笔记：asp.net自定义控件的视图状态管理

写了一段时间的asp.net代码后，对于asp.net自定义控件多了一份了解！重新看回以前有些模糊的自定义视图状态管理

在一个控件的复杂自定义属性中，此属性的状态可以由两种方法进行保存，但比较好的状态保存方法还是实现自定义视图管理，让其实现IStateManager接口

例如：

      MyAddress控件MyControl的一个方法，存储省份，城市，地区三个字符串值

第一种方法是

      声明对象可序列化，然后在控件里重载视图管理方法LoadViewState,SaveViewState

      在其中添加状态管理状态：

      Protected Overrides Function SaveViewState() As Object
          Dim o1 As Object = MyBase.SaveViewState()

  Dim p As New Pair(o1, Me.Address)

  Return p
 End Function

 Protected Overrides Sub LoadViewState(ByVal savedState As Object)

  Try
   Dim p As Pair = CType(savedState, Pair)
   MyBase.LoadViewState(p.First)
   Me._address = CType(p.Second, MyAddress)
  Catch ex As Exception
   MyBase.LoadViewState(savedState)
  End Try
 End Sub

      此方法也能维持视图状态，但结果是因为完整保存了该属性完全的序列化结果，而导致页面视图大小急剧膨胀

第二个方法是对MyAddress实现视图接口IStateManager

<TypeConverter(GetType(ExpandableObjectConverter))> _
Public Class MyAddress
 Implements IStateManager

并实现其视图管理方法

#Region "视图状态"
 Private _viewstate As StateBag

 Protected Property ViewState() As StateBag
  Get
   If _viewstate Is Nothing Then
    _viewstate = New StateBag
    If Me.IsTrackingViewState Then
     CType(_viewstate, IStateManager).TrackViewState()
    End If
   End If
   Return _viewstate
  End Get
  Set(ByVal value As StateBag)
   _viewstate = value
  End Set
 End Property

 Private _IsTrackingViewState As Boolean = False
 Protected ReadOnly Property IsTrackingViewState() As Boolean Implements System.Web.UI.IStateManager.IsTrackingViewState
  Get
   Return _IsTrackingViewState
  End Get
 End Property

 Public Sub LoadViewState(ByVal state As Object) Implements System.Web.UI.IStateManager.LoadViewState
  If state IsNot Nothing Then
   CType(_viewstate, IStateManager).LoadViewState(state)
  End If
 End Sub

 Public Function SaveViewState() As Object Implements System.Web.UI.IStateManager.SaveViewState
  Dim _savestate As Object = Nothing
  If _viewstate IsNot Nothing Then
   _savestate = CType(_viewstate, IStateManager).SaveViewState()
  End If
  Return _savestate
 End Function

 Public Sub TrackViewState() Implements System.Web.UI.IStateManager.TrackViewState
  _IsTrackingViewState = True
  If _viewstate IsNot Nothing Then
   CType(_viewstate, IStateManager).TrackViewState()
  End If
 End Sub

 Protected Sub SetDirty()
  _viewstate.SetDirty(True)
 End Sub
#End Region

然后在MyControl中添加Address属性状态的跟踪与维持代码

 Private _address As MyAddress
 <DesignerSerializationVisibility(DesignerSerializationVisibility.Content)> _
 <PersistenceMode(PersistenceMode.InnerProperty)> _
 <Browsable(True)> _
 Public ReadOnly Property Address() As MyAddress
  Get
   If _address Is Nothing Then
    _address = New MyAddress
    If Me.IsTrackingViewState Then
     CType(_address, IStateManager).TrackViewState()
    End If
   End If

   Return _address
  End Get
 End Property

#Region "视图状态管理"
 Protected Overrides Sub TrackViewState()
  If Me.Address IsNot Nothing Then
   CType(Me.Address, IStateManager).TrackViewState()
  End If
  MyBase.TrackViewState()
 End Sub

 Protected Overrides Sub LoadViewState(ByVal savedState As Object)
  Dim p As Pair = TryCast(savedState, Pair)
  If p IsNot Nothing Then
   MyBase.LoadViewState(p.First)
   CType(Me.Address, IStateManager).LoadViewState(p.Second)
   Return
  End If
  MyBase.LoadViewState(savedState)
 End Sub

 Protected Overrides Function SaveViewState() As Object
  Dim baseobj As Object = MyBase.SaveViewState
  Dim addobj As Object = Nothing
  If Me.Address IsNot Nothing Then
   addobj = CType(Me.Address, IStateManager).SaveViewState()
  End If
  If addobj IsNot Nothing Then
   Return New Pair(baseobj, addobj)
  Else
   Return MyBase.SaveViewState()
  End If

 End Function
#End Region