ASP.NET ViewState的工作原理

它是这样的：

Why some controls retain values
even after disabling the ViewState
while others do not?

The answer is Controls which
implements IPostBackEventHandler IPostBackDataHandler like
Textbox,Checkbox,etc. will retain
the state even after disabling the
viewstate. The reason is during the
Load Postback Data stage,these
controls will get state information
from Posted back form.

But controls like label which do not
implement IPostBackEventHandler IPostBackDataHandler will
not get any state information from
posted back data and hence depend
entirely on viewstate to maintain the
state.

以下是与您的问题相关的段落.

In page life cycle,two events are
associated with ViewState:

• Load View State: This stage follows the initialization stage of
  page lifecycle. During this stage,
  ViewState information saved in the
  previous postback is loaded into
  controls. As there is no need to check
  and load previous data,when the page
  is loaded for the first time this
  stage will not happen. On subsequent
  postback of the page as there may be
  previous data for the controls,the
  page will go through this stage.

• Save View State: This stage precedes the render stage of the page.
  During this stage,current state
  (value) of controls is serialized into
  64 bit encoded string and persisted in
  the hidden control (__ViewState) in
  the page.

• Load Postback Data stage: Though this stage has nothing to do with
  ViewState,it causes most of the
  misconception among developers. This
  stage only happens when the page has
  been posted back. ASP.NET controls
  which implement IPostBackEventHandler IPostBackDataHandler
  will update its value (state) from the
  appropriate postback data. The
  important things to note about this
  stage are as follows:

  1. State (value) of controls are NOT retrieved from ViewState but from
     posted back form.
  2. Page class will hand over the posted back data to only those
     controls which implement
     IPostBackEventHandler IPostBackDataHandler.
  3. This stage follows the Load View State stage,in other words state of controls set during the Load View State stage will be overwritten in this stage.