AndroidJava.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
 
#if USE_ANDROID_JNI
#include "Android/AndroidJavaEnv.h"
#include <jni.h>
 
/*
Wrappers for Java classes.
TODO: make function look up static? It doesn't matter for our case here (we only create one instance of the class ever)
*/
struct FJavaClassMethod
{
    FName       Name;
    FName       Signature;
    jmethodID   Method;
};
 
class FJavaClassObject
{
public:
    static FJavaClassObject GetGameActivity();
 
    // !!  All Java objects returned by JNI functions are local references.
    FJavaClassObject(FName ClassName, const char* CtorSig, ...);
    FJavaClassObject(jclass LocalClass, jobject LocalObject);
    FJavaClassObject(const FJavaClassObject&) = delete;
    ~FJavaClassObject();
 
    FJavaClassObject& operator=(const FJavaClassObject&) = delete;
    
    FJavaClassMethod GetClassMethod(const char* MethodName, const char* FuncSig);
 
    // TODO: Define this for extra cases
    template<typename ReturnType>
    ReturnType CallMethod(FJavaClassMethod Method, ...);
 
    UE_FORCEINLINE_HINT jobject GetJObject() const
    {
        return Object;
    }
 
    static FScopedJavaObject<jstring> GetJString(const FString& String);
 
    static void VerifyException();
 
protected:
 
    jobject         Object;
    jclass          Class;
};
 
template<>
void FJavaClassObject::CallMethod<void>(FJavaClassMethod Method, ...);
 
template<>
bool FJavaClassObject::CallMethod<bool>(FJavaClassMethod Method, ...);
 
template<>
int FJavaClassObject::CallMethod<int>(FJavaClassMethod Method, ...);
 
template<>
jobject FJavaClassObject::CallMethod<jobject>(FJavaClassMethod Method, ...);
 
template<>
jobjectArray FJavaClassObject::CallMethod<jobjectArray>(FJavaClassMethod Method, ...);
 
template<>
int64 FJavaClassObject::CallMethod<int64>(FJavaClassMethod Method, ...);
 
template<>
FString FJavaClassObject::CallMethod<FString>(FJavaClassMethod Method, ...);
 
template<>
float FJavaClassObject::CallMethod<float>(FJavaClassMethod Method, ...);
 
namespace UE::Jni
{
    template <typename T>
    struct TClassObject: FJavaClassObject
    {
        template <typename... TArgs>
        TClassObject(const TArgs&... args)
            : FJavaClassObject{Jni::Class<T>, *[this, &args...]
            {
                auto LocalObject = T::New(Jni::Class<T>, args...);
                VerifyException();
                return LocalObject;
            }()}
        {
        }
    };
}
#endif