iphone - 停止 NSTimer

Question

好吧，这段代码非常基本。用户将答案输入文本框，如果等于“第一+第二”，他们就得到一分。然后，他们有 5 秒钟的时间回答下一个数学问题。如果他们这样做了，函数“doCalculation”将再次运行，他们会得到另一分。如果他们不这样做，那么函数“onTimer”就会运行，然后就开始了。

问题是，当用户连续正确地解决多个问题时，“doCalculation”会运行多次，然后我会同时启动多个计时器。这真的开始搞砸游戏。

我需要停止计时器。显然使用“无效”，但我不知道在哪里。我无法在计时器开始之前使其无效，所以...whhhhhatt？

另一个选项，我不知道该怎么做，如果每当你解决问题时，它只是将计时器设置回 5 秒而不是创建一个新的计时器，该怎么办。但我如何判断计时器是否已经创建呢？我不确定最好的行动方案是什么，或者语法。想法？

非常感谢!

- (IBAction)doCalculation:(id)sender
{
    NSInteger numAnswer = [answer.text intValue];
    if ( numAnswer == first + second) {
        numAnswered++;
        NSString *numberAnsweredCorrectly = [[NSString alloc] initWithFormat:@"%d", numAnswered];
        numCorrectlyAnswered.text = numberAnsweredCorrectly;
        answer.text = @"";

        NSTimer *mathTimer = [NSTimer scheduledTimerWithTimeInterval:5.0 target:self selector:@selector(onTimer) userInfo:nil repeats:YES];     

        //Set the variables to two HUGE numbers, so they can't keep plugging in the same answer

        first = arc4random() % 10;
        second = arc4random() % 10;

        NSString *firstString = [[NSString alloc] initWithFormat:@"%d", first];
        NSString *secondString = [[NSString alloc] initWithFormat:@"%d", second];

        firstNumber.text = firstString;
        secondNumber.text = secondString;
    }

Answer 1

我会将 mathTimer 移到您的类标题中:

//inside your .f file:
@interface YourClassNAme : YourSuperClassesName {
    NSTimer *mathTimer
}


@property (nonatomic, retain) NSTimer *mathTimer;

//inside your .m:
@implementation YourClassNAme 
@synthesize mathTimer;

-(void) dealloc {
   //Nil out [release] the property
   self.mathTimer = nil;
   [super dealloc];
}

并更改您的方法以通过属性访问计时器:

- (IBAction)doCalculation:(id)sender
{
    NSInteger numAnswer = [answer.text intValue];
    if ( numAnswer == first + second) {
        numAnswered++;
        NSString *numberAnsweredCorrectly = [[NSString alloc] initWithFormat:@"%d", numAnswered];
        numCorrectlyAnswered.text = numberAnsweredCorrectly;
        answer.text     = @"";

        [self.mathTimer invalidate];  //invalidate the old timer if it exists
        self.mathTimer = [NSTimer scheduledTimerWithTimeInterval:5.0 target:self selector:@selector(onTimer) userInfo:nil repeats:YES];             

        //Set the variables to two HUGE numbers, so they can't keep plugging in the same answer

        first = arc4random() % 10;
        second = arc4random() % 10;

        NSString *firstString = [[NSString alloc] initWithFormat:@"%d", first];
        NSString *secondString = [[NSString alloc] initWithFormat:@"%d", second];

        firstNumber.text = firstString;
        secondNumber.text = secondString;
    }