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()}");
}