(1)不使用GCD
#import "ServiceManager.h" static ServiceManager *defaultManager; @implementation ServiceManager +(ServiceManager *)defaultManager{ if(!defaultManager) defaultManager=[[self allocWithZone:NULL] init]; return defaultManager; } @end
(2)使用GCD
#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
dispatch_once这个函数,class="s1">它可以保证整个应用程序生命周期中某段代码只被执行一次!