public Task <SlackMessage> SendAccessoryMessage(string channel, string message, string imageUrl)
{
Console.WriteLine("[Send] " + message + " / " + imageUrl);
var ts = new TaskCompletionSource <SlackMessage>();
Slack.PostBlock(
_ => { ProcessCompletion(ts, channel, _); },
channel,
message,
as_user: true,
accessory_image: imageUrl);
return(ts.Task);
}
