iphone NStimer 在 2 秒内启动

Question

我试图让一段代码在“启动”后 2 秒运行。

我认为 NSTimer 可以做到这一点，但无法弄清楚。

Answer 1

可以使用 NSTimer，但另一种选择是使用 performSelector:withObject:afterDelay: 基本上就像稍后发生的方法调用（消息发送）。

此示例将在延迟后发送一条 doStuff: 消息：

[self performSelector:@selector(doStuff:) withObject:self afterDelay:2];

这会导致该方法在 2.0 秒后被调用：

-(void)doStuff:(id)sender 
{
    /// do something
}

Answer 2

以下将满足您的需要：

 NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval: 2 
                                   target:self 
                                   selector:@selector(handleTimer:) 
                                   userInfo:nil
                                   repeats:NO];

然后是委托函数：

-(void)handleTimer: (NSTimer *) timer 
{       
   //code
}

Answer 3

您还可以使用一些方便的代码：

NSObject+PerformBlock.h

@interface NSObject (PerformBlock)

- (void)performBlock:(void(^)(void))block waitUntilDone:(BOOL)wait;
- (void)performBlock:(void(^)(void))block afterDelay:(NSTimeInterval)delay;
- (void)performBlock:(void(^)(void))block repeatCount:(NSUInteger)repeatCount timeInteval:(NSTimeInterval)timeInterval;

@end

NSObject+PerformBlock.m

@interface NSObject (PerformBlockHidden)

- (void)performBlock:(void(^)(void))block;

@end

@implementation NSObject (PerformBlock)

- (void)performBlock:(void(^)(void))block {
    block();
}

- (void)performBlock:(void(^)(void))block waitUntilDone:(BOOL)wait {
    [self performSelector:@selector(performBlock:) onThread:nil withObject:[[block copy] autorelease] waitUntilDone:wait];
}

- (void)performBlock:(void(^)(void))block afterDelay:(NSTimeInterval)delay {
    [self performSelector:@selector(performBlock:) withObject:[[block copy] autorelease] afterDelay:delay];
}

- (void)performBlock:(void(^)(void))block repeatCount:(NSUInteger)repeatCount timeInteval:(NSTimeInterval)timeInterval {
    for (NSInteger repetition = 0; repetition < repeatCount; repetition++)
        [self performBlock:block afterDelay:(repetition*timeInterval)];
}

@end

然后只需导入 NSObject+PerformBlock.h 并调用：

[myObject performBlock:^{
    // Code you want to perform after 2secs
} afterDelay:2];

Answer 4

您应该能够将 NSTimeInterval 设置为 2.0 秒，并且它应该在该时间后触发。你看到什么了？您用来调用计时器的代码是什么？