[Source] ──stream──▶ [Program]   (Đọc)
[Program] ──stream──▶ [Destination]  (Ghi)

FileStream fs;
byte[] fileContents;
AsyncCallback callback;
delegate void InfoMessageDel(String info);

private void btnReadAsync_Click(object sender, EventArgs e)
{
    openFileDialog.ShowDialog();

    callback = new AsyncCallback(fs_StateChanged);

    // Mở FileStream ở chế độ bất đồng bộ (tham số cuối = true)
    fs = new FileStream(
        openFileDialog.FileName,
        FileMode.Open,
        FileAccess.Read,
        FileShare.Read,
        4096,   // Buffer size: 4096 bytes/lần là hiệu quả nhất
        true    // useAsync = true
    );

    fileContents = new Byte[fs.Length];

    // Bắt đầu đọc bất đồng bộ; callback sẽ được gọi khi xong
    fs.BeginRead(fileContents, 0, (int)fs.Length, callback, null);
}

private void fs_StateChanged(IAsyncResult asyncResult)
{
    if (asyncResult.IsCompleted)
    {
        // Chuyển mảng byte thành string theo encoding UTF-8
        string s = Encoding.UTF8.GetString(fileContents);
        InfoMessage(s);  // Cập nhật UI
        fs.Close();
    }
}

private void btnReadSync_Click(object sender, EventArgs e)
{
    openFileDialog.ShowDialog();

    // Tạo và khởi động thread mới để đọc file
    Thread thdSyncRead = new Thread(new ThreadStart(syncRead));
    thdSyncRead.Start();
}

public void syncRead()
{
    FileStream fs;
    try
    {
        fs = new FileStream(openFileDialog.FileName, FileMode.OpenOrCreate);
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
        return;
    }

    fs.Seek(0, SeekOrigin.Begin);   // Di chuyển con trỏ về đầu file
    byte[] fileContents = new byte[fs.Length];
    fs.Read(fileContents, 0, (int)fs.Length);

    string s = Encoding.UTF8.GetString(fileContents);
    InfoMessage(s);
    fs.Close();
}

public void InfoMessage(String info)
{
    if (tbResults.InvokeRequired)
    {
        // Đang ở thread khác → marshal về UI thread
        InfoMessageDel method = new InfoMessageDel(InfoMessage);
        tbResults.Invoke(method, new object[] { info });
        return;
    }

    // Đang ở UI thread → cập nhật trực tiếp
    tbResults.Text = info;
}

// Các cách dùng Encoding:
string s1 = Encoding.UTF8.GetString(fileContents);
string s2 = Encoding.Unicode.GetString(fileContents);   // UTF-16
string s3 = Encoding.ASCII.GetString(fileContents);
string s4 = Encoding.UTF32.GetString(fileContents);

private void btnRead_Click(object sender, EventArgs e)
{
    OpenFileDialog ofd = new OpenFileDialog();
    ofd.ShowDialog();

    FileStream fs = new FileStream(ofd.FileName, FileMode.OpenOrCreate);
    StreamReader sr = new StreamReader(fs);

    int lineCount = 0;
    while (sr.ReadLine() != null)
    {
        lineCount++;
    }

    fs.Close();
    MessageBox.Show($"There are {lineCount} lines in {ofd.FileName}");
}

private void btnWrite_Click(object sender, EventArgs e)
{
    SaveFileDialog sfd = new SaveFileDialog();
    sfd.ShowDialog();

    FileStream fs = new FileStream(sfd.FileName, FileMode.CreateNew);
    BinaryWriter bw = new BinaryWriter(fs);

    int[] myArray = new int[1000];
    for (int i = 0; i < 1000; i++)
    {
        myArray[i] = i;
        bw.Write(myArray[i]);   // Ghi từng int (4 byte) vào file
    }

    bw.Close();   // Tự động flush và đóng stream bên dưới
}

[Object in RAM] ──serialize──▶ [Byte stream] ──deserialize──▶ [Object in RAM]

public enum purchaseOrderStates
{
    ISSUED,
    DELIVERED,
    INVOICED,
    PAID
}

[Serializable]   // Bắt buộc phải có attribute này!
public class lineItem
{
    public string description;
    public int quantity;
    public float unitCost;
}

[Serializable]
public class company
{
    public string name;
    public string phone;
}

[Serializable]
public class purchaseOrder
{
    private DateTime _issuanceDate;
    private DateTime _deliveryDate;
    private purchaseOrderStates _purchaseOrderStatus;

    public company vendor;
    public company buyer;
    public lineItem[] items;

    public purchaseOrder()
    {
        _purchaseOrderStatus = purchaseOrderStates.ISSUED;
        _issuanceDate = DateTime.Now;
    }
}

// Tạo các đối tượng
company Vendor = new company();
Vendor.name = "Acme Inc.";
Vendor.phone = "555-1234";

company Buyer = new company();
Buyer.name = "Wiley Coyote";

lineItem Goods = new lineItem();
Goods.description = "Anti-RoadRunner cannon";
Goods.quantity = 1;
Goods.unitCost = 599.99f;

purchaseOrder po = new purchaseOrder();
po.items = new lineItem[1];
po.items[0] = Goods;
po.buyer = Buyer;
po.vendor = Vendor;

// Ghi ra file dùng SoapFormatter
SoapFormatter sf = new SoapFormatter();
FileStream fs = new FileStream("order.soap", FileMode.Create);
sf.Serialize(fs, po);
fs.Close();

SoapFormatter sf = new SoapFormatter();
FileStream fs = new FileStream("order.soap", FileMode.Open);
purchaseOrder po = (purchaseOrder)sf.Deserialize(fs);
fs.Close();

// Sử dụng object vừa khôi phục
Console.WriteLine($"Customer: {po.buyer.name}");
Console.WriteLine($"Vendor: {po.vendor.name}");

// Serialize
BinaryFormatter bf = new BinaryFormatter();
FileStream fs = new FileStream("order.bin", FileMode.Create);
bf.Serialize(fs, po);
fs.Close();

// Deserialize
BinaryFormatter bf = new BinaryFormatter();
FileStream fs = new FileStream("order.bin", FileMode.Open);
purchaseOrder po = (purchaseOrder)bf.Deserialize(fs);
fs.Close();

// Serialize bằng XmlSerializer
company Vendor = new company();
Vendor.name = "Microsoft Inc.";
Vendor.phone = "425-555-1234";

// ... (tạo object tương tự)

XmlSerializer xs = new XmlSerializer(typeof(purchaseOrder));
FileStream fs = new FileStream("order.xml", FileMode.Create);
xs.Serialize(fs, po);
fs.Close();

// Deserialize bằng XmlSerializer
purchaseOrder po = new purchaseOrder();
XmlSerializer xs = new XmlSerializer(typeof(purchaseOrder));
FileStream fs = new FileStream("order.xml", FileMode.Open);
po = (purchaseOrder)xs.Deserialize(fs);
fs.Close();

private static string strCon;
public static SqlConnection Connect(string serverName, string dbName)
{
    strCon = $"Server={serverName};Database={dbName};Trusted_Connection=True";
    SqlConnection conn = new SqlConnection(strCon);
    try
    {
        conn.Open();
        return conn;
    }
    catch (Exception e)
    {
        MessageBox.Show($"Chi tiết kỹ thuật: {e.Message}");
        return null;
    }
}

public static OleDbConnection Connect(string dbPath)
{
    strCon = $"Provider=Microsoft.Jet.OLEDB.4.0;Data Source={dbPath}";
    OleDbConnection conn = new OleDbConnection(strCon);
    try
    {
        conn.Open();
        return conn;
    }
    catch (Exception e)
    {
        MessageBox.Show($"Chi tiết kỹ thuật: {e.Message}");
        return null;
    }
}

public DataSet Query(string sql, OleDbConnection conn)
{
    OleDbCommand cmd = new OleDbCommand(sql, conn);
    OleDbDataAdapter adapter = new OleDbDataAdapter(cmd);
    DataSet ds = new DataSet();
    adapter.Fill(ds);
    return ds;
}

string szDSN = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=mydb.mdb";
OleDbConnection conn = new OleDbConnection(szDSN);
conn.Open();

OleDbCommand cmd = new OleDbCommand(tbSQL.Text, conn);
OleDbDataAdapter adapter = new OleDbDataAdapter(cmd);
DataSet ds = new DataSet();
adapter.Fill(ds);

// Serialize DataSet thành XML stream
StringWriter sw = new StringWriter();
ds.WriteXml(sw);
tbResults.Text = sw.ToString();   // Hiển thị XML lên textbox

<NewDataSet>
  <companies diffgr:id="companies1" msdata:rowOrder="0">
    <id>1</id>
    <name>Wiley E. Coyote</name>
  </companies>
  <companies diffgr:id="companies2" msdata:rowOrder="1">
    <id>2</id>
    <name>Acme Inc.</name>
  </companies>
</NewDataSet>