I'm scraping an asp.net web-form and it always sends viewstates like this:
<input type="hidden" name="__VIEWSTATE" value="/wEXAQUDX19QDwUNZnJtQ291cnNlSW5mbw8GblQKzmHhzYgCAw==">
When I decode it in the View State decoder I get this object: System.Collections.Hashtable.
The precise value of the __VIEWSTATE varies, but it alwasy decodes to the object System.Collections.Hashtable.
What's going on here? Why does the viewstate value vary but always decode to that?
The Page is stateless and so after each postback, it has no idea what happened before. A ViewState is often used in order to persist the information between postbacks. For example, if you selected an option and created a postback, the site might store your option in a ViewState so that your option is still selected after a postback.
What your seeing is the ViewState storing information on what controls are currently rendered on the site (a Hashtable in this case). The values stored in the table may vary, but the control seems to be present between postbacks.
You can read more on ViewStates on MSDN and how/when to use them here.
Related
I have developed a server control which inherits from CompositeDataBoundControl and INamingContainer. It has 2 TextBoxes and 1 small image.
But when rendering in GridView its ViewState size is up to 500 bytes. It also has about 20 properties, but I don't use ViewState here.
I only use get;set; and I bind it again when postback.
Now I am wondering how to reduce this ViewState size and how I can examine this ViewState . If I can examine the values of ViewState , it would be helpful to fix the problem.
Paste the ViewState into a base-64 decoder. I always find it enlightening to see what is taking up the space.
Keep in mind that the ViewState field also includes ControlState.
It has got 2 TextBoxs and 1 small image.
Some controls can function quite well without ViewState, due to their constant presence in the HTTP request. A TextBox is a good candidate for explicitly disabling ViewState because its value is always posted back to the server as part of the request.
An image is also a good candidate for disabling ViewState, unless calculating the URL requires processing time (e.g. a database call versus static assignment).
But when rendering in GridView...
A GridView almost definitely adds to the ViewState itself. Are you accounting for that?
you could disable the viewstate with
this.EnableViewState = false;
you could also check this link Disable View State for a Page to disable a viewstate from a page.
If you wish to check the viewstate, you could use ASP.NET ViewState Helper or a tool such as Fiddler to analyze the viewstate.
In this article http://www.devx.com/vb2themax/Tip/18714 "Improve performance with the EnableViewState property" I can't see where they do set EnableViewState to false. They just do
If Not Me.IsPostBack() Then
...
DataGrid1.DataBind()
Is Postback same as ViewState ?
Why not do EnableViewState = false on datagrid control ?
The article clearly states, that the first example (the part you're quiting from) ist usually done with the "ViewState" enabled. Since only the first get-request needs to bind the grid to the data source (IF Not Me.IsPostBack()), because the consecutive postbacks will restore the grids data from the saved ViewState.
The second example for the Page_Load method assumes that the ViewState has been disabled in the .aspx file and binds the grid to the data source every time the page is loaded.
The call to Me.IsPostBack only checks if the form was accessed via http post, while ViewState is an object which saves all the information concerned with the visual representation of a ASP.NET server control. So, no, they are not the same!
Grid controls act as containers for a lot of controls. Each control stores a lot of information in the ViewState.
The ViewState by default is stored in a hidden control. This means that it is sent to the client on every page request. To avoid this overhead, you can set the EnableViewState to false.
<asp:GridView ID="GridView1" runat="server" EnableViewState="false">
ViewState and PostBack are two totally unrelated entities. ViewState stores any information that a control wants to retain. A PostBack only refers to a user sending information back to the page.
However ViewState is also very useful to remember values entered by a user on the last PostBack. If your ViewState is very large, and you don't want to send it to the user, consider saving it in the Session. You can do this by setting the PageStatePersister to SessionPageStatePersister
The SessionPageStatePersister utilizes server sessions associated with
the browser session to store the data. Using session instead of a
hidden field avoids an increase in the page size being sent to and
from the browser. In many situations, the page state is a significant
part of the overall markup. However, storing this data in session
consumes valuable server resources.
This is 10KB in my HTML source:
<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="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/>
This represents ~50% of the entire size of the page.
Why does it do this, why so long? Can I do anything about it? It's bad for mobile users.
