Can an app be written to run on any devices? - app-store

I would like to know if it is possible to write apps that can run on any devices.

Assuming you are talking about mobile devices, in theory, yes, there are frameworks out there like Sencha Touch that should be able to run on any device, but often you don't want to have your app look the exact same on every device due to different conventions.

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What kind of iPhone / iPod Touch do I need to test my app?

I've written a fairly basic app for the iPhone, which I would like to test on at least one device and then get it onto the market place.
I don't need a data plan, so I'm considering buying an iPod touch, but I understand it doesn't have a camera, video, compass. While I don't need those for my current app, I might for a future one, nothing for sure there.
My concern about purchasing an iPhone, used or new, is that I believe I won't be able to use it without a sim card unless I jailbreak it. I'd prefer not to get involved with jailbreaking, as I'm unclear how it would my efforts to test the app on the device and/or get the app onto the app store.
If I get a new iPhone, I would have to cancel the contract immediately, and my same concern about the lack of a sim card would apply.
I'd be interested in people's experience with this issue, e.g. starting out with iPhone apps and not having an iPhone, is with this issue.
The newest iPod Touch does have a camera: http://www.apple.com/ipodtouch/
You should be able to test nearly everything you'd need to test on an iPod Touch.
Also, if you want to support older devices, it might be a good idea to also pick up a used, older, iPod Touch on eBay or somewhere, so you can test on a non-Retina display.
I have development going on without an iPhone but is preferred to develop with a device cause you could test your codes once in awhile. iPod Touch 4 does have camera. Anyway i think iPhone would still be able to function properly without a sim card just that you can't call. Otherwise getting an iPad is not that bad, since you can run both iPad and iPhone apps in iPad.
You may want to get the oldest slowest model of device running the oldest version of iOS on which you want you apps to be compatible. This may also be a low cost way to get into testing on devices. If your apps are commercially successful, you will be able to afford acquiring more newer test devices, but the old one may be the most valuable one for app testing purposes.
I have been using my old iPhone 3G for developement, mostly because it allows me to see how my code runs on one of the slowest devices out there.
The phone is not currently signed up with AT&T and it still works fine for development. For data access the wifi works fine without a carrier account. It also has the camera and (basic) GPS/mapping.
I could probably pick up a used iPhone 3G off one of the auction site relatively cheaply.

iPhone - is a unlocked iPhone indistinguishable by Xcode

My question is: is a unlocked iPhone treated the same way by Xcode? or in other words, can one develop using a unlocked iphone without any problem? When I say unlocked I mean not the official way.
I ask this because I have the possibility of beta testing my apps with some friends and some of them use jailbroken iphones and some just unlocked their phones on an unofficial way. I would like to know if it will be trustable to have these devices testing my app.
I think Xcode does not realize that, it treats all devices as not jail-broken.
The only difference you might see is (depending on the stuff you have installed in your jail-broken device) you will get many messages in the console.
I remember once I installed winterBoard and I was getting many many debugging messages about it. Messages not regarding my code!.
Regarding permissions: many things are different. So, you should test at least once you app on a not jailbroken device.
I think it all depends on how you went about jailbreaking and how much you've changed the system. Obviously, there's a difference between unlocking and leaving everything else untouched compared to replacing large parts of the OS.
However, I'm sure there are folks who can go into far more detail.

Can I restrict my iPhone app from being used by iPhone3G's?

My iphone app doesn't run well on the iPhone 3G. Can I make it so users with these models can't download the app? If so, what does a 3G user see when they search for my app in the app store?
Does it appear in the store at all for them? If it does, when are they notified that they can't download the app?
I recommend you use the UIRequiredDeviceCapabilities key in your info.plist. This lets you tell the App Store exactly which capabilities you require instead of which device you require.
If your app "doesn't run well" on a 3G I'll guess it is because of performance and therefore you'd want to require a newer processor. Look into setting arm7 as one of your required device capabilities.
For more info look here:
http://developer.apple.com/iphone/library/documentation/General/Reference/InfoPlistKeyReference/Articles/iPhoneOSKeys.html#//apple_ref/doc/uid/TP40009252-SW3
Make it run better. Or if it's not completely unusable, just let them use it anyway. People with old devices expect them to be a bit slow.
According to the iTunes Connect Developer Guide (which links to the iOS Application Programming Guide), you can't prohibit certain devices. You can, however, require certain features which are only present on new devices:
armv7 is what I'd recommend (older devices are armv6)
magnetometer, because older devices don't have one. Apple might look at you funny if your app doesn't actually use the compass though.
opengles-2, because older devices only support 1.1. Apple might look at you funny too.
auto-focus-camera, except the iPad and all the iPod Touches don't have one. Probably not what you want.
iPhone 3GS uses iOS 6.1.x so if your app support iOS 7+ it will not be able to install on iPhone 3GS, this is the best possible way to avoid download on that device.

Can a deactivated iPhone be used for app development/testing?

I'm thinking of upgrading my iPhone 3G and was wondering if I can continue to use it for appstore application development & testing after I do so. I don't want to continue to pay for an additional line and data plan, and I wouldn't be interested in using is as a phone. Would I be able to provision and debug on it? Would it have to be jailbroken?
You definitely can. I'm currently using my deactivated 2G for development. Aside from the 100 Ad-Hoc devices you can test on, you are also allowed to provision a number of phones that you can build directly to, and it doesn't matter if they are deactivated.
as I think, your phone would function the same as iPod Touch (plus Camera). And since you can use iPod Touch for development, so you can also use your deactivated iPhone.

Do we need an iPhone/iPad for its development?

Today i was going through an website and found something over this iphone and ipad development projects. I had a question whether a developer requires an iphone to actually work with or is there any other simulator type device where we can test it out too.
It would be also great if you can share some docs on getting started.
Thanks.
We have applications that run without a problem on the simulator and crash on the device, so I'd say yes. You might delay it for a bit, and work on the main aspects and buy the device later, but you should have it.
You should start at the iPhone Dev center and depending on your knowledge of Objective C, try some tutorials for it. One of the first tutorials I read about Objective C, and which helped me a lot, is here
You can simulate certain gestures and actions while running the simulator: the developer.apple article is here
You can test many aspects without having an iPad.
There are, however, some that you cannot.
Touch
Acceleration sensor
3G internet
much more
I strongly recommend buying an iPad / iPhone to test the user interface. A PC and the iPad have very different user interaction models, it's hard to create a native feeling app without having an actual device.
You can develop with the iPhone SDK which include an emulator. http://developer.apple.com/iphone/index.action but you would probably be better off having one of the devices if your developing a complex application. For working with Camera's or sensors it's best to have a real device to test you code on.
I dont think there are any devices that run the iPhone system. If there are they are probably illegal.
There is emulator build in XCode.
You dont need a device to run your code etc, but try to test the touch and other sensors in the emulator.
So basically if you are planning on shipping something bigger than helloworld you probably should get the Apple device.
There must be an emulator (I'm not sure, that's a guess), but as with any other development you better have a real device as well so that you have better chances of reproducing problems customers will report.
For iPad development you must have Mac OS X 10.6 Snow Leopard