private void HandleShapeChanged(object sender, ShapeEventArgs e)
{
Shape s = (Shape)sender;
Console.WriteLine($"收到消息，当前面积是：{e.NewArea}");
s.Draw();
}
protected virtual void OnShapeChanged(ShapeEventArgs e)
{
//EventHandler<ShapeEventArgs> handler = ShapeChanged;
//if (handler != null)
//{
// handler(this, e);
//}
ShapeChanged?.Invoke(this, e);
}
protected override void OnShapeChanged(ShapeEventArgs e)
{
base.OnShapeChanged(e);
}
