Managed Extensions: Finding Files by Extension

Welcome to this week's installment of .NET Tips & Techniques! Each week, award-winning Architect and Lead Programmer Tom Archer demonstrates how to perform a practical .NET programming task using either C# or Managed C++ Extensions.

A reader recently asked me how to locate all files with a specific extension so that he could register those files with his application. Basically, all he needs to do is allow the user to specify where he wants the search to begin (accomplished with the .NET FolderBrowserDialog component) and then have a recursive function enumerate each folder and compare the searched-for file extension with the extension of each file found. The "matching" files are returned to the caller in an ArrayList object. Figure 1 shows an example of a demo application I wrote to illustrate this:

Folder-Browser Dialogs in .NET

1. I opened the form whose class will use the folder browser.
2. I opened the Toolbox and dragged a FolderBrowserDialog control onto the form. (I positioned it below the form, as it's a class and not a UI element.)
3. I specified the needed properties. IntelliSense helped here, but the most commonly specified ones were things like Description (the text that will display on the dialog above the folder list), ShowNewFolderButton (a property that allows you to specify if you want the user to be able to create folders while browsing), and RootFolder (whose value is used to specify the top-level folder that the user cannot exceed). The demo's Form::Load method has the following initialization:

   private: System::Void Form1_Load(System::Object *  sender, 
     System::EventArgs *  e)
   {
   ...
   browser->Description = S"Select the directory that you want to use as 
     the starting point for the search";
   browser->ShowNewFolderButton = false;
   browser->RootFolder = Environment::SpecialFolder::Desktop;
   ...
   

4. Once initialized, the following code invokes the FolderBrowserDialog dialog and uses the user-selected path to update a Label (static) control on the form:

   private: System::Void folderBrowserButton_Click(System::Object *  sender, System::EventArgs *  e)
   {
     System::Windows::Forms::DialogResult result = browser->ShowDialog();
     if (DialogResult::OK == result)
       startingFolder->Text = browser->SelectedPath;
   }
   

   Figure 2 shows the result.

   

Searching for Files

1. Call the System::IO::Directory::GetFiles method to retrieve all files for a specified folder. The files' names are returned in an ArrayList object where each file is a String object.
2. Enumerate the returned ArrayList object using a for loop.
3. For each String (file name) in the ArrayList, call the Path::GetExtension method to return the file name's extension and then compare it (ignoring case) to the caller-specified extension. If the strings match, then the file name is added to the caller's passed ArrayList object.
4. Once the current folder has been enumerated, the method checks the Search-Subfolders flag. If it is off, the method returns. If it is on, the method calls the System::IO::Directory::GetDirectories method to retrieve all folders for the current folder. These folders are then enumerated and the FileSearcher::FindByExtension method calls itself for each found folder.

__gc class FileSearcher
{
public:
  static void FindByExtension(String* startingFolder, 
                              String* extension, 
                              ArrayList* matchingFiles,
                              bool recurseSubFolders)
  {
    String* fileList[] = Directory::GetFiles(startingFolder);

    String* fileName;

    // search current folder
    for (int i = 0; i < fileList->Count; i++)
    {
      fileName = static_cast<String*>(fileList->Item[i]);

      if (0 == String::Compare(Path::GetExtension(fileName), 
                               String::Format(S"{0}{1}", 
                                              extension->StartsWith(S".") ? S"" : S".", 
                                              extension), 
                               true))
        matchingFiles->Add(fileName);
    }

    if (recurseSubFolders)
    {
      // for each subfolder
      fileList = Directory::GetDirectories(startingFolder);
      for (int i = 0; i < fileList->Count; i++)
      {
        FindByExtension(static_cast<String*>(fileList->Item[i]), 
                        extension, 
                        matchingFiles,
                        true);
      }
    }
  }
};

ArrayList* matches = new ArrayList();
FileSearcher::FindByExtension(startingFolder->Text, 
                              extensionToFind->Text, 
                              matches, 
                              searchSubfolders->Checked);

listBox1->Items->Clear();

for (int i = 0; i < matches->Count; i++)
{
  listBox1->Items->Add(matches->Item[i]);
}

Areas That Can Be Improved

Not only would that flesh out the FileSearcher class, making it more usable, but it would also represent a great example of where and how asynchronous delegates and events can be used. Depending on the feedback I get from this article, I'll do that article at some time in the future.

Download the Code

To download the accompanying source code for this article, click here.

About the Author

The founder of the Archer Consulting Group (ACG), Tom Archer has been the project lead on three award-winning applications and is a best-selling author of 10 programming books as well as countless magazine and online articles.