[Android] Holding a VM reference to the asset manager jobject to prevent its being garbage collected

Author: halx99

core/platform/android/FileUtils-android.cpp

@@ -28,8 +28,6 @@ THE SOFTWARE.
 #include "platform/Common.h"
 #include "platform/android/jni/JniHelper.h"
 #include "platform/android/jni/Java_dev_axmol_lib_AxmolEngine.h"
-#include "android/asset_manager.h"
-#include "android/asset_manager_jni.h"
 #include "base/ZipUtils.h"
 
 #include <stdlib.h>
@@ -48,19 +46,28 @@ THE SOFTWARE.
 
 namespace ax
 {
-
+static jobject s_assetmanager_hold = nullptr;
 AAssetManager* FileUtilsAndroid::assetmanager = nullptr;
 ZipFile* FileUtilsAndroid::obbfile            = nullptr;
 
-void FileUtilsAndroid::setassetmanager(AAssetManager* a)
+void FileUtilsAndroid::setAssetManagerFromJava(jobject a)
 {
-    if (nullptr == a)
+    auto env = JniHelper::getEnv();
+    if (!s_assetmanager_hold)
+        s_assetmanager_hold = env->NewGlobalRef(a);
+    /*
+    Note: that the caller is responsible for obtaining and holding a VM reference to the jobject to 
+        prevent its being garbage collected while the native object is in use.
+    refer: https://developer.android.com/ndk/reference/group/asset#aassetmanager_fromjava
+    */
+    auto aassetMgr = AAssetManager_fromJava(env, s_assetmanager_hold);
+    if (nullptr == aassetMgr)
     {
         LOGD("setassetmanager : received unexpected nullptr parameter");
         return;
     }
 
-    ax::FileUtilsAndroid::assetmanager = a;
+    ax::FileUtilsAndroid::assetmanager = aassetMgr;
 }
 
 FileUtils* FileUtils::getInstance()

core/platform/android/FileUtils-android.h

@@ -32,8 +32,7 @@ Copyright (c) 2017-2018 Xiamen Yaji Software Co., Ltd.
 #include <vector>
 #include <unordered_map>
 #include <memory>
-#include "jni.h"
-#include "android/asset_manager.h"
+#include <android/asset_manager_jni.h>
 
 namespace ax
 {
@@ -57,7 +56,7 @@ class AX_DLL FileUtilsAndroid : public FileUtils
      */
     virtual ~FileUtilsAndroid();
 
-    static void setassetmanager(AAssetManager* a);
+    static void setAssetManagerFromJava(jobject a);
     static AAssetManager* getAssetManager() { return assetmanager; }
     static ZipFile* getObbFile() { return obbfile; }
 

core/platform/android/jni/Java_dev_axmol_lib_AxmolEngine.cpp

@@ -29,7 +29,6 @@ THE SOFTWARE.
 #include <string>
 #include "platform/android/jni/JniHelper.h"
 #include "platform/android/FileUtils-android.h"
-#include "android/asset_manager_jni.h"
 #include "platform/android/jni/Java_dev_axmol_lib_AxmolEngine.h"
 
 #include "base/UTF8.h"
@@ -55,7 +54,7 @@ JNIEXPORT void JNICALL Java_dev_axmol_lib_AxmolEngine_nativeSetContext(JNIEnv* e
                                                                              jobject assetManager)
 {
     JniHelper::setClassLoaderFrom(context);
-    FileUtilsAndroid::setassetmanager(AAssetManager_fromJava(env, assetManager));
+    FileUtilsAndroid::setAssetManagerFromJava(assetManager);
 }
 
 JNIEXPORT void JNICALL Java_dev_axmol_lib_AxmolEngine_nativeSetEditTextDialogResult(JNIEnv* env,