[转]Maintain Control State in ASP.NET 2.0

最新推荐文章于 2025-08-22 19:33:51 发布

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原文链接：http://www.cnblogs.com/pfengk/articles/529927.html

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本文介绍了一种在 ASP.NET 2.0 自定义 Web 控件中维护控件状态的简单方法。控件状态是视图状态的一种形式，但具有明显优势：使用控件的开发人员无法禁用它。

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[转自 http://www.vbdotnetheaven.com]
Maintain Control State in ASP.NET 2.0
By Scott Lysle September 15, 2006

This article describes a simple approach to maintaining control state in an ASP.NET 2.0 custom web control. Control state is a new construct within ASP.NET 2.0 and it is really nothing more than view state however it is view state with a significant advantage; that advantage is that other developers using your control cannot disable control state as they can view state.

Introduction:

Control state survives even if the developer using the custom control disables view state. The advantage is pretty obvious; in prior versions of Visual Studio, the consumer of a custom control could disable view state; if the control relied on view state to maintain state information, the control would cease to function or at least misbehave. Creating control state removed the ability of a control consumer to disable view state based state management within the control; naturally the control designer may still opt to not use either view state or control state based state management.

One final note, most of the examples I have personally viewed regarding control state show a mechanization in which only one value is stored in the control state; the accompanying example herein shows how store a greater number of values of different data types can be easily stored in the control state.

Getting Started:

In order to get started, open up the Visual Studio 2005 IDE and start a new project. From the new project dialog (Figure 1), under project types, select the "Windows" node from beneath "Visual Basic", then select the "Web Control Library" template in the right hand pane. Key in a name for the project and then click "OK".

Once the project has opened; right click on the solution and click on the "Add" menu option, and then select "New Item". When the "Add New Item" dialog appears (Figure 2), select the "Web Custom Control" template, after selecting the template, key "ExampleStateControl.vb" into the name field and then click "Add" to close the dialog. You may now delete the default web control that was created when the project was originally initialized from the template.

At this point, we should have an open web control library project with a single web control named "ExampleStateControl.vb" in that project.

One last step prior to writing the code for this project will be to validate the references and import statements. Compare your import statements with this list and make any adjustments necessary:

Imports System<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Imports System.ComponentModel

Imports System.Web

Imports System.Web.UI

Imports System.Web.UI.WebControls

Figure 1: Visual Studio 2005 New Project Dialog

Figure 2: Add New Item Dialog

We are now ready to add the code necessary to make this control functional. At this point, the project's code should look something like this:

Imports System

Imports System.ComponentModel

Imports System.Web

Imports System.Web.UI

Imports System.Web.UI.WebControls

<Serializable()>_

<ToolboxData("<{0}:ExampleStateControl runat=server></{0}:ExampleStateControl>")>_

Public Class ExampleStateControl

Inherits WebControl

If we are in sync here, we can now start to write the necessary code. To begin, create a declarations region and add the following code to that region:

#Region "Declarations"

Private mCurrentProps As New CurrentProperties

<Serializable()> _

Private Structure CurrentProperties

Dim pFirstName As String

Dim pLastName As String

Dim pAge As Integer

Dim pCity As String

Dim pState As String

Dim pCountry As String

Dim pCitizen As Boolean

End Structure

#End Region

In examing the declarations, note that there is a structure called CurrentProperties defined and there is a private member variable declared (mCurrentProps) that is of the CurrentProperties structure type. This instance of the structure is what we will be putting into and collecting out of control state.

The next thing to do will be to add the properties necessary to support the example custom web control. There is one property for each element contained in the structure. To accomplish this task, create a properties region and add in the following code:

#Region "Properties"

<Browsable(True)>_

<Category("Name")>_

<DefaultValue("")>_

<Localizable(True)>_

<NotifyParentProperty(True)>_

Public Property FirstName() As String

Get

Return mCurrentProps.pFirstName

End Get

Set(ByVal value As String)

mCurrentProps.pFirstName = value

SaveControlState()

End Set

End Property

<Browsable(True)>_

<Category("Name")>_

<DefaultValue("")>_

<Localizable(True)>_

<NotifyParentProperty(True)>_

Public Property LastName() As String

Get

Return mCurrentProps.pLastName

End Get

Set(ByVal value As String)

mCurrentProps.pLastName = value

SaveControlState()

End Set

End Property

<Browsable(True)>_

<Category("Status")>_

<DefaultValue("")>_

<Localizable(True)>_

<NotifyParentProperty(True)>_

Public Property Age() As Integer

Get

Return mCurrentProps.pAge

End Get

Set(ByVal value As Integer)

mCurrentProps.pAge = value

SaveControlState()

End Set

End Property

<Browsable(True)>_

<Category("Status")>_

<DefaultValue("")>_

<Localizable(True)>_

<NotifyParentProperty(True)>_

Public Property IsCitizen() As Boolean

Get

Return mCurrentProps.pCitizen

End Get

Set(ByVal value As Boolean)

mCurrentProps.pCitizen = value

SaveControlState()

End Set

End Property

<Browsable(True)>_

<Category("Residence")>_

<DefaultValue("")>_

<Localizable(True)>_

<NotifyParentProperty(True)>_

<?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />PublicPropertyCity() As String

Get

Return mCurrentProps.pCity

End Get

Set(ByVal value As String)

mCurrentProps.pCity = value

SaveControlState()

End Set

End Property

<Browsable(True)>_

<Category("Residence")>_

<DefaultValue("")>_

<Localizable(True)>_

<NotifyParentProperty(True)>_

PublicPropertyState() As String

Get

Return mCurrentProps.pState

End Get

Set(ByVal value As String)

mCurrentProps.pState = value

SaveControlState()

End Set

End Property

<Browsable(True)>_

<Category("Residence")>_

<DefaultValue("")>_

<Localizable(True)>_

<NotifyParentProperty(True)>_

Public Property Country() As String

Get

Return mCurrentProps.pCountry

End Get

Set(ByVal value As String)

mCurrentProps.pCountry = value

SaveControlState()

End Set

End Property

#End Region

Note that each property's get and set methods either updates or retrieves from the active instance of the "ControlProps" structure. No other private member variables are used to retain each of the property's current values.

The next step in the process is to add in the methods used by the control. Add a Methods region to the code page and key in the following methods:

#Region "Methods"

Protected Overrides Sub OnInit(ByVal e As System.EventArgs)

Page.RegisterRequiresControlState(Me)

MyBase.OnInit(e)

End Sub

Protected Overrides Function SaveControlState() As Object

Return Me.mCurrentProps

End Function

Protected Overrides Sub LoadControlState(ByVal savedState As Object)

mCurrentProps = New CurrentProperties

mCurrentProps = CType(savedState, CurrentProperties)

End Sub

#End Region

Notice that in the init, the first line is used to instruct the page to maintain control state. The next two methods are used to save the current control state or to reload the control states values from the saved control state.

At this point, the only thing left to do is to define how the control will be rendered. To complete this step, create a "Rendering" region and, within this region, override the RenderContents sub with the following code:

#Region "Rendering"

Protected Overrides Sub RenderContents(ByVal writer As

System.Web.UI.HtmlTextWriter)

Try

writer.RenderBeginTag(HtmlTextWriterTag.Table)

writer.Write("<b>Control State Properties</b><hr />")

'''''''''''''''''''''''''''''''''''''''''''''

writer.RenderBeginTag(HtmlTextWriterTag.Tr)