c# - 阻塞 ForEach 直到异步事件完成

Question

我正在使用 ReportViewer 控件和自定义打印作业工作流程，这给我带来了一些问题。我的代码看起来有点像这样:

        ids.ForEach(delegate(Guid? guid)
            {
                var details = items.Where(e => e.guid == guid);

                var ds = new ReportDataSource("Form", details);
                ReportViewer.LocalReport.DataSources.Clear();
                ReportViewer.LocalReport.DataSources.Add(ds);
                ReportViewer.RefreshReport();

            });

当最终调用 RefreshReport() 时，它会触发其 RenderingComplete 事件，在该事件中，我有逻辑对打印作业进行排队:

        if (DisplayPrintDialog) ReportViewer.PrintDialog();
        else
        {
            var document = new PrintDocument(ReportViewer.LocalReport);
            document.PrinterSettings = ReportViewer.PrinterSettings;
            document.Print();
        }
        DisplayPrintDialog = false;

问题是 ForEach 循环在 RenderingComplete 事件触发之前完成运行，因此我需要一种方法来阻止 ForEach 循环，直到循环的每次传递都触发 RenderingComplete 事件。解决这个问题的好方法是什么？

Answer 1

如果您必须将其保留在 foreach 中，请使用 AutoResetEvent .

// Define this elsewhere in your class
static AutoResetEvent reset = new AutoResetEvent(false);

// This assumes RenderingComplete takes 1 argument, 
// and you aren't going to use it. If you are, change
// the _ to something more meaningful.
ReportViewer.RenderingComplete += _ =>
{
    // This happens after the code below, and this tells the "WaitOne" 
    // lock that it can continue on with the rest of the code.
    reset.Set();
}

ids.ForEach(guid => 
{
    var details = items.Where(e => e.guid == guid);

    var ds = new ReportDataSource("Form", details);
    ReportViewer.LocalReport.DataSources.Clear();
    ReportViewer.LocalReport.DataSources.Add(ds);

    // Begin the async refresh
    ReportViewer.RefreshReport();

    reset.WaitOne(); // This call will block until "reset.Set()" is called.
    reset.Reset(); // This resets the state for the next loop iteration.
});

我也冒昧地让你的匿名委托(delegate)变得不那么难看(此时没有真正的理由再使用关键字delegate，你应该使用简写() => { ... } 代替)。