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1.自己写
#import "HttpManager.h"
static HttpManager *httpManager=nil;
@implementation HttpManager
+(instancetype )shareManager
{
//单例对象为空的时候创建
if (httpManager==nil)
{
httpManager=[[HttpManager alloc] init];
}
return httpManager;
}
//一般单例类，为防止外界 调用alloc方法，需要重写alloc方法
+ (id)allocWithZone:(struct _NSZone *)zone
{
@synchronized(self)
{
if (!httpManager) {
httpManager=[super allocWithZone:zone];
return httpManager;
}
return httpManager;
}
}
//重写初始化方法
-(id)init
{
return httpManager;
}
@end
2.苹果官方建议
Apple官方建议
由于自己设计单态模式存在一定风险，主要是考虑到可能在多线程情况下会出现的问题，因此苹果官方建议使用以下方式来实现单态模式：
static MyGizmoClass *sharedGizmoManager = nil;
+ (MyGizmoClass*)sharedManager
{
@synchronized(self) {
if (sharedGizmoManager == nil) {
[[self alloc] init]; // assignment not done here
}
}
return sharedGizmoManager;
}
+ (id)allocWithZone:(NSZone *)zone
{
@synchronized(self) {
if (sharedGizmoManager == nil) {
sharedGizmoManager = [super allocWithZone:zone];
return sharedGizmoManager; // assignment and return on first
allocation
}
}
return nil; //on subsequent allocation attempts return nil
}
- (id)copyWithZone:(NSZone *)zone
{
return self;
}
- (id)retain
{
return self;
}
- (unsigned)retainCount
{
return UINT_MAX; //denotes an object that cannot be released
}
- (void)release
{
//do nothing
}
- (id)autorelease
{
return self;
}
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原文地址：http://www.cnblogs.com/fuunnyy/p/4942970.html
