如何处理来自非 UI 线程的异步 SQL 查询

Question

所有，我已经成功地使用 ADO.NET 来利用类似于下面的示例的异步 SQL 查询。在所示示例中，方法 ExecNonQuery 是从 UI 线程调用的。这很好用，但我想知道如果我从非 UI 线程调用 ExecNonQuery 我将如何处理回调？

笔记。显然，在这种情况下，我会修改 ExecNonQuery，以便相应地处理或删除诸如 this.toolStripStatusLabel1.Text 之类的内容。

public bool ExecNonQuery(string strCmd, string strUserMsg = "")
{
    try
    {
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = conn;
        cmd.CommandText = strCmd;
        cmd.CommandTimeout = 0;
        bIsExecuting = true;
        AsyncCallback callback = new AsyncCallback(HandleCallback);
        cmd.BeginExecuteNonQuery(callback, cmd); 
        return true;
    }
    catch (Exception Ex)
    {
        bIsExecuting = false;
        this.toolStripStatusLabel1.Text = String.Format("Ready (last error: {0})", Ex.Message);
        if (conn != null)
            conn.Close();
    }
    return false;
}

private delegate void DisplayInfoDelegate(string Text);

private void HandleCallback(IAsyncResult result)
{
    try
    {
        // Retrieve the original command object, passed
        // to this procedure in the AsyncState property
        // of the IAsyncResult parameter.

        SqlCommand command = (SqlCommand)result.AsyncState;
        int rowCount = command.EndExecuteNonQuery(result);
        string rowText = " rows affected.";
        if (rowCount == 1)
            rowText = " row affected.";
        rowText = rowCount + rowText;

        // Call the procedure from the form's thread.
        DisplayInfoDelegate del = new DisplayInfoDelegate(DisplayResults);
        this.Invoke(del, rowText);
    }
    catch (Exception ex)
    {
        // Because you are now running code in a separate thread, 
        // if you do not handle the exception here, none of your other
        // code catches the exception.

        // You can create the delegate instance as you 
        // invoke it, like this:
        this.Invoke(new DisplayInfoDelegate(DisplayResults), 
            String.Format("Ready(last error: {0}", ex.Message));
    }
    finally
    {
        bIsExecuting = false;
        if (conn != null)
            conn.Close();
    }
}

private void DisplayResults(string Text)
{
    this.toolStripStatusLabel1.Text = Text;
    this.toolStripProgressBar1.Style = ProgressBarStyle.Blocks;
    this.toolStripProgressBar1.Value = 100;
}

谢谢你的时间。

Answer 1

哪个线程运行 ExecNonQuery 对您的回调没有影响 - HandleCallback 仍将在线程池线程上运行。

您已经发现需要进行的更改：如果 ExecNonQuery 未在 UI 线程上运行，则不要直接在 ExecNonQuery 中访问 UI 控件。

缺口