iOS common design Patterns-Singleton mode

Part I: Creating a Singleton object

A single case scenario:

Singleton mode is used when a class can have only one instance, Typically, this " singleton " represents a physical device such as a printer, Or some kind of virtual resource or system attribute that cannot have multiple instances at the same time, such as an engine or data for a program. It is necessary to control it with a single-case pattern.

What is a singleton mode?

A single case is a common Software Design Patterns . When you apply this pattern, the class of the Singleton object must guarantee that only one instance exists. Many times the entire system needs to have only one global object , which helps us coordinate the overall behavior of the system.

The singleton design pattern needs to achieve the following objectives: 1.) encapsulates a shared resource; 2.) provides a fixed instance creation method; 3.) provides a standard instance access interface

Common methods for defining a singleton (ARC+GCD)

Implement a class method to create a singleton object static ClassType *objname = nil; + (ClassType *) sharedinstance{static dispatch_once_t Onetoken = 0;dispatch_once (&oncetoken, ^{objName = [[Super Allo Cwithzone:null] [init];}); return objname; }//overrides several methods to prevent errors when creating a singleton object-(ID) init{if (self = [super init]) {//Initialize various properties of the Singleton object}return self;} + (ID) allocwithzone: (struct _nszone *) Zone{return [self sharedinstance];} This is the method that needs to be implemented when a singleton object follows the <NSCopying> protocol-(ID) Copywithzone: (struct _nszone *) Zone{return self;}

Part II: Use of uiapplication single case

Create instance variables directly in Appdelegate, and then use those variables in other files in your project.

Appdelegate *appdelegate = (appdelegate *) [[uiapplication shareapplication] delegate];appdelegate.a = 10086; appdelegate.globalstring = @ "China wants Unicom";

In this way, you can define a global instance variable.

For more information, please refer to:http://blog.csdn.net/casablaneca/article/details/21074413

Part III: Using a singleton design pattern in a project

Item Description: We want to trigger a change in the value of one of the properties in the Singleton object via a button click event, and then use KVO to listen to this property on the two sub-views of Viewcontroller (Leftview, Rightview), which is worth changing, And the changed values are displayed on Leftview and Rightview.

1.) Set a button and a trigger event on the Viewcontroller

-(Ibaction) RefreshData: (ID) SENDER{//STOCKFORKVO is a singleton object stockforkvo.price = Arc4random ()%100;}

2.) Use KVO in Lefeview and Rightview objects to listen for changes in the property values in the Singleton object

STOCKFORKVO = [StockData sharedinstance];    [Stockforkvo addobserver:self forkeypath:@ "Price" options:nskeyvalueobservingoptionnew| Nskeyvalueobservingoptionold context:null];//Implementation callback Method-(void) Observevalueforkeypath: (NSString *) KeyPath OfObject: (ID Object change: (nsdictionary *) Change context: (void *) context{    if ([KeyPath isequaltostring:@ "Price"]) {        Showlabel.text = [NSString stringwithformat:@ "%f", Stockforkvo.price];        NSLog (@ "Left change:%@", change);}    }

3.) Implementation of Effect 2 is shown

Figure 2: The right side is the scene after the button event is triggered, and the left is the scene at the time of initialization

Source of Project: http://download.csdn.net/detail/luozhonglan/8005001

iOS common design Patterns-Singleton mode