public event InteractiveActionExecutingEventHandler InteractiveActionExecuting

Public Event InteractiveActionExecuting As InteractiveActionExecutingEventHandler

void reportViewer1_CustomInteractiveActionExecuting(object sender, Telerik.ReportViewer.Common.InteractiveActionCancelEventArgs args)
{
    var strB = new System.Text.StringBuilder();
    strB.AppendLine("ReportItem name: " + args.Action.ReportItemName);

    var customAction = args.Action as Telerik.Reporting.Processing.CustomAction;
    if (null != customAction)
    {
        foreach (var p in customAction.Parameters)
        {
            strB.AppendLine(string.Format("Parameter \"{0}\" value: {1}", p.Key, p.Value));
        }
    }

    strB.AppendLine(string.Format("Mouse cursor position: {0}; Item bounds: {1}", args.CursorPos, args.Bounds));

    MessageBox.Show(strB.ToString());
}

' Handles the InteractiveActionExecuting event
' Do not forget to add the WithEvents clause on ReportViewer1 instantiation if needed.
Private Sub reportViewer1_CustomInteractiveActionExecuting(sender As Object, args As Telerik.ReportViewer.Common.InteractiveActionCancelEventArgs) Handles ReportViewer1.InteractiveActionExecuting

    Dim strB = New System.Text.StringBuilder()
    strB.AppendLine("ReportItem name: " + args.Action.ReportItemName)

    Dim customAction = TryCast(args.Action, Telerik.Reporting.Processing.CustomAction)
    If customAction IsNot Nothing Then
        For Each p As KeyValuePair(Of String, Object) In customAction.Parameters
            strB.AppendLine(String.Format("Parameter ""{0}"" value: {1}", p.Key, p.Value))
        Next
    End If

    strB.AppendLine(String.Format("Mouse cursor position: {0}; Item bounds: {1}", args.CursorPos, args.Bounds))

    MessageBox.Show(strB.ToString())
End Sub

void reportViewer1_InteractiveActionExecuting(object sender, Telerik.ReportViewer.Common.InteractiveActionCancelEventArgs args)
{
    var navigateToUrlAction = args.Action as Telerik.Reporting.Processing.NavigateToUrlAction;
    if (null != navigateToUrlAction)
    {
        if (!navigateToUrlAction.Url.StartsWith("https"))
        {
            args.Cancel = MessageBox.Show("You are about to navigate to a non-secure page. Continue?", "Warning", MessageBoxButtons.YesNo, MessageBoxIcon.Warning) != System.Windows.Forms.DialogResult.Yes;
        }
    }
}

' Handles the InteractiveActionExecuting event
' Do not forget to add the WithEvents clause on ReportViewer1 instantiation if needed.
Private Sub reportViewer1_InteractiveActionExecuting(sender As Object, args As Telerik.ReportViewer.Common.InteractiveActionCancelEventArgs) Handles ReportViewer1.InteractiveActionExecuting

    Dim navigateToUrlAction = TryCast(args.Action, Telerik.Reporting.Processing.NavigateToUrlAction)
    If navigateToUrlAction IsNot Nothing Then
        If Not navigateToUrlAction.Url.StartsWith("https") Then
            args.Cancel = MessageBox.Show("You are about to navigate to a non-secure page. Continue?", "Warning", MessageBoxButtons.YesNo, MessageBoxIcon.Warning) <> System.Windows.Forms.DialogResult.Yes
        End If
    End If
End Sub