How to perform server-side form reset?

G

Guest

Hi,

Can anyone tell me why in the code below, the call to ClearChildViewState()
has no effect?

To paraphrase the code: I'm using view state. I have a textbox and a submit
button (and a label that can be ignored). When I press the button the first
time, the click handler hides the textbox. Pressing the button a second time
unhides the textbox. The text box is maintaining its value when hidden via
view state. (The value is NOT being populated due to postback data.) I want a
server-side function to reset a form to it's initial state (i.e. the state it
was in when I first browsed to it). I expected Page.ClearChildViewState() to
do this, but it doesn't. Why not? And what can I do to reset my form on the
server without disabling viewstate?

Thanks,
- Lee

<%@ Page language="c#" Codebehind="WebForm1.aspx.cs" AutoEventWireup="false"
Inherits="WebTest.WebForm1" EnableViewState="true" %>
<%@ Register TagPrefix="My" Namespace="WebTest" Assembly="WebTest" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
<HEAD>
<title>WebForm1</title>
</HEAD>
<body >
<form id="Form1" method="post" runat="server">
<My:TextBox id="TextBox1" runat="server" EnableViewState="true"></My:TextBox>
<asp:Button id="Button1" runat="server" Text="Hide"></asp:Button>
<p><asp:Label id="Label1" runat="server"></asp:Label></p>
</form>
</body>
</HTML>

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;

namespace WebTest
{
/// <summary>
/// Summary description for WebForm1.
/// </summary>
public class WebForm1 : System.Web.UI.Page
{
protected System.Web.UI.WebControls.Button Button1;
protected System.Web.UI.WebControls.Label Label1;
protected System.Web.UI.WebControls.TextBox TextBox1;

#region Web Form Designer generated code
override protected void OnInit(EventArgs e)
{
InitializeComponent();
base.OnInit(e);
}

private void InitializeComponent()
{
this.Button1.Click += new System.EventHandler(this.Button1_Click);
}
#endregion

private void Button1_Click(object sender, System.EventArgs e)
{
if (!this.IsTrackingViewState)
throw new ApplicationException();

WebTest.TextBox c = (WebTest.TextBox)this.FindControl("TextBox1");

System.Diagnostics.Trace.WriteLine(c.GetViewState().Count);
this.ClearChildViewState(); // Why does this have no effect?
System.Diagnostics.Trace.WriteLine(c.GetViewState().Count);

if (this.Button1.Text == "Hide")
{
this.Button1.Text = "Show";
this.TextBox1.Visible = false;

if (this.TextBox1.Text.Length > 0)
this.Label1.Text = this.TextBox1.Text;
}
else // "Show"
{
this.Button1.Text = "Hide";
this.TextBox1.Visible = true;
}
}
}
}

using System;
using System.Web.UI;

namespace WebTest
{
public class TextBox : System.Web.UI.WebControls.TextBox
{
protected override object SaveViewState()
{
object vs = null;

vs = base.SaveViewState ();

return vs;
}

protected override void LoadViewState(object savedState)
{
base.LoadViewState (savedState);
}

public StateBag GetViewState()
{
return this.ViewState;
}
}
}
 
B

Bruce Barker

because the click event fires long after the textbox has feteched its value
from viewstate.

-- bruce (sqlwork.com)
 
S

Steven Cheng[MSFT]

Thanks for Bruce's informative inputs,

Hi Lee,

As Bruce has mentioned, the LoadViewState is getting executed before Load
event for controls/page , after that the propertes value is assigned to the
Control/page instance, and these properteis will be persisted into
viewstate again before Rendering. So change the ViewState in PostBack event
handler ( After Load ViewSate before save viewstate) won't have any effect.
also, IMO, I'd recommend you directly clear those entry fields control's
content through the instance properties rather than accessing the ViewState
collection.

