将PushStreamContent C＃代码转换为VB.Net WebAPI 2时出错

Question

I'm having some difficulty converting this C# code to a WebAPI 2 VB.Net project.

Here's the original C# code

[HttpGet]
public HttpResponseMessage FromImages() {

    var imageStream = new ImageStream();
    Func<Stream, HttpContent, TransportContext, Task> func = imageStream.WriteToStream;
    var response = Request.CreateResponse();
    response.Content = new PushStreamContent(func);
    response.Content.Headers.Remove("Content-Type");
    response.Content.Headers.TryAddWithoutValidation("Content-Type", "multipart/x-mixed-replace;boundary=" + imageStream.Boundary);
    return response;

}

internal class ImageStream {
    public object Boundary { get; private set; } = "HintDesk";

    public async Task WriteToStream(Stream outputStream, HttpContent content, TransportContext context) {
        byte[] newLine = Encoding.UTF8.GetBytes("\r\n");

        foreach (var file in Directory.GetFiles(@"TestData\Images", "*.jpg")) {
            var fileInfo = new FileInfo(file);
            var header = $"--{Boundary}\r\nContent-Type: image/jpeg\r\nContent-Length: {fileInfo.Length}\r\n\r\n";
            var headerData = Encoding.UTF8.GetBytes(header);
            await outputStream.WriteAsync(headerData, 0, headerData.Length);
            await fileInfo.OpenRead().CopyToAsync(outputStream);
            await outputStream.WriteAsync(newLine, 0, newLine.Length);
            await Task.Delay(1000 / 30);
        }
    }
}

Here's the VB.Net translation

    <HttpGet> _
    Public Function FromImages() As HttpResponseMessage
        Dim imageStream = New ImageStream()
        Dim func As Func(Of Stream, HttpContent, TransportContext, Task) = imageStream.WriteToStream
        Dim response = Request.CreateResponse()
        response.Content = New PushStreamContent(func)
        response.Content.Headers.Remove("Content-Type")
        response.Content.Headers.TryAddWithoutValidation("Content-Type", "multipart/x-mixed-replace;boundary=" + imageStream.Boundary)
        Return response
    End Function

    Friend Class ImageStream

        Public Function WriteToStream(outputStream As Stream, content As HttpContent, context As TransportContext) As Task
            Dim newLine As Byte() = Encoding.UTF8.GetBytes(vbCr & vbLf)

            For Each file As var In Directory.GetFiles("TestData\Images", "*.jpg")
                Dim fileInfo = New FileInfo(file)
                Dim header = "--{Boundary}" & vbCr & vbLf & "Content-Type: image/jpeg" & vbCr & vbLf & "Content-Length: {fileInfo.Length}" & vbCr & vbLf & vbCr & vbLf
                Dim headerData = Encoding.UTF8.GetBytes(header)
                Await outputStream.WriteAsync(headerData, 0, headerData.Length)
                Await fileInfo.OpenRead().CopyToAsync(outputStream)
                Await outputStream.WriteAsync(newLine, 0, newLine.Length)
                Await Task.Delay(1000 / 30)
            Next
        End Function

    End Class

I'm seeing two problems:

1. On this line is a 'Argument not specified for parameter 'context' of 'Public Function WriteToStream...'

   Dim func As Func(Of Stream, HttpContent, TransportContext, Task) = imageStream.WriteToStream

2. An Overload resolution failed because no accessible 'New' can be called with these arguments

   response.Content = New PushStreamContent(func)

I imagine that I didn't translate this correctly, but I'm having difficulty finding any examples in VB.Net for what I'm trying to accomplish. Can someone tell me what I'm doing wrong?

Answer 1

The main problem is that you are not using 'AddressOf' - here's the VB equivalent:

Option Infer On

Imports Microsoft.VisualBasic

<HttpGet>
Public Function FromImages() As HttpResponseMessage

    Dim imageStream = New ImageStream()
    Dim func As Func(Of Stream, HttpContent, TransportContext, Task) = AddressOf imageStream.WriteToStream
    Dim response = Request.CreateResponse()
    response.Content = New PushStreamContent(func)
    response.Content.Headers.Remove("Content-Type")
    response.Content.Headers.TryAddWithoutValidation("Content-Type", "multipart/x-mixed-replace;boundary=" & imageStream.Boundary)
    Return response

End Function

Friend Class ImageStream
    Private privateBoundary As Object = "HintDesk"
    Public Property Boundary() As Object
        Get
            Return privateBoundary
        End Get
        Private Set(ByVal value As Object)
            privateBoundary = value
        End Set
    End Property

    Public Async Function WriteToStream(ByVal outputStream As Stream, ByVal content As HttpContent, ByVal context As TransportContext) As Task
        Dim newLine() As Byte = Encoding.UTF8.GetBytes(ControlChars.CrLf)

        For Each file In Directory.GetFiles("TestData\Images", "*.jpg")
            Dim fileInfo = New FileInfo(file)
            Dim header = $"--{Boundary}" & ControlChars.CrLf & "Content-Type: image/jpeg" & ControlChars.CrLf & "Content-Length: {1}" & ControlChars.CrLf & ControlChars.CrLf
            Dim headerData = Encoding.UTF8.GetBytes(header)
            Await outputStream.WriteAsync(headerData, 0, headerData.Length)
            Await fileInfo.OpenRead().CopyToAsync(outputStream)
            Await outputStream.WriteAsync(newLine, 0, newLine.Length)
            Await Task.Delay(1000 \ 30)
        Next file
    End Function
End Class