Question

When EnableViewstate = false and I do postback, my textbox control retains the text value but label control does not. I am changing the text for both label and textbox on a button’s click event.

protected void Button1_Click(object sender, EventArgs e)
{
    TextBox1.Text = "Message Changed";
    Label1.Text = "Message Changed";
}

There is another button my page for just postback.

Also if I do no need viewstate for this control, then is there a list of all the controls that don’t need the viewstate?

Answer 1

All controls which implement IPostBackDataHandler load their values even if ViewState is off. Note that events like TextChanged and other properties like ForeColor don’t work when ViewState is disabled.

Here’s a list of controls which implement IPostBackDataHandler

• CheckBox
• CheckBoxList
• DropDownList
• HtmlInputCheckBox
• HtmlInputFile
• HtmlInputHidden
• HtmlInputImage
• HtmlInputRadioButton
• HtmlInputText
• HtmlSelect
• HtmlTextArea
• ImageButton
• ListBox
• RadioButtonList
• TextBox

Why textbox persists data during postback even if View State set to off

Whenever a page is submitted or posted back to server, the entire form
data is posted to the server as a collection with the request. The
collection is in the form of NamedValue collection and this collection
has the mapping with uniqueid of the control and the value of the
control. You can read the data from the form collection by using the
following code snippet

//Reading textbox value from the form collection 
string textboxvalue = Request.Form[textbox1.UniqueID];

ASP.NET uses this primitive to update the control’s value. ASP.NET
uses IPostBackDataHandler for the controls that load the data from
the form collection.