private void button1_Click(object sender, EventArgs e) { MyBook bookcollections = new MyBook(); string msg = ""; string[] gg = { "0", "1", "2", "3" }; //foreach (var book in gg) foreach (var book in bookcollections) { msg += book + "\n"; } MessageBox.Show(msg, "iterator測試(yield追蹤)"); }