有没有办法检查一个文件是否在使用？
我正在用C＃编写一个需要重复访问1个图像文件的程序。 大多数情况下它都能正常工作，但如果我的电脑运行速度很快，它会在文件保存回文件系统之前尝试访问该文件，并抛出一个错误：“正被另一进程使用的文件”。
我想找到一个解决方法，但我所有的谷歌搜索只使用异常处理创建检查。 这是违背我的宗教信仰的，所以我想知道是否有人有更好的方式去做？
已更新此解决方案的注意事项 ：使用FileAccess.ReadWrite检查将无法读取只读文件，因此该解决方案已被修改为使用FileAccess.Read进行检查。 虽然这个解决方案是FileAccess.Read因为试图检查FileAccess.Read将失败，如果文件上有Write或Read锁，但是，如果文件没有Write或Read锁，该解决方案将不起作用，即它已被FileShare.Read或FileShare.Write访问权限打开（用于阅读或写作）。
原文：我在过去几年中使用过这些代码，而且我没有遇到任何问题。
理解你对使用异常的犹豫，但是你无法一直避免它们：
protected virtual bool IsFileLocked(FileInfo file)
{
FileStream stream = null;
try
{
stream = file.Open(FileMode.Open, FileAccess.Read, FileShare.None);
}
catch (IOException)
{
//the file is unavailable because it is:
//still being written to
//or being processed by another thread
//or does not exist (has already been processed)
return true;
}
finally
{
if (stream != null)
stream.Close();
}
//file is not locked
return false;
}
您可能会遇到线程争用情况，因此存在一些用作安全漏洞的文档示例。 如果您检查该文件是否可用，但是尝试并使用该文件，则可能会在此时抛出恶意用户可能用来在您的代码中强制并利用的点。
你最好的选择是尝试获取文件句柄的try catch / finally。
try
{
using (Stream stream = new FileStream("MyFilename.txt", FileMode.Open))
{
// File/Stream manipulating code here
}
} catch {
//check here why it failed and ask user to retry if the file is in use.
}
用它来检查文件是否被锁定：
using System.IO;
using System.Runtime.InteropServices;
internal static class Helper
{
const int ERROR_SHARING_VIOLATION = 32;
const int ERROR_LOCK_VIOLATION = 33;
private static bool IsFileLocked(Exception exception)
{
int errorCode = Marshal.GetHRForException(exception) & ((1 << 16) - 1);
return errorCode == ERROR_SHARING_VIOLATION || errorCode == ERROR_LOCK_VIOLATION;
}
internal static bool CanReadFile(string filePath)
{
//Try-Catch so we dont crash the program and can check the exception
try {
//The "using" is important because FileStream implements IDisposable and
//"using" will avoid a heap exhaustion situation when too many handles
//are left undisposed.
using (FileStream fileStream = File.Open(filePath, FileMode.Open, FileAccess.ReadWrite, FileShare.None)) {
if (fileStream != null) fileStream.Close(); //This line is me being overly cautious, fileStream will never be null unless an exception occurs... and I know the "using" does it but its helpful to be explicit - especially when we encounter errors - at least for me anyway!
}
}
catch (IOException ex) {
//THE FUNKY MAGIC - TO SEE IF THIS FILE REALLY IS LOCKED!!!
if (IsFileLocked(ex)) {
// do something, eg File.Copy or present the user with a MsgBox - I do not recommend Killing the process that is locking the file
return false;
}
}
finally
{ }
return true;
}
}
出于性能原因，我建议您在相同的操作中阅读文件内容。 这里有些例子：
public static byte[] ReadFileBytes(string filePath)
{
byte[] buffer = null;
try
{
using (FileStream fileStream = File.Open(filePath, FileMode.Open, FileAccess.ReadWrite, FileShare.None))
{
int length = (int)fileStream.Length; // get file length
buffer = new byte[length]; // create buffer
int count; // actual number of bytes read
int sum = 0; // total number of bytes read
// read until Read method returns 0 (end of the stream has been reached)
while ((count = fileStream.Read(buffer, sum, length - sum)) > 0)
sum += count; // sum is a buffer offset for next reading
fileStream.Close(); //This is not needed, just me being paranoid and explicitly releasing resources ASAP
}
}
catch (IOException ex)
{
//THE FUNKY MAGIC - TO SEE IF THIS FILE REALLY IS LOCKED!!!
if (IsFileLocked(ex))
{
// do something?
}
}
catch (Exception ex)
{
}
finally
{
}
return buffer;
}
public static string ReadFileTextWithEncoding(string filePath)
{
string fileContents = string.Empty;
byte[] buffer;
try
{
using (FileStream fileStream = File.Open(filePath, FileMode.Open, FileAccess.ReadWrite, FileShare.None))
{
int length = (int)fileStream.Length; // get file length
buffer = new byte[length]; // create buffer
int count; // actual number of bytes read
int sum = 0; // total number of bytes read
// read until Read method returns 0 (end of the stream has been reached)
while ((count = fileStream.Read(buffer, sum, length - sum)) > 0)
{
sum += count; // sum is a buffer offset for next reading
}
fileStream.Close(); //Again - this is not needed, just me being paranoid and explicitly releasing resources ASAP
//Depending on the encoding you wish to use - I'll leave that up to you
fileContents = System.Text.Encoding.Default.GetString(buffer);
}
}
catch (IOException ex)
{
//THE FUNKY MAGIC - TO SEE IF THIS FILE REALLY IS LOCKED!!!
if (IsFileLocked(ex))
{
// do something?
}
}
catch (Exception ex)
{
}
finally
{ }
return fileContents;
}
public static string ReadFileTextNoEncoding(string filePath)
{
string fileContents = string.Empty;
byte[] buffer;
try
{
using (FileStream fileStream = File.Open(filePath, FileMode.Open, FileAccess.ReadWrite, FileShare.None))
{
int length = (int)fileStream.Length; // get file length
buffer = new byte[length]; // create buffer
int count; // actual number of bytes read
int sum = 0; // total number of bytes read
// read until Read method returns 0 (end of the stream has been reached)
while ((count = fileStream.Read(buffer, sum, length - sum)) > 0)
{
sum += count; // sum is a buffer offset for next reading
}
fileStream.Close(); //Again - this is not needed, just me being paranoid and explicitly releasing resources ASAP
char[] chars = new char[buffer.Length / sizeof(char) + 1];
System.Buffer.BlockCopy(buffer, 0, chars, 0, buffer.Length);
fileContents = new string(chars);
}
}
catch (IOException ex)
{
//THE FUNKY MAGIC - TO SEE IF THIS FILE REALLY IS LOCKED!!!
if (IsFileLocked(ex))
{
// do something?
}
}
catch (Exception ex)
{
}
finally
{
}
return fileContents;
}
自己尝试一下：
byte[] output1 = Helper.ReadFileBytes(@"c:temptest.txt");
string output2 = Helper.ReadFileTextWithEncoding(@"c:temptest.txt");
string output3 = Helper.ReadFileTextNoEncoding(@"c:temptest.txt");
上一篇: Is there a way to check if a file is in use?
下一篇: Entity Framwork Unable to Load the specified metadata resource