Question

When doing something like ... = myFileInfo.FullName – does it access the drive or is it loaded to memory with the creation of myFileInfo?

Answer 1

Yes, they are saved in memory – it’s a snapshot of the file when you created the FileInfo class and first accessed a property. You can call the Refresh method to make sure the properties are up to date.

You can also use the static members of the File class to read the file info at that point in time, however, this incurs the overhead of a security check each time.

My evidence for this comes from using ILSpy; we can see that, if we access a property like Length:

    public long Length
    {
        [SecuritySafeCritical]
        get
        {
            if (this._dataInitialised == -1)
            {
                base.Refresh();
            }
            if (this._dataInitialised != 0)
            {
                __Error.WinIOError(this._dataInitialised, base.DisplayPath);
            }
            if ((this._data.fileAttributes & 16) != 0)
            {
                __Error.WinIOError(2, base.DisplayPath);
            }
            return (long)this._data.fileSizeHigh << 32 | ((long)this._data.fileSizeLow & (long)((ulong)-1));
        }
    }

Then, if the internal data has not been initialized, Refresh is called:

public void Refresh()
{
    this._dataInitialised = File.FillAttributeInfo(this.FullPath, ref this._data, false, false);
}

This then populates the data for subsequent checks. So unless you call Refresh again, you’ll get the data from the point in time you first accessed a property.

The reason for caching this data is inferred from the FileInfo MSDN article:

If you are going to reuse an object several times, consider using the
instance method of FileInfo instead of the corresponding static
methods of the File class, because a security check will not always be
necessary.

It obviously caches this data to avoid the expense of a SecurityCheck each time, leaving it up to the user to call Refresh and decide when to pay this cost.