yo sueloUIPasteboard para copiar / pegar texto entre dosUITextView.

El código se ve así:

- (void)viewDidLoad {
   [super viewDidLoad];
   pasteBoard = [UIPasteboard generalPasteboard]; //it is declared in .h as UIPasteboard *pasteBoard;
}

-(IBAction)doCopyBtn {
    if (![toCopyTextView.text isEqualToString:@""]){
        pasteBoard.string = toCopyTextView.text;
        NSLog(@"pasteb1 %@", pasteBoard.string);
    } else {
        NSLog (@"error! enter smth");
    }
}

-(IBAction)doPasteBtn {
    if (![pasteBoard.string isEqualToString:@""]){ 
        toPasteTextView.text = pasteBoard.string;
        NSLog(@"pasteb2 %@", pasteBoard.string);
    } else {
        NSLog (@"error! enter smth");
    }
}

E incluso esto no puede ayudar (NSLog regresa:pasteb2 (null))

-(void) viewWillDisappear:(BOOL)animated{
    [super viewWillDisappear:animated];
    [pasteBoard setString:@""]; 
}