Simplifying exception handling on Enumerators

Question

I have a files search function that iterates over a given directory until a given depth is reached and returns the found files. I did this via the Enumerate methods of the Directory class and yield return the results. Since it's very likely that I hit a directory that I can't access (e.g. system directories) or generate a too long path (if the depth is large), I have to catch the exceptions from these cases. However since I can't use yield in try/catch statements, I find my code pretty bloated, because I have to seperate the critical method calls from the rest.

Is there a better/shorter way to do this, or are there best practices for that case?

private IEnumerable<string> SearchSubdirs(string currentDir, int currentDepth) {
 IEnumerable<string> exeFiles;
 try {
 exeFiles = Directory.EnumerateFiles(currentDir, "*.exe");
 }
 catch (UnauthorizedAccessException uae) {
 Debug.WriteLine(uae.Message);
 yield break;
 }
 catch (PathTooLongException ptle) {
 Debug.WriteLine(ptle.Message);
 yield break;
 }
 foreach (string currentFile in exeFiles) {
 // Ignore unistaller *.exe files
 if (currentFile.IndexOf("unins", 0, StringComparison.CurrentCultureIgnoreCase) == -1) {
 yield return currentFile;
 }
 }
 if (currentDepth < maxDepth) {
 IEnumerable<string> subDirectories;
 currentDepth++;
 try {
 subDirectories = Directory.EnumerateDirectories(currentDir);
 }
 catch (UnauthorizedAccessException uae) {
 Debug.WriteLine(uae.Message);
 yield break;
 }
 catch (PathTooLongException ptle) {
 Debug.WriteLine(ptle.Message);
 yield break;
 }
 foreach (string subDir in subDirectories) {
 foreach (string file in SearchSubdirs(subDir, currentDepth)) {
 yield return file;
 }
 }
 }
}

• Leonid: msdn.microsoft.com/en-us/library/bb513869.aspx
• radarbob: stackoverflow.com/questions/1393178/…

Answer 1

I would use Linq methods to simplify the code. Also I've extracted 2 methods to simplify the main method. And please rename GetFilesWeAreLookingFor to whatever your find appropriate :).

private static IEnumerable<string> GetFilesWeAreLookingFor(string currentDir)
{
 try
 {
 return Directory.EnumerateFiles(currentDir, "*.exe")
 .Where(fileName => fileName.IndexOf("unins", 0, StringComparison.CurrentCultureIgnoreCase) == -1);
 }
 catch (UnauthorizedAccessException uae)
 {
 Debug.WriteLine(uae.Message);
 }
 catch (PathTooLongException ptle)
 {
 Debug.WriteLine(ptle.Message);
 }
 return Enumerable.Empty<string>();
}
private IEnumerable<string> GetNestedFiles(string currentDir, int nestedDepth)
{
 try
 {
 return Directory.EnumerateDirectories(currentDir)
 .SelectMany(subDirectory => SearchSubdirs(subDirectory, nestedDepth));
 }
 catch (UnauthorizedAccessException uae)
 {
 Debug.WriteLine(uae.Message);
 }
 catch (PathTooLongException ptle)
 {
 Debug.WriteLine(ptle.Message);
 }
 return Enumerable.Empty<string>();
}
private IEnumerable<string> SearchSubdirs(string currentDir, int currentDepth)
{
 IEnumerable<string> filesWeAreLookingFor = GetFilesWeAreLookingFor(currentDir);
 if (currentDepth < _maxDepth)
 filesWeAreLookingFor = filesWeAreLookingFor.Concat(GetNestedFiles(currentDir, currentDepth + 1));
 return filesWeAreLookingFor;
}