创建单实例的两种方法

+ (MyClass *)sharedInstance

{

static MyClass *sharedInstance = nil;

static dispatch_once_t onceToken;

dispatch_once(&onceToken, ^{

sharedInstance = [[MyClass alloc] init];

//Do any other initialization stuff here

});

return sharedInstance;

}

another methods

+ (MyClass *)sharedInstance {
static MyClass *sharedInstance;
@synchronized(self) {
if (sharedInstance == nil) {
sharedInstance = [[MyClass alloc] init];
}
}
return sharedInstance;
}