C# 下划线作为 VB.NET 的参数

Question

我有以下 C# 代码要转换为 VB.NET：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System;
using OpenCvSharp;
namespace WindowsFormsApp1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
string sPath = "c:\users\myuser\desktop\lenna.png";
using (var src = new Mat(sPath, ImreadModes.Color))
using (var srcGray = new Mat(sPath, ImreadModes.GrayScale))
using (var hsv = new Mat())
using (var dst = new Mat())
{
Cv2.CvtColor(src, hsv, ColorConversionCodes.BGR2HSV);
Cv2.CvtColor(srcGray, dst, ColorConversionCodes.GRAY2BGR);
var hsvChannels = Cv2.Split(hsv);
var v = hsvChannels[2];
for (int i = 0; i < 8; i++)
{
using (var bin = new Mat())
{
Cv2.Threshold(v, bin, i * 32, 255, ThresholdTypes.Tozero);
Cv2.Threshold(bin, bin, (i + 1) * 32, 255, ThresholdTypes.BinaryInv);
Cv2.FindContours(bin, out var contours, out _, RetrievalModes.External,
ContourApproximationModes.ApproxNone);
Cv2.DrawContours(dst, contours, -1, Scalar.Red, 1);
}
}
Window.ShowImages(dst);
foreach (var m in hsvChannels)
m.Dispose();
}
}
}
}

我设法转换了它，但"_"让我头疼。

如果我用"无"替换它，编译器会告诉我"不是最具体的"。

如果我像这样声明"轮廓"(更具体地说(，编译器告诉我"Nothing"是一个无效的参数：

Dim contours As OpenCvSharp.Mat()

这是我 VB.NET 尝试：

Imports OpenCvSharp
Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
Dim sPath As String = "c:usersmyuserdesktoplenna.png"
Using src = New Mat(sPath, ImreadModes.Color)
Using srcGray = New Mat(sPath, ImreadModes.GrayScale)
Using hsv = New OpenCvSharp.Mat()
Using dst = New Mat()
Cv2.CvtColor(src, hsv, ColorConversionCodes.BGR2HSV)
Cv2.CvtColor(srcGray, dst, ColorConversionCodes.GRAY2BGR)
Dim hsvChannels = Cv2.Split(hsv)
Dim v = hsvChannels(2)
For i As Integer = 0 To 7
Using bin = New Mat()
Cv2.Threshold(v, bin, i * 32, 255, ThresholdTypes.Tozero)
Cv2.Threshold(bin, bin, (i + 1) * 32, 255, ThresholdTypes.BinaryInv)
Dim contours
Cv2.FindContours(bin, contours, Nothing, RetrievalModes.External, ContourApproximationModes.ApproxNone) // Compiler error occurs here
Cv2.DrawContours(dst, contours, -1, Scalar.Red, 1)
End Using
Next i
Window.ShowImages(dst)
For Each m In hsvChannels
m.Dispose()
Next m
End Using
End Using
End Using
End Using
End Sub
End Class

我不确定编译器想从我这里得到什么。有人知道吗？ 使用下划线或双下划线(如一些在线转换器建议的那样(将不起作用。

这些是 FindContours 的声明：

Public Shared Sub FindContours(image As InputOutputArray, ByRef contours() As Mat, hierarchy As OutputArray, mode As RetrievalModes, method As ContourApproximationModes, Optional offset As Point? = Nothing)
Public Shared Sub FindContours(image As InputOutputArray, ByRef contours As Point()(), ByRef hierarchy() As HierarchyIndex, mode As RetrievalModes, method As ContourApproximationModes, Optional offset As Point? = Nothing)

Answer 1

C# 中的下划线参数是丢弃。据我所知，VB没有与此类似的内容。由于这是一个out参数，因此您需要声明一个局部虚拟变量并传递该变量：

Dim contours As Point()()
Dim unused As HierarchyIndex()
Cv2.FindContours(bin, contours, unused, RetrievalModes.External, ContourApproximationModes.ApproxNone) 

另请注意，您当地的contours声明缺少类型，因此不完整。编译器应将其拒绝为无效(如果您使用Option Strict进行编译，则应这样做(。

Answer 2

编译器不知道要使用什么重载，因为您没有为contours提供类型。指定contours的类型，Dim contours as Point()或Dim contours as Mat。

当您对参数值不感兴趣时，会在 csharp 中使用下划线_。由于 VB 没有 out 机制，因此您必须为下划线参数指定一个临时变量Dim hierarchy() As HierarchyIndex或Dim hierarchy As OutputArray。

使用 VB.net 时，请确保指定参数类型 - 如果可能，请启用严格的类型检查。这迫使您编写更简洁的代码，这些代码对类型更加安全。这将为您省去很多麻烦。