画带圆弧的矩形就不能使用自带的方法了，自带的Graphics画出的矩形是方方正正，不带圆弧的，废话不多说，上代码：
private void Form1_Paint(object sender, PaintEventArgs e)
{
Rectangle ren = new Rectangle(100, 100, 300, 250);
Draw(ren, e.Graphics, 16);
}
private void Draw(Rectangle rectangle, Graphics g, int _radius)
{
Pen shadowPen = new Pen(Color.Blue,5);
var gpath = DrawRoundRect(rectangle.X, rectangle.Y, rectangle.Width - 2, rectangle.Height - 1, _radius);
g.DrawPath(shadowPen, gpath);
g.FillPath(Brushes.Blue, gpath);
}
public static GraphicsPath DrawRoundRect(int x, int y, int width, int height, int radius)
{
GraphicsPath gp = new GraphicsPath();
gp.AddArc(x, y, radius, radius, 180, 90);
gp.AddArc(width - radius, y, radius, radius, 270, 90);
gp.AddArc(width - radius, height - radius, radius, radius, 0, 90);
gp.AddArc(x, height - radius, radius, radius, 90, 90);
gp.CloseAllFigures();
return gp;
}运行效果：
