public Task MaximizeDashboardItemAsync(
    string itemName
)

Public Function MaximizeDashboardItemAsync(
    itemName As String
) As Task

using DevExpress.XtraEditors;
using System;
using System.Windows.Forms;

namespace MaximizeSlideShow
{
    public partial class ViewerForm1 : XtraForm {
        bool isSlideShown = false;
        int index = 0;
        Timer slideShowTimer = new Timer() {
            Interval = 5000
        };

        public ViewerForm1() {
            InitializeComponent();
            slideShowTimer.Tick += OnSlideShowTimerTick;
        }

        async void OnSlideShowTimerTick(object sender, EventArgs e) {
            var items = dashboardViewer1.Dashboard.Items;
            int maxIndex = items.Count - 1;

            if(!isSlideShown) {
                slideShowTimer.Stop();
                return;
            }
            await dashboardViewer1.MaximizeDashboardItemAsync(items[index].ComponentName);
            if(index == maxIndex)
                index = 0;
            else
                index++;
        }

        void OnStartClick(object sender, MouseEventArgs e) {
            if(!isSlideShown) {
                isSlideShown = true;
                slideShowTimer.Start();
            }
        }
        async void OnStopClick(object sender, EventArgs e) {
            isSlideShown = false;
            await dashboardViewer1.RestoreDashboardItemAsync();
        }
    }
}

Imports DevExpress.XtraEditors
Imports System
Imports System.Windows.Forms

Namespace MaximizeSlideShow
    Partial Public Class ViewerForm1
        Inherits XtraForm

        Private isSlideShown As Boolean = False
        Private index As Integer = 0
        Private slideShowTimer As New Timer() With {.Interval = 5000}

        Public Sub New()
            InitializeComponent()
            AddHandler slideShowTimer.Tick, AddressOf OnSlideShowTimerTick
        End Sub

        Private Async Sub OnSlideShowTimerTick(ByVal sender As Object, ByVal e As EventArgs)
            Dim items = dashboardViewer1.Dashboard.Items
            Dim maxIndex As Integer = items.Count - 1

            If Not isSlideShown Then
                slideShowTimer.Stop()
                Return
            End If
            Await dashboardViewer1.MaximizeDashboardItemAsync(items(index).ComponentName)
            If index = maxIndex Then
                index = 0
            Else
                index += 1
            End If
        End Sub

        Private Sub OnStartClick(ByVal sender As Object, ByVal e As MouseEventArgs) Handles simpleButton1.MouseClick
            If Not isSlideShown Then
                isSlideShown = True
                slideShowTimer.Start()
            End If
        End Sub
        Private Async Sub OnStopClick(ByVal sender As Object, ByVal e As EventArgs) Handles simpleButton2.Click
            isSlideShown = False
            Await dashboardViewer1.RestoreDashboardItemAsync()
        End Sub
    End Class
End Namespace