我有一个程序可以使用以下方法将一些数据写入文件。

public void ExportToFile(string filename)
{
     using(FileStream fstream = new FileStream(filename,FileMode.Create))
     using (TextWriter writer = new StreamWriter(fstream))
     {
         // try catch block for write permissions 
         writer.WriteLine(text);

     }
}

运行程序时出现错误：

Unhandled Exception: System.UnauthorizedAccessException: Access to the path 'mypath' is denied.
     at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
     at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access,
  nt32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions
  ptions, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy)
     at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access
  FileShare share, Int32 bufferSize, FileOptions options, String msgPath, Boolea
  bFromProxy)

问题：我需要什么代码才能捕获此错误，如何授予访问权限？

解决方案

更新：

根据此答案修改了代码，以摆脱过时的方法。

我们可以使用Security名称空间进行检查：

public void ExportToFile(string filename)
{
    var permissionSet = new PermissionSet(PermissionState.None);    
    var writePermission = new FileIOPermission(FileIOPermissionAccess.Write, filename);
    permissionSet.AddPermission(writePermission);

    if (permissionSet.IsSubsetOf(AppDomain.CurrentDomain.PermissionSet))
    {
        using (FileStream fstream = new FileStream(filename, FileMode.Create))
        using (TextWriter writer = new StreamWriter(fstream))
        {
            // try catch block for write permissions 
            writer.WriteLine("sometext");

        }
    }
    else
    {
        //perform some recovery action here
    }

}

就获得那些许可而言，我们将必须要求用户以某种方式为我们执行此操作。如果我们可以通过编程方式执行此操作，那么我们都会有麻烦;)

当代码执行以下操作时：

• 检查当前用户是否有权执行某项操作。
• 执行需要检入1的权利的操作。

我们冒着权限在1到2之间变化的风险，因为我们无法预测运行时系统上还会发生什么。因此，即使我们先前已经检查了权限，代码也应该处理引发UnauthorizedAccessException的情况。

请注意，SecurityManager类用于检查CAS权限，并且实际上不与OS一起检查当前用户是否对指定位置(通过ACL和ACE)具有写权限。因此，对于本地运行的应用程序，IsGranted将始终返回true。

示例(源自乔希的示例)：

//1. Provide early notification that the user does not have permission to write.
FileIOPermission writePermission = new FileIOPermission(FileIOPermissionAccess.Write, filename);
if(!SecurityManager.IsGranted(writePermission))
{
    //No permission. 
    //Either throw an exception so this can be handled by a calling function
    //or inform the user that they do not have permission to write to the folder and return.
}

//2. Attempt the action but handle permission changes.
try
{
    using (FileStream fstream = new FileStream(filename, FileMode.Create))
    using (TextWriter writer = new StreamWriter(fstream))
    {
        writer.WriteLine("sometext");
    }
}
catch (UnauthorizedAccessException ex)
{
    //No permission. 
    //Either throw an exception so this can be handled by a calling function
    //or inform the user that they do not have permission to write to the folder and return.
}

这很棘手，不建议尝试根据原始ACL(可通过System.Security.AccessControl类获得的所有ACL)以编程方式从文件夹中计算有效权限。有关Stack Overflow和更广泛的网络的其他答案，建议尝试执行该操作以了解是否允许权限。这篇文章总结了实现权限计算所需的知识，并且应该足以使我们摆脱此限制。

我们可以尝试使用以下代码块来检查目录是否具有写访问权限。

它检查FileSystemAccessRule。

string directoryPath = "C:\XYZ"; //folderBrowserDialog.SelectedPath;
           bool isWriteAccess = false;
           try
           {
              AuthorizationRuleCollection collection = Directory.GetAccessControl(directoryPath).GetAccessRules(true, true, typeof(System.Security.Principal.NTAccount));
              foreach (FileSystemAccessRule rule in collection)
              {
                 if (rule.AccessControlType == AccessControlType.Allow)
                 {
                    isWriteAccess = true;
                    break;
                 }
              }
           }
           catch (UnauthorizedAccessException ex)
           {
              isWriteAccess = false;
           }
           catch (Exception ex)
           {
              isWriteAccess = false;
           }
           if (!isWriteAccess)
           {
             //handle notifications                 
           }

抱歉，以前的解决方案都没有帮助我。我需要检查双方：SecurityManager和SO权限。我已经通过Josh代码和iain答案学到了很多东西，但是恐怕我需要使用Rakesh代码(也感谢他)。仅有一个错误：我发现他只检查"允许"而不检查"拒绝"权限。所以我的建议是：

string folder;
        AuthorizationRuleCollection rules;
        try {
            rules = Directory.GetAccessControl(folder)
                .GetAccessRules(true, true, typeof(System.Security.Principal.NTAccount));
        } catch(Exception ex) { //Posible UnauthorizedAccessException
            throw new Exception("No permission", ex);
        }

        var rulesCast = rules.Cast<FileSystemAccessRule>();
        if(rulesCast.Any(rule => rule.AccessControlType == AccessControlType.Deny)
            || !rulesCast.Any(rule => rule.AccessControlType == AccessControlType.Allow))
            throw new Exception("No permission");

        //Here I have permission, ole!