VB.NET 2022中如何让ListBox仅显示图片文件

我用以下代码将文件夹中的文件名加载到ListBox中：

ListBox1.Items.Clear()
If FolderBrowserDialog1.ShowDialog = Windows.Forms.DialogResult.OK And FolderBrowserDialog1.SelectedPath = Folder1Path.Text Or FolderBrowserDialog1.SelectedPath = Folder2Path.Text Or FolderBrowserDialog1.SelectedPath = Folder3Path.Text Then
    MsgBox("Unable to open a same folder")
Else
    SourceFolderPath.Text = FolderBrowserDialog1.SelectedPath
    Dim filenames As String() = IO.Directory.GetFiles(FolderBrowserDialog1.SelectedPath)
    If filenames.Length > 0 Then
        For Each names As String In filenames
            Dim justname As String = IO.Path.GetFileName(names)
            ListBox1.Items.Add(justname)
        Next
    End If
End If

目前ListBox显示结果包含非图片文件：

456.pub
1.img
gmoier.img

我尝试在filenames.Length > 0后添加filenames.OfType(Of Image)但出现错误，该如何解决？

方法1：按文件扩展名筛选 #

直接通过常见图片扩展名判断，代码修改如下：

ListBox1.Items.Clear()
If FolderBrowserDialog1.ShowDialog = Windows.Forms.DialogResult.OK And FolderBrowserDialog1.SelectedPath = Folder1Path.Text Or FolderBrowserDialog1.SelectedPath = Folder2Path.Text Or FolderBrowserDialog1.SelectedPath = Folder3Path.Text Then
    MsgBox("Unable to open a same folder")
Else
    SourceFolderPath.Text = FolderBrowserDialog1.SelectedPath
    ' 定义需筛选的图片扩展名集合，可按需增减
    Dim imageExtensions As New HashSet(Of String) From {".jpg", ".jpeg", ".png", ".gif", ".bmp", ".img"}
    Dim filenames As String() = IO.Directory.GetFiles(FolderBrowserDialog1.SelectedPath)
    
    If filenames.Length > 0 Then
        For Each names As String In filenames
            Dim ext As String = IO.Path.GetExtension(names).ToLower()
            ' 匹配扩展名则添加到ListBox
            If imageExtensions.Contains(ext) Then
                Dim justname As String = IO.Path.GetFileName(names)
                ListBox1.Items.Add(justname)
            End If
        Next
    End If
End If

说明 #

• 用HashSet存储扩展名是为了提升查找效率，也可替换为普通数组
• ToLower()避免大小写匹配问题，比如.JPG和.jpg都能被识别
• 可根据需求添加其他图片格式，比如.webp、.tiff等

方法2：验证文件是否为有效图片（避免扩展名伪装） #

如果需要确保文件是真正可识别的图片（而非改了扩展名的非图片文件），可通过加载文件验证：

ListBox1.Items.Clear()
If FolderBrowserDialog1.ShowDialog = Windows.Forms.DialogResult.OK And FolderBrowserDialog1.SelectedPath = Folder1Path.Text Or FolderBrowserDialog1.SelectedPath = Folder2Path.Text Or FolderBrowserDialog1.SelectedPath = Folder3Path.Text Then
    MsgBox("Unable to open a same folder")
Else
    SourceFolderPath.Text = FolderBrowserDialog1.SelectedPath
    Dim filenames As String() = IO.Directory.GetFiles(FolderBrowserDialog1.SelectedPath)
    
    If filenames.Length > 0 Then
        For Each names As String In filenames
            Try
                ' 尝试加载图片，成功则判定为有效图片
                Using img As Image = Image.FromFile(names)
                    Dim justname As String = IO.Path.GetFileName(names)
                    ListBox1.Items.Add(justname)
                End Using
            Catch ex As Exception
                ' 加载失败则跳过该文件
            End Try
        Next
    End If
End If

说明 #

• 用Try-Catch捕获加载失败的情况，过滤无效图片
• Using语句确保图片资源被及时释放，避免内存泄漏
• 该方法准确性更高，但速度比扩展名筛选慢，适合对精度要求高的场景

为什么OfType(Of Image)会报错？ #

filenames是字符串数组，存储的是文件路径字符串，并非Image对象。OfType(Of Image)只能从集合中筛选指定类型的元素，自然无法从字符串集合中得到Image类型，因此会报错。

内容的提问来源于stack exchange，提问作者Irfan Azhari