/// <summary>
/// Banner will be show up as soon as posible.
/// </summary>
/// <param name="key">key of banner unit</param>
public static void ShowBanner(string key = null)
{
if (instance == null)
{
return;
}
StopShowBannerTask();
showBannerSoonTask = instance.StartCoroutine(ShowBannerSoonTask(key));
}