Question

我有以下要转换为VB.NET的C＃代码：

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();
            }
        }
    }
}

我设法将其转换，但是“ _”让我头疼。

如果我将其替换为“ Nothing”，则编译器会告诉我“不是最具体”。

如果我这样声明“轮廓”（更具体而言），则编译器告诉我“ Nothing”是无效的参数：

Dim contours As OpenCvSharp.Mat()

这是我的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:\users\myuser\desktop\lenna.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

我不确定编译器要我做什么。有人知道吗使用下划线或双下划线（如某些在线转换器建议的那样）将无效。

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discard。据我所知，VB没有与此等效的功能。由于这是一个out参数，因此您需要声明一个本地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)

还要注意，您的contours本地声明缺少类型，因此不完整。编译器应将此视为无效（如果您使用Option Strict进行编译，则应该这样做）。

Answer 2

编译器不知道您要使用什么重载，因为您没有给contours指定类型。指定类型contours是Dim contours as Point()还是Dim contours as Mat。

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

使用VB.net时，请确保指定参数类型-并尽可能启用严格的类型检查。这迫使您编写更加类型安全的更干净的代码。这将为您节省很多头痛。

C＃下划线作为VB.NET的参数

2 个答案: