Question

我已经修改了以下问题的第一个答案，用于制作定期计时器： How do I make the boost/asio library repeat a timer?

我删除了“count”变量，因为我想重复执行的方法不带任何参数进行计算。

编译器因以下错误而失败：

Error   C2825   'F': must be a class or namespace when followed by '::' C:\.conan\wkypad\1\include\boost\bind\bind.hpp  75  
Error   C2510   'F': left of '::' must be a class/struct/union  C:\.conan\wkypad\1\include\boost\bind\bind.hpp  75  
Error   C3646   'type': unknown override specifier  C:\.conan\wkypad\1\include\boost\bind\bind.hpp  75  
Error   C4430   missing type specifier - int assumed. Note: C++ does not support default-int C:\.conan\wkypad\1\include\boost\bind\bind.hpp 75  
Error   C2039   'type': is not a member of 'boost::_bi::result_traits<R,F>' C:\.conan\wkypad\1\include\boost\bind\bind.hpp  1284

我做错了什么？我想我对boost :: bind的使用是错误的，但我无法弄清楚确切的原因。

以下是我的代码的相关部分

class ProjectBrowserComponent ...

private:
    void fetchData(const boost::system::error_code& /*e*/,
        boost::asio::deadline_timer* t);
    std::vector<Project> projects;
    ProjectsController pc;
    std::future<std::vector<Project>> projectsFuture;
    int interval_secs = 1;

...

template<typename R>
bool isReady(std::future<R> const& f)
{
    Logger::writeToLog("check future");
    return f.wait_for(std::chrono::seconds(-1)) == std::future_status::ready;
}

void ProjectBrowserComponent::initData() {
    Logger::writeToLog("requesting projects");
    projectsFuture = std::async(std::launch::async, &ProjectsController::getProjects, &pc);
    Logger::writeToLog("requested projects");
    boost::asio::io_service io_service;
    boost::asio::deadline_timer timer(io_service, boost::posix_time::seconds(interval_secs));
    timer.async_wait(boost::bind(&ProjectBrowserComponent::fetchData, boost::asio::placeholders::error, &timer));
    io_service.run();
}

void ProjectBrowserComponent::fetchData(const boost::system::error_code& /*e*/,
    boost::asio::deadline_timer* timer) {
    if (isReady(projectsFuture)) {
        projects = projectsFuture.get();
        std::cout << "got projs";
    }
    else {
        timer->expires_at(timer->expires_at() + boost::posix_time::seconds(interval_secs));
        // Posts the event
        timer->async_wait(boost::bind(&ProjectBrowserComponent::fetchData, boost::asio::placeholders::error, timer));
    }
}

Answer 1

这个怎么样：

timer.async_wait(boost::bind(&ProjectBrowserComponent::fetchData, this, boost::asio::placeholders::error, &timer));

如果绑定成员函数，则必须将它们绑定到类的对象的正确实例。在这里，我将它绑定到this，我假设你从代码的外观中做了什么。

从评论中注意到：

重要的是要注意，这必须在异步操作的整个持续时间内保持有效。实现此目标的一种流行方法是使ProjectBrowserComponent继承自enable_shared_from_this并绑定到shared_from_this()

使用boost :: bind ...我做错了什么

1 个答案: