private void button1_Click(object sender, EventArgs e) { MyRectangle item = (MyRectangle)comboBox1.SelectedItem; //(MyRectangle)轉型用的 被選到項目(return object) //將被選到的項目(object)轉型成MyRectangle型態 存到 item MessageBox.Show($"{item.Name} 的面積為{item.GetArea()}"); }
private void button1_Click(object sender, EventArgs e) { MyRectangle item = (MyRectangle)comboBox1.SelectedItem; MessageBox.Show($" {item.Name} 的面積為: {item.GetArea()}"); }