Ios 在计时器后启动一个操作

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：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

为了做到这一点，我修改了。我想在设备无法识别我在应用程序中设置的频率时启动计时器。 我这样做：

- (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;
    }
}

---

PS：我理解你告诉我的其他问题，我将在将来解决，因为现在我需要解决计时器问题。：）

使用

NSTimer

。在

else

分支中，检查计时器是否已存在，如果不存在，则创建并计划它。在

if

的主分支中，使计时器失效并销毁

另外，您的

if

语句有许多漏洞，过于复杂。您已经检查过频率>18000，因此无需再次检查。您还可以使用

if，else if

来简化，因为每个范围都是不同的范围，如果检测到一个范围，则其他范围都不能被忽略。通过这种方式，您只需检查内部

if

是否超过上限范围

此外，在背景中设置文本看起来也是错误的。UI更新需要从主线程进行

---

比如：

- (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;
    }
}

-（无效）频率更改，其值为：（浮点）新频率{
FrequencyReceived=新频率；
水印接收=是；
如果（接收频率>18000）{
[自动定时器失效]；
self.timer=nil；
如果（FrequencyReceive我更新了代码，但应用程序没有调用选择器方法。我用新代码更新了我的问题。我希望你能帮助我理解为什么它不起作用。我错过了代码中的一个检查。你为什么在后台做事情？在后台更新UI时，你可能看不到任何更新。停止这样做吧……我做到了。）我在后台更新UI，否则我无法在不停止侦听器的情况下更新它，我也无法停止它。如果我在主线程中更新UI，我必须停止侦听器，否则手机会崩溃。我看到它没有调用选择器方法…我不知道为什么…你对后台的理解是错误的。如果皮疹您还有其他问题。您必须停止在后台更新UI。
- (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;
    }
}