Objective-C辛格尔顿
单例类是一种特殊的类。在一个进程种仅仅会存在一个该类的对象,在iOS应用中仅仅会出现一个对象。这样的设计模式在系统框架中很多地方都使用了。如NSFileManager、UIApplication等。
- 在ARC的环境下,接口文件为:
//
// DVISingleton.h
//
// Copyright (c) 2014 长沙戴维营教育. All rights reserved.
//
#import <Foundation/Foundation.h>
@interface DVISingleton : NSObject
+ (instancetype)sharedSingleton;
@end
实现文件:
//
// DVISingleton.m
//
// Copyright (c) 2014 长沙戴维营教育. All rights reserved.
//
#import "DVISingleton.h"
@implementation DVISingleton
+ (instancetype)sharedSingleton
{
static DVISingleton *sharedObject = nil;
//线程安全。仅仅同意运行依次
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
//使用父类的allocWithZone:方法创建对象
sharedObject = [[super allocWithZone:NULL] init];
});
return sharedObject;
}
- (id)init
{
if (self = [super init]) {
}
return self;
}
+ (id)allocWithZone:(struct _NSZone *)zone
{
return [self sharedSingleton];
}
- (id)copy
{
return self;
}
- (void)dealloc
{
}
@end
- 在非ARC环境下的实现文件:
<code class="objectivec hljs" data-origin="" <pre><code="" "dvisingleton.h""="" style="margin: 0px; padding: 0px; border: 0px; font-size: inherit; font-variant: inherit; font-weight: bold; line-height: inherit; vertical-align: baseline; color: rgb(110, 107, 94); font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important;">#import "DVISingleton.h"
@implementation DVISingleton
+ (instancetype)sharedSingleton
{
static DVISingleton *sharedObject = nil;
//线程安全。仅仅同意运行依次
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
//使用父类的allocWithZone:方法创建对象
sharedObject = [[super allocWithZone:NULL] init];
});
return sharedObject;
}
+ (id)allocWithZone:(NSZone *)zone {
return [[self sharedSingleton] retain];
}
- (id)copyWithZone:(NSZone *)zone {
return self;
}
- (id)retain {
return self;
}
- (unsigned)retainCount {
return UINT_MAX; //denotes an object that cannot be released
}
- (oneway void)release {
// never release
}
- (id)autorelease {
return self;
}
- (id)init {
if (self = [super init]) {
}
return self;
}
- (void)dealloc {
[super dealloc];
}
@end
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