iphone弹出键盘部分按键禁用

实现这个函数：
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    NSString *newString = [textFiled.text stringByReplacingCharactersInRange:range withString:string];
    short strLen = [newString length];
    unichar tempChar = [newString characterAtIndex:strLen-1];
    // 这里判断tempChar是不是你要禁用的键，若要禁用就return NO

  }