Where to insert code for application startup?

Question

Android newbee here, I have some code that I want to run when my android app first starts up. It checks the version of the local database and downloads a new version if the curr

Answer 1

You can write a custom Application class (extend from android.app.Application). Override onCreate to specify what happens when the application is started:

public class MyApplication extends Application {
    @Override
    public void onCreate() {
        super.onCreate();

        // Do something here.
    }
}

You'll then need to register your custom class in the manifest file:

<application ... android:name="fully.qualified.MyApplication">

Edit:

In response to David Cesarino, I disagree with the purpose of the Application class. If you rely on the Activity's onCreate, then what's to stop it from becoming the same huge class of miscellaneous purposes... if you need something to happen when the application starts, you have to write that code somewhere; and the Activity would probably become more cluttered because you have to perform Activity specific logic in it as well. If you're worried about clutter, then separate the logic into other classes and call them from the Application. Using the SharedPreferences to determine whether or not the logic should execute seems like more of a work-around to a problem that's already been solved.

Dianne Hackborn seems to be referring to data, not logic, in which I totally agree. Static variables are much better than Application level variables... better scoping and type safety make maintainability/readability much easier.

Answer 2

First, look at the Activity lifecycle.

Answering your question, you could put code in any of those "start-up" methods, depending on what you want to do and, mostly important, when you want to trigger that. For what you asked, onCreate is the reasonable place.

I have been sticking it in the oncreate of my first activity, pretty sure there has to be a better place to put this.

And why is that? Any code has an entry point, right? In Android Activities it just happens to be onCreate (again, see above link for the full details). Besides event handling, which are responses to events happening outside the main sequence of calls, you put stuff in onCreate.

If you're concerned about the method becoming huge, then that's another problem. Abstract your code better, I say. For checking preliminary stuff, people generally provide a "Loading" activity, before starting the main activity of the app.

edited:

This is a follow up to what drumboog proposed, since my comment started to grow in complexity to be "just a comment".

Personally, I'd avoid extending the Application class for the sole reason of executing code early on, more so a code that is not that sensible in priority (versioning databases). The Application class is mostly used as an easy way to persist state between Activity'ies, not as a way to "do everything". In short, I feel the Application class is commonly abused.

For what you want, you could perfectly achieve that calling code in Activity onCreate. That reduces complexity, because I've seen people stuffing Application until it becomes a huge class of miscellaneous code purposes. And that's a no-no for maintenance, with logic problems of its own.

Besides, if you truly want another solution, completely disassociated with the UI, you should think about implementing a Service instead (but I don't think it's necessary for just that).

Both of those concerns were previously addressed by Dianne Hackborn (or what I got from her message).