在vb.net中使用代理

Question

I'm new to vb.net and trying to build a win CE app in vb.net. The sdk of the handheld device is in C# which I converted with an online converter to vb.net. Below is the C# code:

public class DecodeEventArgs : EventArgs
{
    private string barcode;
    private byte type;

    public DecodeEventArgs(string barcodeData, byte typeData)
    {
        barcode = barcodeData;
        type = typeData;
    }

    public string Barcode
    {
        get { return barcode; }
        set { barcode = value; }
    }

    public byte Type
    {
        get { return type; }
        set { type = value; }
    }

}

Converted to vb.net as:

Public Class DecodeEventArgs
    Inherits EventArgs
    Public barcode As String
    Public type As Byte

    Public Sub New(ByVal barcodeData As String, ByVal typeData As Byte)
        barcode = barcodeData
        type = typeData
    End Sub

    Public Property pBarcode() As String
        Get
            Return barcode
        End Get
        Set(ByVal value As String)
            barcode = value
        End Set
    End Property

    Public Property pType() As Byte
        Get
            Return type
        End Get
        Set(ByVal value As Byte)
            type = value
        End Set
    End Property
End Class

In my conversion from C# I added a 'p' to the name of the Properties as you see in my vb.net code because I had a error that said

Barcode is already declared as a public string in this class

I'm not sure if that is part of my problem but my real issue is, on a form they used .BeginInvoke to call the class with this code:

void scanner_DecodeEvent(object sender, DecodeEventArgs e)
    {
        Win32.sndPlaySound(Properties.Resources.Scan, Win32.SND_ASYNC | Win32.SND_MEMORY);

        this.BeginInvoke((Action<string>)delegate(string barcode)
        {
            scanCount = 0;
            ListViewItem item = new ListViewItem(new string[] { barcode });
            lstView.Items.Insert(0, item);

        }, e.Barcode);
    } 

Which I converted to vb.net as:

Private Sub scanner_DecodeEvent(ByVal sender As Object, ByVal e As DecodeEventArgs)
    PlaySound()

    Me.BeginInvoke(DirectCast(Barcode As String) ) 
    scanCount = 0
    Dim item As New ListViewItem(New String() {barcode})

    lstView.Items.Insert(0, item)


End Sub 

Which gives me an error about Barcode not being declared. This is where I'm stuck. Thanks for your assistance in advance

Answer 1

That C# snippet creates an anonymous method which it invokes to perform the actions on the UI thread, and it sends e.Barcode as a parameter. Your VB.NET conversion only tries to invoke some strange, and incomplete, use of DirectCast . DirectCast is not needed in the VB.NET conversion as you don't have any delegate keyword which you must cast to a delegate method.

Your most simple solution would be to use a Lambda method:

Me.BeginInvoke(Sub() 'Lambda anonymous method.
    scanCount = 0
    Dim item As New ListViewItem(New String() {e.Barcode})
    lstView.Items.Insert(0, item)
End Sub)

---

EDIT:

Since you get errors when using the lambda expression I assume you target .NET Framework 3.5 or lower. For that matter it gets a bit more complicated as you must now put the code in a different method:

Private Sub AddBarcode(ByVal Barcode As String)
    scanCount = 0
    Dim item As New ListViewItem(New String() {Barcode})
    lstView.Items.Insert(0, item)
End Sub

Then you must declare your own delegate method which you can use to perform the invocation:

Delegate Sub AddBarcodeDelegate(ByVal Barcode As String)

Private Sub scanner_DecodeEvent(ByVal sender As Object, ByVal e As DecodeEventArgs)
    Me.BeginInvoke(New AddBarcodeDelegate(AddressOf AddBarcode), e.Barcode)
End Sub