How do I best solve multiple component modifications via a single event?

Question

I'm trying to solve multiple component modifications via a single event. Is there a better way of handling this?

I have an a label entity that cares about when a shield entity's hitpoints component is modified (damage, regeneration, etc).

The label will need to change

• its text to display the current % of shield remaining.
• its text color to display the severity of shield remaining.

When my ShieldSystem resolves the hitPoints component, the below code runs. For eah type of modification I plan to listen for, I need to add a new if-statement to the for-loop. This means I have a bunch of duplicated code between systems if more than one wants to modify any listening text component, sprite component, etc.

for(int i =0; i < listeners.size(); i++)
{
    if(listeners.count(MessageType::CHANGE_TEXT) == 1)
    {
        std::vector<Entity*> entities =  listeners[MessageType::CHANGE_TEXT];
        for(int j; j < entities.size(); j++)
        {
            Entity* e = entities[j];
            MessageInfo* messageInfo = new MessageInfo(MessageType::CHANGE_TEXT, e, "Some Text");
            MessageCenter::Dispatch(messageInfo);
        }
    }

    // Add an If(listeners.count(MessageType::CHANGE_TEXT_COLOR)...

    // Add an If(listeners.count(MessageType::CHANGE_SPRITE_RECT)...

    // etc

}

Answer 1

One way to make this easier to use is to let a user emit message types.

Check out some example implementation (see Messenger.h and .cpp).

The idea is to let a user do something like this:

// Subscribe to a particular message type as a user
messenger.Subscribe( MSG_type, CallThisFunction );

// Notify the client
messenger.Emit( MSG_type ) // calls CallThisFunction

A good way to pass along parameters with a message is to have some generic way to send data. Then you can let the user (in this case inside of CallThisFunction deal with retrieving the data appropriately (typecasting, or some other more intelligent means). This lets the notifier use an alternate Emit version:

// Notify the client with 4 params, pass each
// param to the CallThisFunction
messenger.Emit( MSG_type, somePtr, 5, 1.0f, "a string" );

All in all this mostly looks like an API issue.