WPD 从便携设备拷贝文件到PC文件不完整的解决办法

起初从网上查询到的由便携设备拷贝文件到PC的方法如下：

[csharp] view plain copy

1. private void TransferContentFromDevice(string parentObjectID, string saveToPath)  
2.         {  
3.             string folder = System.IO.Path.GetDirectoryName(saveToPath);  
4.             if (!Directory.Exists(folder))  
5.             {  
6.                 Directory.CreateDirectory(folder);  
7.             }  
8.             if (File.Exists(saveToPath))  
9.             {  
10.                 File.Delete(saveToPath);  
11.             }  
12.             IPortableDeviceContent content;  
13.             ppDevice.Content(out content);  
14.             IPortableDeviceResources resources;  
15.             content.Transfer(out resources);  
16.             PortableDeviceApiLib.IStream wpdStream;  
17.             uint optimalTransferSize = 0;  
18.             PortableDeviceApiLib._tagpropertykey property = new PortableDeviceApiLib._tagpropertykey();  
19.             property.fmtid = new Guid(0xE81E79BE, 0x34F0, 0x41BF, 0xB5, 0x3F, 0xF1, 0xA0, 0x6A, 0xE8, 0x78, 0x42);  
20.             property.pid = 0;  
21.             resources.GetStream(parentObjectID, ref property, 0, ref optimalTransferSize, out wpdStream);  
22.             System.Runtime.InteropServices.ComTypes.IStream sourceStream = (System.Runtime.InteropServices.ComTypes.IStream)wpdStream;  
23.             string filename = Path.GetFileName(saveToPath);  
24.             FileStream targetStream = new FileStream(saveToPath, FileMode.Create, FileAccess.Write);  
25.             {  
26.                 int filesize = int.Parse(optimalTransferSize.ToString());  
27.                 var buffer = new byte[filesize];  
28.                 int bytesRead = 0;  
29.                 do  
30.                 {  
31.                     sourceStream.Read(buffer, filesize, new IntPtr(bytesRead));  
32.                     targetStream.Write(buffer, 0, filesize);  
33.                 } while (bytesRead > 0);  
34.                 targetStream.Close();  
35.                 targetStream.Dispose();  
36.             }  
37.             //若不添此行，在本方法执行一次后再次执行时会报资源占用错误  
38.             Marshal.ReleaseComObject(wpdStream);  
39.         }  

但在实际操作中发现，当文件大小超过256K时，文件拷贝异常，即文件只能拷贝设备建议的最大传输大小256k

解决：

[csharp] view plain copy

1. private void TransferContentFromDevice(string parentObjectID, string saveToPath)  
2.         {  
3.             string folder = System.IO.Path.GetDirectoryName(saveToPath);  
4.             if (!Directory.Exists(folder))  
5.             {  
6.                 Directory.CreateDirectory(folder);  
7.             }  
8.             if (File.Exists(saveToPath))  
9.             {  
10.                 File.Delete(saveToPath);  
11.             }  
12.             IPortableDeviceContent content;  
13.             ppDevice.Content(out content);  
14.             IPortableDeviceResources resources;  
15.             content.Transfer(out resources);  
16.             PortableDeviceApiLib.IStream wpdStream;  
17.             uint optimalTransferSize = int.MaxValue;  
18.             PortableDeviceApiLib._tagpropertykey property = new PortableDeviceApiLib._tagpropertykey();  
19.             property.fmtid = new Guid(0xE81E79BE, 0x34F0, 0x41BF, 0xB5, 0x3F, 0xF1, 0xA0, 0x6A, 0xE8, 0x78, 0x42);  
20.             property.pid = 0;  
21.   
22.             resources.GetStream(parentObjectID, ref property, 0, ref optimalTransferSize, out wpdStream);  
23.             System.Runtime.InteropServices.ComTypes.IStream sourceStream = (System.Runtime.InteropServices.ComTypes.IStream)wpdStream;  
24.             string filename = Path.GetFileName(saveToPath);  
25.   
26.             FileStream targetStream = new FileStream(saveToPath, FileMode.Create, FileAccess.Write);  
27.             {  
28.                 int filesize = int.Parse(optimalTransferSize.ToString());  
29.                 var buffer = new byte[filesize];  
30.                 int bytesRead = 0;  
31.                 IntPtr bytesReadIntPtr = new IntPtr(bytesRead);  
32.                 //设备建议读取长度optimalTransferSize长度一般为262144即256k，  
33.                 //注释掉的sourceStream.Read不能更新bytesRead值，do循环只能执行一次即写入256k数据。  
34.                 //创建nextBufferSize变量，用于每次Read后计算下一次buffer长度  
35.                 int nextBufferSize = 0;  
36.                 do  
37.                 {  
38.                     if (bytesReadIntPtr == IntPtr.Zero)  
39.                     {  
40.                         bytesReadIntPtr = Marshal.AllocCoTaskMem(Marshal.SizeOf(typeof(int)));  
41.                     }  
42.                     //sourceStream.Read(buffer, filesize, new IntPtr(bytesRead));  
43.                     sourceStream.Read(buffer, filesize, bytesReadIntPtr);  
44.                     nextBufferSize = Marshal.ReadInt32(bytesReadIntPtr);  
45.                     if (filesize > nextBufferSize)  
46.                     {  
47.                         filesize = nextBufferSize;  
48.                     }  
49.                       
50.                     targetStream.Write(buffer, 0, filesize);  
51.                 } while (nextBufferSize > 0);  
52.                 //} while (bytesRead > 0);  
53.                 targetStream.Close();  
54.                 targetStream.Dispose();  
55.                 Marshal.FreeCoTaskMem(bytesReadIntPtr);  
56.             }  
57.             //若不添此行，在本方法执行一次后再次执行时会报资源占用错误  
58.             Marshal.ReleaseComObject(wpdStream);  
59.         }