ASP.NET Server Control - Is shared Viewstate between controls possible - asp.net

Question

If I have a master 'composite custom server control', with several child custom controls, is it possible, for the master control to share its viewstate with the child controls, which are also custom composite server controls,(all of the controls are composite custom server controls)?
To expand a little more, say I have a Person control, Address control, Phone control and Notes control. Address, Phone and Notes can exist as either independant controls, or as part of the Person control. Since each control is responsible for its own viewstate, and stores required data in it, so it can render/postback etc, it ends up that there is a lage duplication in the viewstate, since the Person control stores all the data, and then each child control stores its own data again. Also, to further complicate things, the Person Control adds the child controls dynamically, so its possible to add a 2nd address/phone number/note etc,which can cause yet a larger viewstate(up to 1MB).
In the case of when all the Address/Phone/etc controls are children of the the Person Control, is it possible for me to somehow share common viewstate data, so I dont have 2/3/4 copies of some stuff in the viewstate, and when they are not components, just act as normal?
I do have one idea for a solution, but its fairly nasty imo, where I could modify the Person control, expose its viewstate or the data, and then in the child control, would check the control hierarchy, and if the child control is part of a Person, dont use to its own viewstate, use the exposed one. This would require me to rework alot of the existing code, which I'd rather avoid if possible.

Answer 1

The first question I'd ask is, "How much of this data do you really need to keep on the ViewState?" For example, is there enough information in a typical page request to be able to rebuild all of the information that is in some of these controls?
I find that ASP.NET typically uses ViewState far more than I really need it to, and if you're getting a 1MB viewstate, I suspect the same is probably true for you. I highly recommend reading this article to get a more full understanding of how ViewState works, what causes values to get saved to ViewState, and how to avoid using it where it's not necessary. You may be able to solve the bulk of your problem simply by doing more of your work in Page_Init instead of Page_Load, for example.

Answer 2

You can "share" a ViewState between any number of objects by passing it around as a StateBag type, or by using delegate functions that return the ViewState that needs to be shared. The usage of this, however; should be limited to very specific circumstances, because typically controls use Properties to expose their ViewState data to other objects (See the link #StriplingWarrior posted here). That being said, here is some example code:
User Control: SharedState.ascx
<%# Control Language="vb" AutoEventWireup="false" CodeBehind="SharedState.ascx.vb" Inherits="TestSite.SharedState" %>
User Control: SharedState.ascx.vb
Public Class SharedState
Inherits System.Web.UI.UserControl
Public Delegate Function GetStateDelegate() As StateBag
Public Const SharedValueKey = "The key used to access the ViewState dictionary"
Public Property GetState() As GetStateDelegate
' Different ways to get values
Public Function GetTypedValue(Of TValue)() As TValue
Return CTypeDynamic(GetValue(), GetType(TValue))
End Function
Public Function GetValue() As Object
' Use the delegate to get the view state from the parent
Return GetState.Invoke()(SharedValueKey)
End Function
Public Function GetValue(state As StateBag) As Object
Return state(SharedValueKey)
End Function
' Different ways to set values
Public Sub SetTypedValue(Of TValue)(value As TValue)
Me.SetValue(value)
End Sub
Public Sub SetValue(value As Object)
GetState.Invoke()(SharedValueKey) = value
End Sub
Public Sub SetValue(state As StateBag, value As Object)
state(SharedValueKey) = value
End Sub
' Set ViewState value using a key and the delegate
Public Sub SetStateWithKey(key As String, value As Object)
GetState.Invoke()(key) = value
End Sub
' Get ViewState value using a key and the delegate
Public Function GetStateWithKey(key As String) As Object
Return GetState.Invoke()(key)
End Function
End Class
Page: SharedStatePage.aspx
<%# Page Language="vb" AutoEventWireup="false" CodeBehind="SharedStatePage.aspx.vb" Inherits="TestSite.SharedStatePage" %>
<%# Register src="SharedState.ascx" tagname="SharedState" tagprefix="uc1" %>
<uc1:SharedState ID="SharedState1" runat="server" />
<uc1:SharedState ID="SharedState2" runat="server" />
Page: SharedStatePage.aspx.vb
Public Class SharedStatePage
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
' Set up SharedState 1 & 2 to use the delegate '
SharedState1.GetState = AddressOf GetState
SharedState2.GetState = AddressOf GetState
' Set the view state from the page '
ViewState(SharedState.SharedValueKey) = 23
' Read the view state from the user controls '
Dim sharedInt As Integer
sharedInt = SharedState1.GetTypedValue(Of Integer)()
sharedInt = SharedState1.GetValue()
sharedInt = SharedState1.GetValue(ViewState)
sharedInt = SharedState2.GetValue()
' Set the view state from one of the user controls '
SharedState2.SetTypedValue(Of String)("Hello")
Dim sharedStr As String = ViewState(SharedState.SharedValueKey)
sharedStr = SharedState1.GetTypedValue(Of String)()
sharedStr = SharedState2.GetValue()
' Use a different key to set and get view state data '
ViewState("MyKey") = New With {.Name = "Some Object", .Value = 46}
Dim myObj = SharedState1.GetStateWithKey("MyKey")
SharedState2.SetStateWithKey("MyKey", "New Value")
myObj = ViewState("MyKey")
End Sub
Private Function GetState() As StateBag
Return ViewState
End Function
End Class
Use with caution, or don't use with abandon.