ViewState
HTTP POST is a way to submit data from the page to a different page on a server,
postback is an ASP.NET mechanisem to submit data to the same page.
ViewState is a collection of information generated by controls on an .aspx page that’s used by the
controls to restore their state during a postback.
State in this context can include the values of control properties,
results of data binding,
or input from users.
on the
server :
<form id="form1" runat="server">
</form>
generated HTML:
<form name="form1" method="post" action="viewstate1.aspx" id="form1">
<div>
<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE"
value="/wEPDwULLTE2MTY2ODcyMjlkZExM0iM4ebB6mDGwogfzmhu/Ur0P" />
</div>
</form>
You can see the <input> tag containing the __VIEWSTATE field.
the value of the input field is a encoded to base64.
The browser sends the hidden field back to the server when the <form> is submitted, as it does with
all <input> fields.
When the runtime receives the field, it is decoded, deserialized, and used to restore the
state of the controls.
ViewStateUserKey its a property which when used is helpfull for security,
by setting
protected void Page_Init(object sender, EventArgs e)
{
this.ViewStateUserKey = Request.UserHostAddress;
}
The result is that the __VIEWSTATE hidden field will be different for each different IP address,
and users who submit the form from a different IP address will receive an error.
must be created in the Page_Init() event, which is before ViewState is restored in the page life cycle
saving a value to viewstate
void Page_PreRender(object sender, EventArgs e)
{
ViewState.Add("MyVarName", MyVar);
}
when page.Ispostback = true
ViewState can be read and written only after the Page_Init() event and before
Page_PreRender().
viewstate size think about a control that generates a big table with paging links ,
a control like that on the page can have a big viewstate connected to it resulting a long roundtrips.
in this case its beter to disable the viewstate EnableViewState="false" for the page or myControl.EnableViewState = false; for a control
and fatching the relevent data from the DB or
save the viewstate to the DB and provide a GUID to the page and viewstate.
