[generator] Use GC.KeepAlive for reference type method parameters.

tests/generator-Tests/Unit-Tests/CodeGeneratorExpectedResults/JavaInterop1/WriteClass.txt

@@ -162,6 +162,7 @@ public partial class MyClass  {
 				_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 			} finally {
 				JNIEnv.DeleteLocalRef (native_value);
+				global::System.GC.KeepAlive (value);
 			}
 		}
 	}

tests/generator-Tests/Unit-Tests/CodeGeneratorExpectedResults/JavaInterop1/WriteClassProperties.txt

@@ -109,6 +109,7 @@ public virtual unsafe string Key {
 			_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 		} finally {
 			JNIEnv.DeleteLocalRef (native_value);
+			global::System.GC.KeepAlive (value);
 		}
 	}
 }

tests/generator-Tests/Unit-Tests/CodeGeneratorExpectedResults/JavaInterop1/WriteKotlinUnsignedArrayTypeMethodsClass.txt

@@ -27,6 +27,7 @@ public partial class MyClass  {
 				JNIEnv.CopyArray (native_value, value);
 				JNIEnv.DeleteLocalRef (native_value);
 			}
+			global::System.GC.KeepAlive (value);
 		}
 	}
 
@@ -46,6 +47,7 @@ public partial class MyClass  {
 				JNIEnv.CopyArray (native_value, value);
 				JNIEnv.DeleteLocalRef (native_value);
 			}
+			global::System.GC.KeepAlive (value);
 		}
 	}
 
@@ -65,6 +67,7 @@ public partial class MyClass  {
 				JNIEnv.CopyArray (native_value, value);
 				JNIEnv.DeleteLocalRef (native_value);
 			}
+			global::System.GC.KeepAlive (value);
 		}
 	}
 
@@ -84,6 +87,7 @@ public partial class MyClass  {
 				JNIEnv.CopyArray (native_value, value);
 				JNIEnv.DeleteLocalRef (native_value);
 			}
+			global::System.GC.KeepAlive (value);
 		}
 	}
 

tests/generator-Tests/Unit-Tests/CodeGeneratorExpectedResults/JavaInterop1/WriteKotlinUnsignedArrayTypePropertiesClass.txt

@@ -36,6 +36,7 @@ public partial class MyClass  {
 					JNIEnv.CopyArray (native_value, value);
 					JNIEnv.DeleteLocalRef (native_value);
 				}
+				global::System.GC.KeepAlive (value);
 			}
 		}
 	}
@@ -65,6 +66,7 @@ public partial class MyClass  {
 					JNIEnv.CopyArray (native_value, value);
 					JNIEnv.DeleteLocalRef (native_value);
 				}
+				global::System.GC.KeepAlive (value);
 			}
 		}
 	}
@@ -94,6 +96,7 @@ public partial class MyClass  {
 					JNIEnv.CopyArray (native_value, value);
 					JNIEnv.DeleteLocalRef (native_value);
 				}
+				global::System.GC.KeepAlive (value);
 			}
 		}
 	}
@@ -123,6 +126,7 @@ public partial class MyClass  {
 					JNIEnv.CopyArray (native_value, value);
 					JNIEnv.DeleteLocalRef (native_value);
 				}
+				global::System.GC.KeepAlive (value);
 			}
 		}
 	}

tests/generator-Tests/Unit-Tests/CodeGeneratorExpectedResults/XAJavaInterop1-NRT/WriteClass.txt

@@ -162,6 +162,7 @@ public partial class MyClass  {
 				_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 			} finally {
 				JNIEnv.DeleteLocalRef (native_value);
+				global::System.GC.KeepAlive (value);
 			}
 		}
 	}

tests/generator-Tests/Unit-Tests/CodeGeneratorExpectedResults/XAJavaInterop1-NRT/WriteClassProperties.txt

@@ -109,6 +109,7 @@ public virtual unsafe string? Key {
 			_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 		} finally {
 			JNIEnv.DeleteLocalRef (native_value);
+			global::System.GC.KeepAlive (value);
 		}
 	}
 }

tests/generator-Tests/Unit-Tests/CodeGeneratorExpectedResults/XAJavaInterop1/WriteClass.txt

@@ -162,6 +162,7 @@ public partial class MyClass  {
 				_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 			} finally {
 				JNIEnv.DeleteLocalRef (native_value);
+				global::System.GC.KeepAlive (value);
 			}
 		}
 	}

tests/generator-Tests/Unit-Tests/CodeGeneratorExpectedResults/XAJavaInterop1/WriteClassProperties.txt