Thanks,

Steven Cheng
Microsoft Online Support

Get Secure! www.microsoft.com/security
(This posting is provided "AS IS", with no warranties, and confers no
rights.)
--------------------
| From: "Bruce Barker" <[email protected]>
| References: <[email protected]>
| Subject: Re: How to perform server-side form reset?
| Date: Wed, 24 Aug 2005 09:01:14 -0700
| Lines: 148
| X-Priority: 3
| X-MSMail-Priority: Normal
| X-Newsreader: Microsoft Outlook Express 6.00.2900.2180
| X-RFC2646: Format=Flowed; Original
| X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180
| Message-ID: <#[email protected]>
| Newsgroups: microsoft.public.dotnet.framework.aspnet
| NNTP-Posting-Host: rdcsd1.safeco.com 12.144.134.2
| Path: TK2MSFTNGXA01.phx.gbl!TK2MSFTNGP08.phx.gbl!TK2MSFTNGP10.phx.gbl
| Xref: TK2MSFTNGXA01.phx.gbl
microsoft.public.dotnet.framework.aspnet:119990
| X-Tomcat-NG: microsoft.public.dotnet.framework.aspnet
|
| because the click event fires long after the textbox has feteched its
value
| from viewstate.
|
| -- bruce (sqlwork.com)
|
|
| | >
| > Hi,
| >
| > Can anyone tell me why in the code below, the call to
| > ClearChildViewState()
| > has no effect?
| >
| > To paraphrase the code: I'm using view state. I have a textbox and a
| > submit
| > button (and a label that can be ignored). When I press the button the
| > first
| > time, the click handler hides the textbox. Pressing the button a second
| > time
| > unhides the textbox. The text box is maintaining its value when hidden
via
| > view state. (The value is NOT being populated due to postback data.) I
| > want a
| > server-side function to reset a form to it's initial state (i.e. the
state
| > it
| > was in when I first browsed to it). I expected
Page.ClearChildViewState()
| > to
| > do this, but it doesn't. Why not? And what can I do to reset my form on
| > the
| > server without disabling viewstate?
| >
| > Thanks,
| > - Lee
| >
| > <%@ Page language="c#" Codebehind="WebForm1.aspx.cs"
| > AutoEventWireup="false"
| > Inherits="WebTest.WebForm1" EnableViewState="true" %>
| > <%@ Register TagPrefix="My" Namespace="WebTest" Assembly="WebTest" %>
| > <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
| > <HTML>
| > <HEAD>
| > <title>WebForm1</title>
| > </HEAD>
| > <body >
| > <form id="Form1" method="post" runat="server">
| > <My:TextBox id="TextBox1" runat="server"
| > EnableViewState="true"></My:TextBox>
| > <asp:Button id="Button1" runat="server" Text="Hide"></asp:Button>
| > <p><asp:Label id="Label1" runat="server"></asp:Label></p>
| > </form>
| > </body>
| > </HTML>
| >
| > using System;
| > using System.Collections;
| > using System.ComponentModel;
| > using System.Data;
| > using System.Drawing;
| > using System.Web;
| > using System.Web.SessionState;
| > using System.Web.UI;
| > using System.Web.UI.WebControls;
| > using System.Web.UI.HtmlControls;
| >
| > namespace WebTest
| > {
| > /// <summary>
| > /// Summary description for WebForm1.
| > /// </summary>
| > public class WebForm1 : System.Web.UI.Page
| > {
| > protected System.Web.UI.WebControls.Button Button1;
| > protected System.Web.UI.WebControls.Label Label1;
| > protected System.Web.UI.WebControls.TextBox TextBox1;
| >
| > #region Web Form Designer generated code
| > override protected void OnInit(EventArgs e)
| > {
| > InitializeComponent();
| > base.OnInit(e);
| > }
| >
| > private void InitializeComponent()
| > {
| > this.Button1.Click += new System.EventHandler(this.Button1_Click);
| > }
| > #endregion
| >
| > private void Button1_Click(object sender, System.EventArgs e)
| > {
| > if (!this.IsTrackingViewState)
| > throw new ApplicationException();
| >
| > WebTest.TextBox c = (WebTest.TextBox)this.FindControl("TextBox1");
| >
| > System.Diagnostics.Trace.WriteLine(c.GetViewState().Count);
| > this.ClearChildViewState(); // Why does this have no effect?
| > System.Diagnostics.Trace.WriteLine(c.GetViewState().Count);
| >
| > if (this.Button1.Text == "Hide")
| > {
| > this.Button1.Text = "Show";
| > this.TextBox1.Visible = false;
| >
| > if (this.TextBox1.Text.Length > 0)
| > this.Label1.Text = this.TextBox1.Text;
| > }
| > else // "Show"
| > {
| > this.Button1.Text = "Hide";
| > this.TextBox1.Visible = true;
| > }
| > }
| > }
| > }
| >
| > using System;
| > using System.Web.UI;
| >
| > namespace WebTest
| > {
| > public class TextBox : System.Web.UI.WebControls.TextBox
| > {
| > protected override object SaveViewState()
| > {
| > object vs = null;
| >
| > vs = base.SaveViewState ();
| >
| > return vs;
| > }
| >
| > protected override void LoadViewState(object savedState)
| > {
| > base.LoadViewState (savedState);
| > }
| >
| > public StateBag GetViewState()
| > {
| > return this.ViewState;
| > }
| > }
| > }
| >
| >
|
|
|
 
