application-dev/napi/use-sendable-napi.md

# 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.**

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

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

    **Configure compile settings.**

    ```cmake
    # 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.**

    ```cpp
    // 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.

    ```cpp
    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.

    ```cpp
    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:

    ```ts
    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());
    ```