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Kigs Framework Introduction (6/8) - Signal, Slot, Notification

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17 Jun 2020MIT2 min read
A multi purpose, cross-platform, free and Open Source C++ framework. This article will focus on Signal/Slot and Notification mechanisms.
This short article demonstrates the use of Signals, Slots and Notifications in the Kigs framework. Signals, Slots and Notifications are used to communicate between instances.

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Table of Contents

Introduction

Now that we have seen how CoreModifiable methods (Kigs Framework Introduction (4/8) - Methods) works, we are going to see in this short article how to take advantage of this mechanism to easily connect instances together.

Signals and Slots

Signals

A list of signals can be declared at compile time for a given class using helper macro SIGNALS:

C++
// CoreModifiable signals 
SIGNALS(PreInit, 
	PostInit,
	Uninit,
	Destroy,
	Update, // Called before the actual update
	NotifyUpdate,
	AddItem,
	RemoveItem,
	PrepareExport,
	EndExport);

It is then possible to retrieve the list of declared signals for this class using method "GetSignalList" :

C++
// get the list of SimpleClass signals
std::cout << "simpleclass instance has following signals available" << std::endl;
auto signallist=simpleclass->GetSignalList();
for (const auto& s : signallist)
{
#ifdef KEEP_NAME_AS_STRING
	std::cout << s._id_name << std::endl;
#else
	std::cout << s._id << std::endl;
#endif
}

Slots and Connections

A declared signal can be emitted using EmitSignal method:

C++
// emit signal with two parameters
EmitSignal(Signals::SendSignal1,32,64);

It's also possible with the same mechanism to send undeclared signals:

C++
// emit a "runtime" signal (not declared with the SIGNALS macro) 
EmitSignal("doSomething");

Signals can be emitted with or without parameters.

For an instance to receive a signal from another one, a connection must be setup :

C++
// connect this "MethodWithParams" to simpleclass instance "SendSignal1" signal
KigsCore::Connect(simpleclass.get(),"SendSignal1",this, "MethodWithParams");
// connect app undeclared doSomething signal to doSomething method
KigsCore::Connect(app, "doSomething", this, "doSomething");

"MethodWithParams" is a CoreModifiable method declared with WRAP_METHODS macro or with DECLARE_METHOD/COREMODIFIABLE_METHODS. See CoreModifiable method article in this series for details.

C++
// Wrapped MethodWithParams
void	MethodWithParams(float p1, float p2);
WRAP_METHODS(MethodWithParams);
C++
// fixed prototype CoreModifiable method
DECLARE_METHOD(doSomething);
// list methods
COREMODIFIABLE_METHODS(doSomething);

To disconnect two instances, KigsCore::Disconnect method is also available :

C++
// disconnect this so SendSignal1 will not be catched anymore
CMSP simplecass=GetInstanceByPath("simpleclass");
KigsCore::Disconnect(simplecass.get(), "SendSignal1", this, "MethodWithParams");

Lambda Slots

It's also possible to connect signal to a lambda function directly:

C++
// connect to lambda function
KigsCore::Connect(simpleclass.get(), "SendSignal2", this, "lambda", [this](int p1)
{
	std::cout << "lambda received parameter " << p1 << std::endl;
});

Instance Factory Connection

It's possible to ask instance factory to create a connection for each created instance of a particular class:

C++
// ask instance factory to add a connection on each created SimpleClass 
// for the PreInit signal to call this OnSimpleClassPreInit
KigsCore::Instance()->GetInstanceFactory()->addModifiableCallback
                      ("PreInit", this, "OnSimpleClassPreInit", "SimpleClass");

If the last parameter is not set, the connection is added for all types of created instances.

To remove the automatic connection:

C++
// remove instance factory auto connection previously set
KigsCore::Instance()->GetInstanceFactory()->removeModifiableCallback
                      ("PreInit", this, "OnSimpleClassPreInit");

Notifications

Another way to create connections is to use the NotificationCenter class. NotificationCenter can connect two instances like with signal/slot mechanism, but also notify an instance to listen for notification posted by any sender instance.

Observers

The NotificationCenter can register observer instances:

C++
// register this as an observer on notification "doSomethingElseNotif" 
// call method CatchNotifMethod when doSomethingElseNotif is received
KigsCore::GetNotificationCenter()->addObserver(this,"CatchNotifMethod","doSomethingElseNotif");

A fourth CoreModifiable* parameter is possible to listen to notifications only coming from the given sender instance.

To remove an observer:

C++
// remove this as "doSomethingElseNotif" notification observer. 
// a third parameter is needed if observer was set on a specific instance.
KigsCore::GetNotificationCenter()->removeObserver(this, "doSomethingElseNotif");

Post a Notification

A notification can then be sent using NotificationCenter "postNotificationName" method:

C++
// post a notification "doSomethingElseNotif" 
// a vector of CoreModifiable attributes can be set as second parameter : 
// kstl::vector<CoreModifiableAttribute*>& params
// the sender can also be passed (as second or third parameter)
KigsCore::GetNotificationCenter()->postNotificationName("doSomethingElseNotif", this);

Serialization

A signal/slot connection can be set in XML adding this kind of item to an instance:

XML
<Connect Si="SignalName" E="EmitterPath" SL="SlotName" R="ReceiverPath"/>

Emitter path and receiver path are classic CoreModifiable search paths. "this" or "self" can also be used to indicate owning instance.

An observer can also be set on an instance adding this item:

XML
<OnE N="NotificationName" A="CalledMethod"/>

Find all the sample code from this wiki section in Sample6 project (browse the code).

Already Published in this Series

  1. Kigs Framework Introduction (1/8) - Overview
  2. Kigs Framework Introduction (2/8) - CoreModifiable
  3. Kigs Framework Introduction (3/8) - Attributes
  4. Kigs Framework Introduction (4/8) - Methods
  5. Kigs Framework Introduction (5/8) - CoreItem
  6. Kigs Framework Introduction (6/8) - Signal, Slot, Notification
  7. Kigs Framework Introduction (7/8) - Lua Binding
  8. Kigs Framework Introduction (8/8) - Data Driven Application

History

  • 26th February, 2020: Initial version
  • 19th March, 2020:  Article (7/8) added to the series and little fix in sample code
  • 17th June, 2020 : Added final article of the series 

License

This article, along with any associated source code and files, is licensed under The MIT License

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About the Author

Stephane Capo
Chief Technology Officer NEXT-BIM
France France
CTO of NEXT-BIM, I also supervise and participate in the development of Kigs framework.

Comments and Discussions

 
GeneralMy vote of 5 Pin
FenderBaba20-Mar-20 23:35
MemberFenderBaba20-Mar-20 23:35 
Very interesting article serie. Thank You for sharing !

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