G

Guest

Hi,

I see. The examples in ASP.NET Developing Server Controls & Components
implement properties that persist via view state in the following way:

public string Action
{
get
{
string action = (string)(ViewState["Action"]);
return action == null ? String.Empty : action;
}
set
{
ViewState["Action"] = value;
}
}

So I assumed that I would be able to reset the state that a control persists
via view state by clearing view state, even in a click event (which I
understand fires after view state has been restored).

However, I guess most controls must do things differently; perhaps they do
something like:

private string action;

public string Action
{
get { return this.action; }
set { this.action = value; }
}

protected override object SaveViewState()
{
return this.action;
}

protected override void LoadViewState(object savedState)
{
this.action = (string)savedState;
}

Which would explain what's going on.

So going back to my original problem, it looks like I will have to reset my
form manually, as you suggest, by resetting the object properties that I care
about. That's more code - and code that has to remain in sync with the
controls on the page - but if there's no "reset my controls" silver bullet,
then I guess I have no choice.

Thanks,
- Lee
 
S

Steven Cheng[MSFT]

Thanks for the followup Lee,

Yes, manually clear all the entry fields controls may cause the page code
become tight-coupled, but it'll be the most efficient way. Also, if you
want to make it more flexible, we can use the FindControl method to find
all the enty fields controls thorugh the control ID and reset their text
property, but this will be much less efficient.

