HierarchicalDataBoundControl.PerformDataBinding Metodo

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 ()

Esempio

Nell'esempio di codice seguente viene illustrato come implementare il PerformDataBinding metodo in una classe derivata da HierarchicalDataBoundControl. Il GeneologyTree controllo esegue l'iterazione IHierarchicalEnumerable degli oggetti e recuperati dal relativo oggetto associato IHierarchyData e crea una struttura ad albero di testo per i dati a cui è associato HierarchicalDataSourceView. Questo esempio di codice fa parte di un esempio più grande fornito per la HierarchicalDataBoundControl classe.

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

Commenti

Implementare questo metodo anziché il DataBind metodo quando si deriva un controllo associato a dati dalla HierarchicalDataBoundControl classe. L'inserimento della logica PerformDataBinding di data binding del controllo consente di mantenere gli DataBinding eventi e DataBound generati nell'ordine errato.

Anche se la classe base HierarchicalDataBoundControl non fornisce alcuna implementazione specifica per questo metodo, il PerformDataBinding metodo viene chiamato dal PerformSelect metodo per associare i valori di tutti i controlli dell'interfaccia utente ai dati recuperati dal PerformSelect metodo .

Si applica a