I need to grab the base64-encoded representation of the ViewState. Obviously, this would not be available until fairly late in the request lifecycle, which is OK.
For example, if the output of the page includes:
<input type="hidden" name="__VIEWSTATE"
id="__VIEWSTATE" value="/wEPDwUJODU0Njc5MD...==" />
I need a way on the server side to get the value "/wEPDwUJODU0Njc5MD...=="
To clarify, I need this value when the page is being rendered, not on PostBack. e.g. I need to know the ViewState value that is being sent to the client, not the ViewState I'm getting back from them.
Rex, I suspect a good place to start looking is solutions that compress the ViewState -- they're grabbing ViewState on the server before it's sent down to the client and gzipping it. That's exactly where you want to be.
See this blog post where the author describes a method for overriding the default behavior for generating the ViewState and instead shows how to save it on the server Session object.
Although I did not test his code, it seems to show exactly what you want: a way to gain access to ViewState code while still on the server, before postback.
I enabled compression following similar articles to those posted above. The key to accessing the ViewState before the application sends it was overriding this method;
You can call the base method within this override and then add whatever additional logic you require to handle the ViewState.