@@ -109,6 +109,7 @@ public virtual unsafe string Key {
 			_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 		} finally {
 			JNIEnv.DeleteLocalRef (native_value);
+			global::System.GC.KeepAlive (value);
 		}
 	}
 }

tests/generator-Tests/expected.ji/Adapters/Xamarin.Test.AbsSpinner.cs

@@ -83,6 +83,7 @@ static void n_SetAdapter_Lxamarin_test_SpinnerAdapter_ (IntPtr jnienv, IntPtr na
 					__args [0] = new JniArgumentValue ((value == null) ? IntPtr.Zero : ((global::Java.Lang.Object) value).Handle);
 					_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 				} finally {
+					global::System.GC.KeepAlive (value);
 				}
 			}
 		}
@@ -126,6 +127,7 @@ public AbsSpinnerInvoker (IntPtr handle, JniHandleOwnership transfer) : base (ha
 					_members.InstanceMethods.InvokeAbstractVoidMethod (__id, this, __args);
 				} finally {
 					JNIEnv.DeleteLocalRef (native_value);
+					global::System.GC.KeepAlive (value);
 				}
 			}
 		}

tests/generator-Tests/expected.ji/Adapters/Xamarin.Test.AdapterView.cs

@@ -110,6 +110,7 @@ public AdapterViewInvoker (IntPtr handle, JniHandleOwnership transfer) : base (h
 					_members.InstanceMethods.InvokeAbstractVoidMethod (__id, this, __args);
 				} finally {
 					JNIEnv.DeleteLocalRef (native_value);
+					global::System.GC.KeepAlive (value);
 				}
 			}
 		}

tests/generator-Tests/expected.ji/Core_Jar2Xml/Android.Text.SpannableString.cs

@@ -102,6 +102,7 @@ static int n_GetSpanFlags_Ljava_lang_Object_ (IntPtr jnienv, IntPtr native__this
 				var __rm = _members.InstanceMethods.InvokeVirtualInt32Method (__id, this, __args);
 				return (global::Android.Text.SpanTypes) __rm;
 			} finally {
+				global::System.GC.KeepAlive (what);
 			}
 		}
 

tests/generator-Tests/expected.ji/Core_Jar2Xml/Android.Text.SpannableStringInternal.cs

@@ -60,6 +60,7 @@ static int n_GetSpanFlags_Ljava_lang_Object_ (IntPtr jnienv, IntPtr native__this
 				var __rm = _members.InstanceMethods.InvokeVirtualInt32Method (__id, this, __args);
 				return (global::Android.Text.SpanTypes) __rm;
 			} finally {
+				global::System.GC.KeepAlive (p0);
 			}
 		}
 

tests/generator-Tests/expected.ji/Core_Jar2Xml/Android.Views.View.cs

@@ -176,6 +176,7 @@ public virtual unsafe void SetOnClickListener (global::Android.Views.View.IOnCli
 				__args [0] = new JniArgumentValue ((l == null) ? IntPtr.Zero : ((global::Java.Lang.Object) l).Handle);
 				_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 			} finally {
+				global::System.GC.KeepAlive (l);
 			}
 		}
 
@@ -206,6 +207,7 @@ public virtual unsafe void SetOn123Listener (global::Android.Views.View.IOnClick
 				__args [0] = new JniArgumentValue ((l == null) ? IntPtr.Zero : ((global::Java.Lang.Object) l).Handle);
 				_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 			} finally {
+				global::System.GC.KeepAlive (l);
 			}
 		}
 
@@ -238,6 +240,7 @@ public virtual unsafe void AddTouchables (global::System.Collections.Generic.ILi
 				_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 			} finally {
 				JNIEnv.DeleteLocalRef (native_views);
+				global::System.GC.KeepAlive (views);
 			}
 		}
 

tests/generator-Tests/expected.ji/GenericArguments/Com.Google.Android.Exoplayer.Drm.FrameworkMediaDrm.cs

