What is the recommended method of styling an iOS app?

Question

What is the recommended method of styling an iOS app? For example, if there are multiple labels or text views how can updating font style/color at one place update the style

Answer 1

Update: I would recommend starting by understanding UIAppearance APIs, and seeing how well they suit your needs. UIAppearance is a convenient way to provide custom default stylization of specific controls' attributes at multiple levels (e.g. globally or contextually).

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My original answer, which predated UIAppearance's availability:

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since we're working with an object based language...

for the implementation, it depends on how you want it to behave/execute. when the implementation becomes nontrivial, i will often create a protocol. you could use class methods or instance methods and significantly optimize these types for your usage because you create fewer intermediate colors, fonts, images, etc.

a basic interface could take the form:

@protocol MONLabelThemeProtocol

- (UIFont *)labelFont;
- (UIColor *)labelTextColor;
- (UITextAlignment)labelTextAlignment;
// ...
@end

@protocol MONTableViewCellThemeProtocol

- (UIFont *)tableViewCellFont;
- (UIColor *)tableViewCellTextColor;
- (UIImage *)tableViewCellImage;
- (NSInteger)tableViewCellIndentationLevel;
- (CGFloat)tableViewCellIndentationWidth;
// ...
@end

then a simple amalgamate theme could be declared like this:

@interface MONAmalgamateThemeBase : NSObject
   < MONLabelThemeProtocol, MONTableViewCellThemeProtocol >
{
@protected
    /* labels */
    UIFont * labelFont;
    UIColor * labelTextColor;
    UITextAlignment labelTextAlignment;
    // ...
    /* table view cells */
    UIFont * tableViewCellFont;
    UIColor * tableViewCellTextColor;
    UIImage * tableViewCellImage;
    NSInteger tableViewCellIndentationLevel;
    CGWidth tableViewCellIndentationWidth;
    // ...
}

@end

in this example, the amalgamate defines the getters and dealloc and expects the subclasses to initialize the instance variables. you could also support lazy initialization if initialization times are high (e.g. uses many images).

then a specialization could take the form:

@interface MONDarkTheme : MONAmalgamateThemeBase
@end

@implementation MONDarkTheme

- (id)init
{
    self = [super init];
    if (nil != self) {
        labelFont = [[UIFont boldSystemFontOfSize:15] retain];
        labelTextColor = [[UIColor redColor] retain];
        // and so on...
    }
    return self;
}

// ...

@end

/* declare another theme and set it up appropriately */
@interface MONLightTheme : MONAmalgamateThemeBase
@end

then just reuse the theme instances (e.g. MONDarkTheme) throughout the app to stylize the views. if you have a lot of themes or they are not trivial to construct, then you may want to create a collection for themes (theme manager). the amalgamate could also take a parameter, such as init with theme if your needs are simple. you can even configure objects to register for changes to themes, if you need support for dynamic changes.

finally, you can create a simple theme applier to make life easier - like so:

@interface UILabel (MONThemeAdditions)

- (void)mon_applyMONLabelTheme:(id<MONLabelTheme>)theme;

@end

@implementation UILabel (MONThemeAdditions)

- (void)mon_applyMONLabelTheme:(id<MONLabelTheme>)theme
{
    assert(theme);
    if (nil == theme) return;
    self.font = [theme labelFont];
    self.textColor = [theme labelTextColor];
    self.textAlignment = [theme labelTextAlignment];
}

@end