C# 为什么MtpDevice.ImportFile总是失败？
我正在修改一个现有的应用程序，它是用C#in Xamarin编写的，专门为Android构建的 现有的应用程序在摄像头的wifi卡上搜索文件，并通过HTTP接口下载。我试图让它下载的文件使用拴在一个USB电缆代替，但无法得到文件下载 我正在使用MtpDevice尝试下载，但ImportFile函数总是失败。不幸的是，它从未抛出异常，也没有给出任何关于原因的有用信息 下面的代码显示了我正在做的事情，尽管我已经删除了一些与问题无关的东西 当我修改现有的应用程序时，代码有点复杂，因为有一种方法可以找到文件，然后后台线程调用另一种方法来进行实际下载，因此用户可以在下载文件时继续工作 另外，我在GetFileListAsync中显示的一些代码实际上也存在于其他方法中，因为它们被多次使用。。。我没有包括权限的东西，因为这一切似乎都很好 这是首先被调用的方法，用于查找对象句柄列表C# 为什么MtpDevice.ImportFile总是失败？,c#,android,xamarin,import,mtp,C#,Android,Xamarin,Import,Mtp,我正在修改一个现有的应用程序，它是用C#in Xamarin编写的，专门为Android构建的 现有的应用程序在摄像头的wifi卡上搜索文件，并通过HTTP接口下载。我试图让它下载的文件使用拴在一个USB电缆代替，但无法得到文件下载 我正在使用MtpDevice尝试下载，但ImportFile函数总是失败。不幸的是，它从未抛出异常，也没有给出任何关于原因的有用信息 下面的代码显示了我正在做的事情，尽管我已经删除了一些与问题无关的东西 当我修改现有的应用程序时，代码有点复杂，因为有一种方法可以找到
public async Task<List<MyFileClass>> GetFileListAsync()
{
var results = new List<MyFileClass>();
UsbDeviceConnection usbDeviceConnection = null;
MtpDevice mtpDevice = null;
UsbDevice usbDevice = null;
// all this stuff works as expected...
UsbManager usbManager = (UsbManager)Android.App.Application.Context.GetSystemService(Context.UsbService);
try
{
if (usbManager.DeviceList != null && usbManager.DeviceList.Count > 0)
{
foreach (var usbAccessory in usbManager.DeviceList)
{
var device = usbAccessory.Value;
usbDevice = usbAccessory.Value;
break; // should only ever be one, but break here anyway
}
}
}
catch (Exception ex)
{
Log.Error(ex, "Error getting USB devices");
}
if (usbDevice == null)
{
Log.Information("ConnectedDevice is null");
return false;
}
if (!UsbManager.HasPermission(usbDevice))
{
Log.Information("Requesting permission must have failed");
return false;
}
try
{
usbDeviceConnection = UsbManager.OpenDevice(usbDevice);
}
catch (Exception ex)
{
Log.Error(ex, "opening usb connection");
return false;
}
try
{
mtpDevice = new MtpDevice(usbDevice);
}
catch (Exception ex)
{
Log.Error(ex, "creating mtpdevice");
return false;
}
try
{
mtpDevice.Open(usbDeviceConnection);
}
catch (Exception ex)
{
Log.Error(ex, " opening mtpdevice");
usbDeviceConnection.Close();
return false;
}
// then start looking for files
var storageUnits = mtpDevice.GetStorageIds();
if (storageUnits == null || storageUnits.Length == 0)
{
Log.Information("StorageUnits is empty");
mtpDevice.Close();
usbDeviceConnection.Close();
return false;
}
foreach (var storageUnitId in storageUnits)
{
var storageUnit = mtpDevice.GetStorageInfo(storageUnitId);
if (storageUnit != null)
{
// recurse directories to get list of files
await RecurseMTPDirectories(results, storageUnitId, docketId, docket, db);
}
}
}
private async Task RecurseMTPDirectories(List<MyFileClass> files, int storageUnitId, string parentFolder = "\\", int parentHandle = -1)
{
var results = new List<FlashAirFile>();
var directoryObjects = new List<MtpObjectInfo>();
var objectHandles = mtpDevice.GetObjectHandles(storageUnitId, 0, parentHandle);
if (objectHandles != null && objectHandles.Length > 0)
{
foreach (var objectHandle in objectHandles)
{
MtpObjectInfo objectInfo = mtpDevice.GetObjectInfo(objectHandle);
if (objectInfo != null)
{
if (objectInfo.Format == MtpFormat.Association)
{
// add to the list to recurse into, but do this at the end
directoryObjects.Add(objectInfo);
}
else
{
// it' a file - add it only if it's one we want
try
{
var file = new MyFileClass()
{
TotalBytes = objectInfo.CompressedSize,
FileNameOnCard = objectInfo.Name,
DirectoryOnCard = parentFolder,
MTPHandle = objectHandle
};
}
catch (Exception e)
{
Log.Error(e, " trying to create MTP FlashAirFile");
}
}
}
}
}
foreach (var directoryObject in directoryObjects)
{
string fullname = parentFolder + directoryObject.Name;
await RecurseMTPDirectories(files, storageUnitId, $"{fullname}\\", directoryObject.ObjectHandle);
}
return results;
}
public async Task<int> DownloadFileAsync(MyFileClass file, string destination)
{
int receivedBytes = 0;
int objectHandle = file.MTPHandle;
connectedDevice = await GetAttachedDevice();
if (connectedDevice == null || !UsbManager.HasPermission(connectedDevice))
return receivedBytes;
if (!await OpenAttachedDevice())
return receivedBytes;
var rootFolder = await FileSystem.Current.GetFolderFromPathAsync(destination);
var localFile = rootFolder.Path;
try
{
Log.Information($"Attempting to download ID {objectHandle} to {localFile}");
// try downloading just using path
bool success = mtpDevice.ImportFile(objectHandle, localFile);
if (!success)
{
// try it with a / on the end of the path
localFile += '/';
Log.Information($"Attempting to download ID {file.DownloadManagerId} to {localFile}");
success = mtpDevice.ImportFile(objectHandle, localFile);
}
if (!success)
{
// try it with the filename on the end of the path as well
localFile += file.FileNameOnSdCard;
Log.Information($"Attempting to download ID {file.DownloadManagerId} to {localFile}");
success = mtpDevice.ImportFile(objectHandle, localFile);
}
if (!success)
{
throw new Exception($"mtpDevice.ImportFile failed for {file.FileNameOnSdCard}");
}
// do stuff here to handle success
}
catch (Exception ex) when (ex is OperationCanceledException || ex is TaskCanceledException)
{
// do some other stuff here in the database
//rethrow the exception so it can be handled further up the chain.
throw;
}
return receivedBytes;
}
公共异步任务下载FileAsync（MyFileClass文件，字符串目标）
{
int receivedBytes=0；
int objectHandle=file.MTPHandle；
connectedDevice=等待GetAttachedDevice（）；
如果（connectedDevice==null | |！UsbManager.HasPermission（连接