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.