Question

我有一个模态视图，当用户执行某些操作时，倒计时开始。在倒计时结束时，模态视图将关闭。以下是我为此目标编写的程序，但不幸的是，它导致了一些线程问题。有没有办法以一种没有潜在线程问题的方式重写它？

- (void)countDown {
    static int i = 3;
    if (i == 3) {
        i--;
        UIImage *three = [UIImage imageNamed:@"Three"];
        countDownFlag = [[UIImageView alloc] initWithImage:three];
        countDownFlag.frame = CGRectMake(0, 370, countDownFlag.frame.size.width, countDownFlag.frame.size.height);
        countDownFlag.center = CGPointMake(width / 2, countDownFlag.center.y);
        [self.view addSubview:countDownFlag];
        [self performSelector:@selector(countDown) withObject:nil afterDelay:0.5];
    } else if (i == 2) {
        i--;
        UIImage *two = [UIImage imageNamed:@"Two"];
        [countDownFlag setImage:two];
        [self performSelector:@selector(countDown) withObject:nil afterDelay:0.5];
    } else if (i == 1) {
        i--;
        UIImage *one = [UIImage imageNamed:@"One"];
        [countDownFlag setImage:one];
        [self performSelector:@selector(countDown) withObject:nil afterDelay:0.5];
    } else {
        [self dismissViewControllerAnimated:YES completion:nil];
    }
}

编辑：图片显示了XCode告诉我的问题

output

更多编辑

我的代码已更改为反映vadian的答案。这是更新

- (void)startCountDown {
    NSLog(@"starting count down");
    counter = 3;
    [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(countDown:) userInfo:nil repeats:YES];
}

- (void)countDown:(NSTimer *)timer {

    if (counter == 3) {
        countDownFlag = [[UIImageView alloc] init];
        countDownFlag.frame = CGRectMake(0, 370, countDownFlag.frame.size.width, countDownFlag.frame.size.height);
        countDownFlag.center = CGPointMake(width / 2, countDownFlag.center.y);
        dispatch_async(dispatch_get_main_queue(), ^{
            [self.view addSubview:countDownFlag];
        });
    } else if (counter == 0) {
        [timer invalidate];
        [self dismissViewControllerAnimated:YES completion:nil];
        return;
    }
    NSArray *imageNameArray = @[@"", @"One", @"Two", @"Three"];
    UIImage *image = [UIImage imageNamed:imageNameArray[counter]];
    dispatch_async(dispatch_get_main_queue(), ^{
        [self.countDownFlag setImage:image];
    });
    counter--;
}

我新猜测问题可能在于调用倒计时的代码。这是执行此操作的代码。

- (void)changeLanguage:(BOOL) isMyanmar {
    if (hasRun == YES) {
        return;
    }
    hasRun = YES;

    NSUserDefaults * userdefaults = [NSUserDefaults standardUserDefaults];
    [userdefaults setBool:isMyanmar forKey:@"myanmar"];
    [userdefaults synchronize];

    [self updateCurrentLanguageText];
    if ([self isMyanmar]) {
        [self changeLanguageFlag:@"MyanmarFlagBig"];
    } else {
        [self changeLanguageFlag:@"UnitedKingdomFlagBig"];
    }

    //>>>>>>>>>>>>>>>>>>>> the problem is probably here

    [self startCountDown];
}

更改语言代码后运行的任何代码都将失败。可能存在问题。

编辑： 线程问题已经消失，但倒计时不再发生了。

在我将changeLanguage中的代码移动到调用它的方法之后，问题神秘地消失了。（重复但它有效。）

- (void)changeLanguageToEnglish {
    [theLock lock];
    if (hasRun == YES) {
        [theLock unlock];
        return;
    }
    hasRun = YES;

    [userdefaults setBool:false forKey:@"myanmar"];
    [userdefaults synchronize];

    [self updateCurrentLanguageText];
    if ([self isMyanmar]) {
        [self changeLanguageFlag:@"MyanmarFlagBig"];
    } else {
        [self changeLanguageFlag:@"UnitedKingdomFlagBig"];
    }

    [self startCountDown];

    [theLock unlock];

}

- (void)changeLanguageToMyanmar {
    [theLock lock];
    if (hasRun == YES) {
        [theLock unlock];
        return;
    }
    hasRun = YES;

    [userdefaults setBool:true forKey:@"myanmar"];
    [userdefaults synchronize];

    [self updateCurrentLanguageText];
    if ([self isMyanmar]) {
        [self changeLanguageFlag:@"MyanmarFlagBig"];
    } else {
        [self changeLanguageFlag:@"UnitedKingdomFlagBig"];
    }

    [self startCountDown];

    [theLock unlock];

}

但问题是倒计时不再发生了。

Answer 1

您可以使用NSTimer执行倒计时和计数器的静态变量。

方法startCountDown启动计时器。

方法countDown:(NSTimer *)timer每0.5秒调用一次。传递的NSTimer参数正是已启动的计时器。它根据其值执行操作并减少计数器。如果计数器为0，则计时器无效，控制器解除。

static UInt8 counter = 0;

- (void)startCountDown {
  countDownFlag = [[UIImageView alloc] init];
  countDownFlag.frame = CGRectMake(0, 370, countDownFlag.frame.size.width, countDownFlag.frame.size.height);
  countDownFlag.center = CGPointMake(width / 2, countDownFlag.center.y);
  [self.view addSubview:countDownFlag];
  counter = 3;
  [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(countDown:) userInfo:nil repeats:YES];
}

- (void)countDown:(NSTimer *)timer {
  if (counter == 0) {
    [timer invalidate];
    [self dismissViewControllerAnimated:YES completion:nil];
    return;
  }
  NSArray *imageNameArray = @[@"", @"One", @"Two", @"Three"];
  UIImage *image = [UIImage imageNamed:imageNameArray[counter]];
  dispatch_async(dispatch_get_main_queue(), ^{
    [self.countDownFlag setImage:image];
  });
  counter--;

}

Answer 2

将static int i = 3;放在方法countDown之外，就像你每次调用该方法时声明新变量一样。

倒计时和解雇模态视图

2 个答案: