在列表视图中显示文件夹图标

Question

我已经设法使用 shell32 提取在列表视图中显示文件的图标，但是当使用文件夹时，图标似乎没有显示。怎么可能？

这是我的 Shell 提取代码：

' declare the Win32 API function SHGetFileInfo'
Public Declare Auto Function SHGetFileInfo Lib "shell32.dll" (ByVal pszPath As String, ByVal dwFileAttributes As Integer, ByRef psfi As SHFILEINFO, ByVal cbFileInfo As Integer, ByVal uFlags As Integer) As IntPtr
' declare some constants that SHGetFileInfo requires'
Public Const SHGFI_ICON As Integer = &H100
Public Const SHGFI_SMALLICON As Integer = &H1
' define the SHFILEINFO structure'
Structure SHFILEINFO
    Public hIcon As IntPtr
    Public iIcon As Integer
    Public dwAttributes As Integer
    <Runtime.InteropServices.MarshalAs(Runtime.InteropServices.UnmanagedType.ByValTStr, SizeConst:=260)> _
    Public szDisplayName As String
    <Runtime.InteropServices.MarshalAs(Runtime.InteropServices.UnmanagedType.ByValTStr, SizeConst:=80)> _
    Public szTypeName As String
End Structure

Function RetrieveShellIcon(ByVal argPath As String) As Image
    Dim mShellFileInfo As SHFILEINFO
    Dim mSmallImage As IntPtr
    Dim mIcon As System.Drawing.Icon
    Dim mCompositeImage As Image
    mShellFileInfo = New SHFILEINFO
    mShellFileInfo.szDisplayName = New String(Chr(0), 260)
    mShellFileInfo.szTypeName = New String(Chr(0), 80)
    mSmallImage = SHGetFileInfo(argPath, 0, mShellFileInfo, System.Runtime.InteropServices.Marshal.SizeOf(mShellFileInfo), SHGFI_ICON Or SHGFI_SMALLICON)
    ' create the icon from the icon handle'
    Try
        mIcon = System.Drawing.Icon.FromHandle(mShellFileInfo.hIcon)
        mCompositeImage = mIcon.ToBitmap
    Catch ex As Exception
        ' create a blank black bitmap to return'
        mCompositeImage = New Bitmap(16, 16)
    End Try
    ' return the composited image'
    Return mCompositeImage
End Function

Function GetIcon(ByVal argFilePath As String) As Image
    Dim mFileExtension As String = System.IO.Path.GetExtension(argFilePath)
    ' add the image if it doesn't exist''
    If cIcons.ContainsKey(mFileExtension) = False Then
        cIcons.Add(mFileExtension, RetrieveShellIcon(argFilePath))
    End If
    ' return the image'
    Return cIcons(mFileExtension)
End Function

这就是我显示文件图标的方式。

    Dim lvi As ListViewItem
    Dim di As New DirectoryInfo(Form2.TextBox1.Text)
    Dim exts As New List(Of String)
    ImageList1.Images.Clear()
    If di.Exists = False Then
        MessageBox.Show("Source path is not found", "Directory Not Found", MessageBoxButtons.OK, MessageBoxIcon.Error)
    Else
        For Each fi As FileInfo In di.EnumerateFiles("*.*")

            lvi = New ListViewItem
            lvi.Text = fi.Name

            lvi.SubItems.Add(((fi.Length / 1024)).ToString("0.00"))
            lvi.SubItems.Add(fi.CreationTime)

            If exts.Contains(fi.Extension) = False Then
                Dim mShellIconManager As New Form1
                For Each mFilePath As String In My.Computer.FileSystem.GetFiles(Form2.TextBox1.Text)
                    ImageList1.Images.Add(fi.Extension, GetIcon(mFilePath))
                    exts.Add(fi.Extension)
                Next

            End If
            lvi.ImageKey = fi.Extension
            ListView1.Items.Add(lvi)
        Next

这是我显示文件夹图标的方式，但似乎不起作用

For Each fldr As String In Directory.GetDirectories(Form2.TextBox1.Text)
            Dim mShellIconManager As New Form1

            lvi = New ListViewItem
            lvi.Text = Path.GetFileName(fldr)

            lvi.SubItems.Add(((fldr.Length / 1024)).ToString("0.00"))
            lvi.SubItems.Add(Directory.GetCreationTime(fldr))


            ImageList1.Images.Add(GetIcon(fldr))
            ListView1.Items.Add(lvi)            
Next

