E-Dev Blog

Here’s a function I wrote out of necessity. Hope you find it useful.

UPDATE – I realized I could simplify the function, so here’s the rewrite. Also added examples to the header comment.

I don’t have a big post ready, as I’m not sure what I should cover. Please comment with a topic suggestion.

Today I’d like to continue a look into Multi Theft Auto’s event system. In my previous post, Event Handlers (Multi Theft Auto’s CallBacks), I began talking about the Event system and how it is used to trigger functions. I also mentioned that those functions can, in return, trigger and create additional events.

In the chart above, I’ve detailed an example chain of Events and Event Handlers. Again, I’m using the onPlayerJoin event as the basis for the chain. This time, however, I’m showing how a function can call other Events, including custom ones. The example function getSQLAccount() is called when a player joins. This function attempts to retrieve data from a MySQL database about the player, and has three events depending on what occurs.

• onSQLExist
  • Called if SQL row exists for user
• onSQLEmpty
  • Called if SQL row does not exist for user
• onSQLError
  • Called if SQL information doesn’t match, or error occurs

Just like the standard Events, you use the function addEventHandler(). However, you need to declare the new Event with the function addEvent(). In the short example below, I show how the custom event “onMyCustomEvent” is created, and an Event Handler is connected with it.

While this creates the event, and assigns an Event Handler, we don’t have anything triggering it. You need to trigger the event with triggerEvent(). This function can be called loose within the code, within another Event, or when the Resource is started or stopped. By having the triggerEvent() function loose in the code, the function is called when the code is first executed. (For example, on resource start)

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People who are just starting to develop for Multi Theft Auto (MTA) often have trouble grasping Event Handlers. As a developer in C and PHP, I’ve often worked with Callbacks, which are equivalent to Event Handlers. You can think of an Event Handler as “What to do when the situation arises.” So, let’s say you’re waiting for the Bus. The Bus arriving is considered an “Event” and your “Event Handler” is you getting on the Bus when the “Event” occurs.
In this case, the Event chain is: Bus Arrives -> Get on Bus (Event Handler) -> Continue through

In the Chart above, I’ve detailed an example set of three Event Handlers combined with the onPlayerJoin Event. First the Event is triggered, in this case by a Player joining the server. Then the server grabs any Event Handlers, in this case welcomePlayer( ), checkBanStatus( ), and displayRules which all return something relating to the source player. Once all the Event Handlers are called, the Event ceases. Event Handlers can trigger further Events and their Event Handlers.

In the Chart, the Event Handler welcomePlayer( ) is called when the event onPlayerJoin is triggered. Below is an example of what that could be.