vb.net 教程 20-2 base64图片转换 1

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vb.net 教程 20-2 base64图片转换 1

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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。

学习更多vb.net知识，请参看 vb.net 教程目录

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原文链接：https://blog.csdn.net/uruseibest/article/details/77824829

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