HierarchicalDataBoundControl.PerformDataBinding Method ()
When overridden in a derived class, binds data from the data source to the control.
Assembly: System.Web (in System.Web.dll)
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
Available since 2.0