+ (AccountManager *)sharedManager
{
static AccountManager *sharedAccountManagerInstance = nil;
static dispatch_once_t predicate;
dispatch_once(&predicate, ^{
sharedAccountManagerInstance = [[self alloc] init];
});
return sharedAccountManagerInstance;
}
1.线程安全。
2.满足静态分析器的要求。
3.兼容了ARC
