使用BeginExecuteReader异步加载数据

private delegate void DataGridViewHandler(DataTable dt);

/// <summary>
/// 此处开始加在数据
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void button3_Click(object sender, EventArgs e)
{
SqlConnection conn =
new SqlConnection("Data Source=.;Initial Catalog=Test;User Id=sa;Password=*********;Async=true");
conn.Open();
SqlCommand cmd = new SqlCommand("Select top 700000 * from Test", conn) {CommandTimeout = 0};
//此处开始查询数据，执行非常耗时的工作,ProcessData为执行完成后的委托
cmd.BeginExecuteReader(ProcessData, cmd);
//此处不会阻塞当前线程，label2 Text会马上执行
label2.Text = "label2 Text会马上执行";
}

/// <summary>
/// 查询完成后，执行的方法
/// </summary>
/// <param name="ar"></param>
private void ProcessData(IAsyncResult ar)
{
SqlCommand cmd = (SqlCommand) ar.AsyncState;
using (cmd.Connection)
{
using (cmd)
{
SqlDataReader sdr = cmd.EndExecuteReader(ar);
DataTable dt = new DataTable("Product");
dt.Load(sdr);

//将查询的数据，赋给dataGridView1的DataSource
dataGridView1.BeginInvoke(
new DataGridViewHandler((dtResult) => dataGridView1.DataSource = dtResult), dt);
}
}
}