[TrimmableTypeMap] Fix [Export] JNI signature mapping for non-primitive parameter types (#11051)

## Problem

The scanner's `ManagedTypeToJniDescriptor()` method maps managed types to JNI descriptors for `[Export]` method signatures. It correctly handles primitives (`bool` → `Z`, `int` → `I`, etc.) and `string` → `Ljava/lang/String;`, but **falls back to `Ljava/lang/Object;` for all other types**. This means `[Export]` methods with parameters like `Android.Graphics.Bitmap`, `Android.Views.View`, or any custom Java-bound type get incorrect JNI signatures in the generated JCW, causing `NoSuchMethodError` at runtime.

## Fix

`ManagedTypeToJniDescriptor()` now resolves Java-bound types by looking up their `[Register]` attribute via the existing `TryResolveJniObjectDescriptor()` infrastructure (already used by the constructor signature path), falling back to `Ljava/lang/Object;` only for types that truly cannot be resolved.

## Changes Made

- **`ManagedTypeToJniDescriptor`** — Added `TryResolveJniObjectDescriptor` call before the `Ljava/lang/Object;` fallback; converted from `static` to instance to access the assembly cache.
- **`BuildJniSignatureFromManaged`, `ParseExportAttribute`, `ParseExportFieldAsMethod`, `TryGetMethodRegisterInfo`, `CollectExportField`** — Converted from `static` to instance (transitively need the assembly cache for type resolution).
- **`ExportWithJavaBoundParams`** test type — Added with three `[Export]` methods taking `Android.Views.View` parameters.
- **`Scan_ExportMethod_ResolvesJavaBoundParameterTypes`** test theory — Verifies correct JNI signatures for `[Export]` methods with non-primitive Java-bound parameter types.
- **`ExportFieldTests`** — Updated assertion to expect the correctly resolved type name (`my.app.ExportFieldExample`) instead of the previous incorrect `java.lang.Object` fallback.

## Testing

- All 303 TrimmableTypeMap unit tests pass, including 3 new test cases.

Author: Copilot

src/Microsoft.Android.Sdk.TrimmableTypeMap/Scanner/JavaPeerScanner.cs

@@ -956,7 +956,7 @@ List<string> ResolveImplementedInterfaceJavaNames (TypeDefinition typeDef, Assem
 		return resolved is not null ? ResolveRegisterJniName (resolved.Value.typeName, resolved.Value.assemblyName) : null;
 	}
 
-	static bool TryGetMethodRegisterInfo (MethodDefinition methodDef, AssemblyIndex index, out RegisterInfo? registerInfo, out ExportInfo? exportInfo)
+	bool TryGetMethodRegisterInfo (MethodDefinition methodDef, AssemblyIndex index, out RegisterInfo? registerInfo, out ExportInfo? exportInfo)
 	{
 		exportInfo = null;
 		foreach (var caHandle in methodDef.GetCustomAttributes ()) {
@@ -1006,7 +1006,7 @@ static bool TryGetMethodRegisterInfo (MethodDefinition methodDef, AssemblyIndex
 		return null;
 	}
 
-	static (RegisterInfo registerInfo, ExportInfo exportInfo) ParseExportAttribute (CustomAttribute ca, MethodDefinition methodDef, AssemblyIndex index)
+	(RegisterInfo registerInfo, ExportInfo exportInfo) ParseExportAttribute (CustomAttribute ca, MethodDefinition methodDef, AssemblyIndex index)
 	{
 		var value = index.DecodeAttribute (ca);
 
@@ -1050,7 +1050,7 @@ static bool TryGetMethodRegisterInfo (MethodDefinition methodDef, AssemblyIndex
 		);
 	}
 
-	static string BuildJniSignatureFromManaged (MethodSignature<string> sig)
+	string BuildJniSignatureFromManaged (MethodSignature<string> sig)
 	{
 		var sb = new System.Text.StringBuilder ();
 		sb.Append ('(');
@@ -1067,7 +1067,7 @@ static string BuildJniSignatureFromManaged (MethodSignature<string> sig)
 	/// [ExportField] methods use the managed method name as the JNI name and have
 	/// a connector of "__export__" (matching legacy CecilImporter behavior).
 	/// </summary>
-	static (RegisterInfo registerInfo, ExportInfo exportInfo) ParseExportFieldAsMethod (CustomAttribute ca, MethodDefinition methodDef, AssemblyIndex index)
+	(RegisterInfo registerInfo, ExportInfo exportInfo) ParseExportFieldAsMethod (CustomAttribute ca, MethodDefinition methodDef, AssemblyIndex index)
 	{
 		var managedName = index.Reader.GetString (methodDef.Name);
 		var sig = methodDef.DecodeSignature (SignatureTypeProvider.Instance, genericContext: default);
@@ -1080,10 +1080,11 @@ static string BuildJniSignatureFromManaged (MethodSignature<string> sig)
 	}
 
