Recommended ways to produce app portable between Android and "other platforms"

I'm developing an application for Android, and I'm thinking that it's functionality might be useful on other (Java-running) platforms (say a regular desktop app -- although I hope that the other platform(s) involved are immaterial to the question at hand).

It's unlikely that the UI will be in any way portable (there's just too much of a difference between a good touch-开发者_StackOverflow中文版capable, 4in screen UI, and a mouse-and-keyboard 19in screen UI), so I'm happy enough reimplementing that separately.

However, the core "business logic" (ugh, horrid word) and model (data storage) classes could, in theory, be reused in managing the core app. I've noticed that there aren't a lot of classes I'm writing that don't end up referencing some Android-specific bits (I've got XML resources files, images, and SQLite databases, as examples). Basically everything I've written so far has at least one Android-related import.

My question is twofold:

• What tools are available out there to help me use Android-related classes and features (eg resources, databases) on non-Android platforms; and
• What classes, features, etc of the Android platform should I completely avoid using (for the sake of simplicity, let's exclude UI-related items) due to non-portability, and what should I use instead to improve portability.

Answers that consist of "hahahaha, you're doomed" are OK, as long as there's some rationale provided.

(P.S. I'd make this community wiki if that was still available; this seems like a perfect CW question to me -- a list of Android portability tips and tools)

Looks like you have already identified the key point by keeping UI and biz logic / model separate. Also sqlite itself is used not only in Android. But of course the way you interact with it (e.g. SQLDBOpenHelper) is different again.

So I guess having the biz logic and model as separate as possible is the way to go. You can then put a wrapper around it (e.g. "Data Access Object " pattern which talks to the specific DB).

Still keep in mind that the users experience is best when you are as specific to a platform as possible on the UI side. Example: there is an App (Push & Ride) on the Android market, which seems to run in a J2ME emulator. So screen input does not use the normal soft (or hard) keyboard of the device, but a simulated phone keyboard with the "abc" "def" combos on the number keys, which makes data entry a bit strange. This app is for sure very portable (and its functionality is really great), but it just does not feel right.

When you want to go multi-platform, you may perhaps also look at things like Appcelerator or Adobe AIR

I started off doing something similar - I wanted to write an app for Android, Blackberry and J2ME. Conceptually, you can layer your design such that platform-specific components (UI, network access, data storage) are separated from the core business logic.

In practice, I don't find this satisfactory. The issues I faced all related to the core version of Java being different in the different platforms (in Blackberry it is based on J2Se 1.4, while Android used Java 6 as base). This led to annoyances like

• Not able to reuse code that uses generics
• My preferred classes not being available uniformly (for example, forced to use Vector over List)

I have opened discussions regarding this on SO (here and here), but couldn't reach a conclusion.

The logging layer can be made portable by using the Simple Logging Facade for Java(SLF4J) which is available for java/log4j and for android.

Also,you can try this out

http://wp7mapping.interoperabilitybridges.com/Home/Library?source=Android

Contains documentation and tools to map your android app to windows phone

Also read this,even though it contains instructions specific to android - windows phone interop,im sure they apply to other platforms as well

http://windowsphone.interoperabilitybridges.com/media/49652/wp7_guide_for_android_application_developers.pdf

What I do is create a web service outside of the android app which can be used by the android app as well as other systems (websites, windows apps, iphone apps etc).

A simple REST web service which supports JSON is a good example to fetch data and also insert/update data. JSON is particularly suitable because its so lightweight, and doesn't require alot of bandwidth which is great for slow mobile connections.

This way you can store your models/data storage outside of the android app, and it can be used by other apps very easily.

The database layer can be made more portable by using android jdbc or by using a database abstraction layer/object relational mapper/ActiveRecord implementation.

Has anyone tried make android.database(.sqlite) runnable on a non android system?

If you carefully separate business logic from UI and android perks you would be able to reuse it in desktop environment. Android is quite different from it in intialisation and application lifecycle - abstracting creation and setup of BL is also necessary.

Usefull pattern for this purpose would be dependency injection. There are different frameworks around, and some are more suited for android (like roboguice) or desktop (spring or picocontainer or guice).

Android appliactions are very constrained in memory, and this puts limits on what frameworks you can use there. So you may need to abstract data storage as well ( hibernate comes handy on desktop / server side , but too heavy for mobile device)

I'm inclined to suggest trying out the new native extensions for Adobe Air. It allows you to create a device-specific chunk of native code, and connect it to the Air framework, accessing it as you would other objects in Air. (cf. http://www.adobe.com/devnet/air/articles/extending-air.html). This allows you to keep the Android-only code as is, and then replace that code with iOS, Windows DLL, etc. code as needed.

This doesn't solve the problem of translating Java code to other languages/platforms, of course. Still, some of the logic you are doing natively may very well exist already cross-platform in Air. For example, you can access the camera in Air in all supported OSes without writing any device-specific code.

You will probably need to go beyond the current Air classes, so some examples may help:

• Android speech-recognition
• iOS batttery
• Windows and Mac tutorial
• NE tutorial

I am currently trying to implement a database compatibility layer for Spring-Boot-JPA/Android-Room:

"compatibility layer" means my Service-layer-code is pure-non-android-code that can be used in android and in spring-boot. The Service-layer-code uses a common java-repository-interface that is either implemented in android-room or in JPA.

Currently i am stuck here:

Howto use methods of CrudRepository<T, ID> (or SimpleJpaRepository<T, ID>) in a Spring-Data-Repository-Fragment method?