BeginInvoke会重新开一个线程

t = new Thread(new ThreadStart(delegate
{
Play(sender, e);
Console.WriteLine("Play ended.");
}));
t.Start();

private void Play(object sender, EventArgs e)
{
Console.WriteLine("InvokeRequired = " + InvokeRequired);
if (InvokeRequired)
{
Invoke(new PlayDelegate(Play), sender, e);
return;
}
}