#import <Foundation/Foundation.h>
@interface Singleton : NSObject
+ (Singleton*)sharedManager;
@end
#import "Singleton.h"
static Singleton* sharedGizmoManager = nil;//static 静态实例是关键
@implementation Singleton
+ (Singleton*)sharedManager
{
@synchronized(self){
if(sharedGizmoManager == nil) {
[[self alloc] init];// assignment not done here
}
}
return sharedGizmoManager;
}
//唯一一次alloc单例，之后均返回nil
+ (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
}
//copy返回单例本身
- (id)copyWithZone:(NSZone*)zone
{
return self;
}
//retain返回单例本身
- (id)retain
{
return self;
}
//引用计数总是为1
- (unsigned)retainCount
{
return UINT_MAX; //denotes an object that cannot be released
}
//release不做任何处理
- (oneway void)release
{
}
//autorelease返回单例本身
- (id)autorelease
{
return self;
}
@end
