public partial class Form1 : Form
{
public void Processing(int num)
{
int answer = 2;
Task t = new Task(() =>
{
for (int i = 3; i <= num; i++)
{
answer *= i;
}
this.BeginInvoke(new MethodInvoker(() => { Thread.Sleep(3000); MessageBox.Show("Finished!") }));
MessageBox.Show("OK");
});
t.Start();
}
public Form1()
{
InitializeComponent();

}
private void button1_Click(object sender, EventArgs e)
{
MessageBox.Show("First!");
Processing(10);
}
}

public partial class Form1 : Form
{
public void Processing(int num,SynchronizationContext context)
{
int answer = 2;
Task t = new Task(() =>
{
for (int i = 3; i <= num; i++)
{
answer *= i;
}
SynchronizationContext.SetSynchronizationContext(context);
SynchronizationContext.Current.Post((obj) => { Thread.Sleep(3000); MessageBox.Show("Finished"); }, null);
MessageBox.Show("Last");
});
t.Start();
}
public Form1()
{
InitializeComponent();

}
private void button1_Click(object sender, EventArgs e)
{
MessageBox.Show("First!");
Processing(10,SynchronizationContext.Current);
}
}