Objective-c – get the UIButton’s background image

Edited on 2016-02-02

Starting from iOS 6 SKStoreProductViewController class was introduced. You can link an app without leaving your app. Code snippet in Swift 3.x/2.x and Objective-C is here.

A SKStoreProductViewController object presents a store that allows the user to purchase other media from the App Store. For example, your app might display the store to allow the user to purchase another app.

From News and Announcement For Apple Developers.

Drive Customers Directly to Your App on the App Store with iTunes Links With iTunes links you can provide your customers with an easy way to access your apps on the App Store directly from your website or marketing campaigns. Creating an iTunes link is simple and can be made to direct customers to either a single app, all your apps, or to a specific app with your company name specified.

To send customers to a specific application: http://itunes.com/apps/appname

To send customers to a list of apps you have on the App Store: http://itunes.com/apps/developername

To send customers to a specific app with your company name included in the URL: http://itunes.com/apps/developername/appname

Additional notes:

You can replace http:// with itms:// or itms-apps:// to avoid redirects.

Please note that itms:// will send the user to the iTunes store and itms-apps:// with send them to the App Store!

For info on naming, see Apple QA1633:

https://developer.apple.com/library/content/qa/qa1633/_index.html.

Edit (as of January 2015):

itunes.com/apps links should be updated to appstore.com/apps. See QA1633 above, which has been updated. A new QA1629 suggests these steps and code for launching the store from an app:

1. Launch iTunes on your computer.
2. Search for the item you want to link to.
3. Right-click or control-click on the item's name in iTunes, then choose "Copy iTunes Store URL" from the pop-up menu.
4. In your application, create an NSURL object with the copied iTunes URL, then pass this object to UIApplication' s openURL: method to open your item in the App Store.

Sample code:

NSString *iTunesLink = @"itms://itunes.apple.com/app/apple-store/id375380948?mt=8";
[[UIApplication sharedApplication] openURL:[NSURL URLWithString:iTunesLink]];

iOS10+:

 [[UIApplication sharedApplication] openURL:[NSURL URLWithString:iTunesLink] options:@{} completionHandler:nil];

Swift 4.2

   let urlStr = "itms-apps://itunes.apple.com/app/apple-store/id375380948?mt=8"
    if #available(iOS 10.0, *) {
        UIApplication.shared.open(URL(string: urlStr)!, options: [:], completionHandler: nil)
        
    } else {
        UIApplication.shared.openURL(URL(string: urlStr)!)
    }

The last two are identical; "atomic" is the default behavior (note that it is not actually a keyword; it is specified only by the absence of nonatomic -- atomic was added as a keyword in recent versions of llvm/clang).

Assuming that you are @synthesizing the method implementations, atomic vs. non-atomic changes the generated code. If you are writing your own setter/getters, atomic/nonatomic/retain/assign/copy are merely advisory. (Note: @synthesize is now the default behavior in recent versions of LLVM. There is also no need to declare instance variables; they will be synthesized automatically, too, and will have an _ prepended to their name to prevent accidental direct access).

With "atomic", the synthesized setter/getter will ensure that a whole value is always returned from the getter or set by the setter, regardless of setter activity on any other thread. That is, if thread A is in the middle of the getter while thread B calls the setter, an actual viable value -- an autoreleased object, most likely -- will be returned to the caller in A.

In nonatomic, no such guarantees are made. Thus, nonatomic is considerably faster than "atomic".

What "atomic" does not do is make any guarantees about thread safety. If thread A is calling the getter simultaneously with thread B and C calling the setter with different values, thread A may get any one of the three values returned -- the one prior to any setters being called or either of the values passed into the setters in B and C. Likewise, the object may end up with the value from B or C, no way to tell.

Ensuring data integrity -- one of the primary challenges of multi-threaded programming -- is achieved by other means.

Adding to this:

atomicity of a single property also cannot guarantee thread safety when multiple dependent properties are in play.

Consider:

 @property(atomic, copy) NSString *firstName;
 @property(atomic, copy) NSString *lastName;
 @property(readonly, atomic, copy) NSString *fullName;

In this case, thread A could be renaming the object by calling setFirstName: and then calling setLastName:. In the meantime, thread B may call fullName in between thread A's two calls and will receive the new first name coupled with the old last name.

To address this, you need a transactional model. I.e. some other kind of synchronization and/or exclusion that allows one to exclude access to fullName while the dependent properties are being updated.