Answer 1

您的代码中有几件事。其中一些看起来像是以前尝试的残余物。无论如何，这是可行的：

Public Partial Class NativeMethods
    Private Const MAX_PATH As Integer = 256
    Private Const NAMESIZE As Integer = 80
    Private Const SHGFI_ICON As Int32 = &H100

    <StructLayout(LayoutKind.Sequential)> 
    Private Structure SHFILEINFO
        Public hIcon As IntPtr
        Public iIcon As Integer
        Public dwAttributes As Integer
        <MarshalAs(UnmanagedType.ByValTStr, SizeConst:=MAX_PATH)>
        Public szDisplayName As String
        <MarshalAs(UnmanagedType.ByValTStr, SizeConst:=NAMESIZE)>
        Public szTypeName As String
    End Structure

    <DllImport("Shell32.dll")> 
    Private Shared Function SHGetFileInfo(pszPath As String,
                                          dwFileAttributes As Integer,
                                          ByRef psfi As SHFILEINFO,
                                          cbFileInfo As Integer,
                                          uFlags As Integer) As IntPtr
    End Function

    <DllImport("user32.dll", SetLastError:=True)>
    Private Shared Function DestroyIcon(hIcon As IntPtr) As Boolean
    End Function

    Public Shared Function GetShellIcon(path As String) As Bitmap
        Dim shfi As SHFILEINFO = New SHFILEINFO()

        Dim ret As IntPtr = SHGetFileInfo(path, 0, shfi, Marshal.SizeOf(shfi), SHGFI_ICON)
        If ret <> IntPtr.Zero Then
            Dim bmp As Bitmap = System.Drawing.Icon.FromHandle(shfi.hIcon).ToBitmap
            DestroyIcon(shfi.hIcon)
            Return bmp
        Else
            Return Nothing
        End If
    End Function
End Class

将 PInvoke 代码放在它自己的类中有几个好处。首先，它有助于将您的代码与所有这些幻数、结构和常量隔离开来。 PInvoke(s) 可以是私有的，并通过一个方法 (GetShellIcon) 公开，该方法完成所有 scut 工作并调用 API 方法。此外，当使用 NativeMethods 类时，VS CodeAnalysis 工具不会抱怨它。

您的代码没有做的一件事是销毁检索到的图标并释放该资源；你的SHGetFileInfo 看起来也不正确，这可能会导致坏事。当它无法获取图标时，我不会在 PInvoke 代码中创建空白/空位图，而是返回 Nothing 以供代码处理。

最后，封装了 PInvoke 代码更容易使用，更短：

Dim fPath As String = "C:\Temp"
Dim di = New DirectoryInfo(fPath)
' store imagelist index for known/found file types
Dim exts As New Dictionary(Of String, Int32)

Dim img As Image
Dim lvi As ListViewItem
For Each d In di.EnumerateDirectories("*.*", SearchOption.TopDirectoryOnly)
    lvi = New ListViewItem(d.Name)
    lvi.SubItems.Add("")        ' no file name
    lvi.SubItems.Add(Directory.GetFiles(d.FullName).Count().ToString)

    myLV.Items.Add(lvi)

    img = NativeMethods.GetShellIcon(d.FullName)
    imgLst.Images.Add(img)
    lvi.ImageIndex = imgLst.Images.Count - 1
Next

For Each f In di.EnumerateFiles("*.*")
    lvi = New ListViewItem(f.DirectoryName)
    lvi.SubItems.Add(f.Name)        ' no file name
    lvi.SubItems.Add("n/a")

    myLV.Items.Add(lvi)
    If exts.ContainsKey(f.Extension) = False Then
        ' try simplest method
        img = Drawing.Icon.ExtractAssociatedIcon(f.FullName).ToBitmap
        If img Is Nothing Then
            img = NativeMethods.GetShellIcon(f.FullName)
        End If
        If img IsNot Nothing Then
            imgLst.Images.Add(img)
            exts.Add(f.Extension, imgLst.Images.Count - 1)
        Else
            ' ?? use some default or custom '?' one?
        End If

    End If

    lvi.ImageIndex = exts(f.Extension)
Next

对于文件，它首先尝试使用 NET Icon.ExtractAssociatedIcon 方法获取图标，然后求助于由于某种原因失败的 PInvoke。

我将exts List(Of String 更改为Dictionary(Of String, Int32)。一旦代码获得了扩展的图标，它就会将该图像的索引保存在ImageList 中，这样就不需要再次查找扩展/图标。这在大文件夹上加快了速度。

如果你在方法之外声明Dictionary，然后每次都不清除ImageList，你可以让它们在运行时都累积图像。文件夹 Foo 中的 text file 图标不会与其他位置的文本文件的图像不同。

结果：