Develop Reference

Developer wants to build in version 4.0.x and 4.1

I've got a quote from a developer to build a couple of Android apps. For both the contract states: "App will be compatible with Android OS 4.0.x and 4.1".
Can anyone please tell whether this poses any problems for people wanting to run the apps on newer versions of Android's OS? Not sure if I should be worried or not.
Many thanks
Drew

Mostly, newer Android API fully support older API. That means anything that works on 4.1 should work on 4.3, 4.4, etc
Still, not everything that can run on 4.1 can run on 2.2, for example. Backwards compactibility is a huge problem sometimes

Targeting a minimum of 4.0 won't stop the apps from working on the current versions of android. The only major difference that I can think of is the default color accents being changed in 4.4 (The current highest release). This can be addressed by your developer if your desired styling overrides the defaults anyways, otherwise know that in 4.0 youll see lots of blues, but in 4.4+ youll see a more subtle grey accent.
That isn't to say that this will always be the case though. At any point the OS can take a right turn like they did with the HOLO changes that were introduced between 2.3 and 3.0, which would make your "legacy" app not function as it use to. At this point, you would either have to have the app redone, or accept the flaws in this completely hypothetical future state.

Unless the API is depecrated, they will always work on newer versions. The problem usually is older versions unable to support newer API, not the other way round.

why don't I choose all versions for android app?

When I created my application, I chose 1.0 for the minimum SDK and 4.3 for the target SDK, so my application works on all phones.
But why would we choose (for example) a minimum SDK of 2.2?
Is it about performance, or something like that?

First of all i'd like to clear,
android:minSdkVersion="integer"
Despite its name, this element is used to specify the API Level, not the version number of the SDK (software development kit) or Android platform. The API Level is always a single integer. You cannot derive the API Level from its associated Android version number (for example, it is not the same as the major version or the sum of the major and minor versions).
find more detail
we choose minimum and maximum version for our app because , some of the feature which are not supported in lower/higher versions of android are used in app . The Android system will prevent the user from installing the application if the system's API Level is lower/higher than the value specified in this attribute.Hence preventing unwanted force close.
Most of the features of higher versions of android will not work in api level 1 .thwn why will you put level 1 as minimum sdk.

Android is a system that is everytime changing, and that implements new features in each new version.
When you develop an app, you will have to deal with :
Compliance for the user
Nice features for your application
For example, animations of clickable elements are not well implemented in Android 2.3. So when you will have to develop an application, you will have to choose :
Compliance with a maximum users including 2.3 compliance
Develop a lot of nice animations, including on clickable elements
It's why sometimes you decide to develop an applications, you may decide to not include some versions of the SDK.
And for having a clear view on how much users you would loose, you may want to go to :
Dashboards

99,9% of phones use SDK 2.2 and later and all cool features that you can use are avaliable on later SDK versions than 1.1. That is the main reason, but you can use earlier version of SDK for minimum but in has no efect because you are covering all devices with 2.2 SDK.

What are API levels in Android?

I am starting to learn android development. I downloaded adt-bundle-windows-x86 from the android site. Now when I open the SDK manager that comes with the bundle it enlists a number of API levels. My phone has ICS. But when I saw wiki for the same it seems we can have more than one API levels for a single code name.
Which one is to be used? I want backward compatibility and also not miss on the new features that might have been introduced in ICS. what do these API levels mean and how do I decide which one to use?

Here is a link to the list of Platform Version - API Level - VERSION_CODE - Notes
This link shows data about the relative number of devices running a given version of the Android platform.
I recommend:
minimum sdk version = Android 2.3.3 - Gingerbread - Api level 10
target sdk version = Android 4.3 - JellyBean - Api level 18
NOTE the target sdk version most of the time should be the latest release which at current is JellyBean

Here you can find a list of api levels, code names and usage statistics.-
http://developer.android.com/about/dashboards/index.html
You should try making your application compatible with as much devices as possible, so I'd recommend to make sure that works fine at least on Android 2.3.3 - Gingearbread - Api level 10
Regarding new features, sadly, keeping in mind old devices sometimes means forgetting about some new cool features or apis which are included to make our lives much easier.

