问 将代码从BGW转换为异步并等待DataTabale/MySQLDataAdapter

EN

我有一个 series on my blog ，它显示了 BackgroundWorker 与 Task.Run 的比较。

通常，对于I/O受限的操作，不应该使用这两种方法中的任何一种。但是，有一些较旧的API尚未升级以公开TAP方法。我认为“数据适配器”和“数据表”API被认为太旧而无法升级，因此没有可以使用的"FillAsync“。

因此，假设您想保留“数据表”方法，您可以直接使用 Task.Run 作为 BackgroundWorker 的替代。请注意， IProgress<T> 是一种更现代的方式，可以执行任何类型的跨线程调用来进行进度更新：

private async void button1_Click(object sender, EventArgs e)
    button1.Enabled = false;
    var progress = new Progress<string>(update => textBox1.AppendText(update));
    var ds = await Task.Run(() => BackgroundWork(progress));
    dataGridView1.Columns.Clear();
    dataGridView1.DataSource = ds.Tables["StudentNamesAndNumbers"];
    dataGridView1.AutoResizeColumns();
    label1.Text = dataGridView1.Rows.Count.ToString() + " Students";
    button1.Enabled = true;
private DataSet BackgroundWork(IProgress<string> progress)
    string stdNo = File.ReadAllText("stdNo.txt").Replace(Environment.NewLine, ",");
    const string cs = @"what ever";
    MySqlConnection conn = new MySqlConnection(cs);
    MySqlDataAdapter SQLDataAdapter = new MySqlDataAdapter(); ;
    DataSet ds = new DataSet();
    conn.Open();
    if (progress != null)
        progress.Report(string.Format("MySQL version : {0};", conn.ServerVersion));
    DataTable dt = new DataTable("StudentNamesAndNumbers");
    dt.Columns.Add("Student Name", typeof(string));
    dt.Columns.Add("Student ID", typeof(string));
    dt.Columns.Add("First", typeof(float));
    dt.Columns.Add("Second", typeof(float));
    dt.Columns.Add("Section", typeof(string));
    ds.Tables.Add(dt);
        MySqlCommand SQLcmd = new MySqlCommand();
        SQLcmd = conn.CreateCommand();
        SQLcmd.CommandText = String.Format(@"Select u.firstname as 'Student Name', u.username as 'Student ID'"
                                                + ",( select  score from gradebook_result g , gradebook_evaluation e "
                                                + "where g.user_id = u.user_id "
                                                + "and name = 'First' "
                                                + "and g.evaluation_id = e.id "
                                                + "and e.course_code = c.course_code) as 'First' "
                                                + ",( select  score from gradebook_result g , gradebook_evaluation e "
                                                + "where g.user_id = u.user_id "
                                                + "and name = 'Second' "
                                                + "and g.evaluation_id = e.id "
                                                + "and e.course_code = c.course_code) as 'Second' "
                                                + ", c.course_code as 'Section'"
                                                + "from user u, course_rel_user c "
                                                + "where "
                                                + "u.username in ({0}) "
                                                + "and u.username REGEXP '[0-9]+' "
                                                + "and c.course_code like 'IT102CPLUS%' "
                                                + "and  u.user_id = c.user_id ;", stdNo);
        if (progress != null)
            progress.Report(SQLcmd.CommandText);
        SQLDataAdapter = new MySqlDataAdapter(SQLcmd);
        SQLDataAdapter.Fill(dt);
        dt.DefaultView.Sort = "Section ASC, Student Name ASC";
        var lines = new List<string>();
        string[] columnNames = dt.Columns.Cast<DataColumn>().
                                              Select(column => column.ColumnName).
                                              ToArray();
        var header = string.Join(",", columnNames);
        lines.Add(header);
        var valueLines = dt.AsEnumerable().Select(row => string.Join(",", row.ItemArray));            
        lines.AddRange(valueLines);
        File.WriteAllLines("Export.csv", lines, Encoding.UTF8);
        return ds;
    catch (MySqlException ex)
        if (progress != null)
            progress.Report(string.Format("Error: {0}\n\n", ex.ToString()));
    finally
        if (conn != null)
            conn.Close();
}

您应该将该方法标记为 async ，并在可能的情况下等待异步方法。如果没有异步方法，并且您希望在另一个线程上运行同步方法，请等待 Task.Run 。

    private async void button1_Click(object sender, EventArgs e)
        button1.Enabled = false;
            //Use an async method when there is one available
            string stdNo;
            using (var reader = File.OpenText("Words.txt"))
                stdNo = await reader.ReadToEndAsync();
            stdNo = stdNo.Replace(Environment.NewLine, ",");
            const string cs = @"what ever";
            MySqlConnection conn = new MySqlConnection(cs);
            MySqlDataAdapter SQLDataAdapter = new MySqlDataAdapter(); ;
            DataSet ds = new DataSet();
            //Use Task.Run to call a long running code on another thread
            //If available you should use await conn.OpenAsync();
            await Task.Run(() => conn.Open());
            //You don't need invoke, after an await you are back to the synchronization context
            textBox1.AppendText(string.Format("MySQL version : {0};", conn.ServerVersion));
            DataTable dt = new DataTable("StudentNamesAndNumbers");
            dt.Columns.Add("Student Name", typeof(string));
            dt.Columns.Add("Student ID", typeof(string));
            dt.Columns.Add("First", typeof(float));
            dt.Columns.Add("Second", typeof(float));
            dt.Columns.Add("Section", typeof(string));
            ds.Tables.Add(dt);
            //...
        finally