ASP.NET Cookbook

6.3. Preserving Information Between Postbacks

Problem

You have a page with a state whose value the page needs to remember between postbacks to determine how the page should be displayed.

Solution

Use the RegisterHiddenField method of the Page object to create a hidden text field in the rendered page.

Nothing special is required in the .aspx file. Instead, in the code-behind class for the page, use the .NET language of your choice to:

1. Programmatically insert a hidden text field into the form using the RegisterHiddenField method of the Page object.

2. Use this field to store the value of the state you wish to preserve between postbacks.

3. Access the hidden text field on subsequent submissions of the page to the server.

Figure 6-3 shows the output of a simple form that preserves the page state using a hidden field. Clicking the Prev/Next buttons decrements/increments the value in the hidden field by one. Example 6-11 shows the .aspx file that produces the form. Example 6-12 and Example 6-13 show the companion VB and C# code-behind files that demonstrate how to access the application state data.

Figure 6-3. Maintaining page state with a hidden field

Discussion

An approach we favor for remembering the current state of a value between postbacks to the server involves programmatically inserting one or more hidden text fields into a form.

A similar technique is commonly used by classic ASP developers, who ...