單例模式是iOS開發(fā)中最常用的設(shè)計模式，iOS的單例模式有兩種官方寫法，如下：
1，常用寫法
import "ServiceManager.h"
static ServiceManager *defaultManager;
@implementation ServiceManager
+(ServiceManager *)defaultManager{
if(!defaultManager)
defaultManager=[[self allocWithZone:NULL] init];
return defaultManager;
}
@end
2,用GCD創(chuàng)建單例類
import "ServiceManager.h"
@implementation ServiceManager
+(ServiceManager *)sharedManager{
static dispatch_once_t predicate;
static ServiceManager * sharedManager;
dispatch_once(&predicate, ^{
sharedManager=[[ServiceManager alloc] init];
});
return sharedManager;
}
@end
其中dispatch_once函數(shù)只執(zhí)行一次。
