private void 保存OToolStripMenuItem_Click(object sender, EventArgs e)
        {
            SaveFileDialog dlg = new SaveFileDialog();
            dlg.Title = "保存图片";
            dlg.OverwritePrompt = true;
            dlg.InitialDirectory = "D:\\";
            dlg.Filter = "bmp文件(*.bmp)|*.bmp|JPG文件(*.jpg)|*.jpg|GIF文件(*.gif)|*.gif";
            dlg.FilterIndex = 1;
            if (dlg.ShowDialog() == DialogResult.OK)
            {
                pictureBox1.Image.Save(dlg.FileName);
            }
        }未将对象引用设置到对象的实例   是什么意思?