收到 的错误.在 foreach 循环中使用 lambda 表达式来表示无效参数
本文关键字：表达式 lambda 表示 参数 无效 错误 foreach 循环 收到 | 更新日期: 2023-09-27 18:35:48
我正忙于在VS2010中创建索引Windows表单应用程序的文件/文件夹（大学作业）。出于测试目的，文件/文件夹索引类位于控制台应用程序中
我使用以下方法浏览文件夹，它运行良好并写入指定驱动器中的所有文件夹名称。我主要从 msdn 资源（使用递归方法）中将其放在一起，并进行了修改，因为它不包括获取文件夹名称。
我想排除某些文件夹，并决定使用 lambda 表达式和带有单词列表的列表将是最快的，尽管我可以放置一个循环，通过一个带有 if 比较的数组，但在我看来这会更慢（不是我对 c# 中复杂的工作原理有足够的了解）。我简要地查看了 lambda 表达式，看看我自己是否无法修复它。
这是我的代码，没有任何文件夹排除
class Program
{
static System.Collections.Specialized.StringCollection log = new System.Collections.Specialized.StringCollection();
private static List<string> _excludedDirectories = new List<string>() { "Windows", "AppData", "$WINDOWS.~BT", "MSOCache", "ProgramData", "Config.Msi", "$Recycle.Bin", "Recovery", "System Volume Information", "Documents and Settings", "Perflogs" };
//method to check
static bool isExcluded(List<string> exludedDirList, string target)
{
return exludedDirList.Any(d => new DirectoryInfo(target).Name.Equals(d));
}
static void Main()
{
string[] drives = {"C:''"};
foreach (string dr in drives)
{
DriveInfo di = new System.IO.DriveInfo(dr);
// Here we skip the drive if it is not ready to be read.
if (di.IsReady)
{
DirectoryInfo rootDir = di.RootDirectory;
WalkDirectoryTree(rootDir);
}
else
{
Console.WriteLine("The drive {0} could not be read", di.Name);
continue;
}
}
// Write out all the files that could not be processed.
Console.WriteLine("Files with restricted access:");
foreach (string s in log)
{
Console.WriteLine(s);
}
// Keep the console window open in debug mode.
Console.WriteLine("Press any key");
Console.ReadKey();
}
static void WalkDirectoryTree(System.IO.DirectoryInfo root)
{
FileInfo[] files = null;
DirectoryInfo[] subDirs = null;
StreamWriter filex = new System.IO.StreamWriter("test.txt", true);
if (filex != null)
{
filex.Close();
}
// Process all the folders directly under the root
try
{
subDirs = root.GetDirectories();
}// This is thrown if even one of the folders requires permissions greater than the application provides.
catch (UnauthorizedAccessException e)
{
log.Add(e.Message);
}
catch (System.IO.DirectoryNotFoundException e)
{
Console.WriteLine(e.Message);
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
// Process all the files directly under the root
try
{
files = root.GetFiles("*.*");
}// This is thrown if even one of the files requires permissions greater than the application provides.
catch (UnauthorizedAccessException e)
{
log.Add(e.Message);
}
catch (System.IO.DirectoryNotFoundException e)
{
Console.WriteLine(e.Message);
}
catch(Exception e)
{
Console.WriteLine(e.Message);
}
if (files != null)
{
filex = new StreamWriter("test.txt", true);
foreach (FileInfo fi in files)
{
// In this example, we only access the existing FileInfo object. If we
// want to open, delete or modify the file, then
// a try-catch block is required here to handle the case
// where the file has been deleted since the call to TraverseTree().
Console.WriteLine(fi.FullName);
filex.WriteLine(fi.FullName);
}
filex.Close();
}
if (subDirs != null)
{
//var filteredDirs = Directory.GetDirectories(root.Name).Where(d => !isExcluded(_excludedDirectories, d));
foreach (DirectoryInfo subds in subDirs)
{
filex = new StreamWriter("test.txt", true);
Console.WriteLine(subds.FullName);
filex.WriteLine(subds.FullName);
filex.Close();
foreach (DirectoryInfo dirInfo in subDirs)
{
// Resursive call for each subdirectory.
WalkDirectoryTree(dirInfo);
}
}
filex.Close();// Because at end filestream needs to close
}
}
}
所以我尝试合并.其中（d => ！isExcluded（_excludedDirectories， d）） 进入我的循环：
if (subDirs != null)
{
//var filteredDirs = Directory.GetDirectories(root.Name).Where(d => !isExcluded(_excludedDirectories, d));
foreach (DirectoryInfo subds in subDirs.Where(d => !isExcluded(_excludedDirectories, d)))
{
filex = new StreamWriter("test.txt", true);
Console.WriteLine(subds.FullName);
filex.WriteLine(subds.FullName);
filex.Close();
foreach (DirectoryInfo dirInfo in subDirs)
{
// Resursive call for each subdirectory.
WalkDirectoryTree(dirInfo);
}
}
filex.Close();// Because at end filestream needs to close
}
问题：我在感叹号后收到一个错误，说"最佳重载方法匹配有一些无效的参数..."我应该做什么/更改，我应该采取更简单的路线并在循环中使用循环和 if 语句来写入文件夹名称？因为我也知道如何做到这一点。请记住，我目前的做法（至少尝试）是因为我认为它会更优化/更快。如果它没有这么大的区别，请告诉我，我会使用我知道的方式。
我的猜测是，我试图在foreach中放置一个.where，这是一件坏事，我意识到为什么会或可能是这样。
我也试过：
if (subDirs != null)
{
//var filteredDirs = Directory.GetDirectories(root.Name).Where(d => !isExcluded(_excludedDirectories, d));
foreach (DirectoryInfo subds in subDirs)
{
if ((d => !isExcluded(_excludedDirectories, d)))
{
filex = new StreamWriter("test.txt", true);
Console.WriteLine(subds.FullName);
filex.WriteLine(subds.FullName);
filex.Close();
foreach (DirectoryInfo dirInfo in subDirs)
{
// Resursive call for each subdirectory.
WalkDirectoryTree(dirInfo);
}
}
}
filex.Close();// Because at end filestream needs to close
}
但是收到有关无法将 lamba 表达式转换为 bool 类型的错误，因为它不是委托
如果您想查看其他代码，请告诉我，然后我会添加它，只是看起来有点多。
d在这里不是string，而是DirectoryInfo。更改isExcluded方法签名以正确处理d类型。
您的签名是：
static bool isExcluded(List<string> exludedDirList, string target)
它应该是：
static bool isExcluded(List<string> exludedDirList, DirectoryInfo target)
您的方法最终将是：
//method to check
static bool isExcluded(List<string> exludedDirList, DirectoryInfo target)
{
return exludedDirList.Any(d => target.Name.Equals(d));
}
问题就在这里：
foreach (DirectoryInfo subds in subDirs.Where(d => !isExcluded(_excludedDirectories, d)))
subDirs 的类型是 DirectoryInfo，你的 isExcluded 接受一个字符串作为第二个参数。
你想要：
foreach (DirectoryInfo subds in subDirs.Where(d => !isExcluded(_excludedDirectories, d.Name)))