/// <summary>
/// 取消按钮单击事件。
/// </summary>
/// <param name="sender">触发事件的控件对象。</param>
/// <param name="e">事件的参数。</param>
private void CancelButton_Click(object sender, EventArgs e)
{
if (this.GetNextOutMessage(_task) != Message.NoAvailableMessage)
{
Close();
}
else
{
MessagePipe.SendOutMessage(new KeyValuePair <Message, Thread>(Message.UserCancel, _task));
Close();
}
}