vb.net 教程 20-2 base64图片转换 1

base64编码常用于MIME的电子邮件，IE保存的Mht格式网页，也是用的base64编码。

详细请查看查看RFC2045～RFC2049，上面有MIME的详细规范，这里谈谈在vb.net中的实现。

设计界面，包含3个按钮、1个文本框和1个webbrowser控件：

现在form窗体类添加窗体级变量，用于存储图片格式，在下一节中我们会将编码的图片显示出来：

Dim imgFormat As String

图片base64编码的代码：

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click        Dim filename As String = ""        Dim ofDialog As New OpenFileDialog()        With ofDialog            .Filter = "图片文件|*.jpg;*.png;*.gif"            .FileName = ""            If .ShowDialog = DialogResult.OK Then                filename = .FileName            Else                Exit Sub            End If        End With        Dim bmp As New Bitmap(filename)        Select Case bmp.RawFormat.Guid            Case Imaging.ImageFormat.Jpeg.Guid                imgFormat = "jpeg"            Case Imaging.ImageFormat.Gif.Guid                imgFormat = "gif"            Case Imaging.ImageFormat.Png.Guid                imgFormat = "png"            Case Else                MessageBox.Show("不是指定的格式")                Exit Sub        End Select        Dim ms As New System.IO.MemoryStream()        bmp.Save(ms, bmp.RawFormat)        Dim base64String As String        Dim base64Bytes() As Byte        Dim base64Length As Integer        base64Length = ms.Length        ReDim base64Bytes(base64Length - 1)        ms.Position = 0        ms.Read(base64Bytes, 0, base64Length)        ms.Close()        base64String = Convert.ToBase64String(base64Bytes)        TextBox1.Text = base64String    End Sub

base64还原图片的代码：

    Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click        Dim filename As String        Dim sfDialog As New SaveFileDialog()        With sfDialog            .Filter = "图片文件|*." & IIf(imgFormat = "jpeg", "jpg", imgFormat)            .FileName = ""            If .ShowDialog = DialogResult.OK Then                filename = .FileName            Else                Exit Sub            End If        End With        Dim fromBase64Bytes() As Byte        fromBase64Bytes = Convert.FromBase64String(TextBox1.Text)        Dim ms As New System.IO.MemoryStream(fromBase64Bytes)        Dim bmp As New Bitmap(ms)        Dim saveimgformat As Imaging.ImageFormat        Select Case imgFormat            Case "jpeg"                saveimgformat = Imaging.ImageFormat.Jpeg            Case "png"                saveimgformat = Imaging.ImageFormat.Png            Case "gif"                saveimgformat = Imaging.ImageFormat.Gif            Case Else                MessageBox.Show("不是指定的格式")                Exit Sub        End Select        bmp.Save(filename, saveimgformat)        bmp.Dispose()    End Sub

注意，随着图片越大，转换会越慢。

由于.net平台下C#和vb.NET很相似，本文也可以为C#爱好者提供参考。

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