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// self 为 id<V2TIMAdvancedMsgListener>
[[V2TIMManager sharedInstance] addAdvancedMsgListener:self];

class AdvancedMsgListener final : public V2TIMAdvancedMsgListener {
    // 成员 ...
};

// 添加高级消息的事件监听器，注意在移除监听器之前需要保持 advancedMsgListener 的生命期，以免接收不到事件回调
AdvancedMsgListener advancedMsgListener;
V2TIMManager::GetInstance()->GetMessageManager()->AddAdvancedMsgListener(&advancedMsgListener);

- (void)onRecvNewMessage:(V2TIMMessage *)msg {
    if (msg.elemType == V2TIM_ELEM_TYPE_MERGER) {
        // 获取合并消息 elem
        V2TIMMergerElem *mergerElem = msg.mergerElem;
        // 获取 title
        NSString *title = mergerElem.title;
        // 获取摘要列表
        NSArray *abstractList = mergerElem.abstractList;
        // 用户点击合并消息的时候下载合并消息列表
        [msg.mergerElem downloadMergerMessage:^(NSArray<V2TIMMessage *> *msgs) {
            // 下载成功，msgs 即为合并消息列表
            for (V2TIMMessage *subMsg in msgs) {
                // 如果合并消息列表里面还有合并消息，可以继续解析
                if (subMsg.elemType == V2TIM_ELEM_TYPE_MERGER) {
                    V2TIMMergerElem *mergerElem = subMsg.mergerElem;
                    // 获取 title
                    NSString *title = mergerElem.title;
                    // 获取摘要列表
                    NSArray *abstractList = mergerElem.abstractList;
                    // 用户点击合并消息的时候下载合并消息列表
                    [msg.mergerElem downloadMergerMessage:nil fail:nil];
                }
            }
        } fail:^(int code, NSString *desc) {
            // 下载失败
        }];
    }
}

template <class T>
class ValueCallback final : public V2TIMValueCallback<T> {
public:
    using SuccessCallback = std::function<void(const T&)>;
    using ErrorCallback = std::function<void(int, const V2TIMString&)>;

    ValueCallback() = default;
    ~ValueCallback() override = default;

    void SetCallback(SuccessCallback success_callback, ErrorCallback error_callback) {
        success_callback_ = std::move(success_callback);
        error_callback_ = std::move(error_callback);
    }

    void OnSuccess(const T& value) override {
        if (success_callback_) {
            success_callback_(value);
        }
    }
    void OnError(int error_code, const V2TIMString& error_message) override {
        if (error_callback_) {
            error_callback_(error_code, error_message);
        }
    }

private:
    SuccessCallback success_callback_;
    ErrorCallback error_callback_;
};

class AdvancedMsgListener final : public V2TIMAdvancedMsgListener {
public:
    // 收到新消息通知
    void OnRecvNewMessage(const V2TIMMessage& message) override {
        if (message.elemList.Size() == 1) {
            V2TIMElem* elem = message.elemList[0];
            if (elem->elemType == V2TIMElemType::V2TIM_ELEM_TYPE_MERGER) {
                // 获取合并消息 elem
                auto mergerElem = static_cast<V2TIMMergerElem*>(elem);
                // 获取 title
                V2TIMString title = mergerElem->title;
                /// 合并消息摘要列表
                V2TIMStringVector abstractList = mergerElem->abstractList;

                // 用户点击合并消息的时候下载合并消息列表
                auto callback = new ValueCallback<V2TIMMessageVector>{};
                callback->SetCallback(
                    [=](const V2TIMMessageVector& messageList) {
                        // 下载成功，messageList 即为合并消息列表
                        for (size_t i = 0; i < messageList.Size(); ++i) {
                            const V2TIMMessage& message = messageList[i];
                            if (message.elemList.Size() == 1) {
                                V2TIMElem* elem = message.elemList[0];
                                // 如果合并消息列表里面还有合并消息，可以继续解析
                                if (elem->elemType == V2TIMElemType::V2TIM_ELEM_TYPE_MERGER) {
                                    // ...
                                }
                            }
                        }
                        delete callback;
                    },
                    [=](int error_code, const V2TIMString& error_message) { delete callback; });

                mergerElem->DownloadMergerMessage(callback);
            }
        }
    }
    // 其他成员 ...
};

// 添加高级消息的事件监听器，注意在移除监听器之前需要保持 advancedMsgListener 的生命期，以免接收不到事件回调
AdvancedMsgListener advancedMsgListener;
V2TIMManager::GetInstance()->GetMessageManager()->AddAdvancedMsgListener(&advancedMsgListener);

// self 为 id<V2TIMAdvancedMsgListener>
[[V2TIMManager sharedInstance] removeAdvancedMsgListener:self];

class AdvancedMsgListener final : public V2TIMAdvancedMsgListener {
    // 成员 ...
};

// advancedMsgListener 是 AdvancedMsgListener 的实例
V2TIMManager::GetInstance()->GetMessageManager()->RemoveAdvancedMsgListener(&advancedMsgListener);

// 创建转发消息，转发消息的 elem 内容和原消息完全一致
V2TIMMessage *forwardMessage = [[V2TIMManager sharedInstance] createForwardMessage:originMsg];
// 发送消息给用户 "denny"
[[V2TIMManager sharedInstance] sendMessage:forwardMessage receiver:@"denny"  groupID:nil
 priority:V2TIM_PRIORITY_NORMAL  onlineUserOnly:NO  offlinePushInfo:nil progress:nil succ:nil fail:nil];

class SendCallback final : public V2TIMSendCallback {
public:
    using SuccessCallback = std::function<void(const V2TIMMessage&)>;
    using ErrorCallback = std::function<void(int, const V2TIMString&)>;
    using ProgressCallback = std::function<void(uint32_t)>;

    SendCallback() = default;
    ~SendCallback() override = default;

    void SetCallback(SuccessCallback success_callback, ErrorCallback error_callback,
                     ProgressCallback progress_callback) {
        success_callback_ = std::move(success_callback);
        error_callback_ = std::move(error_callback);
        progress_callback_ = std::move(progress_callback);
    }

    void OnSuccess(const V2TIMMessage& message) override {
        if (success_callback_) {
            success_callback_(message);
        }
    }
    void OnError(int error_code, const V2TIMString& error_message) override {
        if (error_callback_) {
            error_callback_(error_code, error_message);
        }
    }
    void OnProgress(uint32_t progress) override {
        if (progress_callback_) {
            progress_callback_(progress);
        }
    }

private:
    SuccessCallback success_callback_;
    ErrorCallback error_callback_;
    ProgressCallback progress_callback_;
};

// 创建转发消息，转发消息的 elem 内容和原消息完全一致
V2TIMMessage forwardMessage = V2TIMManager::GetInstance()->GetMessageManager()->CreateForwardMessage(originMsg);

auto callback = new SendCallback{};
callback->SetCallback([=](const V2TIMMessage& message) { delete callback; },
                      [=](int error_code, const V2TIMString& error_message) { delete callback; },
                      [=](uint32_t progress) {});

// 发送消息给用户 "denny"
V2TIMManager::GetInstance()->GetMessageManager()->SendMessage(
    forwardMessage, "denny", {}, V2TIMMessagePriority::V2TIM_PRIORITY_NORMAL, false, {}, callback);