I think this can help you a lotclick

You should set api level as minimum as possible like 2.3.3 gingerbread. 35% of android devices still runs on Gingerbread. But as per your question it seems like you wanted to start development from 4.0.4 ICS. So set your min SDK 14. And as far as new graphical or library changes google provides support library for use.
One suggestion set max api level as high as possible. I mean 4.3 for now. hope this would help

Targeting the most appropriate API

Currently, I tend to target all my app development to API 8, so that I can hit the largest number of devices 'out there', basically from Android 2.2 upwards.
Do any experienced Android developers reading this have a perspective on what features, as a developer am I 'missing out' on, and more importantly, what are my users missing out on? In this day and age, what API is the 'best' one for my apps to target? Or is there no such thing, and each app should be targeted for a given API on its merits?
I'm not looking for pointers such as read the android developer docs (I have, or at least what I consider the salient parts), I'm more interested in the views of experienced developers as to how they decide which API to target.
Thanks.

if you set your target and minSdkVersion to 7 and use support (compatibility) library v4, then your app will support nearly 95% of all android phones, and still you are able to use modern features of newer APIs (by using support library).

I usually target the minimum API required by the apps functionality. If there is a minor feature needing a higher API, I make it optional instead of increasing the minimum for the whole app. In addition to using ActionBarSherlock and the compatibility libraries, I occasionally back port a few things from later APIs to keep the current basis.
While I decide the minimum on a per app basis, most of my apps target 2.1, as they were written almost one and a half years ago. Now days, I have new apps target 2.2, though I plan to change it to 2.3 very soon.
I guess my point is that there is no defined minimum API target. You should choose the one which offers maximum user reach, along with as much major functionality as possible. UI elements like the action bar and ViewPager can be used via libraries, and the ones not available in libraries can sometimes be back ported. However, it is usually not worth it to sacrifice users running a lower API version just for a better UI.

Android dalvik problem

Please i have different platforms installed. I just wanted to know what am supposed to do. If i develop with 3.0 platform, would those with a 2.2 be able to use my app??..
The second question which is the main question is I always get this error when i create android projects..
[2011-05-16 16:32:21 - Hello World] Dx no classfiles specified
[2011-05-16 16:32:21 - Hello World] Conversion to Dalvik format failed with error 1
What do I do to it?

There are several reports out there for that error (e.g., this one. All the solutions point simply to reload the project (select it in the tree at your left, and press F5).
Regarding the first question, unless you want to support Honeycomb-only features, then set up the api level to 8 (Froyo).
Eclair, Froyo and Gingerbread are android versions 2.1, 2.2 and 2.3 respectively (also referred in the documentation as API levels 7, 8 and 9). See the table here. If you want to support just mobile phones, set your target to 2.1 or even lower. That way you will be able to target most of the phones in the market. Your app will also run in Honeycomb (3.x) devices.
Honeycomb has new features to support larger screen devices, so if that is your main target, you might consider taking advantage of those features and drop cell phone support. All will depend on what is your objective.

you should have a look at the minSdk and targetSdk features of a manifest file :
<uses-sdk android:minSdkVersion="4" android:targetSdkVersion="8" />
This will help you target a android sdk version and precise what is the minimum sdk level that can run your app.
Regards,
Steff

Developing for Honeycomb or non-tablet version of Android, is different in various things. Your 2.2 application should run correctly on a tablet, but if you want to optimize the graphical interface and use all the notification and other things included only in Honeycomb, then you must use the appropriate API. Until Ice Cream Sandwich is released, we have to develope two different application for the best result.
Regarding the error you get with android projects (I suppose under eclipse?) you'll find some detail at this link, but if you follow all the instruction provided by google in the developers page, you'll be able to write and run your Hello World application.