Question

我的应用听到一些音频水印，它工作正常。现在我想通过使用隐藏视图使我的应用程序非常漂亮，我在其中放置标签和按钮。我在Storyboard中绘制了一个视图，然后我将此视图放在视图控制器的顶部（恰好位于x = 0和y = -200的位置）。现在我需要在手机听到水印时显示此视图（识别我使用的水印Pitch detector）。我写了下面的代码来识别信号的频率：

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

    NSLog(@"%f", frequencyRecived);

    if (frequencyRecived > 18000) {
        if (frequencyRecived >= 18000 && frequencyRecived <= 18140 && !water1) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"1"];
            water2 = water3 = water4 = NO;
            water1 = YES;
        }
        if (frequencyRecived >= 18150 && frequencyRecived <= 18290 && !water2) {
            [self performSelectorInBackground:@selector(setTextInLabel:) withObject:@"2"];
            water1 = water3 = water4 = NO;
            water2 = YES;
        }
        if (frequencyRecived >= 18300 && 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(redLed) withObject:nil];
    }
}

并且选择如下：

- (void)redLed {
    [self.imageLed setImage:[UIImage imageNamed:@"image_led_red.png"]];
    self.labelPosition.font=[UIFont fontWithName:@"DBLCDTempBlack" size:20.0];
}

- (void)setTextInLabel:(NSString*)position {
    self.labelPosition.font=[UIFont fontWithName:@"DBLCDTempBlack" size:20.0];
    self.labelPosition.text = position;
    self.labelPositionHiddenView.text = position;
    NSString *textForToast = [NSString stringWithFormat:@"Postazione %@", position];
    [self.view makeToast:textForToast duration:3.0 position:@"bottom"];
    [self.imageLed setImage:[UIImage imageNamed:@"image_led_green.png"]];
}

当设备识别频率时，会调用选择器setTextInLabel，因此我更新了选择器：

- (void)setTextInLabel:(NSString*)position {
    self.labelPosition.font=[UIFont fontWithName:@"DBLCDTempBlack" size:20.0];
    self.labelPosition.text = position;
    self.labelPositionHiddenView.text = position;
    // Instructions to recall my hide view
    [UIView transitionWithView:self.view
                      duration:0.5
                       options:UIViewAnimationOptionAllowAnimatedContent
                    animations:^{
                        [self.viewHidden setFrame:CGRectOffset(self.viewHidden.frame, 0, 340)];
                    }
                    completion:nil];
    //-----------------------------
    NSString *textForToast = [NSString stringWithFormat:@"Postazione %@", position];
    [self.view makeToast:textForToast duration:3.0 position:@"bottom"];
    [self.imageLed setImage:[UIImage imageNamed:@"image_led_green.png"]];
}

当我尝试运行应用程序并且设备听到它识别它的水印时，它会调用选择器setTextInLabel，但它不会执行代码来调用视图。我不明白为什么，我希望你能帮我解决这个问题。

Answer 1

问题是因为您正在调用performSelectorInBackground:，而您在后台调用的那些方法正在对UIKit元素进行更改。 UIKit元素的所有更改都需要在主线程上完成。因此，redLed和setTextInLabel:都需要在主线程上执行，而不是后台线程。

从主线程调用UIKit方法的确切行为在技术上是未定义的。从我所看到的，这样做有时会导致UI元素永远不会更新。在其他一些情况下，它们会更新，但只有在长时间延迟之后或者在UI元素对其进行了一些其他更改后才会更新其状态。我认为你看到的情况是它从来没有做过你想要它做的事情，可能是因为你试图从另一个线程做动画，这很可能永远不会奏效。

在iOS中显示隐藏视图

1 个答案: