如何从IDialogContext获取活动信息

using Microsoft.Bot.Builder.Dialogs;
using Microsoft.Bot.Connector;

[Serializable]
public class MyDialog : IDialog<object>
{
    public async Task StartAsync(IDialogContext context)
    {
        context.Wait(MessageReceivedAsync);
    }

    private async Task MessageReceivedAsync(IDialogContext context, IAwaitable<IMessageActivity> result)
    {
        var message = await result;

        // 获取活动信息
        var activity = context.Activity;
        var sender = activity.From;
        var recipient = activity.Recipient;
        var conversationId = activity.Conversation.Id;
        var dialogId = activity.Id;
        var dialogType = activity.Type;
        var messageText = activity.Text;

        // 处理活动信息
        // ...

        context.Wait(MessageReceivedAsync);
    }
}