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allow observers to return an error code to abort further processing

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Will allow me to use observers to generalize the various hooks
that need to run to preflight sleep entry.
This commit is contained in:
geeksville
2020-04-10 12:40:44 -07:00
parent 6ad451eb5f
commit 640cb3bf7f
4 changed files with 22 additions and 8 deletions
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20
src/Observer.h
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@@ -24,7 +24,11 @@ template <class T> class Observer
friend class Observable<T>;
protected:
virtual void onNotify(T arg) = 0;
/**
* returns 0 if other observers should continue to be called
* returns !0 if the observe calls should be aborted and this result code returned for notifyObservers
**/
virtual int onNotify(T arg) = 0;
};
/**
@@ -32,7 +36,7 @@ template <class T> class Observer
*/
template <class Callback, class T> class CallbackObserver : public Observer<T>
{
typedef void (Callback::*ObserverCallback)(T arg);
typedef int (Callback::*ObserverCallback)(T arg);
Callback *objPtr;
ObserverCallback method;
@@ -41,7 +45,7 @@ template <class Callback, class T> class CallbackObserver : public Observer<T>
CallbackObserver(Callback *_objPtr, ObserverCallback _method) : objPtr(_objPtr), method(_method) {}
protected:
virtual void onNotify(T arg) { (objPtr->*method)(arg); }
virtual int onNotify(T arg) { return (objPtr->*method)(arg); }
};
/**
@@ -55,13 +59,19 @@ template <class T> class Observable
public:
/**
* Tell all observers about a change, observers can process arg as they wish
*
* returns !0 if an observer chose to abort processing by returning this code
*/
void notifyObservers(T arg)
int notifyObservers(T arg)
{
for (typename std::list<Observer<T> *>::const_iterator iterator = observers.begin(); iterator != observers.end();
++iterator) {
(*iterator)->onNotify(arg);
int result = (*iterator)->onNotify(arg);
if (result != 0)
return result;
}
return 0;
}
private: