How to delete all files and folders in a directory?

Yes, that's the correct way to do it. If you're looking to give yourself a "Clean" (or, as I'd prefer to call it, "Empty" function), you can create an extension method.

public static void Empty(this System.IO.DirectoryInfo directory)
{
    foreach(System.IO.FileInfo file in directory.GetFiles()) file.Delete();
    foreach(System.IO.DirectoryInfo subDirectory in directory.GetDirectories()) subDirectory.Delete(true);
}

This will then allow you to do something like..

System.IO.DirectoryInfo directory = new System.IO.DirectoryInfo(@"C:\...");

directory.Empty();

System.IO.DirectoryInfo di = new DirectoryInfo("YourPath");

foreach (FileInfo file in di.GetFiles())
{
    file.Delete(); 
}
foreach (DirectoryInfo dir in di.GetDirectories())
{
    dir.Delete(true); 
}

---

If your directory may have many files, EnumerateFiles() is more efficient than GetFiles(), because when you use EnumerateFiles() you can start enumerating it before the whole collection is returned, as opposed to GetFiles() where you need to load the entire collection in memory before begin to enumerate it. See this quote here:

Therefore, when you are working with many files and directories, EnumerateFiles() can be more efficient.

The same applies to EnumerateDirectories() and GetDirectories(). So the code would be:

foreach (FileInfo file in di.EnumerateFiles())
{
    file.Delete(); 
}
foreach (DirectoryInfo dir in di.EnumerateDirectories())
{
    dir.Delete(true); 
}

For the purpose of this question, there is really no reason to use GetFiles() and GetDirectories().

The following code will clear the folder recursively:

private void clearFolder(string FolderName)
{
    DirectoryInfo dir = new DirectoryInfo(FolderName);

    foreach(FileInfo fi in dir.GetFiles())
    {
        fi.Delete();
    }

    foreach (DirectoryInfo di in dir.GetDirectories())
    {
        clearFolder(di.FullName);
        di.Delete();
    }
}