未将对象的引用设置到对象的实例，怎么解决啊

qijun1994 2013-06-30 12:01:35

直接上代码，从网上下载的一个将AVI视频拆分为BMP图像文件的程序。
自己单步调试了一下，发现 private void cmdGetBitmaps_Click(object sender, EventArgs e)函数中，执行到 bih = (BITMAPINFOHEADER)Marshal.PtrToStructure(new IntPtr(pDib), bih.GetType());
语句之后，便没有执行后面的处理得到BMP文件的代码，直接跳到了报错，未将对象的引用设置到对象的实例。
前面已经定义了一下BITMAPINFOHEADER bih = new BITMAPINFOHEADER();为什么还会报错呢？求大神指点

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

using System.Runtime.InteropServices;

using System.Globalization;

using System.IO;



namespace GetAVIFrames

{

    public partial class Form1 : Form

    {

        public const int BMP_MAGIC_COOKIE = 19778;

        [DllImport("avifil32.dll")] public static extern void AVIFileInit();

        [DllImport("avifil32.dll")] public static extern int AVIFileOpen(ref int ppFile, String szFile, int Mode, int pclsidHandler);

        [DllImport("avifil32.dll")] public static extern int AVIFileGetStream(int pFile, out IntPtr ppAvi, int fccType, int lParam);



        [DllImport("avifil32.dll")] public static extern int AVIStreamStart(int pavi);

        [DllImport("avifil32.dll")] public static extern int AVIStreamLength(int pavi);

        [DllImport("avifil32.dll")] public static extern int AVIStreamInfo(int pAVIStream, ref AVI_STREAM_INFO pStrInfo, int Size);



        [DllImport("avifil32.dll")] static extern int AVIFileInfo(int pFile, ref AVI_FILE_INFO aviInfo, int Size);

        [DllImport("avifil32.dll")] static extern int AVIStreamGetFrameOpen(IntPtr pAvi, ref BITMAPINFOHEADER bih);

        [DllImport("avifil32.dll")] public static extern int AVIStreamGetFrame(int pGetFrame, int Pos);

        [DllImport("avifil32.dll")] public static extern int AVIStreamGetFrameClose(int pGetFrame);



        public struct AVI_RECT

        {

            public UInt32 left;

            public UInt32 top;

            public UInt32 right;

            public UInt32 bottom;

        };



        public struct AVI_STREAM_INFO

        {

            public UInt32 fccType;

            public UInt32 fccHandler;

            public UInt32 dwFlags;

            public UInt32 dwCaps;

            public UInt16 wPriority;

            public UInt16 wLanguage;

            public UInt32 dwScale;

            public UInt32 dwRate;

            public UInt32 dwStart;

            public UInt32 dwLength;

            public UInt32 dwInitialFrames;

            public UInt32 dwSuggestedBufferSize;

            public UInt32 dwQuality;

            public UInt32 dwSampleSize;

            public AVI_RECT rcFrame;

            public UInt32 dwEditCount;

            public UInt32 dwFormatChangeCount;

            public string szName;

        } ;





        public struct AVI_FILE_INFO

        {

            long dwMaxBytesPerSecond;

            long dwFlags;

            long dwCaps;

            long dwStreams;

            long dwSuggestedBufferSize;

            long dwWidth;

            long dwHeight;

            long dwScale;

            long dwRate;

            long dwLength;

            long dwEditCount;

            long szFileType;

        }



        [StructLayout(LayoutKind.Sequential, Pack=1)]

        public struct BITMAPINFOHEADER

        {

            public UInt32 biSize;

            public Int32 biWidth;

            public Int32 biHeight;

            public Int16 biPlanes;

            public Int16 biBitCount;

            public UInt32 biCompression;

            public UInt32 biSizeImage;

            public Int32 biXPelsPerMeter;

            public Int32 biYPelsPerMeter;

            public UInt32 biClrUsed;

            public UInt32 biClrImportant;

        }



        [StructLayout(LayoutKind.Sequential, Pack = 1)]

        public struct BITMAPFILEHEADER

        {

            public Int16 bfType;

            public Int32 bfSize;

            public Int16 bfReserved1;

            public Int16 bfReserved2;

            public Int32 bfOffBits;

        }



        int writeDenied = 0x20;

        BITMAPINFOHEADER bih = new BITMAPINFOHEADER();



        int streamtypeVIDEO = 1935960438; // 'equivalent to: mmioStringToFOURCC("vids", 0&)



        int AVIFile = 0;

        IntPtr aviStream;

      



        public Form1()

        {

            InitializeComponent();

        }



        private IntPtr IntPtr(int pDib)

        {

            throw new Exception("The method or operation is not implemented.");

        }



        private void Form1_Load(object sender, EventArgs e)

        {

            AVIFileInit();

        }



        private void cmdGetBitmaps_Click(object sender, EventArgs e)

        {

            int result;

            String fileName;

            int pointerAVI = 0;

            int pointerAVIStream = 0;

            int numberFrames = 0;

            int firstFrame = 0;



            AVI_FILE_INFO fileInfo = new AVI_FILE_INFO();

            AVI_STREAM_INFO streamInfo = new AVI_STREAM_INFO();



            fileName = "D:\\highway.avi";



            try

            {

                result = AVIFileOpen(ref pointerAVI, fileName, writeDenied, 0);

                result = AVIFileGetStream(pointerAVI, out aviStream, streamtypeVIDEO, 0);

                firstFrame = AVIStreamStart(aviStream.ToInt32());

                numberFrames = AVIStreamLength(aviStream.ToInt32());

