的NSTimer选择不重复

Question

在我AppDelegate我已经定义

AppDelegate.h

@property (strong, nonatomic) NSTimer *notificationTimer; 

AppDelegate.m

@synthesize notificationTimer = _notificationTimer; 

- (void)applicationDidBecomeActive:(UIApplication *)application { 
    NSLog(@"applicationDidBecomeActive"); 
    self.notificationTimer = [NSTimer timerWithTimeInterval:5 
                target:self 
                selector:@selector(checkForNotifications:) 
                userInfo:nil 
                repeats:YES]; 
    [self.notificationTimer fire]; 
} 

达到的checkForNotifications:一次，但绝不重复。为什么？

Answer 1

使用：
self.notificationTimer = [NSTimer scheduledTimerWithTimeInterval:5 target:self selector:@selector(checkForNotifications) userInfo:nil repeats:YES];