我对这个问题做了一些研究,但还没有得出具体的解决方案。我真的很想能够做到这一点:
public delegate void VoidFloatCallback(float elapsedTime);
public VoidFloatCallback OnEveryUpdate;
public VoidFloatCallback OnNextUpdate;
public virtual void Update(GameTime gameTime)
{
if (OnNextUpdate != null)
{
OnNextUpdate(gameTime);
OnNextUpdate = null;
}
if (OnEveryUpdate != null)
{
OnEveryUpdate(gameTime);
}
this.OnUpdate(gameTime);
}
当然是在 C++ 中。我发现只有一个解决方案可以为我提供这样的功能;但后来被下线了,但我在这里重新发布了它http://codepad.org/WIVvFHv0 .我发现的解决方案的唯一问题是它不是现代 C++11 代码并且缺乏 lambda 支持。
我知道我可以用
std::function
但唯一的问题是它不支持运算符“+=
、-=
、==
”。现在我考虑过制作自己的 Events 类并拥有一个
vector<std::function>
使用一些模板,但我发现 std::function 没有实现运算符 ==
所以我无法让它看起来像 C# 那样。
无论如何,我的问题是:
我想知道如何使用 C++11 实现这样一个事件系统——或者它是否可能。或者即使您知道实现支持多个监听器的回调的更好/正确方法(如果可能的话,我想避免完全成熟的观察者模式实现。)
更新#1
我对运营商的意图是:
void some_func(float f) { /** do something with f **/ }
void some_other_func(float f) { /** do something else with f **/ }
OnNextUpdate += some_func();
OnNextUpdate += some_other_func();
OnNextUpdate(5.0f);
// both some_func() and some_other_func() are called
OnNextUpdate -= some_other_func();
OnNextUpdate(5.0f);
// only some_func() is called
最佳答案
C++ 函数对象机制与 C# 方法有很大不同。特别是,函数对象基于值而不是引用。在 C++ 中删除函数对象时可以识别它们的原因是函数对象具有标识,即调用它们的对象和被调用的成员函数。此外,在 C++ 中,不可能同时直接获取对象和成员函数的地址。
要使委托(delegate)系统工作并允许删除函数,您可以创建类似于 std::function<Signature>
的东西但使用多个函数并要求每个使用的函数都是 EqualityComparable
.下面是这种委托(delegate)系统的简单实现,以及成员函数的绑定(bind)器的示例实现。有许多明显的扩展机会,因为此实现仅用作演示。
#include <algorithm>
#include <iostream>
#include <memory>
#include <utility>
#include <vector>
template <typename Signature>
struct delegate;
template <typename... Args>
struct delegate<void(Args...)>
{
struct base {
virtual ~base() {}
virtual bool do_cmp(base* other) = 0;
virtual void do_call(Args... args) = 0;
};
template <typename T>
struct call: base {
T d_callback;
template <typename S>
call(S&& callback): d_callback(std::forward<S>(callback)) {}
bool do_cmp(base* other) {
call<T>* tmp = dynamic_cast<call<T>*>(other);
return tmp && this->d_callback == tmp->d_callback;
}
void do_call(Args... args) {
return this->d_callback(std::forward<Args>(args)...);
}
};
std::vector<std::unique_ptr<base>> d_callbacks;
delegate(delegate const&) = delete;
void operator=(delegate const&) = delete;
public:
delegate() {}
template <typename T>
delegate& operator+= (T&& callback) {
this->d_callbacks.emplace_back(new call<T>(std::forward<T>(callback)));
return *this;
}
template <typename T>
delegate& operator-= (T&& callback) {
call<T> tmp(std::forward<T>(callback));
auto it = std::remove_if(this->d_callbacks.begin(),
this->d_callbacks.end(),
[&](std::unique_ptr<base>& other) {
return tmp.do_cmp(other.get());
});
this->d_callbacks.erase(it, this->d_callbacks.end());
return *this;
}
void operator()(Args... args) {
for (auto& callback: this->d_callbacks) {
callback->do_call(args...);
}
}
};
// ----------------------------------------------------------------------------
template <typename RC, typename Class, typename... Args>
class member_call {
Class* d_object;
RC (Class::*d_member)(Args...);
public:
member_call(Class* object, RC (Class::*member)(Args...))
: d_object(object)
, d_member(member) {
}
RC operator()(Args... args) {
return (this->d_object->*this->d_member)(std::forward<Args>(args)...);
}
bool operator== (member_call const& other) const {
return this->d_object == other.d_object
&& this->d_member == other.d_member;
}
bool operator!= (member_call const& other) const {
return !(*this == other);
}
};
template <typename RC, typename Class, typename... Args>
member_call<RC, Class, Args...> mem_call(Class& object,
RC (Class::*member)(Args...)) {
return member_call<RC, Class, Args...>(&object, member);
}
// ----------------------------------------------------------------------------
void f(char const* str) { std::cout << "f(" << str << ")\n"; }
void g(char const* str) { std::cout << "g(" << str << ")\n"; }
void h(char const* str) { std::cout << "h(" << str << ")\n"; }
// ----------------------------------------------------------------------------
struct foo
{
int d_id;
explicit foo(int id): d_id(id) {}
void bar(char const* str) {
std::cout << "foo(" << this->d_id << ")::bar(" << str << ")\n";
}
void cbs(char const* str) {
std::cout << "foo(" << this->d_id << ")::cbs(" << str << ")\n";
}
};
// ----------------------------------------------------------------------------
int main()
{
delegate<void(char const*)> d0;
foo f0(0);
foo f1(1);
d0 += f;
d0 += g;
d0 += g;
d0 += h;
d0 += mem_call(f0, &foo::bar);
d0 += mem_call(f0, &foo::cbs);
d0 += mem_call(f1, &foo::bar);
d0 += mem_call(f1, &foo::cbs);
d0("first call");
d0 -= g;
d0 -= mem_call(f0, &foo::cbs);
d0 -= mem_call(f1, &foo::bar);
d0("second call");
}
关于C#-Like Delegates in C++,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/23973914/