT context:

	E AndroidRuntime: Process: net.dot.hellonativeaot, PID: 30744
	E AndroidRuntime: net.dot.jni.internal.JavaProxyThrowable: System.TypeInitializationException: TypeInitialization_Type_NoTypeAvailable
	E AndroidRuntime:  ---> System.ArgumentNullException: ArgumentNull_Generic Arg_ParamName_Name, method
	E AndroidRuntime:    at Java.Interop.JniEnvironment.StaticMethods.CallStaticObjectMethod(JniObjectReference, JniMethodInfo, JniArgumentValue*) + 0x1c8
	E AndroidRuntime:    at Android.Runtime.JNIEnv.FindClass(String) + 0xb4
	E AndroidRuntime:    at Java.Lang.Class..cctor() + 0x7c
	E AndroidRuntime:    at System.Runtime.CompilerServices.ClassConstructorRunner.EnsureClassConstructorRun(StaticClassConstructionContext*) + 0xb4
	E AndroidRuntime:    Exception_EndOfInnerExceptionStack
	E AndroidRuntime:    at System.Runtime.CompilerServices.ClassConstructorRunner.EnsureClassConstructorRun(StaticClassConstructionContext*) + 0x160
	E AndroidRuntime:    at System.Runtime.CompilerServices.ClassConstructorRunner.CheckStaticClassConstructionReturnNonGCStaticBase(StaticClassConstructionContext*, IntPtr) + 0x14
	E AndroidRuntime:    at Android.Runtime.JNIEnv.FindClass(String) + 0xc0
	E AndroidRuntime:    at Android.App.Application.get_Context() + 0x50
	E AndroidRuntime:    at Microsoft.Maui.Hosting.EssentialsExtensions.<>c.<UseEssentials>b__0_0(ILifecycleBuilder life) + 0x18
	E AndroidRuntime:    at Microsoft.Maui.LifecycleEvents.LifecycleEventService..ctor(IEnumerable`1) + 0x94
	E AndroidRuntime:    at Microsoft.Maui.LifecycleEvents.MauiAppHostBuilderExtensions.<>c.<ConfigureLifecycleEvents>b__0_0(IServiceProvider sp) + 0x3c
	E AndroidRuntime:    at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitRootCache(ServiceCallSite, RuntimeResolverContext) + 0x68
	E AndroidRuntime:    at Microsoft.Extensions.DependencyInjection.ServiceProvider.CreateServiceAccessor(ServiceIdentifier serviceIdentifier) + 0x180
	E AndroidRuntime:    at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey, Func`2) + 0x11c
	E AndroidRuntime:    at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(ServiceIdentifier, ServiceProviderEngineScope) + 0x44
	E AndroidRuntime:    at Microsoft.Maui.MauiContext.WrappedServiceProvider.GetService(Type) + 0x48
	E AndroidRuntime:    at Microsoft.Maui.MauiContext.WrappedServiceProvider.GetService(Type) + 0x48
	E AndroidRuntime:    at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider) + 0x3c
	E AndroidRuntime:    at Microsoft.Maui.LifecycleEvents.LifecycleEventServiceExtensions.<GetLifecycleEventDelegates>d__3`1.MoveNext() + 0x38
	E AndroidRuntime:    at Microsoft.Maui.LifecycleEvents.LifecycleEventServiceExtensions.InvokeLifecycleEvents[TDelegate](IServiceProvider, Action`1) + 0x68
	E AndroidRuntime:    at Microsoft.Maui.MauiApplication.OnCreate() + 0xb0
	E AndroidRuntime:    at Android.App.Application.n_OnCreate(IntPtr jnienv, IntPtr native__this) + 0xb0
	E AndroidRuntime: at my.MainApplication.n_onCreate(Native Method)
	E AndroidRuntime: at my.MainApplication.onCreate(MainApplication.java:24)
	E AndroidRuntime: at android.app.Instrumentation.callApplicationOnCreate(Instrumentation.java:1386)
	E AndroidRuntime: at android.app.ActivityThread.handleBindApplication(ActivityThread.java:7398)
	E AndroidRuntime: at android.app.ActivityThread.-$$Nest$mhandleBindApplication(Unknown Source:0)
	E AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2379)
	E AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:107)
	E AndroidRuntime: at android.os.Looper.loopOnce(Looper.java:232)
	E AndroidRuntime: at android.os.Looper.loop(Looper.java:317)
	E AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:8592)
	E AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
	E AndroidRuntime: at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:580)
	E AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:878)

This also allows us to remove these fields that are now unused:

  * `JnienvInitializeArgs.Class_forName`
  * `JNIEnv.BinaryName()`

TODO?  While `JNIEnv.FindClass()` was using [`Class.forName()`][0],
`JniEnvironment.Types.FindClass()` uses [`ClassLoader.loadClass()`][1].
`JNIEnv.FindClass()` originally used `ClassLoader.loadClass()`, but
was changed to use `Class.forName()` in xamarin/monodroid@ed984a3a as
part of supporting the Xamarin.Android Designer.

