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Selection Drag Drop

RadSyntaxEditor allows the end-users to drag the selection and drop it onto another position in the loaded document. The SyntaxEditorElement.Selection exposes several events that allow you to control the drag and drop operation:

  • PreviewDragStart - Occurs when selection dragging is about to be started. The PreviewDragStartEventArgs offers the CanStart and StartPosition arguments. If the drag operation is not allowed, setting the CanStart argument to false indicates that the drag operation won't be started at all. The StartPostion returns the CaretPosition from which the drag operation will start. The start position is always within the current selection.

  • PreviewDragOver - Occurs upon moving the selection over the document. The PreviewDragOverEventArgs offers the following arguments:

    • CanDrop - Determines whether the selection can be dropped. This property is taken into consideration when changing the mouse cursor. If it is not allowed to drop the selection being dragged, set the CanDrop property to false.
    • StartPostion - The CaretPosition at which the drag operation has been start. The start position is always within the current selection.
    • DropPosition - The CaretPosition at which the selection is being dragged over.
  • PreviewDragDrop - Occurs upon releasing the mouse and dropping the selection. The PreviewDragDropEventArgs offers the following arguments:

    • Handled - Determines whether the event is handled. If the property is set to true, the selection will not be moved to the dragged position.
    • DropPosition - The CaretPosition at which the selection will be dropped.
    • StartPostion - The CaretPosition at which the drag operation has been started. The start position is always within the current selection.

Handling drag and drop events

        private void WireEvents()
            this.radSyntaxEditor1.SyntaxEditorElement.Selection.PreviewDragStart += Selection_PreviewDragStart;
            this.radSyntaxEditor1.SyntaxEditorElement.Selection.PreviewDragOver += Selection_PreviewDragOver;
            this.radSyntaxEditor1.SyntaxEditorElement.Selection.PreviewDragDrop += Selection_PreviewDragDrop;

        private void Selection_PreviewDragStart(object sender, Telerik.WinForms.Controls.SyntaxEditor.UI.PreviewDragStartEventArgs e)
            //disable dragging the even lines

            e.CanStart &= (e.StartPostion.LineNumber + 1) % 2 != 0;

        private void Selection_PreviewDragOver(object sender, Telerik.WinForms.Controls.SyntaxEditor.UI.PreviewDragOverEventArgs e)
            //disable dropping over a text that contains "Telerik"

            CaretPosition start = new CaretPosition(e.DropPosition);
            CaretPosition end = new CaretPosition(start);
            string targetText = this.radSyntaxEditor1.SyntaxEditorElement.GetText(start, end);
            if (targetText.Contains("Telerik"))
                e.CanDrop = false;
                e.CanDrop = true;

        private void Selection_PreviewDragDrop(object sender, Telerik.WinForms.Controls.SyntaxEditor.UI.PreviewDragDropEventArgs e)
            //handle the drop operation
            e.Handled = true;

    Private Sub WireEvents()
        AddHandler Me.radSyntaxEditor1.SyntaxEditorElement.Selection.PreviewDragStart, AddressOf Selection_PreviewDragStart
        AddHandler Me.radSyntaxEditor1.SyntaxEditorElement.Selection.PreviewDragOver, AddressOf Selection_PreviewDragOver
        AddHandler Me.radSyntaxEditor1.SyntaxEditorElement.Selection.PreviewDragDrop, AddressOf Selection_PreviewDragDrop
    End Sub

    Private Sub Selection_PreviewDragStart(ByVal sender As Object, ByVal e As Telerik.WinForms.Controls.SyntaxEditor.UI.PreviewDragStartEventArgs)
        e.CanStart = e.CanStart And (e.StartPostion.LineNumber + 1) Mod 2 <> 0
    End Sub

    Private Sub Selection_PreviewDragOver(ByVal sender As Object, ByVal e As Telerik.WinForms.Controls.SyntaxEditor.UI.PreviewDragOverEventArgs)
        Dim start As CaretPosition = New CaretPosition(e.DropPosition)
        Dim [end] As CaretPosition = New CaretPosition(start)
        Dim targetText As String = Me.radSyntaxEditor1.SyntaxEditorElement.GetText(start, [end])

        If targetText.Contains("Telerik") Then
            e.CanDrop = False
            e.CanDrop = True
        End If
    End Sub

    Private Sub Selection_PreviewDragDrop(ByVal sender As Object, ByVal e As Telerik.WinForms.Controls.SyntaxEditor.UI.PreviewDragDropEventArgs)
        e.Handled = True
    End Sub

Disable dropping over "Telerik"

WinForms RadSyntaxEditor Disable dropping over Telerik

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