1
所有的,我已经成功地使用了ADO.NET来使用类似于下面例子的异步SQL查询。在所示的例子中,ExecNonQuery方法正在从UI线程中调用。这很好,但我想知道如果我要从非UI线程调用ExecNonQuery,我将如何处理回调?如何处理来自非UI线程的异步SQL查询
注意。显然,在这种情况下,我会修改ExecNonQuery,以便诸如this.toolStripStatusLabel1.Text
这样的事情得到相应处理或删除。
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;
}
感谢您的时间。
我想到的第一件事就是使用并发异常。您可以在数据库中创建一个时间戳类型字段,用于指示记录上次更新的时间。如果您的时间戳与数据库中的时间戳冲突,则会引发并发错误。 –
什么是'SynchronizationContext'或什么UI框架你使用(ASP,WinForms,WPF等) – SliverNinja
道歉。这是用WinForms完成的。 – MoonKnight