 	/// <summary>
-	/// Maps a managed type name to its JNI descriptor. Falls back to
-	/// "Ljava/lang/Object;" for unknown types (used by [Export] signature computation).
+	/// Maps a managed type name to its JNI descriptor. Resolves Java-bound types
+	/// via their [Register] attribute, falling back to "Ljava/lang/Object;" only
+	/// for types that cannot be resolved (used by [Export] signature computation).
 	/// </summary>
-	static string ManagedTypeToJniDescriptor (string managedType)
+	string ManagedTypeToJniDescriptor (string managedType)
 	{
 		var primitive = TryGetPrimitiveJniDescriptor (managedType);
 		if (primitive is not null) {
@@ -1094,6 +1095,12 @@ static string ManagedTypeToJniDescriptor (string managedType)
 			return $"[{ManagedTypeToJniDescriptor (managedType.Substring (0, managedType.Length - 2))}";
 		}
 
+		// Try to resolve as a Java peer type with [Register]
+		var resolved = TryResolveJniObjectDescriptor (managedType);
+		if (resolved is not null) {
+			return resolved;
+		}
+
 		return "Ljava/lang/Object;";
 	}
 
@@ -1515,7 +1522,7 @@ static List<JavaConstructorInfo> BuildJavaConstructors (List<MarshalMethodInfo>
 	/// Checks a single method for [ExportField] and adds a JavaFieldInfo if found.
 	/// Called inline during Pass 1 to avoid a separate iteration.
 	/// </summary>
-	static void CollectExportField (MethodDefinition methodDef, AssemblyIndex index, List<JavaFieldInfo> fields)
+	void CollectExportField (MethodDefinition methodDef, AssemblyIndex index, List<JavaFieldInfo> fields)
 	{
 		foreach (var caHandle in methodDef.GetCustomAttributes ()) {
 			var ca = index.Reader.GetCustomAttribute (caHandle);

tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Generator/ExportFieldTests.cs

@@ -20,8 +20,8 @@ public void Scanner_DetectsExportFieldsWithCorrectProperties ()
 		var staticField = peer.JavaFields.First (f => f.FieldName == "STATIC_INSTANCE");
 		Assert.True (staticField.IsStatic);
 		Assert.Equal ("GetInstance", staticField.InitializerMethodName);
-		// Reference type — mapped via JNI signature, not fallback to java.lang.Object
-		Assert.Equal ("java.lang.Object", staticField.JavaTypeName);
+		// Reference type — mapped via JNI signature to the actual Java type
+		Assert.Equal ("my.app.ExportFieldExample", staticField.JavaTypeName);
 
 		var instanceField = peer.JavaFields.First (f => f.FieldName == "VALUE");
 		Assert.False (instanceField.IsStatic);

tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Scanner/JavaPeerScannerTests.Behavior.cs

@@ -53,6 +53,19 @@ public void Scan_MarshalMethod_ConstructorsAndSpecialCases ()
 			FindFixtureByManagedName ("Android.Views.IOnClickListener").InvokerTypeName);
 	}
 
+	[Theory]
+	[InlineData ("processView", "(Landroid/view/View;)V")]
+	[InlineData ("handleClick", "(Landroid/view/View;I)Z")]
+	[InlineData ("getViewName", "(Landroid/view/View;)Ljava/lang/String;")]
+	public void Scan_ExportMethod_ResolvesJavaBoundParameterTypes (string jniName, string expectedSig)
+	{
+		var method = FindFixtureByJavaName ("my/app/ExportWithJavaBoundParams")
+			.MarshalMethods.FirstOrDefault (m => m.JniName == jniName);
+		Assert.NotNull (method);
+		Assert.Equal (expectedSig, method.JniSignature);
+		Assert.Null (method.Connector);
+	}
+
 	[Theory]
 	[InlineData ("android/app/Activity", "Android.App.Activity")]
 	[InlineData ("my/app/SimpleActivity", "Android.App.Activity")]

tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/TestFixtures/TestTypes.cs

@@ -284,6 +284,23 @@ public class ExportExample : Java.Lang.Object
 		public void MyExportedMethod () { }
 	}
 
+	/// <summary>
+	/// Has [Export] methods with non-primitive Java-bound parameter types.
+	/// The JCW should resolve parameter types via [Register] instead of falling back to Object.
+	/// </summary>
+	[Register ("my/app/ExportWithJavaBoundParams")]
+	public class ExportWithJavaBoundParams : Java.Lang.Object
+	{
+		[Java.Interop.Export ("processView")]
+		public void ProcessView (Android.Views.View view) { }
+
+		[Java.Interop.Export ("handleClick")]
+		public bool HandleClick (Android.Views.View view, int action) { return false; }
+
+		[Java.Interop.Export ("getViewName")]
+		public string GetViewName (Android.Views.View view) { return ""; }
+	}
+
 	/// <summary>
 	/// Has [Export] methods with different access modifiers.
 	/// The JCW should respect the C# visibility for [Export] methods.