private void button1_Click(object sender, EventArgs e)
{
List<Task> mylist = new List<Task>();
mylist.Add(Task.Run(()=> {
Thread.Sleep(3000);
MessageBox.Show("去买菜");
}));
mylist.Add(Task.Run(() =>
{
Thread.Sleep(5000);
MessageBox.Show("菜做好了");
}));
Task.WhenAll(mylist).ContinueWith(t => {
MessageBox.Show("菜做好了,可以吃饭了");
});