controlvalidator.vb

讲解visual studio的应用

Imports System.ComponentModel
Imports System.Drawing.Design

<ProvideProperty("Validate", GetType(Control))> _
Public Class ControlValidator
    Inherits Component
    Implements IExtenderProvider

#Region "Rules Validator"
    Private Structure Validator
        Public Rule As Predicate(Of IRulesList.RuleParams)
        Public Information As ValidationAttribute
        Public Sub New(ByVal r As Predicate(Of IRulesList.RuleParams), _
                       ByVal info As ValidationAttribute)
            Me.Rule = r
            Me.Information = info
        End Sub
    End Structure
#End Region


    Private m_ErrorProvider As ErrorProvider
    Private rulesHash As New Dictionary(Of String, Validator)
    Public controlHash As New Dictionary(Of Control, Boolean)

    Public Sub New(ByVal container As IContainer)
        MyBase.New()
        container.Add(Me)
    End Sub


#Region "Error provider and Rules"

    Public Property ErrorProvider() As ErrorProvider
        Get
            Return m_ErrorProvider
        End Get
        Set(ByVal value As ErrorProvider)
            m_ErrorProvider = value
        End Set
    End Property


    Public Sub AddRules(ByVal ruleslist As IRulesList)
        For Each rule As Predicate(Of IRulesList.RuleParams) In ruleslist.Rules
            Dim attributes As ValidationAttribute() = _
                            TryCast(rule.Method.GetCustomAttributes _
                                            (GetType(ValidationAttribute), True), _
                                                             ValidationAttribute())
            If Not attributes Is Nothing Then
                For Each attrib As ValidationAttribute In attributes
                    rulesHash.Add(attrib.ColumnName.ToLower, _
                                                       New Validator(rule, attrib))
                Next
            End If
        Next
    End Sub
#End Region

#Region "Extender Provider to turn validation on"
    Public Function CanExtend(ByVal extendee As Object) As Boolean _
                       Implements System.ComponentModel.IExtenderProvider.CanExtend
        Return TypeOf (extendee) Is Control
    End Function

    Public Sub SetValidate(ByVal control As Control, _
                           ByVal shouldValidate As Boolean)
        If shouldValidate Then
            AddHandler control.Validating, AddressOf Validating
        End If
        controlHash.Item(control) = shouldValidate
    End Sub

    Public Function GetValidate(ByVal control As Control) As Boolean
        If controlHash.ContainsKey(control) Then
            Return controlHash.Item(control)
        End If
        Return False
    End Function
#End Region

#Region "Validation"
    Private ReadOnly Property ItemError(ByVal ctrl As Control) As String
        Get
            Try
                If ctrl.DataBindings.Count = 0 Then Return ""
                Dim key As String = ctrl.DataBindings.Item(0).BindingMemberInfo.BindingField
                Dim bs As BindingSource = TryCast(ctrl.DataBindings.Item(0).DataSource, BindingSource)
                If bs Is Nothing Then Return ""
                Dim drv As DataRowView = TryCast(bs.Current, DataRowView)
                If drv Is Nothing Then Return ""

                Dim valfield As String = ctrl.DataBindings.Item(0).PropertyName
                Dim val As Object = ctrl.GetType.GetProperty(valfield, _
                                             New Type() {}).GetValue(ctrl, Nothing)
                Return ItemError(drv, key, val)
            Catch ex As Exception
                Return ""
            End Try
        End Get
    End Property

    Private ReadOnly Property ItemError(ByVal drv As DataRowView, ByVal columnName As String, ByVal newValue As Object) As String
        Get
            columnName = columnName.ToLower
            If Not rulesHash.ContainsKey(columnName) Then Return ""
            Dim p As Validator = rulesHash.Item(columnName)
            If p.Rule Is Nothing Then Return ""
            If p.Rule(New IRulesList.RuleParams(drv.Row, newValue)) Then Return ""

            If p.Information Is Nothing Then Return ""
            Return p.Information.ErrorString
        End Get
    End Property

    Private Sub Validating(ByVal sender As Object, ByVal e As CancelEventArgs)
        Dim err As String = InternalValidate(sender)
        e.Cancel = Not (err = "")
    End Sub

    Private Function InternalValidate(ByVal sender As Object) As String
        If Me.m_ErrorProvider Is Nothing Then Return ""
        Dim ctrl As Control = TryCast(sender, Control)
        If ctrl Is Nothing Then Return ""
        If Not Me.controlHash.ContainsKey(ctrl) OrElse Not Me.controlHash.Item(ctrl) Then Return ""
        Dim err As String = Me.ItemError(ctrl)
        Me.m_ErrorProvider.SetError(ctrl, err)
        Return err
    End Function

    Private Sub ChangedItem(ByVal sender As Object, ByVal e As EventArgs)
        InternalValidate(sender)
    End Sub
#End Region

#Region "Validation Attribute"
    <AttributeUsage(AttributeTargets.Method)> _
    Public Class ValidationAttribute
        Inherits Attribute

        Private m_ColumnName As String
        Private m_ErrorString As String

        Public Sub New(ByVal columnName As String, ByVal errorString As String)
            Me.ColumnName = columnName
            Me.ErrorString = errorString
        End Sub

        Public Property ColumnName() As String
            Get
                Return m_ColumnName
            End Get
            Set(ByVal value As String)
                m_ColumnName = value
            End Set
        End Property

        Public Property ErrorString() As String
            Get
                Return m_ErrorString
            End Get
            Set(ByVal value As String)
                m_ErrorString = value
            End Set
        End Property
    End Class
#End Region

#Region "Rules Interface"
    Public Interface IRulesList

        Structure RuleParams
            Public ExistingData As DataRow
            Public NewData As Object
            Public Sub New(ByVal data As DataRow, ByVal newStuff As Object)
                Me.ExistingData = data
                Me.NewData = newStuff
            End Sub
        End Structure

        ReadOnly Property Rules() As Predicate(Of RuleParams)()

    End Interface
#End Region

End Class