UIAppearance proxy for custom objects

Question

I have a custom object, it inherits from NSObject. This object does \"some things\", one of it is creating an UIView with some UIKit objects (UILabel, UIButtons ecc ecc...)

Answer 1

After some reserach I "give up" about using a standard Apple object. It doesn't exists, for now. I've created my own proxy, it's quite simple (works only with "appearance:" by now).

Let's explain it. I want to set the appearance of "textColor" on a NSObject subclass, let's call it "FLObject". Make FLObject conforms to UIAppearance protocol and override the appearance method. In this method, you should return a proxy class (the one I created):

+ (id)appearance
{
    return [FLAppearance appearanceForClass:[self class]];
}

How it works? FLAppearance creates a single instance of itself for each class passed by the appearanceForClass: method. If you call it two times for the same class, the same instance is returned.

Then, you can do something like this:

[[FLObject appearance] setTextColor:[UIColor redColor]]; 

FLAppearance overrides the forwardInvocation: method, so it accepts all methods sent. Then, it puts all invocations in an array. When FLObject is initialized, a simple call to

[(FLAppearance *)[FLAppearance appearanceForClass:[self class]] startForwarding:self];

will start to send invocations and set the appearance. Sure, this needs some tuning and error checking, but I think it's a good start.

@interface FLAppearance ()

@property (strong, nonatomic) Class mainClass;
@property (strong, nonatomic) NSMutableArray *invocations;

@end

static NSMutableDictionary *dictionaryOfClasses = nil;

@implementation FLAppearance

// this method return the same object instance for each different class
+ (id) appearanceForClass:(Class)thisClass
{
    // create the dictionary if not exists
    // use a dispatch to avoid problems in case of concurrent calls
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        if (!dictionaryOfClasses)
            dictionaryOfClasses = [[NSMutableDictionary alloc]init];
    });



    if (![dictionaryOfClasses objectForKey:NSStringFromClass(thisClass)])
    {
        id thisAppearance = [[self alloc]initWithClass:thisClass];
        [dictionaryOfClasses setObject:thisAppearance forKey:NSStringFromClass(thisClass)];
        return thisAppearance;
    }
    else
        return [dictionaryOfClasses objectForKey:NSStringFromClass(thisClass)];
}

- (id)initWithClass:(Class)thisClass
{
    self = [self initPrivate];
    if (self) {
        self.mainClass = thisClass;
        self.invocations = [NSMutableArray array];
    }
    return self;
}

- (id)init
{
    [NSException exceptionWithName:@"InvalidOperation" reason:@"Cannot invoke init. Use appearanceForClass: method" userInfo:nil];
    return nil;
}

- (id)initPrivate
{
    if (self = [super init]) {

    }
    return self;
}

-(void)forwardInvocation:(NSInvocation *)anInvocation;
{
    // tell the invocation to retain arguments
    [anInvocation retainArguments];

    // add the invocation to the array
    [self.invocations addObject:anInvocation];
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
    return [self.mainClass instanceMethodSignatureForSelector:aSelector];
}

-(void)startForwarding:(id)sender
{
    for (NSInvocation *invocation in self.invocations) {
        [invocation setTarget:sender];
        [invocation invoke];
    }
}