private void Form1_Paint(object sender, PaintEventArgs e)
{
    //获取画布的绘制指针
    Graphics g = e.Graphics;
    //红色笔绘制一个矩形
    Rectangle rc = new Rectangle(10, 10, 100, 100);
    g.DrawRectangle(new Pen(Color.Red), rc);
    //利用带透明度的画刷填充矩形
    SolidBrush sb = new SolidBrush(Color.FromArgb(80, 255, 255, 0));
    g.FillRectangle(sb, rc);

    //在前面的矩形中绘制字符串
    string drawString = "35℃";
    //创建字符串的绘制字体和画刷
    Font drawFont = new Font("Arial", 16);
    SolidBrush drawBrush = new SolidBrush(Color.Red);
    //设置字符串格式
    StringFormat drawFormat = new StringFormat();
    drawFormat.Alignment = StringAlignment.Center;
    //在矩形中绘制字符串，并且使用drawFormat的性质
    g.DrawString(drawString, drawFont, drawBrush, rc, drawFormat);
}