Example - First Chat Bot

On the previous page we got an access token and used the getMe method to check our setup. Now, it is time to make an interactive bot that gets users' messages and replies to them like in this screenshot:

Copy the following code to Program.cs.

⚠️ Replace {YOUR_ACCESS_TOKEN_HERE} with the access token from the [@BotFather].

using Telegram.Bot;
using Telegram.Bot.Exceptions;
using Telegram.Bot.Polling;
using Telegram.Bot.Types;
using Telegram.Bot.Types.Enums;

var botClient = new TelegramBotClient("{YOUR_ACCESS_TOKEN_HERE}");

using CancellationTokenSource cts = new ();

// StartReceiving does not block the caller thread. Receiving is done on the ThreadPool.
 ReceiverOptions receiverOptions = new ()
{
    AllowedUpdates = Array.Empty<UpdateType>() // receive all update types except ChatMember related updates
};

botClient.StartReceiving(
    updateHandler: HandleUpdateAsync,
    pollingErrorHandler: HandlePollingErrorAsync,
    receiverOptions: receiverOptions,
    cancellationToken: cts.Token
);

var me = await botClient.GetMeAsync();

Console.WriteLine($"Start listening for @{me.Username}");
Console.ReadLine();

// Send cancellation request to stop bot
cts.Cancel();

async Task HandleUpdateAsync(ITelegramBotClient botClient, Update update, CancellationToken cancellationToken)
{
    // Only process Message updates: https://core.telegram.org/bots/api#message
    if (update.Message is not { } message)
        return;
    // Only process text messages
    if (message.Text is not { } messageText)
        return;

    var chatId = message.Chat.Id;

    Console.WriteLine($"Received a '{messageText}' message in chat {chatId}.");

    // Echo received message text
    Message sentMessage = await botClient.SendTextMessageAsync(
        chatId: chatId,
        text: "You said:\n" + messageText,
        cancellationToken: cancellationToken);
}

Task HandlePollingErrorAsync(ITelegramBotClient botClient, Exception exception, CancellationToken cancellationToken)
{
    var ErrorMessage = exception switch
    {
        ApiRequestException apiRequestException
            => $"Telegram API Error:\n[{apiRequestException.ErrorCode}]\n{apiRequestException.Message}",
        _ => exception.ToString()
    };

    Console.WriteLine(ErrorMessage);
    return Task.CompletedTask;
}

Run the program:

dotnet run

It runs waiting for text messages unless forcefully stopped by pressing Enter. Open a private chat with your bot in Telegram and send a text message to it. Bot should reply in no time.

By invoking StartReceiving(...) bot client starts fetching updates using getUpdates method for the bot from Telegram servers. This operation does not block the caller thread, because it is done on the ThreadPool. We use Console.ReadLine() to keep the app running.

When user sends a message, the HandleUpdateAsync(...) method gets invoked with the Update object passed as an argument. We check Message.Type and skip the rest if it is not a text message. Finally, we send a text message back to the same chat we got the message from.

The HandlePollingErrorAsync(...) method is invoked in case of an error that occurred while fetching updates.

If you take a look at the console, the program outputs the chatId value. Copy the chat id number to make testing easier for yourself on the next pages.

Received a 'text' message in chat 123456789.