What is this view state anyway and how to mitigate its size
In Asp.net WebForms every control saves its state because HTTP protocol is stateless and Asp.net WebForms pages bypass that by saving every control's state in this Base 64 encoded string. This is the only way for Asp.net framework to know whether some control's value has changed or not. But... This automatically means that static controls that don't get POSTed back to server (like label for instance) don't need to save their state. You can always set their EnableViewState="false".
Unfortunately this can't be set without any other code changes on other controls, that do get POSTed back (every server-side control that renders some sort of an input in HTML). This basically means that setting EnableViewState="false" on page level (within #Page directive) will have consequences that are seen as controls loosing their values, controls not firing certain events etc.
So, the more server-side controls you have the larger it will get (without turning it off on certain controls).
But I wouldn't worry if its size is 10k. That will go back and forth rather fast and painless. You will have problems when it gets much larger. I once worked on a project and we had an issue with a certain page (done by less experienced developer) where view state grew over 1MB. Imagine that. What a slowdown!
How to turn it off completely on page level
When you turn view state off on page level you have to be aware that certain controls that were loaded (or better said data bound) in on of your page's events, will have to be reloaded each time your page gets POSTed back at server. Otherwise they will show up as empty when your page gets back to the client.
Your server controls are filling the ViewState with data they will need on postback. If your page does not postback you can just disable the ViewState for the page.
To disable ViewState for the page you can just add EnableViewState="false" to the #Page directive. Please be aware you should only use this as a solution if you are 100% sure the page does not postback.
You also might want to check this MSDN article to get a better idea of what the ViewState does.
Disable viewstate for static controls, like a gridview.
Check out this question for more info:
If you are concerned about the viewstate on the client side, then think about storing it on the server side. Perhaps in a session variable. Take a look at this article as there is statistical comparison given. Download the solution and check out how to store it on the server side.
An Analysis of Keeping ViewState out of the Page
This article explained it neatly to me in the past: Taking a Bite Out of ASP.NET ViewState.
Basically viewstate's on by default and, depending on which controls you use, it can get out of hand pretty fast. Especially data controls like the gridview are responsible for massive injection of viewstate. You can disable that on a per control basis by setting the EnableViewState property to false. Be careful however as taking out viewstate might also take out functionality of the controls. So do it one by one and test test test.
Another way, and likely better for mobile, is to make use of ASP.NET MVC instead which doesn't have to deal with automatic viewstate injection.
I have an aspx page that I want to convert to an HttpHandler, but I'm struggling with ViewState that's been used in the code behind of the aspx page. How do you solve this?
If your page relies on ViewState it's probably not a good candidate for an HttpHandler. ViewState is used to persist values of controls between postbacks. Handlers should be stateless and not depend on postbacks.
Viewstate is rendered to the client as a hidden form field. You can emulate Viewstate by rendering an <Input Type="Hidden" tag to your (now manually generated?) html.
Like Darin says though, it's better to either make your response stateless, or leave it as a Page
If I have a simple piece of data to store (an integer or string for example) I might choose to store that in ViewState, or using a HiddenField control.
Why would I choose one over the other?
ViewState
Hard for the user to decode (thought not impossible), which might be desirable
HiddenField
Value can be used in JavaScript
Are there other pros and cons?
Not really, ViewState is actually stored in a hidden field so the only real difference is the encoding.
Unless you need to manipulate the value with JavaScript or you hope to turn off ViewState on this page altogether then I'd use ViewState. Mostly just because there are third party tools (like this one) which understand ViewState and which won't understand your custom hidden field.
From a maintainability point of view, I'd use ViewState. It's less code for you to write, which comes down to fewer points of failure in your software. It also means that any developers coming after you will have an easier time maintaining your solution.
If you're not entirely comfortable with that, write a property accessor on the page that acts as a facade to retrieve the value from the ViewState. Later, if you feel compelled to convert it to a hidden field, the accessor can handle that switch seemlessly for the rest of the code. Just be sure you document your reasons for doing so.
Viewstate is only good on the page you are on or posting back to. With a hidden field you can access the data on the next page you navigate to (as well as other data) by using PreviousPage method of the Page object like so:
string term = ((TextBox)Page.PreviousPage.FindControl("txtSearchTerm")).Text;
The ViewState is stored in the page itself so it increases the page size and it may cause performance issues.
Also we can configure the application to save the viewstate on server rather than on page itself which might protect from some security issues.
Jomit
The hidden field are invisible on page and their values can be viewed in view source but the value of view-state are encoded and are not readable.
The hidden field value are posted on next page. (Note: use server.transfer to get the value of hidden fields).