Programming Visual Basic 2005

Custom Validation

There are times when the validation of your data is so specific to your application that you will need to write your own validation method. The CustomValidator is designed to provide all the infrastructure support you need. You provide the name of your validation method and have it return a Boolean value: True or False. The CustomValidator control takes care of all the rest of the work.

Because validation can be done on the client or on the server, depending on the browser, the CustomValidator has attributes for specifying both a server-side and a client-side method for validation. The server-side method can be written in any .NET language, (we, of course will use Visual Basic 2005), while the client-side method must be written in a scripting language understood by the browser, such as VBScript or JavaScript.

Add one more row to your form (below the ZIP-code row), asking the user for an even number, as shown in Figure 9-23.

Figure 9-23. Even number row

Once again, the middle column has a text box (txtEven). Drag a CustomValidator into the third column and set its attributes as shown in Table 9-9.

Table 9-9. CustomValidator properties and events

Property	Value
ID	cvEven
ControlToValidate	txtEven
ClientValidationFunction	ClientEventValidator
ValidateEmptyText	False
ErrorMesssage	Your number is rather odd
Text	*
ServerValidate [EVENT] ...