以下代码最后一句运行时候报错无效参数

Question

 Graphics g = this.groupBox1.CreateGraphics();
            g.Clear(Color.SeaShell);
            Brush b = new SolidBrush(Color.Blue);
            Font f = new Font("Arial", 9, FontStyle.Regular);
            Pen p = new Pen(b);            using (da = new SqlDataAdapter("select * from hjb where 温度='" + str + "' order by 温度", con))
            {
                ds = new DataSet();
                da.Fill(ds,"温度");
                int a = MaxValue - MinValue;
                
                for (double i = 0; i < a; i = i + 0.25)
                {
                    Point p1 = new Point();
                    p1.X = 0;
                    p1.Y = Convert.ToInt16(190 - 30 * (i * 4));
                    g.DrawString(Convert.ToString(8+i*2),f,b,p1);
                    Point p2 = new Point();
                    Point p3 = new Point();
                    p2.X = 30; p2.Y = Convert.ToInt16(200 - 30 * (i * 4));
                    p3.X = 360; p3.Y = Convert.ToInt16(200 - 30 * (i * 4));
                    g.DrawLine(p, p2,p3);
                }
                NUM = ds.Tables[0].Rows.Count;
                double[] velocity = new double[NUM];
                for (int C = 0; C < NUM; C++)
                {
                    velocity[C] = Convert.ToDouble(ds.Tables[0].Rows[C][2].ToString());
                    g.DrawString(Convert.ToDateTime(ds.Tables[0].Rows[C][1].ToString()).Day + "日", f, b, 30 * (C + 1) - 10, 210);
                    g.DrawLine(p, 30 * (C + 1), 200, 30 * (C + 1), 10); 
                }
               Point[] P = new Point[NUM];
               for (int i = 0; i < NUM; i++)
                {
                    P[i].X = 30 * (i + 1);
                    P[i].Y = Convert.ToInt32( 200 - (velocity[i]-8)*2*30);
                }
               Pen pp = new Pen(Color.Red, 2f);
                g.DrawLines(pp,P);
               }

Answer 1

参数无效，你就仔细看看MSDN啊

Answer 2

Pen pen = new Pen(Color.Black, 3);
    Point[] points =
             {
                 new Point(10,  10),
                 new Point(10, 100),
                 new Point(200,  50),
                 new Point(250, 300)
             };
    e.Graphics.DrawLines(pen, points);
 单步看看数据

Answer 3

NUM = ds.Tables[0].Rows.Count;
if(NUM <=0)
{
return;
}确保NUM〉0不然后面的无意义

Answer 4

设断点看Point[] P的值都是什么

Answer 5

 private void DrowPic(string str)
        {
            int MaxValue = 0, MinValue = 0; int NUM;
            using (cmd = new SqlCommand("select Max(温度) from hjb'" + str + "'", con))
            {
                con.Open();
                MaxValue = Convert.ToInt32(cmd.ExecuteScalar());
                con.Close();
            }
            using (cmd = new SqlCommand("select Min(温度) from hjb '" + str + "'", con))
            {
                con.Open();
                MinValue = Convert.ToInt32(cmd.ExecuteScalar());
                con.Close();
            }
            Graphics g = this.groupBox1.CreateGraphics();
            g.Clear(Color.SeaShell);
            Brush b = new SolidBrush(Color.Blue);
            Font f = new Font("Arial", 9, FontStyle.Regular);
            Pen p = new Pen(b);            using (da = new SqlDataAdapter("select * from hjb where 温度='" + str + "' order by 温度", con))
            {
                ds = new DataSet();
                da.Fill(ds,"温度");
                int a = MaxValue - MinValue;
                for (double i = 0; i < a; i = i + 0.25)
                {
                    Point p1 = new Point();
                    p1.X = 0;
                    p1.Y = Convert.ToInt32(190 - 30 * (i * 4));
                    g.DrawString(Convert.ToString(8+i*2),f,b,p1);
                    Point p2 = new Point();
                    Point p3 = new Point();
                    p2.X = 30; p2.Y = Convert.ToInt16(200 - 30 * (i * 4));
                    p3.X = 360; p3.Y = Convert.ToInt16(200 - 30 * (i * 4));
                    g.DrawLine(p, p2,p3);
                }
                NUM = ds.Tables[0].Rows.Count;
                double[] velocity = new double[NUM];
                NUM = ds.Tables[0].Rows.Count;
                if (NUM <= 0)
                {
                    return;
                }                for (int C = 0; C < NUM; C++)
                {
                    velocity[C] = Convert.ToDouble(ds.Tables[0].Rows[C][2].ToString());
                    g.DrawString(Convert.ToDateTime(ds.Tables[0].Rows[C][1].ToString()).Day + "日", f, b, 30 * (C + 1) - 10, 210);
                    g.DrawLine(p, 30 * (C + 1), 200, 30 * (C + 1), 10); 
                }
               Point[] P = new Point[NUM];
               for (int i = 0; i < NUM; i++)
                {
                    P[i].X = 30 * (i + 1);
                    P[i].Y = Convert.ToInt32( 200 - (velocity[i]-8)*2*30);
                }
               Pen pp = new Pen(Color.Red, 2f);
                g.DrawLines(pp,P);
 这样还是不行 大侠们帮忙  谢谢