Modern Objective c

Use 'Modern Objective-C Syntax'

Objective-C makes heavy use of the @ operator, which generally denotes Objective-C objects. For example, "string" is a char*, while @"string" is an NSString. These have been standard in Objective-C for a long time, but only recently, in Objective-C 2.0, did Apple add in definitions for NSDictionary, NSArray, and NSNumber, all using literals specified with @ directives.

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NSNumber *number = [NSNumber numberWithInteger:7];

NSNumber *modernNumber = @(7); // or @7

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NSArray *array = [NSArray arrayWithObjects:number, modernNumber, nil];

NSArray *modernArray = @[number, modernNumber];

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NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:number, @"number"];

NSDictionary *modernDictionary = @{@"number" : number};

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It's more concise, and still somehow more readable.

Enum 

Replace your enum declarations, such as this one:

enum {

UITableViewCellStyleDefault,

UITableViewCellStyleValue1,

UITableViewCellStyleValue2,

UITableViewCellStyleSubtitle

};

typedef NSInteger UITableViewCellStyle;

with the NS_ENUM syntax:

typedef NS_ENUM(NSInteger, UITableViewCellStyle) {

UITableViewCellStyleDefault,

UITableViewCellStyleValue1,

UITableViewCellStyleValue2,

UITableViewCellStyleSubtitle

};

But when you use enum to define a bitmask, such as here:

enum {

UIViewAutoresizingNone                 = 0,

UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,

UIViewAutoresizingFlexibleWidth        = 1 << 1,

UIViewAutoresizingFlexibleRightMargin  = 1 << 2,

UIViewAutoresizingFlexibleTopMargin    = 1 << 3,

UIViewAutoresizingFlexibleHeight       = 1 << 4,

UIViewAutoresizingFlexibleBottomMargin = 1 << 5

};

typedef NSUInteger UIViewAutoresizing;

use the NS_OPTIONS macro.

typedef NS_OPTIONS(NSUInteger, UIViewAutoresizing) {

UIViewAutoresizingNone                 = 0,

UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,

UIViewAutoresizingFlexibleWidth        = 1 << 1,

UIViewAutoresizingFlexibleRightMargin  = 1 << 2,

UIViewAutoresizingFlexibleTopMargin    = 1 << 3,

UIViewAutoresizingFlexibleHeight       = 1 << 4,

UIViewAutoresizingFlexibleBottomMargin = 1 << 5

};

Alternatively, you can use the modern Objective-C converter in Xcode to make this change to your code automatically. 

iOS 7.1 App Life Cycle

Launching an app into the foreground

Launching an app into the background 

iOS regulates background processing very tightly, and offers three approaches to implement it:

• Register a Background Task - If an application needs to complete an important task, it can ask iOS not to interrupt the task when the application moves into the background. For example, an application might need to finish logging in a user, or finish downloading a large file.
• Register as a Background-Necessary Application - An app can register as a specific type of application that has known, specific backgrounding requirements, such as Audio, VoIP, External Accessory,Newsstand, and Location. These applications are allowed continuous background processing privileges as long as they are performing tasks that are within the parameters of the registered application type.
• Enable Background Updates - Applications can trigger background updates with Region Monitoring or by listening for Significant Location Changes. As of iOS 7, applications can also register to update content in the background using Background Fetch or Remote Notifications.

Change of App State in iOS