c# - FromEventPattern 如何知道事件何时完成？

Question

我有一个由大量事件填充的可观察集合。我想从 EventArg 中获取信息，按名称对其进行分组，然后为每个名称选择最大日期。我试过这个:

_subscription = Observable
            .FromEventPattern<NewLoanEventHandler, NewLoanEventArgs>(
                h => loan.NewLoanEvent += h, 
                h => loan.NewLoanEvent -= h)
            .Select(a => a.EventArgs.Counterpatry)
            .GroupBy(c => c.Name)
            .SelectMany(grp => grp.Max( c => c.MaturityDate ).Select( maturity => new {grp.Key, maturity}) )
            .Subscribe( 
                i => Console.WriteLine("{0} --> {1}", i.Key, i.maturity),
                Console.WriteLine,
                () => Console.WriteLine("completed")
                );

我认为它可能会做我想做的事，但订阅永远不会完成:我从来没有得到完整的消息，也没有得到任何输出。也就是说，我怀疑，因为 Observable 仍在等待更多事件。我如何告诉它停止等待并给我输出？

Answer 1

如果您只等待服务的单个响应，请考虑在查询表达式中使用 .Take(1) 或 .FirstAsync():

_subscription = Observable
            .FromEventPattern<NewLoanEventHandler, NewLoanEventArgs>(
                h => loan.NewLoanEvent += h, 
                h => loan.NewLoanEvent -= h)
            .Take(1)
            .Select(a => a.EventArgs.Counterpatry)
            .GroupBy(c => c.Name)
            .SelectMany(grp => grp.Max( c => c.MaturityDate ).Select( maturity => new {grp.Key, maturity}) )
            .Subscribe( 
                i => Console.WriteLine("{0} --> {1}", i.Key, i.maturity),
                Console.WriteLine,
                () => Console.WriteLine("completed")
                );