HierarchicalDataBoundControl.PerformDataBinding Methode

Definition

Bindet beim Überschreiben in einer abgeleiteten Klasse Daten aus der Datenquelle an das Steuerelement.When overridden in a derived class, binds data from the data source to the control.

protected public:
 virtual void PerformDataBinding();
protected internal virtual void PerformDataBinding ();
abstract member PerformDataBinding : unit -> unit
override this.PerformDataBinding : unit -> unit
Protected Friend Overridable Sub PerformDataBinding ()

Beispiele

Im folgenden Codebeispiel wird veranschaulicht, wie die PerformDataBinding -Methode in einer von HierarchicalDataBoundControlabgeleiteten Klasse implementiert wird.The following code example demonstrates how to implement the PerformDataBinding method in a class derived from HierarchicalDataBoundControl. Das GeneologyTree -Steuerelement durchläuft IHierarchicalEnumerable die IHierarchyData -Objekte und-Objekte HierarchicalDataSourceView, die aus der zugeordneten abgerufen wurden, und erstellt eine Text Struktur für die Daten, an die es gebunden ist.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. Dieses Codebeispiel ist Teil eines größeren Beispiels, das für die HierarchicalDataBoundControl -Klasse bereitgestellt wird.This code example is part of a larger example provided for the HierarchicalDataBoundControl class.

protected override void PerformDataBinding() {
    base.PerformDataBinding();

    // Do not attempt to bind data if there is no
    // data source set.
    if (!IsBoundUsingDataSourceID && (DataSource == null)) {
        return;
    }
    
    HierarchicalDataSourceView view = GetData(RootNode.DataPath);
    
    if (view == null) {
        throw new InvalidOperationException
            ("No view returned by data source control.");
    }                                  
    
    IHierarchicalEnumerable enumerable = view.Select();
    if (enumerable != null) {
                    
        Nodes.Clear();
                        
        try {
            RecurseDataBindInternal(RootNode, enumerable, 1);
        }
        finally {
        
        }
    }
}
private void RecurseDataBindInternal(TreeNode node, 
    IHierarchicalEnumerable enumerable, int depth) {                                    
                
    foreach(object item in enumerable) {
        IHierarchyData data = enumerable.GetHierarchyData(item);

        if (null != data) {
            // Create an object that represents the bound data
            // to the control.
            TreeNode newNode = new TreeNode();
            RootViewNode rvnode = 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) {
                newNode.Text = DataBinder.GetPropertyValue
                    (data, DataTextField, null);
            }
            else {
                PropertyDescriptorCollection props = 
                    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) {                        
                    if (null != props[0].GetValue(data)) {
                        newNode.Text = 
                            props[0].GetValue(data).ToString();
                    } 
                }
            }

            Nodes.Add(rvnode);                    
            
            if (data.HasChildren) {
                IHierarchicalEnumerable newEnumerable = 
                    data.GetChildren();
                if (newEnumerable != null) {                            
                    RecurseDataBindInternal(newNode, 
                        newEnumerable, depth+1 );
                }
            }
            
            if ( _maxDepth < depth) _maxDepth = depth;
            
        }
    }
}
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

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

Hinweise

Implementieren Sie diese Methode anstelle der DataBind -Methode, wenn Sie ein Daten gebundenes Steuerelement HierarchicalDataBoundControl von der-Klasse ableiten.Implement this method instead of the DataBind method when you derive a data-bound control from the HierarchicalDataBoundControl class. Wenn Sie die Daten Bindungs Logik Ihres Steuer Elements PerformDataBinding in platzieren DataBinding , DataBound werden das-Ereignis und das-Ereignis nicht in der falschen Reihenfolge ausgelöst.Placing your control's data-binding logic in PerformDataBinding keeps the DataBinding and DataBound events from being raised in the wrong order.

Obwohl die- HierarchicalDataBoundControl Basisklasse keine spezifische Implementierung für diese Methode bereitstellt PerformDataBinding , wird die-Methode PerformSelect von der-Methode aufgerufen, um die Werte aller Benutzeroberflächen Steuerelemente an die Daten zu PerformSelect binden, die von der-Methode abgerufen werden.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.

Gilt für: