stop deletion of complete text in case of secure Textfield on backspace.--- IOS

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
   
    // backspace functionality
    if (range.location > 0 && range.length == 1 && string.length == 0)
    {
        UITextPosition *beginning = textField.beginningOfDocument;
        UITextPosition *start = [textField positionFromPosition:beginning offset:range.location];
        NSInteger cursorOffset = [textField offsetFromPosition:beginning toPosition:start] + string.length;
        NSString *text = textField.text;

        // Trigger deletion
        [textField deleteBackward];

        if (textField.text.length != text.length - 1)
        {
            textField.text = [text stringByReplacingCharactersInRange:range withString:string];
            UITextPosition *newCursorPosition = [textField positionFromPosition:textField.beginningOfDocument offset:cursorOffset];
            UITextRange *newSelectedRange = [textField textRangeFromPosition:newCursorPosition toPosition:newCursorPosition];
            [textField setSelectedTextRange:newSelectedRange];
        }
        return NO;
    }   
       
    return YES;
}