@@ -58,6 +58,7 @@ public unsafe void SetOnEventListener (global::Com.Google.Android.Exoplayer.Drm.
 				__args [0] = new JniArgumentValue ((p0 == null) ? IntPtr.Zero : ((global::Java.Lang.Object) p0).Handle);
 				_members.InstanceMethods.InvokeAbstractVoidMethod (__id, this, __args);
 			} finally {
+				global::System.GC.KeepAlive (p0);
 			}
 		}
 

tests/generator-Tests/expected.ji/NormalMethods/Xamarin.Test.SomeObject.cs

@@ -109,6 +109,8 @@ static int n_Handle_Ljava_lang_Object_Ljava_lang_Throwable_ (IntPtr jnienv, IntP
 				var __rm = _members.InstanceMethods.InvokeVirtualInt32Method (__id, this, __args);
 				return __rm;
 			} finally {
+				global::System.GC.KeepAlive (o);
+				global::System.GC.KeepAlive (t);
 			}
 		}
 
@@ -255,6 +257,7 @@ public virtual unsafe void VoidMethodWithParams (string astring, int anint, glob
 				_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 			} finally {
 				JNIEnv.DeleteLocalRef (native_astring);
+				global::System.GC.KeepAlive (anObject);
 			}
 		}
 
@@ -318,6 +321,7 @@ public virtual unsafe void ArrayListTest (global::System.Collections.Generic.ILi
 				_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 			} finally {
 				JNIEnv.DeleteLocalRef (native_p0);
+				global::System.GC.KeepAlive (p0);
 			}
 		}
 

tests/generator-Tests/expected.ji/NormalProperties/Xamarin.Test.SomeObject.cs

@@ -210,6 +210,7 @@ public override unsafe int SomeInteger {
 					__args [0] = new JniArgumentValue ((value == null) ? IntPtr.Zero : ((global::Java.Lang.Object) value).Handle);
 					_members.InstanceMethods.InvokeAbstractVoidMethod (__id, this, __args);
 				} finally {
+					global::System.GC.KeepAlive (value);
 				}
 			}
 		}

tests/generator-Tests/expected.ji/ParameterXPath/Xamarin.Test.A.cs

@@ -60,6 +60,7 @@ public virtual unsafe void SetA (global::Java.Lang.Object adapter)
 				_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 			} finally {
 				JNIEnv.DeleteLocalRef (native_adapter);
+				global::System.GC.KeepAlive (adapter);
 			}
 		}
 
@@ -92,6 +93,7 @@ public virtual unsafe void ListTest (global::System.Collections.Generic.IList<gl
 				_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 			} finally {
 				JNIEnv.DeleteLocalRef (native_p0);
+				global::System.GC.KeepAlive (p0);
 			}
 		}
 

tests/generator-Tests/expected.ji/StaticProperties/Xamarin.Test.SomeObject.cs

@@ -102,6 +102,7 @@ public static unsafe void SetSomeObject (global::Java.Lang.Object newvalue)
 				__args [0] = new JniArgumentValue ((newvalue == null) ? IntPtr.Zero : ((global::Java.Lang.Object) newvalue).Handle);
 				_members.StaticMethods.InvokeVoidMethod (__id, __args);
 			} finally {
+				global::System.GC.KeepAlive (newvalue);
 			}
 		}
 

tests/generator-Tests/expected.ji/Streams/Java.IO.InputStream.cs

@@ -216,6 +216,7 @@ public virtual unsafe int Read (byte[] buffer)
 					JNIEnv.CopyArray (native_buffer, buffer);
 					JNIEnv.DeleteLocalRef (native_buffer);
 				}
+				global::System.GC.KeepAlive (buffer);
 			}
 		}
 
@@ -257,6 +258,7 @@ public virtual unsafe int Read (byte[] buffer, int byteOffset, int byteCount)
 					JNIEnv.CopyArray (native_buffer, buffer);
 					JNIEnv.DeleteLocalRef (native_buffer);
 				}
+				global::System.GC.KeepAlive (buffer);
 			}
 		}
 

tests/generator-Tests/expected.ji/Streams/Java.IO.OutputStream.cs

@@ -136,6 +136,7 @@ public virtual unsafe void Write (byte[] buffer)
 					JNIEnv.CopyArray (native_buffer, buffer);
 					JNIEnv.DeleteLocalRef (native_buffer);
 				}
+				global::System.GC.KeepAlive (buffer);
 			}
 		}
 
@@ -175,6 +176,7 @@ public virtual unsafe void Write (byte[] buffer, int offset, int count)
 					JNIEnv.CopyArray (native_buffer, buffer);
 					JNIEnv.DeleteLocalRef (native_buffer);
 				}
+				global::System.GC.KeepAlive (buffer);
 			}
 		}
 

tests/generator-Tests/expected.ji/TestInterface/Test.ME.GenericImplementation.cs

@@ -82,6 +82,7 @@ public virtual unsafe void SetObject (byte[] value)
 					JNIEnv.CopyArray (native_value, value);
 					JNIEnv.DeleteLocalRef (native_value);
 				}
+				global::System.GC.KeepAlive (value);
 			}
 		}
 

tests/generator-Tests/expected.ji/TestInterface/Test.ME.GenericObjectPropertyImplementation.cs

