g.Clear(this.BackColor);////未将对象引用设置到对象的实例。????

Question

private Image myImage = Image.FromFile("d:/1.gif");
        public Graphics g;
        private void set_Click(object sender, EventArgs e)
        {
            int width = Convert.ToInt32(width_T.Text);
            int height = Convert.ToInt32(height_T.Text);
            this.BackColor = Color.White;
            if (width > 290 | height > 270)
            {
                MessageBox.Show("height or width too large");
                return;            }
           
            g.Clear(this.BackColor);
            g.DrawImage(myImage, 5, 5, width, height);
        }
   g.Clear(this.BackColor);////未将对象引用设置到对象的实例。????

Answer 1

Graphics g = this.CreateGraphics();

Answer 2

Graphics g = this.CreateGraphics();