#pragma mark  UITextFieldDelegate

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{

    //  判斷輸入的是否為數字 (只能輸入數字)

    NSString *validRegEx =@"^[0-9]*$";

    NSPredicate *regExPredicate =[NSPredicate predicateWithFormat:@"SELF MATCHES %@", validRegEx];

    BOOL myStringMatchesRegEx = [regExPredicate evaluateWithObject:string];

    if (myStringMatchesRegEx)

        return YES;

    else

        return NO;

}