Winforms Textbox Autocomplete Crash Application - sql

Question

Sometimes the program crashes when I write in the textbox. I can't find the solution. It is very weird situation. Why is program crashes sometimes. Here codes:
Private Sub CreateProductNameAutoCompleteSource(ByVal tamamlamaturu As Byte)
Dim sql_ProductName As String
Dim gorkemDAL As New Aktuel.Data.SqlClient(cns_ScalaConnectionString)
Dim dtbl_ProductName As DataTable
Dim X As New AutoCompleteStringCollection
Dim parcakodu
If tamamlamaturu = tamamlamatipi.talepedilenparca Then parcakodu = txt_talepedilenparca.Text
If tamamlamaturu = tamamlamatipi.gonderilenparca Then parcakodu = txt_gonderilenparca.Text
sql_ProductName = "select distinct urunkodu from urunler where urunkodu like '" & parcakodu & "%' order by urunkodu asc"
gorkemDAL.OpenDbConnection()
dtbl_ProductName = gorkemDAL.ExecuteTable(sql_ProductName)
gorkemDAL.CloseDbConnection()
For Each row As DataRow In dtbl_ProductName.Rows
X.Add(row(0).ToString)
Next
If tamamlamaturu = tamamlamatipi.talepedilenparca Then
txt_talepedilenparca.AutoCompleteSource = AutoCompleteSource.CustomSource
txt_talepedilenparca.AutoCompleteCustomSource = X
txt_talepedilenparca.AutoCompleteMode = AutoCompleteMode.Suggest
End If
If tamamlamaturu = tamamlamatipi.gonderilenparca Then
txt_gonderilenparca.AutoCompleteSource = AutoCompleteSource.CustomSource
txt_gonderilenparca.AutoCompleteCustomSource = X
txt_gonderilenparca.AutoCompleteMode = AutoCompleteMode.Suggest
End If
End Sub
And Textchange event :
Private Sub txt_talepedilenparca_TextChanged(sender As Object, e As EventArgs) Handles txt_talepedilenparca.TextChanged
CreateProductNameAutoCompleteSource(tamamlamatipi.talepedilenparca)
End Sub
And I found error message in event viewer:
Error Message
Error Message

Answer 1

The code looks pretty clean, I can't see anything too obvious but I would make sure that parcakodu doesn't contain any sql terminating speech marks:
i.e.
sql_ProductName = "select distinct urunkodu from urunler where urunkodu like '" & parcakodu & "%' order by urunkodu asc"
becomes:
sql_ProductName = "select distinct urunkodu from urunler where urunkodu like '" & parcakodu.Replace("'", "''") & "%' order by urunkodu asc"
(you may want to copy & paste as hard to see what I've done there)
I would also wrap your ForEach statement in a null check - could it be you're trying to access dtbl_ProductName when it's null? Accessing the property .Rows will raise an exception if the object is null itself is Nothing.
Try something like:
If (dtbl_ProductName IsNot Nothing)
For Each row As DataRow In dtbl_ProductName.Rows
X.Add(row(0).ToString)
Next
End If
Failing that - check if you can make it crash every time by using a known search string that has caused it to crash in the past. Is there a character in the string sql doesn't like, or is the result set of your sql query empty?

Answer 2

In your reply to the question about the error you're receiving you said the program is just closing.
Thus, the first step is to wrap your code in a Try...Catch block in order to get a meaningful error message without getting the program to close.
Private Sub CreateProductNameAutoCompleteSource(ByVal tamamlamaturu As Byte)
Try
Dim sql_ProductName As String
Dim gorkemDAL As New Aktuel.Data.SqlClient(cns_ScalaConnectionString)
Dim dtbl_ProductName As DataTable
Dim X As New AutoCompleteStringCollection
Dim parcakodu
If tamamlamaturu = tamamlamatipi.talepedilenparca Then
parcakodu = txt_talepedilenparca.Text
ElseIf tamamlamaturu = tamamlamatipi.gonderilenparca Then
parcakodu = txt_gonderilenparca.Text
Else
Exit Sub
End If
sql_ProductName = "select distinct urunkodu from urunler where urunkodu like '" & parcakodu.Replace("'", "''") & "%' order by urunkodu asc"
gorkemDAL.OpenDbConnection()
dtbl_ProductName = gorkemDAL.ExecuteTable(sql_ProductName)
gorkemDAL.CloseDbConnection()
If (dtbl_ProductName IsNot Nothing) Then
For Each row As DataRow In dtbl_ProductName.Rows
X.Add(row(0).ToString)
Next
End If
If tamamlamaturu = tamamlamatipi.talepedilenparca Then
txt_talepedilenparca.AutoCompleteSource = AutoCompleteSource.CustomSource
txt_talepedilenparca.AutoCompleteCustomSource = X
txt_talepedilenparca.AutoCompleteMode = AutoCompleteMode.Suggest
End If
If tamamlamaturu = tamamlamatipi.gonderilenparca Then
txt_gonderilenparca.AutoCompleteSource = AutoCompleteSource.CustomSource
txt_gonderilenparca.AutoCompleteCustomSource = X
txt_gonderilenparca.AutoCompleteMode = AutoCompleteMode.Suggest
End If
Catch ex As Exception
MessageBox.Show(String.Format("The following error has occured:{0}{1}", vbCrLf, ex.Message), "An error has occured")
End Try
End Sub
Private Sub txt_talepedilenparca_TextChanged(sender As Object, e As EventArgs) Handles txt_talepedilenparca.TextChanged
If txt_talepedilenparca.Text.Length >= 3 Then
CreateProductNameAutoCompleteSource(tamamlamatipi.talepedilenparca)
End If
End Sub
This will give a clear idea about what's happening before tackling the main issue.
I've also escaped the string value being passed to the query so it doesn't create an SQL injection if the user entered a single quote in the text boxes.
I've also limited the function not trigger but until the textbox has at least 3 letters.
If the program still closes without an error message, then the issue is happening elsewhere, but if you got an error message, then we can take it from there.

Answer 3

Try to use this trick:
Private Sub txt_talepedilenparca_TextChanged(sender As Object, e As EventArgs) Handles txt_talepedilenparca.TextChanged
Dim sql_ProductName As String
Dim gorkemDAL As New Aktuel.Data.SqlClient(cns_ScalaConnectionString)
Dim dtbl_ProductName As DataTable
Dim X As New AutoCompleteStringCollection
sql_ProductName = "select distinct urunkodu from urunler where urunkodu order by urunkodu asc"
gorkemDAL.OpenDbConnection()
dtbl_ProductName = gorkemDAL.ExecuteTable(sql_ProductName)
gorkemDAL.CloseDbConnection()
try
If txt_talepedilenparca.lenght >= 3 and txt_talepedilenparca.lenght mod 3 = 0 then
For Each row As DataRow In dtbl_ProductName.select("urunkodu like '*" & parcakodu & "*'")
X.Add(row(0).ToString)
Next
if x.count > 0
txt_talepedilenparca.AutoCompleteSource = AutoCompleteSource.CustomSource
txt_talepedilenparca.AutoCompleteCustomSource = X
txt_talepedilenparca.AutoCompleteMode = AutoCompleteMode.Suggest
end if
End If
catch ex as exception
msgbox(ex.tostring)
end try
End Sub