Thanks,

Steven Cheng
Microsoft Online Support

Get Secure! www.microsoft.com/security
(This posting is provided "AS IS", with no warranties, and confers no
rights.)
--------------------
| Thread-Topic: How to perform server-side form reset?
| thread-index: AcWpW6aq6sDuDiD+SgiDrP/xnnn3Lw==
| X-WBNR-Posting-Host: 194.200.242.250
| From: "=?Utf-8?B?TGVlIENoYXBtYW4=?=" <[email protected]>
| References: <[email protected]>
<#[email protected]>
<[email protected]>
| Subject: Re: How to perform server-side form reset?
| Date: Thu, 25 Aug 2005 02:59:15 -0700
| Lines: 253
| Message-ID: <[email protected]>
| MIME-Version: 1.0
| Content-Type: text/plain;
| charset="Utf-8"
| Content-Transfer-Encoding: 7bit
| X-Newsreader: Microsoft CDO for Windows 2000
| Content-Class: urn:content-classes:message
| Importance: normal
| Priority: normal
| X-MimeOLE: Produced By Microsoft MimeOLE V6.00.3790.0
| Newsgroups: microsoft.public.dotnet.framework.aspnet
| NNTP-Posting-Host: TK2MSFTNGXA03.phx.gbl 10.40.2.250
| Path: TK2MSFTNGXA01.phx.gbl!TK2MSFTNGXA03.phx.gbl
| Xref: TK2MSFTNGXA01.phx.gbl
microsoft.public.dotnet.framework.aspnet:120205
| X-Tomcat-NG: microsoft.public.dotnet.framework.aspnet
|
|
| Hi,
|
| I see. The examples in ASP.NET Developing Server Controls & Components
| implement properties that persist via view state in the following way:
|
| public string Action
| {
| get
| {
| string action = (string)(ViewState["Action"]);
| return action == null ? String.Empty : action;
| }
| set
| {
| ViewState["Action"] = value;
| }
| }
|
| So I assumed that I would be able to reset the state that a control
persists
| via view state by clearing view state, even in a click event (which I
| understand fires after view state has been restored).
|
| However, I guess most controls must do things differently; perhaps they
do
| something like:
|
| private string action;
|
| public string Action
| {
| get { return this.action; }
| set { this.action = value; }
| }
|
| protected override object SaveViewState()
| {
| return this.action;
| }
|
| protected override void LoadViewState(object savedState)
| {
| this.action = (string)savedState;
| }
|
| Which would explain what's going on.
|
| So going back to my original problem, it looks like I will have to reset
my
| form manually, as you suggest, by resetting the object properties that I
care
| about. That's more code - and code that has to remain in sync with the
| controls on the page - but if there's no "reset my controls" silver
bullet,
| then I guess I have no choice.
|
| Thanks,
| - Lee
|
|
| "Steven Cheng[MSFT]" wrote:
|
| > Thanks for Bruce's informative inputs,
| >
| > Hi Lee,
| >
| > As Bruce has mentioned, the LoadViewState is getting executed before
Load
| > event for controls/page , after that the propertes value is assigned to
the
| > Control/page instance, and these properteis will be persisted into
| > viewstate again before Rendering. So change the ViewState in PostBack
event
| > handler ( After Load ViewSate before save viewstate) won't have any
effect.
| > also, IMO, I'd recommend you directly clear those entry fields
control's
| > content through the instance properties rather than accessing the
ViewState
| > collection.
| >
| > Thanks,
| >
| > Steven Cheng
| > Microsoft Online Support
| >
| > Get Secure! www.microsoft.com/security
| > (This posting is provided "AS IS", with no warranties, and confers no
| > rights.)
| > --------------------
| > | From: "Bruce Barker" <[email protected]>
| > | References: <[email protected]>
| > | Subject: Re: How to perform server-side form reset?
| > | Date: Wed, 24 Aug 2005 09:01:14 -0700
| > | Lines: 148
| > | X-Priority: 3
| > | X-MSMail-Priority: Normal
| > | X-Newsreader: Microsoft Outlook Express 6.00.2900.2180
| > | X-RFC2646: Format=Flowed; Original
| > | X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180
| > | Message-ID: <#[email protected]>
| > | Newsgroups: microsoft.public.dotnet.framework.aspnet
| > | NNTP-Posting-Host: rdcsd1.safeco.com 12.144.134.2
| > | Path: TK2MSFTNGXA01.phx.gbl!TK2MSFTNGP08.phx.gbl!TK2MSFTNGP10.phx.gbl
| > | Xref: TK2MSFTNGXA01.phx.gbl
| > microsoft.public.dotnet.framework.aspnet:119990
| > | X-Tomcat-NG: microsoft.public.dotnet.framework.aspnet
| > |
| > | because the click event fires long after the textbox has feteched its
| > value
| > | from viewstate.
| > |
