VB.NET绑定NewFrame事件报错，C#正常运行，求解决方案

报错信息 #

Error   3   Argument not specified for parameter 'sender' of 'Private Sub VideoCaptureDevice_NewFrame(sender As Object, eventArgs As AForge.Video.NewFrameEventArgs)'.  C:\Users\Admin\documents\visual studio 2012\Projects\Barcode Scanner using Webcam in VB.NET\Barcode Scanner using Webcam in VB.NET\Form1.vb 16  40  Barcode Scanner using Webcam in VB.NET
Error   2   Argument not specified for parameter 'eventArgs' of 'Private Sub VideoCaptureDevice_NewFrame(sender As Object, eventArgs As AForge.Video.NewFrameEventArgs)'.   C:\Users\Admin\documents\visual studio 2012\Projects\Barcode Scanner using Webcam in VB.NET\Barcode Scanner using Webcam in VB.NET\Form1.vb 16  40  Barcode Scanner using Webcam in VB.NET
Error   1   'Public Event NewFrame(sender As Object, eventArgs As AForge.Video.NewFrameEventArgs)' is an event, and cannot be called directly. Use a 'RaiseEvent' statement to raise an event.  C:\Users\Admin\documents\visual studio 2012\Projects\Barcode Scanner using Webcam in VB.NET\Barcode Scanner using Webcam in VB.NET\Form1.vb 16  9   Barcode Scanner using Webcam in VB.NET

我的VB.NET代码 #

Private Sub btnStart_Click_1(sender As Object, e As EventArgs) Handles btnStart.Click
    videoCaptureDevice = New VideoCaptureDevice(filterInfoCollection(cboCamera.SelectedIndex).MonikerString)
'报错代码行
    videoCaptureDevice.NewFrame += VideoCaptureDevice_NewFrame
    videoCaptureDevice.Start()
End Sub

Private Sub VideoCaptureDevice_NewFrame(ByVal sender As Object, ByVal eventArgs As AForge.Video.NewFrameEventArgs)
    Dim bitmap As Bitmap = DirectCast(eventArgs.Frame.Clone(), Bitmap)
    Dim reader As New BarcodeReader()
    Dim result = reader.Decode(bitmap)
    If result IsNot Nothing Then
        txtBarcode.Invoke(New MethodInvoker(Sub()
                                                txtBarcode.Text = result.ToString()
                                            End Sub))
    End If
    pictureBox.Image = bitmap
End Sub

可正常运行的C#代码 #

private void btnStart_Click(object sender, EventArgs e)
{
    videoCaptureDevice = new VideoCaptureDevice(filterInfoCollection[cboCamera.SelectedIndex].MonikerString);
    videoCaptureDevice.NewFrame += VideoCaptureDevice_NewFrame;
    videoCaptureDevice.Start();
}
private void VideoCaptureDevice_NewFrame(object sender, AForge.Video.NewFrameEventArgs eventArgs)
{
    Bitmap bitmap = (Bitmap)eventArgs.Frame.Clone();
    BarcodeReader reader = new BarcodeReader();
    var result = reader.Decode(bitmap);
    if (result != null)
    {
        txtBarcode.Invoke(new MethodInvoker(delegate()
        {
            txtBarcode.Text = result.ToString();
        }));
    }
    pictureBox.Image = bitmap;
}

问题原因 #

VB.NET与C#的事件绑定语法不同：C#使用+=绑定事件处理方法，但VB.NET不支持这种写法，当前代码会被编译器误认为是直接调用NewFrame事件（而非绑定处理方法），因此触发了“不能直接调用事件”和“参数缺失”的报错。

解决方案 #

将报错行替换为VB.NET标准的事件绑定语句：

AddHandler videoCaptureDevice.NewFrame, AddressOf VideoCaptureDevice_NewFrame

修改后的完整btnStart_Click_1方法：

Private Sub btnStart_Click_1(sender As Object, e As EventArgs) Handles btnStart.Click
    videoCaptureDevice = New VideoCaptureDevice(filterInfoCollection(cboCamera.SelectedIndex).MonikerString)
    AddHandler videoCaptureDevice.NewFrame, AddressOf VideoCaptureDevice_NewFrame
    videoCaptureDevice.Start()
End Sub

这样就能正确绑定事件处理方法，消除所有报错，逻辑与C#代码保持一致。

内容的提问来源于stack exchange，提问作者roy