Wrapping a Native Object in a Sendable ArkTS Object

When to Use

You can use napi_wrap_sendable to wrap a C++ object in a sendable ArkTS object, and use napi_unwrap_sendable to retrieve the C++ object previously wrapped in the sendable ArkTS object for subsequent operations.

Example

1. Declare the APIs, configure compile settings, and register the module.

Declare the APIs.

// index.d.ets
@Sendable
export class MyObject {
  constructor(arg: number);
  plusOne(): number;

  public get value();
  public set value(newVal: number);
}

Configure compile settings.

# the minimum version of CMake.
cmake_minimum_required(VERSION 3.5.0)
project(napi_wrap_sendable_demo)

set(NATIVERENDER_ROOT_PATH ${CMAKE_CURRENT_SOURCE_DIR})

if(DEFINED PACKAGE_FIND_FILE)
    include(${PACKAGE_FIND_FILE})
endif()

include_directories(${NATIVERENDER_ROOT_PATH}
                    ${NATIVERENDER_ROOT_PATH}/include)

add_definitions("-DLOG_DOMAIN=0x0000")
add_definitions("-DLOG_TAG=\"testTag\"")

add_library(entry SHARED napi_init.cpp)
target_link_libraries(entry PUBLIC libace_napi.z.so libhilog_ndk.z.so)

Register the module.

// napi_init.cpp
#include "napi/native_api.h"
#include "hilog/log.h"

// A native class. Its instance is wrapped in a sendable ArkTS object.
class MyObject {
public:
    static napi_value Init(napi_env env, napi_value exports);
    static void Destructor(napi_env env, void *nativeObject, void *finalize_hint);

private:
    explicit MyObject(double value_ = 0);
    ~MyObject();

    static napi_value New(napi_env env, napi_callback_info info);
    static napi_value GetValue(napi_env env, napi_callback_info info);
    static napi_value SetValue(napi_env env, napi_callback_info info);
    static napi_value PlusOne(napi_env env, napi_callback_info info);

    double value_;
    napi_env env_;
};

static thread_local napi_ref g_ref = nullptr;

MyObject::MyObject(double value) : value_(value), env_(nullptr) {}

MyObject::~MyObject() {}

void MyObject::Destructor(napi_env env, void *nativeObject, [[maybe_unused]] void *finalize_hint) {
    OH_LOG_INFO(LOG_APP, "MyObject::Destructor called");
    reinterpret_cast<MyObject *>(nativeObject)->~MyObject();
}

napi_value MyObject::Init(napi_env env, napi_value exports) {
    napi_value num;
    napi_create_double(env, 0, &num);
    napi_property_descriptor properties[] = {
        {"value", nullptr, nullptr, GetValue, SetValue, nullptr, napi_default, nullptr},
        {"plusOne", nullptr, PlusOne, nullptr, nullptr, nullptr, napi_default, nullptr},
    };

    napi_value cons;
    // Define a sendable class MyObject.
    napi_define_sendable_class(env, "MyObject", NAPI_AUTO_LENGTH, New, nullptr,
                              sizeof(properties) / sizeof(properties[0]), properties, nullptr, &cons);

    napi_create_reference(env, cons, 1, &g_ref);
    // Mount the MyObject class to the exports object.
    napi_set_named_property(env, exports, "MyObject", cons);
    return exports;
}

EXTERN_C_START
// Initialize the module.
static napi_value Init(napi_env env, napi_value exports) {
    MyObject::Init(env, exports);
    return exports;
}
EXTERN_C_END

// Information about the module. Record information such as the Init() function and module name.
static napi_module nativeModule = {
    .nm_version = 1,
    .nm_flags = 0,
    .nm_filename = nullptr,
    .nm_register_func = Init,
    .nm_modname = "entry",
    .nm_priv = nullptr,
    .reserved = {0},
};

// When the .so file is loaded, this function is automatically called to register the nativeModule module with the system.
extern "C" __attribute__((constructor)) void RegisterObjectWrapModule() { napi_module_register(&nativeModule); }

