WindowsForm PictureBox.Image为null,即使表单中显示了图像

Question

我正在尝试捕获此设备扫描的指纹 - > http://www.nitgen.com/eng/product/finkey.html

我能够扫描指纹并成功保存二进制数据.我也可以在图片框中显示指纹.但是,当我试图保存图片框中显示的指纹时,我收到一个错误,即图片框的图像为空.

下面是我的捕获指纹和从图片框保存图像的代码.

public class Form1 : System.Windows.Forms.Form
{
    public NBioBSPCOMLib.NBioBSP objNBioBSP;
    public NBioBSPCOMLib.IExtraction objExtraction;
    private PictureBox pictureExtWnd;

    private void Form1_Load(object sender, System.EventArgs e)
    {
        // Create NBioBSP object
        objNBioBSP = new NBioBSPCOMLib.NBioBSPClass();
        objExtraction = (NBioBSPCOMLib.IExtraction)objNBioBSP.Extraction;
        pictureExtWnd.Image = new Bitmap(pictureExtWnd.Width, pictureExtWnd.Height);
    }

    private void buttonEnroll_Click(object sender, System.EventArgs e)
    {
        //tell NBIO to not display their fingerprint scanning window
        objExtraction.WindowStyle = NBioBSPType.WINDOW_STYLE.INVISIBLE;

        //set the color of the fingerprint captured
        objExtraction.FPForeColor = "000000";

        //set the color of the background where the fingerprint will be displayed
        objExtraction.FPBackColor = "FFFFFF";

        //tell NBIO that the scanned fingerprint will be displayed in the picturebox
        //by giving the handle control to NBIO
        objExtraction.FingerWnd = pictureExtWnd.Handle.ToInt32();

        //start scanning the fingerprint. This is also where the fingerprint
        //is displayed in the picturebox. 
        objExtraction.Capture((int)NBioBSPType.FIR_PURPOSE.VERIFY);

        //if there's no problem while scanning the fingerprint, save the fingerprint image
        if (objExtraction.ErrorCode == NBioBSPError.NONE)
        {
            string fileName = RandomString.GetRandomString(16, true) + ".bmp";

            using (SaveFileDialog sfdlg = new SaveFileDialog())
            {
                sfdlg.Title = "Save Dialog";
                sfdlg.Filter = "Bitmap Images (*.bmp)|*.bmp|All files(*.*)|*.*";
                if (sfdlg.ShowDialog(this) == DialogResult.OK)
                {
                    pictureExtWnd.Image.Save(sfdlg.FileName, ImageFormat.Bmp);
                    MessageBox.Show("FingerPrint Saved Successfully.");
                }
            }
        }
        else
        {
            MessageBox.Show("FingerPrint Saving Failed!");
        }
    }
}

我试过封闭在里面

using(Graphics g = new Graphics)
{
    objExtraction.Capture((int)NBioBSPType.FIR_PURPOSE.VERIFY);
} 

因为我读过在对图像进行编辑时,你需要使用图形.但是没有任何事情发生,因为api没有使用我实例化的图形对象.

更新: 这是我最终做的事情:

using (SaveFileDialog sfdlg = new SaveFileDialog())
        {
            sfdlg.Title = "Save Dialog";
            sfdlg.Filter = "Bitmap Images (*.bmp)|*.bmp|All files(*.*)|*.*";
            if (sfdlg.ShowDialog(this) == DialogResult.OK)
            {
                Graphics gfx = this.pictureExtWnd.CreateGraphics();
                Bitmap bmp = new Bitmap(this.pictureExtWnd.Width, this.pictureExtWnd.Height);
                this.pictureExtWnd.DrawToBitmap(bmp, new Rectangle(0, 0, this.pictureExtWnd.Width, this.pictureExtWnd.Height));
                bmp.Save(sfdlg.FileName, ImageFormat.Bmp);

                gfx.Dispose();
                //pictureExtWnd.Image.Save(sfdlg.FileName, ImageFormat.Bmp);
                MessageBox.Show("Saved Successfully...");
            }
        }

Answer 1

    objExtraction.FingerWnd = pictureExtWnd.Handle.ToInt32();

您将窗口句柄传递给了指纹扫描仪。这是告诉本机代码块有关它可以绘制到的窗口的常见方法。它通常会子类化窗口过程来响应 WM_PAINT 请求，例如，与 NativeWindow.WndProc() 的想法相同。

然而，这意味着 Image 属性是无用的。该本机代码不知道这是一个 PictureBox 控件并且它具有 Image 属性。它只知道为控件创建的本机窗口。

请在 api 中查找保存图像的选项，该选项应该可用。如果没有，那么您保存它的第一步是使用图片框的 DrawToBitmap() 方法。如果扫描仪实现了 WM_PRINT 消息处理程序，这可能会起作用。如果这不起作用，那么您唯一的其他备份计划是使用 Graphics.CopyFromScreen()。只要窗口位于前台，这将始终有效。与使用键盘上的 PrtSc 按钮类似，屏幕截图。