c# - 使用定时器刷新界面，不断获取 "There is already an open DataReader associated with this Connection which must be closed first."

Question

我一直在使用计时器来刷新应用程序上的 ListView ，但半秒后，我首先收到错误消息 try/catch method在RefreshPlot()在 PlotComponent.cs 中:

An exception of type 'MySql.Data.MySqlClient.MySqlException' occurred in Marketplace.exe but was not handled in user code

Additional information: There is already an open DataReader associated with this Connection which must be closed first.

这到底是怎么回事？我尝试使用 using和try/catch ，所以我不太清楚我可能犯的错误。当我禁用计时器时，一切正常。但我需要每 0.5 秒访问一次数据库才能刷新 ListView 。

如果我没有以正确的方式做，我还能做些什么吗？

代码如下:

MainWindow.cs

public MainWindow()
{
    InitializeComponent();

    // Reset lists
    SetPlotList(_filterPlotReference);

    // Refresh lists
    Refresh();
}

public void Refresh()
{
    var myTimer = new System.Timers.Timer();
    myTimer.Elapsed += RefreshPlotList;
    myTimer.Interval = 500;
    myTimer.Enabled = true;
}

public void RefreshPlotList(object source, ElapsedEventArgs e)
{
    PlotComponent.RefreshPlot();
    Dispatcher.Invoke(() =>
    {
        if (!string.IsNullOrWhiteSpace(FilterTextBox.Text) &&
            (!Regex.IsMatch(FilterTextBox.Text, "[^0-9]")))
        {
            _filterPlotReference = Convert.ToInt32(FilterTextBox.Text);
        }
    });
    SetPlotList(_filterPlotReference);
    FocusPlotItem(_focusPlotReference);
}

public void SetPlotList(int filterReference)
{
    // Fill plot list view
    List<PlotComponent.PlotList> plotList = PlotComponent.SelectPlotLists(filterReference);

    // Find the plot list item in the new list
    PlotComponent.PlotList selectPlotList =
        plotList.Find(x => Convert.ToInt32(x.PlotId) == _focusPlotReference);

    Dispatcher.Invoke(
        (() =>
        {
            PlotListView.ItemsSource = plotList;
            if (selectPlotList != null)
            {
                PlotListView.SelectedItem = selectPlotList;
            }
        }));

    int jobSum = 0;
    int bidSum = 0;
    foreach (PlotComponent.PlotList item in PlotListView.Items)
    {
        jobSum += Convert.ToInt32(item.Jobs);
        bidSum += Convert.ToInt32(item.Bids);
    }

    // Determine job/bid list ratio
    Dispatcher.BeginInvoke(
        new ThreadStart(() => JobBidRatioTextBlock.Text = jobSum + " jobs - " + bidSum + " bids"));
}

private void FocusPlotItem(int focusPlotReference)
{
    Dispatcher.Invoke(
        (() =>
        {
            PlotComponent.PlotList plotList =
                PlotListView.Items.OfType<PlotComponent.PlotList>()
                    .FirstOrDefault(p => Convert.ToInt32(p.PlotId) == focusPlotReference);
            if (plotList == null) return;
            //get visual container
            var container = PlotListView.ItemContainerGenerator.ContainerFromItem(plotList) as ListViewItem;
            if (container == null) return;
            container.IsSelected = true;
            container.Focus();
        }));
}

DbConnect.cs

http://pastebin.com/pZ0PGrg1

PlotComponent.cs

http://pastebin.com/xiRhKyMM

非常感谢您提前提供的帮助。

Answer 1

这是一个锁定计时器直到其完成工作的示例:

bool timerRunning = false; // define it as a global variable

// then in your timer process add this easy check
public void RefreshPlotList(object source, ElapsedEventArgs e)
{
    if(timerRunning) return; // return if it is busy
    timerRunning = true;  // set it to busy

    PlotComponent.RefreshPlot();
    Dispatcher.Invoke(() =>
    {
        if (!string.IsNullOrWhiteSpace(FilterTextBox.Text) &&
            (!Regex.IsMatch(FilterTextBox.Text, "[^0-9]")))
        {
            _filterPlotReference = Convert.ToInt32(FilterTextBox.Text);
        }
    });
    SetPlotList(_filterPlotReference);
    FocusPlotItem(_focusPlotReference);

    timerRunning = false;  // reset it for next time use
}

P.S:我通过添加(确切地)这个答案来编辑另一个答案，然后我被拒绝了，同行评审说

This edit was intended to address the author of the post and makes no sense as an edit. It should have been written as a comment or an answer

我毫不怀疑他们确实阅读了编辑并对其进行了评估，更不用说它不适合评论，所以在这里我将其作为答案发布