UILabel causes app to crash when added to view (Xc

问题:

I have transitioned my project to Xcode 6 in order to build for iOS 8. However, a particular UILabel is causing the app to crash when it is added to the view hierarchy. This is the only error log I receive:

-[MyViewController _contentInsetsFromFonts]: unrecognized selector sent to instance     0x16d90da0

I have been unable to locate the contentInsetsFromFonts method anywhere in my project. Additionally, I have not even been able to find a reference for it anywhere online, including Apple's documentation. I am not using a NIB for this UIViewController so the UI is built in the loadView method:

- (void)loadView {
    UIImage *trackImage = [UIImage imageNamed:@"sliderTrack.png"];
    sliderBackground = [[UIImageView alloc] initWithImage:trackImage];
    UIView *view = [[UIView alloc] initWithFrame:sliderBackground.frame];
    [view addSubview:sliderBackground];

    slider = [[UISlider alloc] initWithFrame:sliderBackground.frame];
    CGRect sliderFrame = slider.frame;
    sliderFrame.size.width -= 46; 
    slider.frame = sliderFrame;
    slider.center = sliderBackground.center;
    slider.backgroundColor = [UIColor clearColor];
    [slider setMinimumTrackImage:[UIImage imageNamed:@"sliderMaxMinTrackImage.png"] forState:UIControlStateNormal];
    [slider setMaximumTrackImage:[UIImage imageNamed:@"sliderMaxMinTrackImage.png"] forState:UIControlStateNormal];
    UIImage *thumbImage = [UIImage imageNamed:@"cancel-slider.png"];
    [slider setThumbImage:thumbImage forState:UIControlStateNormal];
    slider.minimumValue = 0.0;
    slider.maximumValue = 1.0;
    slider.continuous = YES;
    slider.value = 0.0;

    // Set the slider action methods
    [slider addTarget:self 
           action:@selector(sliderUp:) 
     forControlEvents:UIControlEventTouchUpInside];
    [slider addTarget:self 
           action:@selector(sliderDown:) 
     forControlEvents:UIControlEventTouchDown];
    [slider addTarget:self 
           action:@selector(sliderChanged:) 
     forControlEvents:UIControlEventValueChanged];    

    NSString *labelText = @"label text";
    UIFont *labelFont;
    NSString *osVersion = [[UIDevice currentDevice] systemVersion];
    if ([osVersion floatValue] >= 7.0) {
        labelFont = [UIFont systemFontOfSize:22.0];

    } else {
        labelFont = [UIFont systemFontOfSize:24.0];
    }

    CGSize labelSize = [labelText sizeWithAttributes:[NSDictionary dictionaryWithObjectsAndKeys:labelFont, NSFontAttributeName, nil]];

    label = [[UILabel alloc] initWithFrame:CGRectMake(0.0, 0.0, labelSize.width, labelSize.height)];

    CGFloat labelHorizontalCenter = slider.center.x + (thumbImage.size.width / 2);
    label.center = CGPointMake(labelHorizontalCenter, slider.center.y);

    // Set other label attributes and add it to the view
    label.textColor = [UIColor whiteColor];
    label.textAlignment = NSTextAlignmentCenter;
    label.backgroundColor = [UIColor clearColor];
    label.font = labelFont;
    label.text = labelText;

    [view addSubview:label];

    [view addSubview:slider];

    label.layer.delegate = self;

    self.view = view;
}

The app does not crash at [view addSubview:label]; it crashes after the loadView method returns.

回答1:

From the UIView documentation:

Never change the delegate of this layer object.

Delete this line:

label.layer.delegate = self;

Whatever you're trying to accomplish here, you'll need to do in another way.