Arma Reforger:ScriptInvoker Usage

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See Event Handlers for ScriptInvoker guidelines.

A ScriptInvoker is an object that allows other objects to subscribe to the event it represents by registering a method. Such event can provide arguments and it is important for the subscribing methods to fit the proper method signature.

The interest of using Events is that the subscribed method is be executed only if and when a specific event occurs (e.g a fired weapon, someone leaving a vehicle, etc) - no periodical check is done, saving CPU cycles and executing exactly on event.

Usage

Show example

class TAG_Dog { protected ref ScriptInvoker m_OnBark; // initialised on request - this allows saving RAM as ScriptInvokers are not small objects // IN GENERAL, do NOT expose the ScriptInvoker variable directly (as anyone could delete it) //! This method provides the ScriptInvoker for outsiders to subscribe to it ScriptInvoker GetOnBark() { if (!m_OnBark) m_OnBark = new ScriptInvoker(); // the invoker is only created on external request return m_OnBark; } void Bark() { if (m_OnBark) // the invoker can be null if nobody subscribed to it - no need to create it m_OnBark.Invoke(); Print("Dog barked", LogLevel.DEBUG); } } class TAG_Neighbour { protected TAG_Dog m_Dog; // no strong ref protected int m_iBarkCount; protected void OnDogBark() { if (m_iBarkCount < 1) Print("The dog barked!", LogLevel.NORMAL); else if (m_iBarkCount < 10) Print("Oh, it barked again!", LogLevel.NORMAL); else Print("MAKE IT STOP", LogLevel.WARNING); m_iBarkCount++; } //! Constructor void TAG_Neighbour(notnull TAG_Dog dog) { m_Dog = dog; m_Dog.GetOnBark().Insert(OnDogBark); // GetOnBark() creates the invoker // Insert() adds OnDogBark to the list of methods to be called } //! Destructor void ~TAG_Neighbour() { // do not forget to unsubscribe for good practice, clean code aaand to avoid potential memory leaks if (m_Dog) m_Dog.GetOnBark().Remove(OnDogBark); // removes OnDogBark from the list of methods to be called } }

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Signature Declaration

The ScriptInvoker class used above is the "default" one used for methods without arguments. In order to provide arguments to the subscribed methods, a generic ScriptInvokerBase type must be used, e.g ScriptInvokerBase<func>.

A method signature can be declared using typedef:

void ScriptInvokerIntMethod(int i); typedef func ScriptInvokerIntMethod; typedef ScriptInvokerBase<ScriptInvokerIntMethod> ScriptInvokerInt;

And used like this:

protected ref ScriptInvokerInt m_OnEventWithIntParameter = new ScriptInvokerInt();

Show full example

class TAG_EventHolder { protected in m_iScore; protected ref ScriptInvokerInt m_OnScoreChanged; // still created on request ScriptInvokerInt GetOnScoreChanged() { if (!m_OnScoreChanged) m_OnScoreChanged = new ScriptInvokerInt(); return m_OnScoreChanged; } void AddScore(int points) { m_iScore += points; if (m_OnScoreChanged) m_OnScoreChanged.Invoke(m_iScore); } } class TAG_Subscriber { protected TAG_EventHolder m_EventHolder; protected void WarnOfScoreChange(int newScore) // note the similarity with ScriptInvokerIntMethod's signature { Print("The score is now " + newScore + "!", LogLevel.NORMAL); } void Subscribe(notnull TAG_EventHolder eventHolder) { if (!eventHolder) return; if (m_EventHolder) UnSubscribe(); eventHolder.Insert(WarnOfScoreChange); // if the method signature were not matching, the compiler would warn here m_EventHolder = eventHolder; } void UnSubscribe() { if (!m_EventHolder) return; m_EventHolder.Remove(WarnOfScoreChange); m_EventHolder = null; } void ~TAG_Subscriber() { UnSubscribe(); } }

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That's it! Remember that ScriptInvokers/Event Handlers are very powerful, but dangerous tools. Be sure not to fall into any trap or loop!