mysql - 使用 longblob 数据类型在 mysql 数据库中插入图像

Question

有人检查了我的将图像插入数据库的代码。我知道有一些错误，但无法弄清楚。当我运行代码时它有效但是当我单击完成按钮时它总是显示 NullReferenceException 这是我得到的

Imports MySql.Data.MySqlClient
Imports System.IO

Public Class adminreg

Dim con As MySqlConnection
Dim cmd As MySqlCommand
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim reader As MySqlDataReader
    Dim mstream As New System.IO.MemoryStream
    PictureBox1.Image.Save(mstream, System.Drawing.Imaging.ImageFormat.Jpeg)
    Dim arrImage() As Byte = mstream.GetBuffer()
    mstream.Close()

    con = New MySqlConnection
    con.ConnectionString = "server=localhost;userid=root;password=1234;database=dat"


    Try
        con.Open()
        Dim query As String

        query = "insert into dat.login (idlogin,user,password,name,position,ownpic) values ('" & id.Text & "','" & usertxt.Text & "','" & passtxt.Text & "','" & nmetxt.Text & "','" & postxt.Text & "',@ownpic)"
        cmd.Parameters.AddWithValue("@ownpic", arrImage)

        cmd = New MySqlCommand(query, con)
        reader = cmd.ExecuteReader

        MessageBox.Show("Data Saved")

        con.Close()
    Catch ex As MySqlException
        MessageBox.Show(ex.Message)
    Finally
        con.Dispose()
    End Try

End Sub

Private Sub adminreg_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

End Sub

Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
    OpenFileDialog1.Filter = "imahe lang (*.jpg, *.bmp, *.png) | *.jpg; *.bmp; *.png| all files (*.*) | *.*"
    If OpenFileDialog1.ShowDialog <> Windows.Forms.DialogResult.Cancel Then
        PictureBox1.Image = Image.FromFile(OpenFileDialog1.FileName)

    End If
End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
    Login.Show()
    Me.Hide()
End Sub
End Class

非常感谢任何建议谢谢...只是 VB.net 的初学者

Answer 1


Private Sub pbStudentImage_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles pbStudentImage.Click, txtStudentImage.Enter, txtStudentImage.Click
Try
Dim fileOpener As OpenFileDialog = New OpenFileDialog()
fileOpener.Filter = "Image files | *.jpg"



<pre><code> If fileOpener.ShowDialog() = Windows.Forms.DialogResult.OK Then
pbStudentImage.Image = Image.FromFile(fileOpener.FileName)
txtStudentImage.Text = fileOpener.FileName
End If
Catch ex As Exception
MsgBox(ex.ToString())
End Try
</code></pre>

<p>End Sub</p>

<p>Private Sub btnSaveImage_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSaveImage.Click
Dim con As MySqlConnection = New MySqlConnection(ConString)
Dim cmd As MySqlCommand
Dim fs As FileStream
Dim br As BinaryReader</p>

<pre><code> Try
If txtFirstName.Text.Length > 0 And txtStudentImage.Text.Length > 0 Then
Dim FileName As String = txtStudentImage.Text
Dim ImageData() As Byte

fs = New FileStream(FileName, FileMode.Open, FileAccess.Read)
br = New BinaryReader(fs)
ImageData = br.ReadBytes(CType(fs.Length, Integer))
br.Close()
fs.Close()

Dim CmdString As String = "INSERT INTO Students(FirstName, LastName, Image, Address) VALUES(@FirstName, @LastName, @Image, @Address)"
cmd = New MySqlCommand(CmdString, con)

cmd.Parameters.Add("@FirstName", MySqlDbType.VarChar, 45)
cmd.Parameters.Add("@LastName", MySqlDbType.VarChar, 45)
cmd.Parameters.Add(";@Image", MySqlDbType.Blob)
cmd.Parameters.Add("@Address", MySqlDbType.VarChar, 100)

cmd.Parameters("@FirstName").Value = txtFirstName.Text
cmd.Parameters("@LastName").Value = txtLastName.Text
cmd.Parameters("@Image").Value = ImageData
cmd.Parameters("@Address").Value = txtAddress.Text
con.Open()
Dim RowsAffected As Integer = cmd.ExecuteNonQuery()
If (RowsAffected > 0) Then
MsgBox("Image saved successfully!")
End If
con.Close()
Else
MsgBox("Incomplete data!", MsgBoxStyle.Critical, "")
End If

Catch ex As Exception
MsgBox(ex.ToString())
Finally
If con.State = ConnectionState.Open Then
con.Close()
End If
End Try
</code></pre>

<p>End Sub</p>

<p>Private Sub pbStudentImage_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles pbStudentImage.Click, txtStudentImage.Enter, txtStudentImage.Click
Try
Dim fileOpener As OpenFileDialog = New OpenFileDialog()
fileOpener.Filter = "Image files | *.jpg"</p>

<pre><code> If fileOpener.ShowDialog() = Windows.Forms.DialogResult.OK Then
pbStudentImage.Image = Image.FromFile(fileOpener.FileName)
txtStudentImage.Text = fileOpener.FileName
End If
</code></pre>

<p>Catch ex As Exception
MsgBox(ex.ToString())
End Try</p>

<p>End Sub</p>

<p>Private Sub pbStudentImage_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles pbStudentImage.Click, txtStudentImage.Enter, txtStudentImage.Click
Try
Dim fileOpener As OpenFileDialog = New OpenFileDialog()
fileOpener.Filter = "Image files | *.jpg"</p>

<pre><code> If fileOpener.ShowDialog() = Windows.Forms.DialogResult.OK Then
pbStudentImage.Image = Image.FromFile(fileOpener.FileName)
txtStudentImage.Text = fileOpener.FileName
End If
</code></pre>

<p>Catch ex As Exception
MsgBox(ex.ToString())
End Try</p>

<p>End Sub</p>

<p>Private Sub btnSaveImage_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSaveImage.Click
Dim con As MySqlConnection = New MySqlConnection(ConString)
Dim cmd As MySqlCommand
Dim fs As FileStream
Dim br As BinaryReader</p>