I tried to fixed and figure out to move bottom and top for swap. it won't move.

private void topbutton_Click(object sender, EventArgs e)
        {
            int moveSpace = postProcesslistBox.SelectedIndex;
            int ItemIndexOfItemToMove = postProcesslistBox.SelectedIndex;

            if (this.postProcesslistBox.SelectedIndex != 0)
            {
                for (int i = ItemIndexOfItemToMove; i != 0; i--)
                {
                    Swap(i, i - 1);
                    this.postProcesslistBox.SelectedIndex = i-1;
                }
            }
        }

private void Swap(int a, int b)
        {
            int temp = a;
            a = b;
            b = temp;

        }

thanks

Nothing ever seems to happen with the variable moveSpace defined on line 4

private void topbutton_Click(object sender, EventArgs e) {
    int ItemIndexOfItemToMove = postProcesslistBox.SelectedIndex;

    if (this.postProcesslistBox.SelectedIndex != 0) {
        for (int i = ItemIndexOfItemToMove; i != 0; i--) {
                object o = myListBox1.Items[i];
                myListBox1.Items.RemoveAt(i);
                myListBox1.Items.Insert(i-1, o);        }
    }
}

This code will move the selected item to the top. You can do it much faster just by using:

private void topbutton_Click(object sender, EventArgs e) {
    int i = postProcesslistBox.SelectedIndex;

    object o = myListBox1.Items[i];
    myListBox1.Items.RemoveAt(i);
    myListBox1.Items.Insert(0, o);
}

I took the error because I use to type postProcessList.Add("Item1") with any list, then postProcessListBox.DataSource = postProcessList. I can't move top button but it is error again.

I took your example, it is work but I work for DataSource and I read message error, it said Items Collection cannot be modified when the DataSource property is set. Let me know how do I work? Thanks.

Like it says, if you use a DataSource you can't modify the collection. You'll have to take the data from the DataSource and add it to the listbox yourself, rather than setting the DataSource property.