Load fil asynkront

Kode 

        private void button1_Click(object sender, EventArgs e)
        {
            FileStream s = new FileStream(@"c:\\temp\\output.txt", FileMode.Open, FileAccess.Read, FileShare.Read, 256, true);
            AsyncCallback callback = new AsyncCallback(EndReadCallback);
            State state = new State(s);
            s.BeginRead(state.ReadArray, 0, state.ReadArray.Length, callback, state);

        }

        private void EndReadCallback(IAsyncResult res)
        {
            State state = (State) res.AsyncState;
            int count = state.File.EndRead(res);
            string text = System.Text.Encoding.UTF8.GetString(state.ReadArray);
            OpdaterTextBox(text);

            state.File.Close();
        }

        delegate void OpdaterTextBoxDelegate(string text);

        private void OpdaterTextBox(string text)
        {
            if (InvokeRequired)
                Invoke(new OpdaterTextBoxDelegate(OpdaterTextBox), new object[] { text });
            else
                textBox1.Text = text;
        }

        private class State
        {
            byte[] readArray;
            FileStream file;

            public State(FileStream file)
            {
                readArray = new byte[256 * 1024];
                this.file = file;
            }

            public byte[] ReadArray { get { return readArray; } }
            public FileStream File { get { return file; } }
        }