Basic UIResponder additions to handle commands

AGCommand.h

@interface AGCommand : NSObject

@property(nonatomic, weak) UIResponder *firingObject;
@property(nonatomic, readonly) SEL action;

+ (instancetype)command;

@end

AGCommand.m

@implementation AGCommand

+ (instancetype)command {
    return [[self alloc] init];    
}

- (SEL)action {
    return @selector(performGenericCommand:);
}

@end

UIResponder+AGCommands.h

@interface UIResponder (AGCommands)
- (BOOL)canPerformCommand:(AGCommand *)command;
- (UIResponder *)targetForCommand:(AGCommand *)command;
- (BOOL)sendCommand:(AGCommand *)command;
@end

UIResponder+AGCommands.m

#import "UIResponder+AGCommands.h"
#import <objc/runtime.h>

@implementation UIResponder (AGCommands)

- (BOOL)canPerformCommand:(AGCommand *)command {
    return [self respondsToSelector:command.action];
}

- (UIResponder *)targetForCommand:(AGCommand *)command {
    UIResponder *implementor = self;
    while (implementor) {
        if ([implementor canPerformCommand:command] == YES) {
            return implementor;
        }
        implementor = [implementor nextResponder];
    }
    return nil;
}


- (BOOL)sendCommand:(AGCommand *)command {
    if (!command) return NO;
    if (command.firingObject == nil) {
        command.firingObject = self;
    }
    
    UIResponder *target = [self targetForCommand:command];
    if (target) {
        [self performCommand:command onResponder:target];
        return YES;
    }
    return NO;
}

- (void)performCommand:(AGCommand *)command onResponder:(UIResponder *)responder {
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:[[responder class] instanceMethodSignatureForSelector:command.action]];
    [invocation setSelector:command.action];
    [invocation setTarget:responder];
    [invocation setArgument:&command atIndex:2];
    [invocation invoke];
}

@end