找出仪表板订阅里的bug

public sealed class Dashboard
{
    private readonly PriceFeed _feed;

    public Dashboard(PriceFeed feed)
    {
        _feed = feed;
        _feed.Changed += (_, price) => Show(price);
    }

    public void Disconnect()
    {
        _feed.Changed -= (_, price) => Show(price);
    }

    private void Show(decimal price) { }
}