@@ -101,6 +101,7 @@ static void n_SetObject_Ljava_lang_Object_ (IntPtr jnienv, IntPtr native__this,
 					__args [0] = new JniArgumentValue ((value == null) ? IntPtr.Zero : ((global::Java.Lang.Object) value).Handle);
 					_members.InstanceMethods.InvokeVirtualVoidMethod (__id, this, __args);
 				} finally {
+					global::System.GC.KeepAlive (value);
 				}
 			}
 		}

tests/generator-Tests/expected.ji/TestInterface/Test.ME.GenericStringImplementation.cs

@@ -82,6 +82,7 @@ public virtual unsafe void SetObject (string[] value)
 					JNIEnv.CopyArray (native_value, value);
 					JNIEnv.DeleteLocalRef (native_value);
 				}
+				global::System.GC.KeepAlive (value);
 			}
 		}
 

tests/generator-Tests/expected.ji/TestInterface/Test.ME.TestInterfaceImplementation.cs

@@ -179,6 +179,7 @@ public override unsafe int GetSpanFlags (global::Java.Lang.Object tag)
 				var __rm = _members.InstanceMethods.InvokeAbstractInt32Method (__id, this, __args);
 				return __rm;
 			} finally {
+				global::System.GC.KeepAlive (tag);
 			}
 		}
 
@@ -194,6 +195,7 @@ public override unsafe void Append (global::Java.Lang.ICharSequence value)
 				_members.InstanceMethods.InvokeAbstractVoidMethod (__id, this, __args);
 			} finally {
 				JNIEnv.DeleteLocalRef (native_value);
+				global::System.GC.KeepAlive (value);
 			}
 		}
 
@@ -210,6 +212,7 @@ public override unsafe void Append (global::Java.Lang.ICharSequence value)
 				return global::Java.Lang.Object.GetObject<Java.Lang.ICharSequence> (__rm.Handle, JniHandleOwnership.TransferLocalRef);
 			} finally {
 				JNIEnv.DeleteLocalRef (native_value);
+				global::System.GC.KeepAlive (value);
 			}
 		}
 

tests/generator-Tests/expected.ji/java.lang.Enum/Java.Lang.Enum.cs

@@ -44,6 +44,7 @@ public unsafe int CompareTo (global::Java.Lang.Object o)
 				return __rm;
 			} finally {
 				JNIEnv.DeleteLocalRef (native_o);
+				global::System.GC.KeepAlive (o);
 			}
 		}
 

tools/generator/Java.Interop.Tools.Generator.CodeGeneration/JavaInteropCodeGenerator.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Linq;
 using Mono.Options;
 
 namespace MonoDroid.Generation {
@@ -182,9 +183,37 @@ internal override void WriteMethodBody (Method method, string indent, GenBase ty
 			writer.WriteLine ("{0}}} finally {{", indent);
 			foreach (string cleanup in method.Parameters.GetCallCleanup (opt))
 				writer.WriteLine ("{0}\t{1}", indent, cleanup);
+			foreach (var p in method.Parameters.Where (GenerateKeepAlive))
+				writer.WriteLine ($"{indent}\tglobal::System.GC.KeepAlive ({opt.GetSafeIdentifier (p.Name)});");
+
 			writer.WriteLine ("{0}}}", indent);
 		}
 
+		bool GenerateKeepAlive (Parameter p)
+		{
+			if (p.Symbol.IsEnum)
+				return false;
+
+			return p.Type switch {
+				"bool" => false,
+				"sbyte" => false,
+				"char" => false,
+				"double" => false,
+				"float" => false,
+				"int" => false,
+				"long" => false,
+				"short" => false,
+				"uint" => false,
+				"ushort" => false,
+				"ulong" => false,
+				"byte" => false,
+				"ubyte" => false,	// Not a C# type, but we will see it from Kotlin unsigned types support
+				"string" => false,
+				"Android.Graphics.Color" => false,
+				_ => true
+			};
+		}
+
 		internal override void WriteFieldIdField (Field field, string indent)
 		{
 			// No field id_ field required