#鸿蒙通关秘籍#如何在鸿蒙系统中使用callback方式进行异步任务开发？

在鸿蒙系统中，通过Node-API进行异步任务开发时，除了使用Promise，还可以使用callback方式。在这种方式下，可以通过传递一个回调函数以接收任务完成后的结果。下面是一个关于如何使用callback方式进行异步操作的代码示例：

cpp struct CallbackData { napi_async_work asyncWork = nullptr; napi_ref callbackRef = nullptr; double args[2] = {0}; double result = 0; };

napi_value AsyncWork(napi_env env, napi_callback_info info) { size_t argc = 3; napi_value args[3]; napi_get_cb_info(env, info, &argc, args, nullptr, nullptr); auto asyncContext = new CallbackData(); napi_get_value_double(env, args[0], &asyncContext->args[0]); napi_get_value_double(env, args[1], &asyncContext->args[1]); napi_create_reference(env, args[2], 1, &asyncContext->callbackRef); napi_value resourceName = nullptr; napi_create_string_utf8(env, "asyncWorkCallback", NAPI_AUTO_LENGTH, &resourceName); napi_create_async_work(env, nullptr, resourceName, ExecuteCB, CompleteCB, asyncContext, &asyncContext->asyncWork); napi_queue_async_work(env, asyncContext->asyncWork); return nullptr; }

static void ExecuteCB(napi_env env, void *data) { CallbackData *callbackData = reinterpret_cast<CallbackData *>(data); callbackData->result = callbackData->args[0] + callbackData->args[1]; }

static void CompleteCB(napi_env env, napi_status status, void *data) { CallbackData *callbackData = reinterpret_cast<CallbackData *>(data); napi_value callbackArg[1] = {nullptr}; napi_create_double(env, callbackData->result, &callbackArg[0]); napi_value callback = nullptr; napi_get_reference_value(env, callbackData->callbackRef, &callback); napi_value result; napi_value undefined; napi_get_undefined(env, &undefined); napi_call_function(env, undefined, callback, 1, callbackArg, &result); napi_delete_reference(env, callbackData->callbackRef); napi_delete_async_work(env, callbackData->asyncWork); delete callbackData; }

static napi_value Init(napi_env env, napi_value exports) { napi_property_descriptor desc[] = { { "asyncWork", nullptr, AsyncWork, nullptr, nullptr, nullptr, napi_default, nullptr } }; napi_define_properties(env, exports, sizeof(desc) / sizeof(desc[0]), desc); return exports; }

let num1: number = 123; let num2: number = 456; nativeModule.asyncWork(num1, num2, (result) => { hilog.info(0x0000, 'XXX', 'result is %{public}d', result); });