             

                result = AVIFileInfo(pointerAVI, ref fileInfo, System.Runtime.InteropServices.Marshal.SizeOf(fileInfo));

                result = AVIStreamInfo(aviStream.ToInt32(), ref streamInfo, Marshal.SizeOf(streamInfo));



                bih.biBitCount = 24;

                bih.biClrImportant = 0;

                bih.biClrUsed = 0;

                bih.biCompression = 0;

                bih.biHeight = (Int32)(streamInfo.rcFrame.bottom);

                bih.biWidth = (Int32)streamInfo.rcFrame.right;

                bih.biPlanes = 1;

                bih.biSize = (UInt32)Marshal.SizeOf(bih);

                bih.biXPelsPerMeter = 0;

                bih.biYPelsPerMeter = 0;



                int getFrameObject = 0;



                String dstFileName = "D:\\bitmap";



                getFrameObject = AVIStreamGetFrameOpen(aviStream, ref bih);







                for (int i = firstFrame; i < numberFrames - 1; i++)

                {

                    int pDib = AVIStreamGetFrame(getFrameObject, firstFrame + i);

                  

                 

                    bih = (BITMAPINFOHEADER)Marshal.PtrToStructure(new IntPtr(pDib), bih.GetType());



                    //Copy the image

                    byte[] bitmapData = new byte[bih.biSizeImage];

                    int address = pDib + Marshal.SizeOf(bih);

                    for (int offset = 0; offset < bitmapData.Length; offset++)

                    {

                        bitmapData[offset] = Marshal.ReadByte(new IntPtr(address));

                        address++;

                    }





                    //Copy bitmap info

                    byte[] bitmapInfo = new byte[Marshal.SizeOf(bih)];

                    IntPtr ptr;

                    ptr = Marshal.AllocHGlobal(bitmapInfo.Length);

                    Marshal.StructureToPtr(bih, ptr, false);

                    address = ptr.ToInt32();

                    for (int offset = 0; offset < bitmapInfo.Length; offset++)

                    {

                        bitmapInfo[offset] = Marshal.ReadByte(new IntPtr(address));

                        address++;

                    }



                    //Create file header

                    BITMAPFILEHEADER bfh = new BITMAPFILEHEADER();

                    bfh.bfType = BMP_MAGIC_COOKIE;

                    bfh.bfSize = (Int32)(55 + bih.biSizeImage); //size of file as written to disk

                    bfh.bfReserved1 = 0;

                    bfh.bfReserved2 = 0;

                    bfh.bfOffBits = Marshal.SizeOf(bih) + Marshal.SizeOf(bfh);







                    //Create or overwrite the destination file

                    FileStream fs = new FileStream(dstFileName + i.ToString() + ".bmp", System.IO.FileMode.Create);

                    BinaryWriter bw = new BinaryWriter(fs);



                    //Write header

                    bw.Write(bfh.bfType);

                    bw.Write(bfh.bfSize);

                    bw.Write(bfh.bfReserved1);

                    bw.Write(bfh.bfReserved2);

                    bw.Write(bfh.bfOffBits);

                    //Write bitmap info

                    bw.Write(bitmapInfo);

                    //Write bitmap data

                    bw.Write(bitmapData);

                    bw.Close();

                    fs.Close();

                }

            }

            catch (Exception ex)

            {

                MessageBox.Show(ex.Message);

            }

        }



    }

}

...全文

503 7 打赏收藏转发到动态举报

写回复

用AI写文章

7 条回复

切换为时间正序

请发表友善的回复…

发表回复

linghujun2000 2013-07-08

打赏
举报

我也遇到这个问题，怎么办？坐等答案

tcmakebest 2013-06-30

打赏
举报

那就可能是pDib是0啊

以专业开发人员为伍 2013-06-30

打赏
举报

你在异常时，从vs调试器上，确认了 bih 是null了吗？没有调试，你怎么认定一定是这个变量值的问题？

threenewbee 2013-06-30

打赏
举报

http://hi.baidu.com/dongyuejiang/item/1badc7eadd263c2f5b7cfbe9

qijun1994 2013-06-30

打赏
举报

引用 1 楼 sp1234 的回复:

你在异常时，从vs调试器上，确认了 bih 是null了吗？没有调试，你怎么认定一定是这个变量值的问题？

查看了MSDN中对于AVIStreamGetFrameOpen function的解释，返回值的阐述如下： Return value Returns a GetFrame object that can be used with the AVIStreamGetFrame function. If the system cannot find a decompressor that can decompress the stream to the given format, or to any RGB format, the function returns NULL. 其中的If the system cannot find a decompressor（如果系统无法找到解压器），怎么理解啊，还望大神指点，十分感谢

qijun1994 2013-06-30

打赏
举报

引用 2 楼 tcmakebest 的回复:

那就可能是pDib是0啊

是的，pDib的值为0，bih没有问题。再调调看吧，十分感谢

qijun1994 2013-06-30

打赏
举报

引用 1 楼 sp1234 的回复:

你在异常时，从vs调试器上，确认了 bih 是null了吗？没有调试，你怎么认定一定是这个变量值的问题？

十分感谢，跟踪了一下，发现是getFrameObject = AVIStreamGetFrameOpen(aviStream, ref bih);这一句有问题，getFrameObject得值始终为0，导致后面的 int pDib = AVIStreamGetFrame(getFrameObject, firstFrame + i); pDib的值也为0,而aviStream与 bih都不为Null。