How to know when text is copied from a specific textfield in Objective-C?

Question

I have some textFields which are editable. when user selects its text copy and paste menu items are shown.
I want to know when user taps on the copy. because I want to change the copied text.
Is it possible?

More details: I want to change the copy of 3 textfields. I want to concatenate all these 3 textfields texts into clipboard when one of the textfields are copied. There are other textfields in this page too but I don't want to do anything for them.

Answer 1

You can implement the copy() method to "intercept" the copy operation and modify what gets placed on the clipboard.

Easiest way is probably a simple subclass of UITextField:

//
//  MyTextField.h
//
//  Created by Don Mag on 5/29/19.
//

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface MyTextField : UITextField

@end

NS_ASSUME_NONNULL_END

and

//
//  MyTextField.m
//
//  Created by Don Mag on 5/29/19.
//

#import "MyTextField.h"

@implementation MyTextField

- (void)copy:(id)sender {

    // debugging
    NSLog(@"copy command selected");

    // get the selected range
    UITextRange *textRange = [self selectedTextRange];

    // if text was selected
    if (textRange) {

        // get the selected text
        NSString *selectedText = [self textInRange:textRange];

        // change it how you want
        NSString *modifiedText = [NSString stringWithFormat:@"Prepending to copied text: %@", selectedText];

        // get the general pasteboard
        UIPasteboard *pb = [UIPasteboard generalPasteboard];

        // set the modified copied text to the pasteboard
        pb.string = modifiedText;
    }

}

@end