通过JNI C＆＃x2B;＆＃x2B读取Android Asset File失败了

Question

我用JNI C ++代码制作了Android应用。

要在Android本机代码（C ++）上创建APK时读取模型文件，我将模型文件放在Assets文件夹中。 （因此，文件路径为my_app/src/main/assets/model.tflite）

然后，我尝试读取以下代码的模型，但错误已增加：

kotlin代码>代码：

private val context: Context
    get() = getApplication<Application>().applicationContext

asset_manager = context.assets

c ++代码：

AAssetManager* mgr = AAssetManager_fromJava(env, asset_manager);
AAssetDir* assetDir = AAssetManager_openDir(mgr, "");
const char* filename = (const char*)NULL;
while ((filename = AAssetDir_getNextFileName(assetDir)) != NULL) {
    AAsset* asset = AAssetManager_open(mgr, filename, AASSET_MODE_STREAMING);
    __android_log_print(ANDROID_LOG_INFO, "tag", "file name is: %s", filename);  <- file name reading is ok
    char buf[BUFSIZ];
    int nb_read = 0;
    FILE* out = fopen(filename, "w");                            <- out has null FILE*
    while ((nb_read = AAsset_read(asset, buf, BUFSIZ)) > 0)
        fwrite(buf, nb_read, 1, out);
    fclose(out);
    AAsset_close(asset);
}
AAssetDir_close(assetDir);

logcat：

2022-06-19 22:45:54.449 12180-12180/com.my.first.app I/tag: file name is: model.tflite
2022-06-19 22:45:54.449 12180-12180/com.my.first.app A/libc: FORTIFY: fwrite: null FILE*
2022-06-19 22:45:54.450 12180-12180/com.my.first.app A/libc: Fatal signal 6 (SIGABRT), code -1 (SI_QUEUE) in tid 12180 (st.app), pid 12180 (st.app)

为什么fopen（fileName，“ w”）返回null？看来aassetManager是有效的。

Answer 1

多亏了@botje，我可以按以下方式将model.tflite加载到资产中：

AAssetManager* mgr = AAssetManager_fromJava(env, asset_manager);
AAssetDir* assetDir = AAssetManager_openDir(mgr, "");
const char* filename = nullptr;
while ((filename = AAssetDir_getNextFileName(assetDir)) != nullptr) {
    AAsset* asset = AAssetManager_open(mgr, filename, AASSET_MODE_STREAMING);
    size_t size = AAsset_getLength(asset);
    buf = new char[size];
    memmove(buf, AAsset_getBuffer(asset), size);

    AAsset_close(asset);
  }
AAssetDir_close(assetDir);

std::unique_ptr<tflite::FlatBufferModel> model = tflite::FlatBufferModel::BuildFromBuffer((const char*)buf, size);
std::unique_ptr<tflite::Interpreter> interpreter;
tflite::ops::builtin::BuiltinOpResolver op_resolver;
tflite::InterpreterBuilder(*model, op_resolver)(&interpreter);

Answer 2

Looks like you want to combine this loading code to load the asset into a memory buffer and then use the

std::unique_ptr<tflite::Allocation> readAsset(std::string target) {
  AAssetManager* mgr = AAssetManager_fromJava(env, asset_manager);
  AAssetDir* assetDir = AAssetManager_openDir(mgr, "");
  const char* filename = nullptr;
  while ((filename = AAssetDir_getNextFileName(assetDir)) != nullptr) {
    if (target != filename)
      continue;

    AAsset* asset = AAssetManager_open(mgr, filename, AASSET_MODE_STREAMING);
    auto len = AAsset_getLength(asset);
    uint8_t *buf = new uint8_t[len];
    std::copy_n(AAsset_getBuffer(asset), len, buf);
    auto ret = std::make_unique<tflite::Allocation>(buf , len);
    AAsset_close(asset);
    AAssetDir_close(assetDir);
    return ret;
  }
  AAssetDir_close(assetDir);
  return {};
}

然后稍后将其使用为：

auto ptr = readAssset("model.tflite");
if (!ptr) {
  // do something
}

auto modelPtr = tflite::FlatBufferModel::BuildFromAllocation(ptr, some_error_reporter);
if (!modelPtr) {
  // do something
}

注意：this will> will 泄漏内存，因为tflite拥有所有权缓冲区。