Updating `JNIEnv.FindClass()` to use `JniEnvironment.Types.FindClass()`
effectively reverts that original change.  This is "fine" for now --
the Xamarin.Android Designer is no longer supported -- but in the
future we may want to update `JniEnvironment.Types.FindClass()` to
use `Class.forName()`; see dotnet/java-interop#23.

[0]: https://developer.android.com/reference/java/lang/Class#forName(java.lang.String)
[1]: https://developer.android.com/reference/java/lang/ClassLoader#loadClass(java.lang.String)

Author: jonathanpeppers

src/Mono.Android/Android.Runtime/JNIEnv.cs

@@ -280,52 +280,9 @@ public static IntPtr FindClass (System.Type type)
 			}
 		}
 
-		const int nameBufferLength = 1024;
-		[ThreadStatic] static char[]? nameBuffer;
-
-		static unsafe IntPtr BinaryName (string classname)
+		public static IntPtr FindClass (string classname)
 		{
-			int index = classname.IndexOf ('/');
-
-			if (index == -1)
-				return NewString (classname);
-
-			int length = classname.Length;
-			if (length > nameBufferLength)
-				return NewString (classname.Replace ('/', '.'));
-
-			if (nameBuffer == null)
-				nameBuffer = new char[nameBufferLength];
-
-			fixed (char* src = classname, dst = nameBuffer) {
-				char* src_ptr = src;
-				char* dst_ptr = dst;
-				char* end_ptr = src + length;
-				while (src_ptr < end_ptr) {
-					*dst_ptr = (*src_ptr == '/') ? '.' : *src_ptr;
-					src_ptr++;
-					dst_ptr++;
-				}
-			}
-			return NewString (nameBuffer, length);
-		}
-
-		public unsafe static IntPtr FindClass (string classname)
-		{
-			JniObjectReference local_ref;
-
-			IntPtr native_str = BinaryName (classname);
-			try {
-				JniArgumentValue* parameters = stackalloc JniArgumentValue [3] {
-					new JniArgumentValue (native_str),
-					new JniArgumentValue (true),
-					new JniArgumentValue (JNIEnvInit.java_class_loader),
-				};
-				local_ref = JniEnvironment.StaticMethods.CallStaticObjectMethod (Java.Lang.Class.Members.JniPeerType.PeerReference, JNIEnvInit.mid_Class_forName!, parameters);
-			} finally {
-				DeleteLocalRef (native_str);
-			}
-
+			JniObjectReference local_ref = JniEnvironment.Types.FindClass (classname);
 			IntPtr global_ref = NewGlobalRef (local_ref.Handle);
 			JniObjectReference.Dispose (ref local_ref);
 			return global_ref;

src/Mono.Android/Android.Runtime/JNIEnvInit.cs

@@ -20,7 +20,6 @@ internal struct JnienvInitializeArgs {
 			public IntPtr          grefLoader;
 			public IntPtr          Loader_loadClass;
 			public IntPtr          grefClass; // TODO: remove, not needed anymore
-			public IntPtr          Class_forName;
 			public uint            logCategories;
 			public int             version; // TODO: remove, not needed anymore
 			public int             grefGcThreshold;
@@ -46,7 +45,6 @@ internal struct JnienvInitializeArgs {
 		internal static IntPtr grefIGCUserPeer_class;
 		internal static IntPtr grefGCUserPeerable_class;
 		internal static IntPtr java_class_loader;
-		internal static JniMethodInfo? mid_Class_forName;
 
 		internal static JniRuntime? androidRuntime;
 
@@ -100,8 +98,6 @@ internal static unsafe void Initialize (JnienvInitializeArgs* args)
 			MarshalMethodsEnabled = args->marshalMethodsEnabled;
 			java_class_loader = args->grefLoader;
 
-			mid_Class_forName = new JniMethodInfo (args->Class_forName, isStatic: true);
-
 			BoundExceptionType = (BoundExceptionType)args->ioExceptionType;
 			androidRuntime = new AndroidRuntime (args->env, args->javaVm, args->grefLoader, args->Loader_loadClass, args->jniAddNativeMethodRegistrationAttributePresent != 0);
 			ValueManager = androidRuntime.ValueManager;

src/native/mono/monodroid/monodroid-glue-internal.hh

@@ -89,7 +89,6 @@ namespace xamarin::android::internal
 			jobject         grefLoader;
 			jmethodID       Loader_loadClass;
 			jclass          grefClass;
-			jmethodID       Class_forName;
 			unsigned int    logCategories;
 			int             version;
 			int             grefGcThreshold;

src/native/mono/monodroid/monodroid-glue.cc

@@ -860,7 +860,6 @@ MonodroidRuntime::init_android_runtime (JNIEnv *env, jclass runtimeClass, jobjec
 
 	init.grefClass = RuntimeUtil::get_class_from_runtime_field (env, runtimeClass, "java_lang_Class", true);
 	Class_getName  = env->GetMethodID (init.grefClass, "getName", "()Ljava/lang/String;");
-	init.Class_forName = env->GetStaticMethodID (init.grefClass, "forName", "(Ljava/lang/String;ZLjava/lang/ClassLoader;)Ljava/lang/Class;");
 
 	MonoAssembly *mono_android_assembly;