倒计时器

Question

我正在尝试创建一个倒计时器,它将倒计时,一个连接到文本字段的IBOutlet,从60秒降低到0.我不确定

A.如何将重复限制为60和

B.如何提前减少倒计时:

- (IBAction)startCountdown:(id)sender
{
    NSTimer *countdownTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self     selector:@selector(advanceTimer:) userInfo:nil repeats:YES];
    NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
    [runLoop addTimer:countdownTimer forMode:NSDefaultRunLoopMode];
}

- (void)advanceTimer:(NSTimer *)timer
{
    [countdown setIntegerValue:59];
}

Answer 1

到目前为止,你走在正确的轨道上.

坚持使用您已有的代码,这里是advanceTimer方法应该如何使其工作:

- (void)advanceTimer:(NSTimer *)timer
{
    [countdown setIntegerValue:([countdown integerValue] - 1)];
    if ([countdown integerValue] == 0)
    {
        // code to stop the timer
    }
}

编辑: 为了使整个事物更加面向对象,并避免每次从字符串转换为数字并返回,我会做这样的事情:

// Controller.h:
@interface Controller
{
    int counter;
    IBOutlet NSTextField * countdownField;
}
@property (assign) int counter;
- (IBAction)startCountdown:(id)sender;
@end

// Controller.m:
@implementation Controller

- (IBAction)startCountdown:(id)sender
{
    counter = 60;

    NSTimer *countdownTimer = [NSTimer scheduledTimerWithTimeInterval:1
                                         target:self
                                       selector:@selector(advanceTimer:)
                                       userInfo:nil
                                        repeats:YES];
}

- (void)advanceTimer:(NSTimer *)timer
{
    [self setCounter:(counter -1)];
    [countdownField setIntegerValue:counter];
    if (counter <= 0) { [timer invalidate]; }
}

@end

And, if you can make use of bindings, you could simply bind the text field's intValue到的counter属性Controller.这将允许您IBOutlet在类接口和setIntegerValue:线路中消除advanceTimer.

更新:删除了将计时器添加到运行循环两次的代码.感谢Nikolai Ruhe和nschmidt注意到这个错误.

更新:setIntegerValue根据nschmidt,使用该方法简化代码.

编辑:错误定义(void)advanceTimer:(NSTimer*)计时器...导致恼人的'无法识别的选择器发送到实例'异常

Answer 2

您可以添加实例变量int _timerValue来保存计时器值,然后执行以下操作.另请注意,您正在创建的NSTimer已在当前运行循环中安排.

- (IBAction)startCountdown:(id)sender
{
    _timerValue = 60;
    [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(advanceTimer:) userInfo:nil repeats:NO];
}

- (void)advanceTimer:(NSTimer *)timer
{
    --_timerValue;
    if(self.timerValue != 0)
       [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(advanceTimer:) userInfo:nil repeats:NO];

    [countdown setIntegerValue:_timerValue];
}