Allowing users to enter any kind of text is a crucial and often used function in almost any interactive Peakboard application. However, it is also crucial to expect users to make false entries and entries that don’t match the expectations of the procedures that process the entered values. In this article, we will discuss a highly efficient and standardized way of checking user entries against certain rules by using regular expressions, or simply called Regex.
What is Regex?
Simply spoken, a regex is a single string that contains the rule another string (the payload) is checked against. For example, let’s take the regex ^.{0,6}$. It defines the rule that the payload’s length must not exceed a maximum length of six characters. So the payload “Hello” is aligned with the rule ^.{0,6}$, but the payload “Hello world” is not. How these regex strings or rules are defined we will learn in the next paragraph.
Crash course regex
Every regex starts with the character ^ and ends with character $. So for example ^abc$ only matches if the text is exactly “abc”.
The brackets [] are used to define what is allowed:
[0-9]→ a digit between 0 and 9[a-z]→ lowercase letters[A-Za-z0-9]→ letters and digits\d→ any single digit[^...]→ NOT these characters
The brackets {} are used to define the allowed length:
{n}→ exactly n times{n,}→ at least n times{n,m}→ between n and m times (inclusive)
So let’s take the typical serial numbers of Peakboard boxes. They usually look like “PB1020”, so they start with “PB” and then are followed by a 4–5 digit string. The correct regex would be ^PB\d{4,5}$:
^→ start of the stringPB→ the literal characters PB (fixed)\d{4,5}→ 4 or 5 digits (0–9)$→ end of the string
Things can get really complicated when the requirements go up, e.g. ^(?=.*[A-Za-z])(?=.*\d).{8,}$ is a password with at least one letter, one number, and a minimum of eight characters.
Regex in Peakboard applications
The text boxes in Peakboard offer a validation attribute that can be switched on. It comes along with the actual Regex expression to be checked against and also a dedicated border color. As long as the user entry doesn’t match the regex, the border is automatically set to the color.
Besides the changing border color we can use building blocks in our processing procedure to check for validity and react accordingly if the user entry doesn’t match the requirement. We can just use the “IsValid” property and in case it’s not valid inform the user (e.g. by shaking the text box) or start the processing in case the entry is ok.
Result
The animation shows the check in action for the regex of the Peakboard serial numbers PBXXXX with XXXX being 4–5 digits. So the regex is ^PB\d{4,5}$. First we try to submit a wrong entry; there are two digits missing. After the number of digits is correct, the entry is accepted.
