[Android] FileUtils::listFiles implementation that works with empty folders (#2463)

* Use Android Java method for listing files and folders

* Update comment

* Figure out if paths are files or folders

* Rename method to better reflect its purpose

Author: rh101

core/platform/android/FileUtils-android.cpp

@@ -242,15 +242,32 @@ int64_t FileUtilsAndroid::getFileSize(std::string_view filepath) const
 
 std::vector<std::string> FileUtilsAndroid::listFiles(std::string_view dirPath) const
 {
-
     if (!dirPath.empty() && dirPath[0] == '/')
         return FileUtils::listFiles(dirPath);
 
     std::vector<std::string> fileList;
-    std::string fullPath = fullPathForDirectory(dirPath);
-
     static const std::string apkprefix("assets/");
     std::string relativePath;
+
+    if (obbfile)
+    {
+        std::string fullPath = fullPathForDirectory(dirPath);
+
+        size_t position = fullPath.find(apkprefix);
+        if (0 == position)
+        {
+            // "assets/" is at the beginning of the path and we don't want it
+            relativePath += fullPath.substr(apkprefix.size());
+        }
+        else
+        {
+            relativePath = fullPath;
+        }
+
+        return obbfile->listFiles(relativePath);
+    }
+
+    std::string fullPath = std::string(dirPath); // don't call fullPathForDirectory(dirPath), since empty folders will not return a valid result
     size_t position = fullPath.find(apkprefix);
     if (0 == position)
     {
@@ -262,9 +279,6 @@ std::vector<std::string> FileUtilsAndroid::listFiles(std::string_view dirPath) c
         relativePath = fullPath;
     }
 
-    if (obbfile)
-        return obbfile->listFiles(relativePath);
-
     if (nullptr == assetmanager)
     {
         LOGD("... FileUtilsAndroid::assetmanager is nullptr");
@@ -276,22 +290,8 @@ std::vector<std::string> FileUtilsAndroid::listFiles(std::string_view dirPath) c
         relativePath.erase(relativePath.length() - 1);
     }
 
-    auto* dir = AAssetManager_openDir(assetmanager, relativePath.c_str());
-    if (nullptr == dir)
-    {
-        LOGD("... FileUtilsAndroid::failed to open dir %s", relativePath.c_str());
-        AAssetDir_close(dir);
-        return fileList;
-    }
-    const char* tmpDir = nullptr;
-    while ((tmpDir = AAssetDir_getNextFileName(dir)) != nullptr)
-    {
-        std::string filepath(tmpDir);
-        if (isDirectoryExistInternal(filepath))
-            filepath += "/";
-        fileList.emplace_back(fullPath + filepath);
-    }
-    AAssetDir_close(dir);
+    fileList = JniHelper::callStaticStringArrayMethod("dev/axmol/lib/AxmolEngine", "getAssetsList", relativePath);
+
     return fileList;
 }
 

core/platform/android/java/src/dev/axmol/lib/AxmolEngine.java

@@ -746,4 +746,31 @@ private static AxmolAccelerometer getAccelerometer() {
 
         return sAccelerometer;
     }
+
+    public static String[] getAssetsList(String path) {
+        try {
+            String basePath;
+            if (!path.isEmpty()) {
+                basePath = path + "/";
+            } else {
+                basePath = path;
+            }
+
+            AssetManager assetManager = getAssetManager();
+            String[] list = assetManager.list(path);
+            for (int i = 0; i < list.length; i++) {
+                try {
+                    list[i] = basePath + list[i];
+                    java.io.InputStream stream = assetManager.open(list[i]);
+                    stream.close(); // if we got to here, then it is a file
+                } catch (IOException e) {
+                    list[i] += "/";
+                }
+            }
+            return list;
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        return null;
+    }
 }

core/platform/android/jni/JniHelper.h

@@ -220,6 +220,50 @@ class AX_DLL JniHelper
         return ret;
     }
 
+    /**
+    @brief Call of Java static method
+    @return std::vector<std::string>
+    */
+    template <typename... Ts>
+    static std::vector<std::string> callStaticStringArrayMethod(const char* className, const char* methodName, Ts&&... xs)
+    {
+        ax::JniMethodInfo t;
+        const auto signature = "(Ljava/lang/String;)[Ljava/lang/String;";
+        if (ax::JniHelper::getStaticMethodInfo(t, className, methodName, signature))
+        {
+            LocalRefMapType localRefs;
+            jobjectArray array =
+                    (jobjectArray)t.env->CallStaticObjectMethod(t.classID, t.methodID, convert(localRefs, t, xs)...);
+
+            if (array == nullptr)
+            {
+                t.env->DeleteLocalRef(t.classID);
+                deleteLocalRefs(t.env, localRefs);
+                return {};
+            }
+
+            jsize len = t.env->GetArrayLength(array);
+            std::vector<std::string> result(len);
+            for (int i=0; i < len; ++i)
+            {
+                jstring string = (jstring)t.env->GetObjectArrayElement(array, i);
+                const char* arrayItem = t.env->GetStringUTFChars(string, 0);
+                result[i] = std::move((std::string(arrayItem)));
+                t.env->ReleaseStringUTFChars(string, arrayItem);
+                t.env->DeleteLocalRef(string);
+            }
+
+            t.env->DeleteLocalRef(t.classID);
+            deleteLocalRefs(t.env, localRefs);
+            return result;
+        }
+        else
+        {
+            reportError(className, methodName, signature);
+        }
+        return {};
+    }
+
     /**
     @brief Call of Java static float* method
     @return axstd::pod_vector