- Rename the
list
attribute inASubject
to something else , sayobservedShops
(as named in your comment already). - Avoid
using namespace std
in library code.
Implementing Observer pattern C++
-
08-10-2022 - |
Question
I'm working on a C++ project in Android. What I want to achieve is make an async call in C++, then send the data back over JNI. It's a simple proof of concept, but that also means my C++ knownledge is limited.
I've got all the functionalities working, but wanting to make the C++ side of the project "better" I want to implement an Observer Pattern. I used this as tutorial: http://www.codeproject.com/Articles/328365/Understanding-and-Implementing-Observer-Pattern-in
After adding everything (ofc modified to my project) I'm getting the following compile error: template argument 2 is invalid in the ASubject.h at the line:
std::vector<PoCCplusplus*> list;
Subject h and cpp:
#pragma once
#include <vector>
#include <list>
#include <algorithm>
#include "PoCCplusplus.h"
class ASubject
{
//Lets keep a track of all the shops we have observing
std::vector<PoCCplusplus*> list;
public:
void Attach(PoCCplusplus *cws);
void Detach(PoCCplusplus *cws);
void Notify(char *xml);
};
#include "ASubject.h"
using namespace std;
void ASubject::Attach(PoCCplusplus *cws)
{
list.push_back(cws);
}
void ASubject::Detach(PoCCplusplus *cws)
{
list.erase(std::remove(list.begin(), list.end(), cws), list.end());
}
void ASubject::Notify(char *xml)
{
for(vector<PoCCplusplus*>::const_iterator iter = list.begin(); iter != list.end(); ++iter)
{
if(*iter != 0)
{
(*iter)->Update(xml);
}
}
}
It's probably something really simple I'm missing, but I just cant find the solution for it.
La solution
Autres conseils
You
#include <list>
so 'list' is already a defined type. Choose a different variable name.
This is why it's a good idea to not use:
using namespace std;
Also, observer can be done shorter, if you use boost::signals2:
#include <boost/signals2.hpp>
#include <boost/bind.hpp>
using namespace std;
using boost::signals2::signal;
using boost::bind;
struct Some {
void Update(char* xml) {
cout << "Update\n";
}
void operator()(char* xml) {
cout << "operator\n";
}
};
void func(char* xml) {
cout << "func\n";
}
int main() {
signal<void(char*)> s;
Some some;
Some other;
s.connect(some);
s.connect(bind(&Some::Update, other, _1));
s.connect(func);
char str[10] = "some str";
s(str);
return 0;
}