VB.NET/C#;使用 BitBlt；在两者中使用相同的代码，内存泄漏出现在 VB.NET 而不是 C#

Question

为了将 BitBlt 用于应用程序，我在 BitBlt code not working 找到了 C# 参考并将其转换为 VB.net。我主要使用 VB.net 这就是我转换它并尝试这样使用它的原因。它在 C# 中工作正常，但在 VB.net 中它有内存泄漏，我不确定如何修复它。

代码：

C# 版本（从上面的源代码修改了一点）。打开新项目，添加1个按钮和1个图片框，修改lstPics.Add():

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.Runtime.InteropServices;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        [DllImport("gdi32.dll", EntryPoint = "SelectObject")]
        public static extern System.IntPtr SelectObject(
        [In()] System.IntPtr hdc,
        [In()] System.IntPtr h);

        [DllImport("gdi32.dll", EntryPoint = "DeleteObject")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool DeleteObject(
            [In()] System.IntPtr ho);

        [DllImport("gdi32.dll", EntryPoint = "BitBlt")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool BitBlt(
            [In()] System.IntPtr hdc, int x, int y, int cx, int cy,
            [In()] System.IntPtr hdcSrc, int x1, int y1, uint rop);

        public Form1()

        {
            InitializeComponent();
        }

        public Int16 lstLoc = 0;

        private void button1_Click(object sender, EventArgs e)
        {
            List<string> lstPics = new List<string>();
            lstPics.Add("C:\1.jpg");
            lstPics.Add("C:\2.jpg");
            lstPics.Add("C:\3.jpg");
            if ((lstLoc == lstPics.Count))
            {
                lstLoc = 0;
            }

            string strLoc = lstPics[lstLoc];
            lstLoc++;

            using (Bitmap bmp = (Bitmap)Bitmap.FromFile(strLoc))
            using (Graphics grDest = Graphics.FromHwnd(pictureBox1.Handle))
            using (Graphics grSrc = Graphics.FromImage(bmp))
            {
                IntPtr hdcDest = IntPtr.Zero;
                IntPtr hdcSrc = IntPtr.Zero;
                IntPtr hBitmap = IntPtr.Zero;
                IntPtr hOldObject = IntPtr.Zero;

                try
                {
                    hdcDest = grDest.GetHdc();
                    hdcSrc = grSrc.GetHdc();
                    hBitmap = bmp.GetHbitmap();

                    hOldObject = SelectObject(hdcSrc, hBitmap);
                    if (hOldObject == IntPtr.Zero)
                        throw new Win32Exception();

                    if (!BitBlt(hdcDest, 0, 0, pictureBox1.Width, pictureBox1.Height,
                        hdcSrc, 0, 0, 0x00CC0020U))
                        throw new Win32Exception();
                }
                finally
                {
                    if (hOldObject != IntPtr.Zero) SelectObject(hdcSrc, hOldObject);
                    if (hBitmap != IntPtr.Zero) DeleteObject(hBitmap);
                    if (hdcDest != IntPtr.Zero) grDest.ReleaseHdc(hdcDest);
                    if (hdcSrc != IntPtr.Zero) grSrc.ReleaseHdc(hdcSrc);
                }
            }
        }
    }
}

VB.net 版本（由我转换）。打开新项目，添加1个按钮和1个图片框，修改lstPics.Add():

Imports System.ComponentModel

Public Class Form1
    Public Declare Function SelectObject Lib "gdi32.dll" Alias "SelectObject" (ByVal hdc As System.IntPtr, ByVal h As System.IntPtr) As System.IntPtr
    Public Declare Function DeleteObject Lib "gdi32.dll" Alias "DeleteObject" (ByVal ho As System.IntPtr) As Boolean
    Public Declare Function BitBlt Lib "gdi32.dll" Alias "BitBlt" (ByVal hdc As System.IntPtr, ByVal x As Integer, ByVal y As Integer, ByVal cx As Integer, ByVal cy As Integer, ByVal hdcSrc As System.IntPtr, ByVal x1 As Integer, ByVal y1 As Integer, ByVal rop As UInteger) As Boolean

