IPhone开发学习笔记：单例模式的实现

首先推荐非常棒的文章：http://www.duckrowing.com/2010/05/21/using-the-singleton-pattern-in-objective-c/

下面是实现代码：

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;
}

简单解释下，详细的请看上面的那篇文章。

 

@synchronized(self) ： 这个就是同步语义，这里会自动加锁，以保证多线程的环境，不会new出多个实例来。
[[self alloc] 会默认调用 [self allocWithZone] 所以在sharedManager里没有将值给 sharedGizmoManager