Converting iOS 6 App to iOS 7

UICollectionView Error in converting ios 6 to ios 7

It looks to me from this description of your error:

UICollectionView on iOS versions prior to 6.0

That you're trying to build an app that has the deployment target (the oldest OS version) set to something older than iOS 6. UICollectionView only works on devices running iOS 6 & newer OS'es. Do you have your project settings set to run this app with iOS 5 or 4?

And if you change it to iOS 6, do you get better results?

Is it possible to install iOS 7 SDK on Xcode 6?

Seems like if you symlink the relevant SDK from a previous installation of Xcode to the Xcode 6 Beta directory, Xcode 6 will be able to use it. Assuming you still have Xcode 5.1.1 on your machine, try the following in terminal:

ln -s /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS7.1.sdk /Applications/Xcode6-Beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS7.1.sdk

This should link the iOS 7 SDK for iPhone (not sim), allowing you to select iOS 7 as the Base SDK in Xcode 6 Beta. If you want to do this for the simulator, replace iPhoneOS.platform with iPhoneSimulator.platform.

NOTE: Just because you have the iOS 7 SDK now doesn't mean it'll build. I'm personally having trouble with the fact that Xcode 6 Beta is using the Apple LLVM 6.0 compiler, which apparently isn't compatible with some of the stuff I'm trying to build.

ref: https://stackoverflow.com/a/11424966/2383003

Will apps built for iOS 6 or earlier versions run without issues on iOS 7?

This comes up every year. This is not specific to iOS 7 (or any other version of iOS).

As a developer you must test your existing app(s) to be sure they will work as-is under the upcoming version of iOS. Some apps will work just fine with no changes. Many apps will have some issue ranging from a small UI glitch to frequent crashes.

You need to install the beta iOS on a test device and test your app from the app store and see what issues you have, if any.

If you find any issues you then need to fins solutions. In many cases you can fix your app without the need to update to the latest Base SDK. But in some cases you may want to update to the latest and use some new features while fixing any issues.

Differences between iOS 7 API and iOS 6 API

This is the ultimate answer what I was looking for. I hope this will be helpful for others as well.

Can I still develop apps for iOS6 in 2017?

sorry, but iOS 6 is deprecated
you can develop iOS 6 application in Xcode 5 or 6, but you can't publish your application

Do apple allow custom iOS 5/6 style UI for iOS7?

Well no, it doesn't necessarily mean that if your apps are running in iOS7, it needs to immediately have the new look. You can use iOS 7.0 as your base sdk but you need to do a custom modification in your app to implement the look and feel of iOS5/6 (but this is a tedious process...not recommended). Using 7.0 SDK will transform all appearance of UI Objects into iOS 7.0 objects (flat, no bezels, borderless, etc).

If you aren't ready yet to accept iOS 7 design in your application, you can still build your app using iOS 6.1 SDK. This will retain the previous look and feel of iOS UI, and will still run on iOS 7. Be careful though, some fonts (like Hirakaku pron) change their line spacing when they are run in iOS 7 (even though it is compiled against iOS 6.1). You may wanna do a forward compatibility check in iOS 7 for your iOS 6.1 Base SDK application.

(Cons of using iOS 6.1/6.0 as Base SDK: We still do not know if (or when) Apple will restrict submission of apps into iOS 7 only. But for now, uploading apps in iOS 6.1/6.0 is still ok.)

Summary:

Using iOS 7.0 as Base SDK: (Use Auto-Layout to properly design your objects)

When you run application in iOS 7.0 device: UI objects will appear flat (NEW UI LOOK)
When you run application in iOS 6.1 device and below: UI objects will retain their OLD LOOK

Using iOS 6.1/6.0 as Base SDK:

When you run application in iOS 7.0 device: UI objects will retain their OLD LOOK
When you run application in iOS 6.1 device and below: UI objects will retain their OLD LOOK

Interface Builder: What are the UIView's Layout iOS 6/7 Deltas for?

This actually refers to the Delta between layout position from iOS6 to iOS7.

In iOS7, some views can hide the status bar or have it transparent and, in effect, it is overlaid on top of your view. So if you put a UI element at (0.0, 0.0) on iOS6, it will appear below the status bar, but on iOS7 it would appear partially covered underneath the status bar. So in that case you would want a delta that matches the status bar height (20.0 points) so that the layout looks the same in iOS6 and iOS7.

I believe this isn't needed if you use autolayout, but of course, then you lose iPad1 support, which many of us aren't willing to concede at this point in time.