How to Add Code and Validation Controls to a Form - How to use the required field validator

To use the required field validator, you set the properties shown in the table at the top of figure 2-14. These are the properties that are used by all the validators.

To start, you associate the validation control with a specific input control on the form through its ControlToValidate property. Then, when the focus leaves the input control or the user clicks on a button whose CausesValidation property is set to True, the validator checks whether a value has been entered into the input control. If not, the message in the ErrorMessage property is displayed.

When an error occurs, the Display property of the validation control determines how the message in the ErrorMessage property is displayed. When you use flow layout, Dynamic usually works the best for this property. If you use a validation summary control as explained in chapter 7, though, you can change this property to None.

If you look at the aspx code in this figure, you can see how the properties are set for the two required field validators that are shown in the previous figure. The first one validates the text box named txtInterestRate. The second one validates the text box named txtYears. This aspx code will be added after the end tag for the table in the code in figure 2-12.

How to use the range validator

The range validator lets you set the valid range for an input value. To use this control, you set the properties in the first table in figure 2-14, plus the properties in the second table. In particular, you set the minimum and maximum values for an input value.

For this control to work correctly, you must set the Type property to the type of data you’re testing for. Because the interest rate entry can have decimal positions, for example, the Type property for the first range validator is set to Double. In contrast, because the year entry should be a whole number, the Type property for the second range validator is set to Integer. You can see how all of the properties for the two range validators are set by reviewing the aspx code.

Common validation control properties  

Additional properties of a range validator  

The aspx code for the validation controls on the Future Value form

  <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server"
      ControlToValidate="txtInterestRate" Display="Dynamic"
      ErrorMessage="Interest rate is required.">
  </asp:RequiredFieldValidator&nbsp;>
  <asp:RangeValidator ID="RangeValidator1" runat="server" 
      ControlToValidate="txtInterestRate" Display="Dynamic"
      ErrorMessage="Interest rate must range from 1 to 20."
      MaximumValue="20" MinimumValue="1" Type="Double">
  </asp:RangeValidator><br />
  <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server"
      ControlToValidate="txtYears" Display="Dynamic"
      ErrorMessage="Number of years is required.">
  </asp:RequiredFieldValidator>&nbsp;
  <asp:RangeValidator ID="RangeValidator2" runat="server"
      ControlToValidate="txtYears" Display="Dynamic"
      ErrorMessage="Years must range from 1 to 45."
      MaximumValue="45" MinimumValue="1" Type="Integer">
  </asp:RangeValidator>

Description

1. The required field validator is typically used with text box controls, but can also be used with list controls.
   
2. The range validator tests whether a user entry falls within a valid range. 
    
3. If the user doesn’t enter a value into the input control that a range validator is associated with, the range validation test passes. Because of that, you should also provide a required field validator if a value is required.

--------------------------------------------Figure 2-14   How to use the required field and range validators

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This article is an excerpt from chapter two of Murach's ASP.NET 3.5 Web Programming with VB 2008, written by Anne Boehm (Murach, 2008; ISBN: 1890774472). Check it out today at your favorite bookstore. Buy this book now.