Subclass with Internal Delegate and Message Forwarding

MyTextView.h

#import <UIKit/UIKit.h>

@interface MyTextView : UITextView

@end

MyTextView.m

#import "MyTextView.h"

// UITextViewDelegate impl for internal use only by MyTextView
@interface MyTextViewInternalDelegate : NSObject <UITextViewDelegate>
@property (weak, nonatomic) id<UITextViewDelegate> userDelegate;
@end

@interface MyTextView ()
@property (strong, nonatomic) MyTextViewInternalDelegate *internalDelegate;
@end

@implementation MyTextView

- (id)initWithCoder:(NSCoder *)coder {
    self = [super initWithCoder:coder];
    if (self) {
        self.internalDelegate = [[MyTextViewInternalDelegate alloc] init];
        [super setDelegate:self.internalDelegate];
    }
    return self;
}

#pragma mark UITextViewDelegate custom work

- (void)didBeginEditing {
    NSLog(@"================> whatever MyTextView needs to do internall as a delegate");
}

#pragma mark Overrides

- (void)setDelegate:(id<UITextViewDelegate>)delegate {
    self.internalDelegate.userDelegate = delegate;
}

- (id<UITextViewDelegate>)delegate {
    return self.internalDelegate.userDelegate;
}

@end

@implementation MyTextViewInternalDelegate

- (void)textViewDidBeginEditing:(UITextView *)textView {
    [(MyTextView *)textView didBeginEditing];
    if ([self.userDelegate respondsToSelector:_cmd]) {
        [self.userDelegate textViewDidBeginEditing:textView];
    }
}

#pragma mark Message Forwarding

- (BOOL)respondsToSelector:(SEL)selector {
    return [self.userDelegate respondsToSelector:selector] || [super respondsToSelector:selector];
}

- (void)forwardInvocation:(NSInvocation *)invocation {
    [invocation invokeWithTarget:self.userDelegate];
}

@end

TestViewController.h

#import <UIKit/UIKit.h>

@class MyTextView;

@interface TestViewController : UIViewController

@end

TestViewController.m

#import "TestViewController.h"
#import "MyTextView.h"

@interface TestViewController () <UITextViewDelegate>
@property (weak, nonatomic) IBOutlet MyTextView *myTextView;
@end

@implementation TestViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.myTextView.delegate = self;
}

#pragma mark <UITextViewDelegate>

- (void)textViewDidBeginEditing:(UITextView *)textView {
    NSLog(@"================> user delegate gets to do stuff too");
}

@end