iOS 5: Curious about UIAppearance

Question

On the tech talk 2011 I saw a speech about the new UIAppearance protocol. There is not a lot of documentation out there yet. I will shortly summarize what I remember to explain where my question is coming from:

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About UIAppearance:

So far you had to customize EVERY navigation bar (toolbar, etc.) property in all your app view controllers. With the new appearance property you can do it in only one place for all navigation bars in your app. For instance: if you want to customize your Navigation bar background image you could do it like this:

[[UINavigationBar appearance] setBackgroundImage:
   [UIImage imageNamed:@"MyImageName"] forBarMetrics:UIBarMetricsDefault]; 

This will set the background image of ALL navigation bars within your application. With the barMetrics you specify whether you want the image to be used also in landscape mode or not.

If you want to specify the appearance to be applied only in some view controllers there is also a method in the docs to control that by specifying where your objects are located:

[[UIBarButtonItem appearanceWhenContainedIn:
    [ABPeoplePickerNavigationController class], nil] setTintColor:myNavBarColor];

Also worth to mention is, if you have single customized instances, differing from your appearance settings, theses instances will not be effected by the appearance proxy.

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Some questions:

a) How do I know which properties of a class work with the appearance property? For e.g. since UITableView conforms to the UIAppearance protocol I was thinking I could do something like

[[UITableView appearance] setBackgroundColor:mytableViewColor];

to manipulate the background color of all my table views, but I can't!

b) Is there a list of all classes that are manipulatable with the appearance property?

c) At what point is the appearance customization being called? I was hoping to make changes threw the appearance property at runtime, but unfortunately the changes aren't taking place.

Answer 1

a) How do I know which instances of a class work with the appearance property? For e.g. since UITableView conforms to the UIAppearance protocol I was thinking I could do something like

You look in the header of the class (and the headers of all the superclasses). Any method that has UI_APPEARANCE_SELECTOR next to it is supported for use with the UIAppearance proxy.

[[UITableView appearance] setBackgroundColor:mytableViewColor];

The backgroundColor property is not decorated with UI_APPEARANCE_SELECTOR in UIView.h. Thus it is not technically supported for use with the appearance proxy. It will probably work, but (given the lack of method decoration) isn't guaranteed to.

From the UIAppearance Protocol Reference:

To support appearance customization, a class must conform to the UIAppearanceContainer protocol and relevant accessor methods must be marked with UI_APPEARANCE_SELECTOR.

(note "and relevant accessor methods must be marked..." [emphasis added])

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b) Is there a list of all properties that are manipulatable with the appearance property?

Is there a single page showing every setter that works with the appearance proxy? I don't know of one, nor is there a way to build the list at runtime.

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c) At what point is the appearance customization being called? I was hoping to make changes threw the appearance property at runtime, but unfortunately the changes aren't taking place.

You can use the appearance proxy at any point during execution. The changes won't be applied to the affected views until the next time those views have their -layoutSubviews method invoked.

Answer 2

UIAppearance is documented within the headers of each class. Look within there for methods marked UI_APPEARANCE_SELECTOR at the very end. Those are the methods you can call through the appearance proxy. I'm not aware of a list outside of the headers.

The appearance customization is called immediately after passing through the proxy, as well as whenever a new object is constructed. But this will only work for methods marked with that UI_APPEARANCE_SELECTOR

Answer 3

a: The following line

 [[UITableView appearance] setBackgroundColor:[UIColor blueColor]];

Will make every table view blue! Just tested on iOS 5 simulator.

b: The UIAppearance should work on every property on a UIView. All the subclasses of UIView conforms to UIAppearance Protocol

c: I think that the most of will create an class and or method that will customize the appearance and will call it in:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

Something like: [ApplicationAppearance setApplicationSchemaTo:ASchemaBlue];

Edit:

For example, UIBarButtonItem defines these methods:

@property(nonatomic,retain) UIColor *tintColor UI_APPEARANCE_SELECTOR;

From UIAppearanceContainer Protocol Reference

And in the UIBarButtonItem Class Reference the tintColor is defined

@property(nonatomic, retain) UIColor *tintColor

But in the UIBarButtonItem.h is defined:

@property(nonatomic,retain) UIColor *tintColor __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_5_0) UI_APPEARANCE_SELECTOR;

I think that the docs are not up to date.