| > | -- bruce (sqlwork.com)
| > |
| > |
| > | | > | >
| > | > Hi,
| > | >
| > | > Can anyone tell me why in the code below, the call to
| > | > ClearChildViewState()
| > | > has no effect?
| > | >
| > | > To paraphrase the code: I'm using view state. I have a textbox and
a
| > | > submit
| > | > button (and a label that can be ignored). When I press the button
the
| > | > first
| > | > time, the click handler hides the textbox. Pressing the button a
second
| > | > time
| > | > unhides the textbox. The text box is maintaining its value when
hidden
| > via
| > | > view state. (The value is NOT being populated due to postback
data.) I
| > | > want a
| > | > server-side function to reset a form to it's initial state (i.e.
the
| > state
| > | > it
| > | > was in when I first browsed to it). I expected
| > Page.ClearChildViewState()
| > | > to
| > | > do this, but it doesn't. Why not? And what can I do to reset my
form on
| > | > the
| > | > server without disabling viewstate?
| > | >
| > | > Thanks,
| > | > - Lee
| > | >
| > | > <%@ Page language="c#" Codebehind="WebForm1.aspx.cs"
| > | > AutoEventWireup="false"
| > | > Inherits="WebTest.WebForm1" EnableViewState="true" %>
| > | > <%@ Register TagPrefix="My" Namespace="WebTest" Assembly="WebTest"
%>
| > | > <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
| > | > <HTML>
| > | > <HEAD>
| > | > <title>WebForm1</title>
| > | > </HEAD>
| > | > <body >
| > | > <form id="Form1" method="post" runat="server">
| > | > <My:TextBox id="TextBox1" runat="server"
| > | > EnableViewState="true"></My:TextBox>
| > | > <asp:Button id="Button1" runat="server" Text="Hide"></asp:Button>
| > | > <p><asp:Label id="Label1" runat="server"></asp:Label></p>
| > | > </form>
| > | > </body>
| > | > </HTML>
| > | >
| > | > using System;
| > | > using System.Collections;
| > | > using System.ComponentModel;
| > | > using System.Data;
| > | > using System.Drawing;
| > | > using System.Web;
| > | > using System.Web.SessionState;
| > | > using System.Web.UI;
| > | > using System.Web.UI.WebControls;
| > | > using System.Web.UI.HtmlControls;
| > | >
| > | > namespace WebTest
| > | > {
| > | > /// <summary>
| > | > /// Summary description for WebForm1.
| > | > /// </summary>
| > | > public class WebForm1 : System.Web.UI.Page
| > | > {
| > | > protected System.Web.UI.WebControls.Button Button1;
| > | > protected System.Web.UI.WebControls.Label Label1;
| > | > protected System.Web.UI.WebControls.TextBox TextBox1;
| > | >
| > | > #region Web Form Designer generated code
| > | > override protected void OnInit(EventArgs e)
| > | > {
| > | > InitializeComponent();
| > | > base.OnInit(e);
| > | > }
| > | >
| > | > private void InitializeComponent()
| > | > {
| > | > this.Button1.Click += new System.EventHandler(this.Button1_Click);
| > | > }
| > | > #endregion
| > | >
| > | > private void Button1_Click(object sender, System.EventArgs e)
| > | > {
| > | > if (!this.IsTrackingViewState)
| > | > throw new ApplicationException();
| > | >
| > | > WebTest.TextBox c = (WebTest.TextBox)this.FindControl("TextBox1");
| > | >
| > | > System.Diagnostics.Trace.WriteLine(c.GetViewState().Count);
| > | > this.ClearChildViewState(); // Why does this have no effect?
| > | > System.Diagnostics.Trace.WriteLine(c.GetViewState().Count);
| > | >
| > | > if (this.Button1.Text == "Hide")
| > | > {
| > | > this.Button1.Text = "Show";
| > | > this.TextBox1.Visible = false;
| > | >
| > | > if (this.TextBox1.Text.Length > 0)
| > | > this.Label1.Text = this.TextBox1.Text;
| > | > }
| > | > else // "Show"
| > | > {
| > | > this.Button1.Text = "Hide";
| > | > this.TextBox1.Visible = true;
| > | > }
| > | > }
| > | > }
| > | > }
| > | >
| > | > using System;
| > | > using System.Web.UI;
| > | >
| > | > namespace WebTest
| > | > {
| > | > public class TextBox : System.Web.UI.WebControls.TextBox
| > | > {
| > | > protected override object SaveViewState()
| > | > {
| > | > object vs = null;
| > | >
| > | > vs = base.SaveViewState ();
| > | >
| > | > return vs;
| > | > }
| > | >
| > | > protected override void LoadViewState(object savedState)
| > | > {
| > | > base.LoadViewState (savedState);
| > | > }
| > | >
| > | > public StateBag GetViewState()
| > | > {
| > | > return this.ViewState;
| > | > }
| > | > }
| > | > }
| > | >
| > | >
| > |
| > |
| > |
| >
| >
|
 

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