How to display channels in ListView using Graph API?

I’m developing a small Windows form app to test Graph API functions. I have two functionalities in the application, user's log in and get channels for specified team. I created a class that contains functions for user login and for returning channels for specified team. I have a ListView on Form in which I want to show all the channels, but when I call a function for returning channels in button event, nothing happens, nothing is displayed in the ListView. Here is the code:

public static class GraphHelper
{
public static GraphServiceClient graphClient;
public static string token;
private static string[] scopes = new string[] { "user.read" };
public static string TokenForUser = null;
public static DateTimeOffset expiration;
private const string ClientId = "599ed98d-4356-4a96-ad37-04391e9c48dc";
private const string Tenant = "common"; // Alternatively "[Enter your tenant, as obtained from the Azure portal, e.g. kko365.onmicrosoft.com]"
private const string Authority = "https://login.microsoftonline.com/" + Tenant;
// The MSAL Public client app
private static IPublicClientApplication PublicClientApp;
private static string MSGraphURL = "https://graph.microsoft.com/beta/";
private static AuthenticationResult authResult;
public static GraphServiceClient GetGraphClient(string token)
{
if (graphClient == null)
{
// Create Microsoft Graph client.
try
{
graphClient = new GraphServiceClient(
"https://graph.microsoft.com/v1.0",
new DelegateAuthenticationProvider(
async (requestMessage) =>
{
requestMessage.Headers.Authorization = new AuthenticationHeaderValue("bearer", token);
// This header has been added to identify our sample in the Microsoft Graph service. If extracting this code for your project please remove.
requestMessage.Headers.Add("SampleID", "uwp-csharp-snippets-sample");
}));
return graphClient;
}
catch (Exception ex)
{
Debug.WriteLine("Could not create a graph client: " + ex.Message);
}
}
return graphClient;
}
public static async Task<string> GetTokenForUserAsync()
{
if (TokenForUser == null || expiration <= DateTimeOffset.UtcNow.AddMinutes(10))
{
PublicClientApp = PublicClientApplicationBuilder.Create(ClientId)
.WithAuthority(Authority)
.WithRedirectUri("https://login.microsoftonline.com/common/oauth2/nativeclient")
.WithLogging((level, message, containsPii) =>
{
Debug.WriteLine($"MSAL: {level} {message} ");
}, LogLevel.Warning, enablePiiLogging: false, enableDefaultPlatformLogging: true)
.Build();
// It's good practice to not do work on the UI thread, so use ConfigureAwait(false) whenever possible.
IEnumerable accounts = await PublicClientApp.GetAccountsAsync().ConfigureAwait(false);
IAccount firstAccount = accounts.FirstOrDefault();
try
{
authResult = await PublicClientApp.AcquireTokenSilent(scopes, firstAccount)
.ExecuteAsync();
}
catch (MsalUiRequiredException ex)
{
// A MsalUiRequiredException happened on AcquireTokenSilentAsync. This indicates you need to call AcquireTokenAsync to acquire a token
Debug.WriteLine($"MsalUiRequiredException: {ex.Message}");
authResult = await PublicClientApp.AcquireTokenInteractive(scopes)
.ExecuteAsync()
.ConfigureAwait(false);
}
TokenForUser = authResult.AccessToken;
}
return TokenForUser;
}
public static async Task GetMeAsync(string token)
{
GraphHelper.graphClient = GraphHelper.GetGraphClient(token);
try
{
// GET /me
return await GraphHelper.graphClient.Me
.Request()
.Select(u => new
{
u.DisplayName
})
.GetAsync();
}
catch (ServiceException ex)
{
Console.WriteLine($"Error getting signed-in user: {ex.Message}");
return null;
}
}
public static async Task> GetChannels(string teamId)
{
graphClient = GetGraphClient(token);
var channels = await graphClient.Teams[teamId].Channels
.Request()
.GetAsync();
return channels;
}
}
public partial class Form1 : Form
{
public static GraphServiceClient graphClient;
public static string token;
public Form1()
{
InitializeComponent();
}
private async void button1_Click(object sender, EventArgs e)
{
token = await GraphHelper.GetTokenForUserAsync();
User graphUser = await GraphHelper.GetMeAsync(token);
label2.Text = graphUser.DisplayName;
}
private async void button3_Click(object sender, EventArgs e)
{
var channels = GraphHelper.GetChannels("8557483b-a233-4710-82de-e1bdb03bb9a9").Result;
foreach (var ch in channels)
{
ListViewItem item = new ListViewItem(new string[] { ch.DisplayName, ch.Id});
listView1.Items.Add(item);
}
}
}

Does anyone know how to solve this?