Lambda 函数省略号（C# 中的下划线）在 VB.NET 中等效

Question

I have the following lambda function in C# which I want to migrate to VB.NET:

    private static void CreateAndVisualizeSensitiveFilteredFixationsStream()
    {
        _fixationDataStream = _host.Streams.CreateFixationDataStream();
        _fixationDataStream
            .Begin((x, y, _) =>
                {
                    Console.WriteLine("\n" +
                                      "Fixation started at X: {0}, Y: {1}", x, y);
                    _fixationBeginTime = DateTime.Now;
                })
            .Data((x, y, _) =>
                {
                    Console.WriteLine("During fixation, currently at: X: {0}, Y: {1}", x, y);
                })
            .End((x, y, _) =>
                {
                    Console.WriteLine("Fixation ended at X: {0}, Y: {1}", x, y);
                    if (_fixationBeginTime != default(DateTime))
                    {
                        Console.ForegroundColor = ConsoleColor.Cyan;
                        Console.WriteLine("Fixation duration: {0}", DateTime.Now - _fixationBeginTime);
                        Console.ForegroundColor = _defaultForegroundColor;
                    }
                });
    }

As one can see, the third argument of ".Begin(x, y, _)" is an ellipsis.

VB.NET won't accept this underscore. What would be the equivalent in VB.NET?

Here is my attempt of a conversion, I'm not sure if I did it correctly, but the underscore is very likely to be wrong in VB.NET, I guess. Thanks you.

    Private Shared Sub CreateAndVisualizeSensitiveFilteredFixationsStream()
        _fixationDataStream = _host.Streams.CreateFixationDataStream()
        _fixationDataStream.Begin(Function(x, y, _)
                                      Console.WriteLine(Constants.vbLf & "Fixation started at X: {0}, Y: {1}", x, y)
                                      _fixationBeginTime = DateTime.Now
               ).Data(Function(x, y, _ )
                    Console.WriteLine("During fixation, currently at: X: {0}, Y: {1}", x, y)
               ).End(Function(x, y, _)
                    Console.WriteLine("Fixation ended at X: {0}, Y: {1}", x, y)
                                      If _fixationBeginTime IsNot Nothing Then
                                          Console.ForegroundColor = ConsoleColor.Cyan
                                          Console.WriteLine("Fixation duration: {0}", DateTime.Now.Subtract(_fixationBeginTime))
                                          Console.ForegroundColor = _defaultForegroundColor
                                      End If
                                  End Function
               )
    End Sub

This is the Begin function:

public class FixationDataStream : DataStreamBase<FixationDataBehavior, FixationData>
{
    public FixationDataStream(FixationDataBehavior fixationDataBehavior, Action hasSubscribersChanged, bool enabled);

    public FixationDataStream Begin(Action<double, double, double> action);
    public FixationDataStream Data(Action<double, double, double> action);
    public FixationDataStream End(Action<double, double, double> action);
}

Answer 1

Those lambdas should be 'Sub' lambdas. In addition, you are not closing most of them (with 'End Sub'). Also, you cannot use an underscore by itself as a variable name in VB:

    Private Shared Sub CreateAndVisualizeSensitiveFilteredFixationsStream()
        _fixationDataStream = _host.Streams.CreateFixationDataStream()
        _fixationDataStream.Begin(Sub(x, y, underscore)
                    Console.WriteLine(vbLf & "Fixation started at X: {0}, Y: {1}", x, y)
                    _fixationBeginTime = Date.Now
        End Sub).Data(Sub(x, y, underscore)
                    Console.WriteLine("During fixation, currently at: X: {0}, Y: {1}", x, y)
        End Sub).End(Sub(x, y, underscore)
                    Console.WriteLine("Fixation ended at X: {0}, Y: {1}", x, y)
                    If _fixationBeginTime <> Date.MinValue Then
                        Console.ForegroundColor = ConsoleColor.Cyan
                        Console.WriteLine("Fixation duration: {0}", Date.Now - _fixationBeginTime)
                        Console.ForegroundColor = _defaultForegroundColor
                    End If
        End Sub)
    End Sub