HierarchicalDataBoundControl.PerformDataBinding Method ()

 

When overridden in a derived class, binds data from the data source to the control.

Namespace:   System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)

Protected Friend Overridable Sub PerformDataBinding

Implement this method instead of the DataBind method when you derive a data-bound control from the HierarchicalDataBoundControl class. Placing your control's data-binding logic in PerformDataBinding keeps the DataBinding and DataBound events from being raised in the wrong order.

While the base HierarchicalDataBoundControl class provides no specific implementation for this method, the PerformDataBinding method is called by the PerformSelect method to bind the values of any user interface controls to the data that is retrieved by the PerformSelect method.

The following code example demonstrates how to implement the PerformDataBinding method in a class derived from HierarchicalDataBoundControl. The GeneologyTree control iterates through the IHierarchicalEnumerable and IHierarchyData objects retrieved from its associated HierarchicalDataSourceView, and creates a text tree structure for the data it is bound to. This code example is part of a larger example provided for the HierarchicalDataBoundControl class.

Protected Overrides Sub PerformDataBinding()
    MyBase.PerformDataBinding()

    ' Do not attempt to bind data if there is no
    ' data source set.
    If Not IsBoundUsingDataSourceID AndAlso DataSource Is Nothing Then
        Return
    End If

    Dim view As HierarchicalDataSourceView = GetData(RootNode.DataPath)

    If view Is Nothing Then
        Throw New InvalidOperationException _
        ("No view returned by data source control.")
    End If

    Dim enumerable As IHierarchicalEnumerable = view.Select()
    If Not (enumerable Is Nothing) Then

        Nodes.Clear()

        Try
            RecurseDataBindInternal(RootNode, enumerable, 1)
        Finally
        End Try
    End If

End Sub ' PerformDataBinding

Private Sub RecurseDataBindInternal(ByVal node As TreeNode, _
    ByVal enumerable As IHierarchicalEnumerable, _
    ByVal depth As Integer)

    Dim item As Object
    For Each item In enumerable

        Dim data As IHierarchyData = enumerable.GetHierarchyData(item)

        If Not data Is Nothing Then

            ' Create an object that represents the bound data
            ' to the control.
            Dim newNode As New TreeNode()
            Dim rvnode As New RootViewNode()

            rvnode.Node = newNode
            rvnode.Depth = depth

            ' The dataItem is not just a string, but potentially
            ' an XML node or some other container. 
            ' If DataTextField is set, use it to determine which 
            ' field to render. Otherwise, use the first field.                    
            If DataTextField.Length > 0 Then
                newNode.Text = DataBinder.GetPropertyValue _
                (data, DataTextField, Nothing)
            Else
                Dim props As PropertyDescriptorCollection = _
                TypeDescriptor.GetProperties(data)

                ' Set the "default" value of the node.
                newNode.Text = String.Empty

                ' Set the true data-bound value of the TextBox,
                ' if possible.
                If props.Count >= 1 Then
                    If Not props(0).GetValue(data) Is Nothing Then
                        newNode.Text = props(0).GetValue(data).ToString()
                    End If
                End If
            End If

            Nodes.Add(rvnode)

            If data.HasChildren Then
                Dim newEnumerable As IHierarchicalEnumerable = _
                    data.GetChildren()
                If Not (newEnumerable Is Nothing) Then
                    RecurseDataBindInternal(newNode, _
                    newEnumerable, depth + 1)
                End If
            End If

            If MaxDepth < depth Then
                MaxDepth = depth
            End If
        End If
    Next item

End Sub 'RecurseDataBindInternal

.NET Framework
Available since 2.0
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