1.0 苹果官方写法:
static AccountManager *DefaultManager = nil; + (AccountManager *)defaultManager {
if (!DefaultManager) DefaultManager = [[self allocWithZone:NULL] init];
return DefaultManager;
}
2.0 在iOS4之后有了另外一种写法:
+ (AccountManager *)sharedManager
{
static AccountManager *sharedAccountManagerInstance = nil;
static dispatch_once_t predicate;
dispatch_once(&predicate, ^{
sharedAccountManagerInstance = [[self alloc] init];
});
return sharedAccountManagerInstance;
}