Objective-c – Apple’s Singleton example

Answer:

Use a Singleton if:

• You need to have one and only one object of a type in system

Do not use a Singleton if:

• You want to save memory
• You want to try something new
• You want to show off how much you know
• Because everyone else is doing it (See cargo cult programmer in wikipedia)
• In user interface widgets
• It is supposed to be a cache
• In strings
• In Sessions
• I can go all day long

How to create the best singleton:

• The smaller, the better. I am a minimalist
• Make sure it is thread safe
• Make sure it is never null
• Make sure it is created only once
• Lazy or system initialization? Up to your requirements
• Sometimes the OS or the JVM creates singletons for you (e.g. in Java every class definition is a singleton)
• Provide a destructor or somehow figure out how to dispose resources
• Use little memory

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)!)
    }