Handle deletion of SignalObservers

Add a beingDeleted signal called in the SignalObserver destructor.

Fwk/AppFwk/cafProjectDataModel/cafPdmCore/cafSignal.h

@@ -44,18 +44,77 @@
 
 namespace caf
 {
-class SignalObserver
+class SignalEmitter;
+class SignalObserver;
+
+//==================================================================================================
+/// Basic delete signal emitted by any observer when deleted.
+/// Allows a regular signal to disconnect from the observer.
+//==================================================================================================
+class DeleteSignal
 {
 public:
-    virtual ~SignalObserver() = default;
+    using DisconnectCallback = std::function<void( SignalObserver* )>;
+
+    DeleteSignal( SignalObserver* observer )
+        : m_observer( observer )
+    {
+    }
+
+    template <typename ClassType>
+    void connect( ClassType* signal )
+    {
+        static_assert( std::is_convertible<ClassType*, SignalObserver*>::value,
+                       "Only classes that inherit SignalObserver can connect as an observer of a Signal." );
+
+        DisconnectCallback lambda       = [=]( SignalObserver* observer ) { ( signal->disconnect )( observer ); };
+        auto               signalCasted = dynamic_cast<SignalObserver*>( signal );
+
+        if ( signalCasted ) m_disconnectCallbacks[signalCasted] = lambda;
+    }
+    void disconnect( SignalObserver* observer ) { m_disconnectCallbacks.erase( observer ); }
+    void send()
+    {
+        for ( auto signalCallbackPair : m_disconnectCallbacks )
+        {
+            signalCallbackPair.second( m_observer );
+        }
+    }
+
+private:
+    std::map<SignalObserver*, DisconnectCallback> m_disconnectCallbacks;
+
+    SignalObserver* m_observer;
 };
 
+//==================================================================================================
+/// SignalEmitter
+/// Should be inherited by any object that emits signals.
+//==================================================================================================
 class SignalEmitter
 {
 public:
     virtual ~SignalEmitter() = default;
 };
 
+//==================================================================================================
+/// SignalObserver.
+/// Should be inherited by any object that observes and reacts to signals.
+//==================================================================================================
+class SignalObserver
+{
+public:
+    DeleteSignal beingDeleted;
+
+public:
+    SignalObserver()
+        : beingDeleted( this )
+    {
+    }
+    virtual ~SignalObserver() { beingDeleted.send(); }
+
+}; // namespace caf
+
 //==================================================================================================
 /// General signal class.
 /// Connect any member function with the signature void(const Signal*, const SignalData* data)
@@ -63,7 +122,7 @@ public:
 /// The method should accept that data may be nullptr
 //==================================================================================================
 template <typename... Args>
-class Signal
+class Signal : public SignalObserver
 {
 public:
     using MemberCallback              = std::function<void( const SignalEmitter*, Args... args )>;
@@ -74,7 +133,13 @@ public:
         : m_emitter( emitter )
     {
     }
-    virtual ~Signal() = default;
+    virtual ~Signal()
+    {
+        for ( auto observerCallbackPair : m_observerCallbacks )
+        {
+            observerCallbackPair.first->beingDeleted.disconnect( this );
+        }
+    }
 
     template <typename ClassType>
     void connect( ClassType* observer, void ( ClassType::*method )( const SignalEmitter*, Args... args ) )
@@ -86,9 +151,14 @@ public:
             ( observer->*method )( emitter, args... );
         };
         m_observerCallbacks[observer] = std::make_pair( lambda, true );
+        observer->beingDeleted.connect( this );
     }
 
-    void disconnect( SignalObserver* observer ) { m_observerCallbacks.erase( observer ); }
+    void disconnect( SignalObserver* observer )
+    {
+        m_observerCallbacks.erase( observer );
+        observer->beingDeleted.disconnect( this );
+    }
     void send( Args... args )
     {
         for ( auto observerCallbackPair : m_observerCallbacks )