Question

我想在启动它后2秒钟运行一段代码。

我认为NSTimer可以做到这一点，但无法理解。

Answer 1

可以使用NSTimer，但另一种选择是使用performSelector:withObject:afterDelay:它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doStuff：消息：

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

导致此方法在2.0秒后被调用：

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

Answer 2

以下将满足您的需求：

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

然后委托功能：

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

Answer 3

您还可以使用一些方便的代码：

NSObject的+ 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的+ 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，并且应该在该时间后触发。你在看什么？你用来调用计时器的代码是什么？

iphone NStimer在2秒内启动

4 个答案: