加密的UITextField在重新输入密码时，总会clear之前的内容


-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
NSString *updatedString = [textField.text stringByReplacingCharactersInRange:range withString:string]; textField.text = updatedString; return NO;
}


UITextField with secure entry, always getting cleared before editing