C++ Boost 函数回调。如何调用函数作为回调并在内部传递参数？

Question

我有类 Manager 和类 Scheduler。 Manager 有 Scheduler 的实例。 Manager 启动 Scheduler。 Scheduler 做某事，Scheduler 必须异步返回结果给 Manager。我怎样才能让它像下面的例子一样？

class Manager{
private:
    Scheduler *mScheduler;

public:
    Manager(){
        mScheduler = new Scheduler(boost::bind(&Manager::acceptResult, this));
        mScheduler->run();
    }

    void acceptResult(Result::Shared result){
        //do something with result, it's doesn't matter=)
    }
};

typedef boost::function<void()> callback;

class Scheduler {
private:
    callback mManagerCallback;

public:
    Scheduler(callback call){
        mManagerCallback = call;
    }

    void run(){
        //some logic
        mManagerCallback(result);
    }

}

typedef boost::posix_time::ptime Timestamp;
typedef boost::posix_time::time_duration Duration;
typedef uint64_t microseconds_timestamp;

class CommandResult {
public:
    typedef shared_ptr<const CommandResult> SharedConst;

private:
    CommandUUID mCommandUUID;
    uint16_t mResultCode;
    Timestamp mTimestampCompleted;
    string mResultInformation;

public:
    CommandResult(
            const CommandUUID &commandUUID,
            const uint16_t resultCode);

    CommandResult(
            const CommandUUID &commandUUID,
            const uint16_t resultCode,
            string &resultInformation);

    const CommandUUID &commandUUID() const;

    const uint16_t resultCode() const;

    const Timestamp &timestampCompleted() const;

    const string serialize() const;

};

CommandResult 与示例中的结果相同。

我需要在Scheduler产生结果时，在他的方法run()中，调用Manager的方法acceptResult() 并将结果作为参数传递。我是 C++ 新手，只是不知道该怎么做。

Answer 1

首先你必须让回调可以接受一个参数:

typedef boost::function<void(CommandResult::SharedConst)> callback;

然后您需要在绑定(bind)中匹配该签名。看起来您想在 Scheduler::run() 逻辑中自由绑定(bind)结果，所以让我们使用一个占位符:

 mScheduler = new Scheduler(boost::bind(&Manager::acceptResult, this, ::_1));

现在在您的逻辑中，您以某种方式得出结果，然后将其传递给回调:

void run(){
    boost::uuids::random_generator rgen;
    CommandResult::SharedConst result(new CommandResult(rgen(), 404u, "Not found"));
    //some logic
    mManagerCallback(result);
}

完整演示: Live On Coliru (C++03)

#include <boost/function.hpp>
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/date_time/posix_time/posix_time_io.hpp>
#include <boost/uuid/uuid.hpp>
#include <boost/uuid/uuid_io.hpp>
#include <boost/uuid/random_generator.hpp>

typedef boost::posix_time::ptime Timestamp;
typedef boost::posix_time::time_duration Duration;
typedef uint64_t microseconds_timestamp;

typedef boost::uuids::uuid CommandUUID;

class CommandResult {
public:
    typedef boost::shared_ptr<const CommandResult> SharedConst;

private:
    CommandUUID mCommandUUID;
    uint16_t mResultCode;
    Timestamp mTimestampCompleted;
    std::string mResultInformation;

public:
    CommandResult(
            const CommandUUID &commandUUID,
            const uint16_t resultCode,
            std::string const &resultInformation = "")
      : mCommandUUID(commandUUID),
        mResultCode(resultCode),
        mTimestampCompleted(boost::posix_time::second_clock::local_time()),
        mResultInformation(resultInformation)
    { }

    const CommandUUID &commandUUID() const { return mCommandUUID; }
    uint16_t resultCode() const { return mResultCode; }
    const Timestamp &timestampCompleted() const { return mTimestampCompleted; }
};

typedef boost::function<void(CommandResult::SharedConst)> callback;

class Scheduler {
private:
    callback mManagerCallback;

public:
    Scheduler(callback call){
        mManagerCallback = call;
    }

    void run(){
        boost::uuids::random_generator rgen;
        CommandResult::SharedConst result(new CommandResult(rgen(), 404u, "Not found"));
        //some logic
        mManagerCallback(result);
    }
};

#include <iostream>

class Manager{
private:
    Scheduler *mScheduler;

public:
    Manager(){
        //mScheduler = new Scheduler([this](CommandResult::SharedConst result) { acceptResult(result); });
        mScheduler = new Scheduler(boost::bind(&Manager::acceptResult, this, ::_1));
        mScheduler->run();
    }

    void acceptResult(CommandResult::SharedConst result){
        //do something with result, it's doesn't matter=)
        std::cout << "Accepted: " << result->commandUUID() << ", " << result->resultCode() << ": " << result->timestampCompleted() << " \n";
    }
};

int main() {
    Manager m;
}

打印:

Accepted: cf946fb0-49f3-425a-8235-558d19bf6f8d, 404: 2016-Dec-23 12:18:01 

奖励:C++11

Bind 有点不合时宜(虽然我有时很喜欢它，但对于很少见的工作)，所以请考虑改用 lambda:

mScheduler = new Scheduler([this](CommandResult::SharedConst result) { acceptResult(result); });