SFOParser.SFOParser C# (CSharp) Method

    public SFOParser(string filePath)
    {
        FileAttributes attr = File.GetAttributes(filePath);

        //detect whether its a directory or file
        if ((attr & FileAttributes.Directory) == FileAttributes.Directory)
            throw new Exception("不是正確的SFO檔");
        this.filePath = filePath;
        BinaryReader bs = new BinaryReader(new FileStream(filePath, FileMode.Open));
        byte[] tmpbuffer = bs.ReadBytes(Marshal.SizeOf(typeof(PsfHdr)));
        GCHandle handle = GCHandle.Alloc(tmpbuffer, GCHandleType.Pinned);
        psfHdr = (PsfHdr)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(PsfHdr));
        handle.Free();

        if (!Enumerable.SequenceEqual( psfHdr.psf, new char[] {'\0','P', 'S', 'F'})) {
            throw new Exception("不是正確的SFO檔");
        }
        #if DEBUG
        Console.WriteLine("{0}個區塊", psfHdr.nsects);
        #endif
        psfSec = new PsfSec[psfHdr.nsects];
        for (int i = 0; i < psfHdr.nsects; i++) {
            tmpbuffer = bs.ReadBytes(Marshal.SizeOf(typeof(PsfSec)));
            handle = GCHandle.Alloc(tmpbuffer, GCHandleType.Pinned);
            psfSec[i] = (PsfSec)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(PsfSec));
            handle.Free();
        }

        pairs = new SFOPair[psfHdr.nsects];
        for (int i = 0; i < psfHdr.nsects; i++) {
            bs.BaseStream.Position = psfSec[i].label_off + psfHdr.label_ptr;
            tmpbuffer = readByteString(bs);
            pairs[i] = new SFOPair();
            pairs[i].label = encode.GetString(tmpbuffer);
            pairs[i].psfsec = psfSec[i];
            bs.BaseStream.Position = psfSec[i].data_off + psfHdr.data_ptr;
            tmpbuffer = bs.ReadBytes(psfSec[i].datafield_used);
            pairs[i].type = psfSec[i].data_type;
            switch (psfSec[i].data_type) {
                case 0:
                    pairs[i].value = tmpbuffer;
                    break;
                case 2:
                    pairs[i].value = encode.GetString(tmpbuffer);
                    break;
                case 4:
                    pairs[i].value = BitConverter.ToInt32(tmpbuffer, 0);
                    break;
                default:
                    break;
            }
        #if DEBUG
            Console.WriteLine("Label:{0}, Type:{1:X}, Value:{2}", pairs[i].label, pairs[i].type, pairs[i].value);
        #endif
        }

        bs.Close();
    }