How do I apply UIAppearance Proxy properties to UILabel?

I have been getting unreliable results while trying to apply UIAppearance proxy styles to the UILabel class proxy. For example, the following works as I would expect:

[[UILabel appearance] setFont:[UIFont fontWithName:SOME_FONT size:SOME_SIZE]];
[[UILabel appearance] setShadowColor:[UIColor blackColor]];

Setting the textColor doesn't work, however, this:

[[UILabel appearance] setColor:[UIColor greenColor]];

does work. Kind of. It's somewhat unreliable and causes any instance-specific calls to setTextColor: to be ignored.

What is the correct way to apply UIAppearance styles to a UILabel?

OK, it turns out that you cannot style any UILabel properties using the UIAppearance proxy.

While the UILabel class conforms to the UIAppearanceContainer protocol, a check of UILabel.h shows that none of its properties are marked with UI_APPEARANCE_SELECTOR, the prerequisite for the use of UIAppearance.

Bugger.

I have subclassed UILabel

@interface SmallLabel : UILabel

@end

@implementation SmallLabel

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
    }
    return self;
}

@end

Then I use appearanceWhenContainedIn:

UIFont *smallFont = [UIFont fontWithName:@"Arial" size:15];
[[SmallLabel appearanceWhenContainedIn:[UIView class], nil] setFont:smallFont];

This works to use the desired font for all SmallLabels in my app. I just need to set the Custom Class to SmallLabel in the XCode Identity Inspector. It does not seem to work with labels create programmatically, only those in NIBs.

After further testing this method does not always work reliably.

In Swift you do the following to customize the appearance attributes for a UILabel when contained in a UITableViewHeaderFooterView:

UILabel.appearance(whenContainedInInstancesOf: [UITableViewHeaderFooterView.self]).font = UIFont.boldSystemFont(ofSize: 18)
UILabel.appearance(whenContainedInInstancesOf: [UITableViewHeaderFooterView.self]).textColor = .white

This will apply to the textLabel attribute when you use UITableViewHeaderFooterView in:

 public func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
    var headerView = tableView.dequeueReusableHeaderFooterView(withIdentifier: headerViewId)
    if headerView == nil {
        headerView = UITableViewHeaderFooterView(reuseIdentifier: headerViewId)
    }
    headerView?.textLabel?.text = "My Header".uppercased()
    return headerView
}

This really helps when using the UITableViewStyle.grouped, as those section header views seem to be overridden with a default style even if you customize the UITableViewHeaderFooterView.textLabel in viewForHeaderInSection