    Public lstLoc As Int16 = 0

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim mil1 As Int64 = 0
        Dim mil2 As Int64 = 0
        Dim mil3 As Int64 = 0

        Dim lstPics As New List(Of String)
        lstPics.Add("C:.jpg")
        lstPics.Add("C:.jpg")
        lstPics.Add("C:.jpg")

        If lstLoc = lstPics.Count Then lstLoc = 0
        Dim strLoc As String = lstPics(lstLoc)
        lstLoc += 1

        Using bmp As Bitmap = Bitmap.FromFile(strLoc),
            grDest As Graphics = Graphics.FromHwnd(PictureBox1.Handle),
            grSrc As Graphics = Graphics.FromImage(bmp)

            Dim hdcDest As IntPtr = IntPtr.Zero
            Dim hdcSrc As IntPtr = IntPtr.Zero
            Dim hBitmap As IntPtr = IntPtr.Zero
            Dim hOldObject As IntPtr = IntPtr.Zero

            Try
                hdcDest = grDest.GetHdc()
                hdcSrc = grSrc.GetHdc()
                hBitmap = bmp.GetHbitmap()

                hOldObject = SelectObject(hdcSrc, bmp.GetHbitmap)

                If (hOldObject = IntPtr.Zero) Then Throw New Win32Exception()

                If Not BitBlt(hdcDest, 0, 0, PictureBox1.Width, PictureBox1.Height, hdcSrc, 0, 0, 13369376) Then Throw New Win32Exception()

            Catch ex As Exception
                MessageBox.Show(ex.Message.ToString & vbNewLine & vbNewLine & ex.ToString)

            Finally
                If (hOldObject <> IntPtr.Zero) Then SelectObject(hdcSrc, hOldObject)
                If (hBitmap <> IntPtr.Zero) Then DeleteObject(hBitmap)
                If (hdcDest <> IntPtr.Zero) Then grDest.ReleaseHdc(hdcDest)
                If (hdcSrc <> IntPtr.Zero) Then grSrc.ReleaseHdc(hdcSrc)

            End Try

        End Using

    End Sub

End Class

当您按下按钮并循环浏览不同的图片时，C# 版本的内存使用量会激增，但随后又会下降。然而，VB.net 版本的内存使用量会不断增加。这种泄漏是从哪里来的，为什么只发生在 VB.net?

我知道我还有其他可用的选项，例如 DrawImage 或直接在图片框中显示。我想使用 BitBlt 来提高速度。并想在将其放入主应用程序（处理图像）之前对其进行测试并使其正常工作。

感谢您的帮助。

还有一个额外的问题，有没有办法在上面的代码中降低内存使用量（主要是在它达到峰值时）。只是想确保我没有浪费。谢谢。

Answer 1

VB版本调用bmp.GetHbitmap()两次：

hBitmap = bmp.GetHbitmap()
hOldObject = SelectObject(hdcSrc, bmp.GetHbitmap)
'                                      ^^^ Here it is again

而C#版本只调用一次：

hBitmap = bmp.GetHbitmap();
hOldObject = SelectObject(hdcSrc, hBitmap);
//                                ^^^ uses the handle from the previous line

请注意 documentation on GetHbitmap 中的这些摘录：

Creates a GDI bitmap object from this Bitmap.
...

Remarks:

You are responsible for calling the GDI DeleteObject method to free the memory used by the GDI bitmap object.

因此 GetHbitmap() 方法的命名令人困惑，因为它不仅为您提供已经存在的句柄，而且实际上创建了一个您必须清理的新 GDI 资源。要使 VB 代码等同于 C#，请执行以下操作：

hBitmap = bmp.GetHbitmap()
hOldObject = SelectObject(hdcSrc, hBitmap)

VB.NET/C#;使用 BitBlt；在两者中使用相同的代码，内存泄漏出现在 VB.NET 而不是 C#

VB.NET/C#; Using BitBlt; Using same code in both, memory leak appearing in VB.NET but not C#

c#

.net

vb.net

memory-leaks

bitblt

Remarks: