ios - 定时器后开始 Action

Question

在我的 iOS 应用程序中，我必须在延迟后执行操作。我会更好地解释它:我的应用程序可以识别一些音频:

• 18100 赫兹
• 18200 赫兹
• 18300 赫兹
• 18500 赫兹

为此，我修改了 pitch detector .当设备无法识别我在我的应用程序中设置的频率之一时，我想启动一个计时器。我是这样做的:

- (void)frequencyChangedWithValue:(float)newFrequency {
    frequencyRecived = newFrequency;
    watermarkReceived = YES;
    
    if (frequencyRecived > 18000) {
        if (frequencyRecived >= 18000 && frequencyRecived <= 18110 && !water1) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"1"];
            water2 = water3 = water4 = NO;
            water1 = YES;
        }
        if (frequencyRecived >= 18115 && frequencyRecived <= 18250 && !water2) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"2"];
            water1 = water3 = water4 = NO;
            water2 = YES;
        }
        if (frequencyRecived >= 18255 && frequencyRecived <= 18440 && !water3) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"3"];
            water1 = water2 = water4 = NO;
            water3 = YES;
        }
        if (frequencyRecived >= 18450 && !water4) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"4"];
            water1 = water2 = water3 = NO;
            water4 = YES;
        }
    } else {
        
        [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"Nessuna postazione"];
        water1 = water2 = water3 = water4 = NO;
    }
}

在else这部分我必须启动一个计时器，它会计时 10 秒，之后我必须写一个标签。我尝试使用以下解决方案:

[self performSelector:<#(SEL)#> withObject:<#(id)#> afterDelay:<#(NSTimeInterval)#> inModes:<#(NSArray *)#>]

，但它从不调用选择器方法，因为每次应用程序执行 else 中的代码时它重新启动计时器。你能建议我解决这个问题的方法吗？谢谢

更新

我遵循答案，但它不起作用。我在这里发布更新的代码:

@interface ViewController () {
    BOOL watermarkReceived;
    float frequencyRecived;
    CABasicAnimation *theAnimation;
    BOOL water1, water2, water3, water4;
}

@property(nonatomic,strong)NSTimer *timer;

@end

- (void)frequencyChangedWithValue:(float)newFrequency {
    frequencyRecived = newFrequency;
    watermarkReceived = YES;
    
    if (frequencyRecived > 18000) {
        
        [self.timer invalidate];
        self.timer = nil;
        
        if (frequencyRecived >= 18000 && frequencyRecived <= 18110 && !water1) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"1"];
            water2 = water3 = water4 = NO;
            water1 = YES;
        }
        if (frequencyRecived >= 18115 && frequencyRecived <= 18250 && !water2) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"2"];
            water1 = water3 = water4 = NO;
            water2 = YES;
        }
        if (frequencyRecived >= 18255 && frequencyRecived <= 18440 && !water3) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"3"];
            water1 = water2 = water4 = NO;
            water3 = YES;
        }
        if (frequencyRecived >= 18450 && !water4) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"4"];
            water1 = water2 = water3 = NO;
            water4 = YES;
        }
    } else {
        self.timer = [NSTimer scheduledTimerWithTimeInterval:10.0 target:self selector:@selector(noPosition) userInfo:nil repeats:NO];
//        [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"Nessuna postazione"];
        water1 = water2 = water3 = water4 = NO;
    }
}

- (void)noPosition {
    [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"Nessuna postazione"];
}

PS:你说的其他问题我都理解了，以后会解决的，暂时先解决timer的问题。 :)

Answer 1

使用 NSTimer。在 else 分支中，检查计时器是否已经存在，如果不存在，则创建并安排它。在 if 的主分支中，使计时器失效并销毁。

另外，您的 if 语句有很多漏洞并且过于复杂。您已经检查过频率是否 > 18000，因此您无需再次检查。您还使用 if, else if 来简化，因为每个范围都是一个不同的范围，如果检测到一个范围，则其他范围都不会检测到。通过这种方式，您可以在内部 if 中检查是否超出范围上限。

此外，在背景中设置文本看起来也不对。 UI更新需要从主线程进行

---

类似于:

- (void)frequencyChangedWithValue:(float)newFrequency {
    frequencyRecived = newFrequency;
    watermarkReceived = YES;

    if (frequencyRecived > 18000) {

        [self.timer invalidate];
        self.timer = nil;

        if (frequencyRecived <= 18110) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"1"];
            water2 = water3 = water4 = NO;
            water1 = YES;
        }
        else if (frequencyRecived <= 18250) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"2"];
            water1 = water3 = water4 = NO;
            water2 = YES;
        }
        else if (frequencyRecived <= 18440) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"3"];
            water1 = water2 = water4 = NO;
            water3 = YES;
        }
        else {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"4"];
            water1 = water2 = water3 = NO;
            water4 = YES;
        }
    } else {
        if (self.timer == nil) {
            self.timer = [NSTimer scheduledTimerWithTimeInterval:... target:self selector:... userInfo:nil repeats:NO];
        }

        water1 = water2 = water3 = water4 = NO;
    }
}