为了将BitBlt用于应用程序，我在BitBlt code not working找到了一个C＃引用并将其转换为VB.net。我主要使用VB.net，这就是我转换它的原因，并尝试使用它。它在C＃中运行良好，但在VB.net中它有内存泄漏，我不知道如何解决它。
代码：
C＃版本（从上面的源代码修改了一下）。 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:\1.jpg")
lstPics.Add("C:\2.jpg")
lstPics.Add("C:\3.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＃版本的内存使用率将会飙升，但之后会再次下降。然而，VB.net版本将继续增加内存使用量。这个泄漏来自哪里，为什么它只发生在VB.net？
我知道我还有其他可用选项，例如DrawImage或直接在图片框中显示。我想用BitBlt来提高速度。并希望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。
和奖金问题，有没有办法在上面的代码中降低内存使用率（主要是在它出现峰值时）。只是想确保我不浪费。感谢。
答案 0 :(得分：1)
VB版本调用bmp.GetHbitmap()两次：
hBitmap = bmp.GetHbitmap()
hOldObject = SelectObject(hdcSrc, bmp.GetHbitmap)
' ^^^ Here it is again
虽然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：
的摘录从此位图创建GDI位图对象 ......
说明：
您负责调用GDI DeleteObject 方法来释放GDI位图对象使用的内存。
所以GetHbitmap()方法容易引起混淆，因为它并不只是给你已经存在的句柄，但实际上创建了一个你必须清理的新GDI资源。要使VB代码等效于C＃，请执行以下操作：
hBitmap = bmp.GetHbitmap()
hOldObject = SelectObject(hdcSrc, hBitmap)