IPhone開發學習筆記：單例模式的實現

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

下面是實現代碼：

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;
}

簡單解釋下，詳細的請看上面的那篇文章。

 

@synchronized(self) ： 這個就是同步語義，這裡會自動加鎖，以保證多線程的環境，不會new出多個執行個體來。
[[self alloc] 會預設調用 [self allocWithZone] 所以在sharedManager裡沒有將值給 sharedGizmoManager