I'm trying to write a simple winforms application that executes a SQL SELECT statement asynchronous. When the sql server starts returning results, I want to execute an event handler I've wired up to the SqlCommand's StatementCompleted event.

The form contains two buttons, a textbox, and a label. When button1 is clicked, I create the SqlCommand and wire up the event handler, then I open the SqlConnection and call BeginExecuteReader in order to start the asynchronous operation. I set my label to show the command is executing.

In the event handler, I simply set the label to show the command is finished.

When button 2 is clicked, I change the label to show we're processing the results. Then I call EndExecuteReader and assign its return value to a new SqlDataReader which I then process.

What I see is that the event handler doesn't get called when the command is ready. In stead, it gets called when my code finishes processing the reader returned by EndExecuteReader.

Am I missing something here? Do I misinterpret the intended use of the event? I've tried to find an example of StatementCompleted, but I could only find general descriptions of it, no working code. The example at the SqlCommand.BeginExecuteReader page at MSDN uses a loop and waits for the IAsyncResult.IsCompleted property to be true. I would expect that at the same time that property gets true, the StatementCompleted event fires.

public Form1() {
    InitializeComponent();
}

private IAsyncResult iAsyncResult;
private SqlCommand sqlCommand;

private void statementCompleted(object sender,
                                StatementCompletedEventArgs e) {
    label1.Text = "Statement completed";
}

private void button1_Click(object sender, EventArgs e) {
    var northWindConnection =
        new SqlConnection(
            "Data Source=.\\SqlExpress;Initial Catalog=Northwind;" +
            "Integrated Security=True;" +
            "asynchronous processing=true");
    sqlCommand = new SqlCommand("WAITFOR DELAY '00:00:05';" +
                                " SELECT * FROM [Order Details]",
                                northWindConnection);
    sqlCommand.StatementCompleted += statementCompleted;
    northWindConnection.Open();
    iAsyncResult = sqlCommand.BeginExecuteReader();
    label1.Text = "Executing";
}

private void button2_Click(object sender, EventArgs e) {
    label1.Text = "Not waiting anymore, reading";
    var results = new StringBuilder();
    var reader = sqlCommand.EndExecuteReader(iAsyncResult);
    while (reader.Read()) {
        for (int i = 0; i < reader.FieldCount; i++) {
            results.Append(reader[i].ToString() + "\t");
        }
        results.Append(Environment.NewLine);
    }
    reader.Close();
    sqlCommand.Connection.Close();
    textBox1.Text = results.ToString();
}