2. Wrap a C++ object in a sendable ArkTS object in a constructor.

napi_value MyObject::New(napi_env env, napi_callback_info info) {
    OH_LOG_INFO(LOG_APP, "MyObject::New called");

    napi_value newTarget;
    napi_get_new_target(env, info, &newTarget);
    if (newTarget != nullptr) {
        // Invoked as the constructor `new MyObject(...)`.
        size_t argc = 1;
        napi_value args[1];
        napi_value jsThis;
        napi_get_cb_info(env, info, &argc, args, &jsThis, nullptr);

        double value = 0.0;
        napi_valuetype valuetype;
        napi_typeof(env, args[0], &valuetype);
        if (valuetype != napi_undefined) {
            napi_get_value_double(env, args[0], &value);
        }

        MyObject *obj = new MyObject(value);

        obj->env_ = env;
        // Use napi_wrap_sendable to wrap obj (the C++ object) in jsThis (the sendable ArkTS object).
        napi_wrap_sendable(env, jsThis, reinterpret_cast<void *>(obj), MyObject::Destructor, nullptr);

        return jsThis;
    } else {
        // Invoked as the plain function `MyObject(...)`.
        size_t argc = 1;
        napi_value args[1];
        napi_get_cb_info(env, info, &argc, args, nullptr, nullptr);

        napi_value cons;
        napi_get_reference_value(env, g_ref, &cons);
        napi_value instance;
        napi_new_instance(env, cons, argc, args, &instance);

        return instance;
    }
}

3. Retrieve the C++ object from the sendable ArkTS object and perform subsequent operations on the C++ object.

napi_value MyObject::GetValue(napi_env env, napi_callback_info info) {
    OH_LOG_INFO(LOG_APP, "MyObject::GetValue called");

    napi_value jsThis;
    napi_get_cb_info(env, info, nullptr, nullptr, &jsThis, nullptr);

    MyObject *obj;
    // Use napi_unwrap_sendable to retrieve obj (the C++ object) previously wrapped in jsThis (the sendable ArkTS object), and perform subsequent operations.
    napi_unwrap_sendable(env, jsThis, reinterpret_cast<void **>(&obj));
    napi_value num;
    napi_create_double(env, obj->value_, &num);

    return num;
}

napi_value MyObject::SetValue(napi_env env, napi_callback_info info) {
    OH_LOG_INFO(LOG_APP, "MyObject::SetValue called");

    size_t argc = 1;
    napi_value value;
    napi_value jsThis;

    napi_get_cb_info(env, info, &argc, &value, &jsThis, nullptr);

    MyObject *obj;
    // Use napi_unwrap_sendable to retrieve obj (the C++ object) previously wrapped in jsThis (the sendable ArkTS object), and perform subsequent operations.
    napi_unwrap_sendable(env, jsThis, reinterpret_cast<void **>(&obj));
    napi_get_value_double(env, value, &obj->value_);

    return nullptr;
}

napi_value MyObject::PlusOne(napi_env env, napi_callback_info info) {
    OH_LOG_INFO(LOG_APP, "MyObject::PlusOne called");

    napi_value jsThis;
    napi_get_cb_info(env, info, nullptr, nullptr, &jsThis, nullptr);

    MyObject *obj;
    // Use napi_unwrap_sendable to retrieve obj (the C++ object) previously wrapped in jsThis (the sendable ArkTS object), and perform subsequent operations.
    napi_unwrap_sendable(env, jsThis, reinterpret_cast<void **>(&obj));
    obj->value_ += 1;
    napi_value num;
    napi_create_double(env, obj->value_, &num);

    return num;
}

4. ArkTS code:

import hilog from '@ohos.hilog';
import { MyObject } from 'libentry.so';

let object : MyObject = new MyObject(0);
object.value = 1023;
hilog.info(0x0000, 'testTag', 'MyObject value after set: %{public}d', object.value);
hilog.info(0x0000, 'testTag', 'MyObject plusOne: %{public}d', object.plusOne());