CODEWITHSUNDEEP
actionscript-3apache-flexoopeventsactionscript
DominicM
DominicM

Reputation: 6898

Actionscript OOP multiple method call architecture issue

I have a class: DatabaseService.as This class creates a local sqlite connection and creates tables if they do not exist. Connection link will be used by several other classes. Some classes will be called on startup others on user interaction. "DatabaseService" class dispatches event when database connection is opened. Other classes initialise "DatabaseService" class and awaits for "DatabaseReadyEvent". This works great but what can I do when I need to call a function/method from the same class several times?

Example:

I create an instance of "PrefService" class in mxml component. "PrefService" creates a new "DatabaseService" class in it's constructor. It then waits for "DatabaseReadyEvent" and executes sql query(this works fine). but then I also need to call "addDir" method (and few others) in "PrefService" class and the sqlConnection property is not set yet causing an error. How can I deal with this? I am new to OOP so I am probably missing something quite simple...

What I've tried / My ideas:

  1. I could check if if sqlConnection exists in "PrefService" class but I think this would be poor practice and still require a delay mechanism of some sort.

  2. I could also create a new instance of "DatabaseService" class for each method and add a new event listener but this would be very cumbersome with 2 functions for each method call not to mention events.

What is the best option in this scenario?

Upvotes: 0

Views: 183

Answers (2)

Amy Blankenship
Amy Blankenship

Reputation: 6961

The hate for Singleton is well-deserved. I'd suggest not ever getting in the habit of using it, so you don't have to break that habit when you find how horrible it is to maintain.

Your biggest mistake is having your View creating and executing your service. Unfortunately, this is encouraged by how the FB service generation code works. What you want, instead, is something more like MVCS (Model-View-Control-Service) of the type encouraged by Frameworks like Robotlegs.

To walk through how to go from a tightly-coupled architecture to a loosely-coupled one, start with this example. Note that the Service is a static Class, which pretty much has all the issues as a Singleton as far as encouraging tight coupling. Even though there is only one Class using the Service, imagine what would happen if you have a large project where tens or hundreds of Classes are referencing it. Now imagine something needs to change. Ick.

Now look at the project, refactored so that the View is simply generating an Event that results in calling the service. The service is still static, but in this case there is exactly one thing that knows about it (Mate), so if you want to make that not static or sometimes use a different service, you easily can, now.

In fact, you can change things around so easily that this is the project, refactored to use Robotlegs. You don't necessarily have to use a Framework, as I did--you can see that the basic structure involved in the core Classes doesn't care a bit about how the Event is being handled or how the data gets into the Views. If you're not comfortable using a Framework, handle it your own way. But Frameworks have been around a while, and they've worked out a lot of issues you haven't thought of yet.

Upvotes: 3

net.uk.sweet
net.uk.sweet

Reputation: 12431

It's tricky to advise without seeing any code, but it might be worth considering making the DatabaseService class a Singleton and initialising it (and the database connection) once as part of your start-up routine (ie. before the classes which use it are instantiated). This would ensure that the classes which use the DatabaseService all share a single connection link to the database, and that the link is available when they come to use it.

Singletons in ActionScript generate a fair bit of debate because in other languages the pattern relies on the ability to set the access modifier of the class constructor as private (which you cannot do in ActionScript 3.0). However, you could choose from a couple of approaches detailed here.

Also, Singletons in general generate a fair bit of debate which might be worth understanding before you use one in anger (since you state you are new to OOP I am assuming you have not done so before).

Upvotes: 2

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