Difficulty retrieving text in TextBox upon selecting an ID in ComboBox - sql-server

Question

Upon selecting a Question ID in the combo box the relating question should then appear in the text box. I am unsure how to get this to work though. I receive an error "Value of type......cannot be converted to string" on retrieveQuestion(). Any help is appreciated, thankyou.
Private Sub cmbQuestion_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmbQuestion.SelectedIndexChanged
txtExistingQuestion.Text = retrieveQuestion() 'Add question, relevant to Question ID, to text box, DO I NEED .ToString?????????????????
loaded = True
End Sub
Public Function retrieveQuestion() As List(Of Question) 'Retrieves selected question into text box
Dim typeList As New List(Of Question)
Dim Str As String = "SELECT Question_ID, Question_Text FROM Question WHERE Question_ID =" & cmbQuestion.SelectedValue
Try
Using conn As New SqlClient.SqlConnection(DBConnection)
conn.Open()
Using cmdQuery As New SqlClient.SqlCommand(Str, conn)
Using drResult As SqlClient.SqlDataReader = cmdQuery.ExecuteReader()
While drResult.Read
typeList.Add(New Question(drResult("Question_ID"), drResult("Question_Text")))
End While
End Using 'Automatically closes connection
End Using
End Using
Catch ex As Exception
MsgBox("Question List Exception: " & ex.Message & vbNewLine & Str)
End Try
Return typeList
End Function
Public Class Question 'defining one club within class
Public Sub New(ByVal questionID As Integer, ByVal questionText As String)
mQuestionID = questionID 'm is for member of the class
mQuestionText = questionText
End Sub
Private mQuestionID As String = ""
Private mQuestionText As String = ""
Public Property QuestionID() As String
Get
Return mQuestionID
End Get
Set(ByVal value As String)
mQuestionID = value
End Set
End Property
Public Property QuestionText() As String
Get
Return mQuestionText
End Get
Set(ByVal value As String)
mQuestionText = value
End Set
End Property
End Class

Answer 1

Your issue is this line:
mQuestionID = questionID
In your class you have defined this:
Private mQuestionID As String = ""
But in your constructor, you are saying that questionID should be an Integer, like this:
Public Sub New(ByVal questionID As Integer, ByVal questionText As String)
You need to change your backing variable in your class (mQuestionID) to be an Integer, like this:
Private mQuestionID As Integer
This will also necessitate a change to the property syntax for QuestionID, like this:
Public Property QuestionID() As Integer
Get
Return mQuestionID
End Get
Set(ByVal value As Integer)
mQuestionID = value
End Set
End Property

Answer 2

Your error is originated by the return value of retrieveQuestion declared as a List(Of Question) but then you try to set the text property of a TextBox (and there is no way to convert automatically a List(Of Question) to a string)
So you could write something like this to extract the text of the first question in the list
Dim qList = retrieveQuestion()
if qList.Count > 0 then
txtExistingQuestion.Text = qList(0).QuestionText
loaded = True
End If
Of course, if your query returns zero or just one question, then there is no need to return a List(Of Question) and you can change the retrieveQuestion method to return just a Question or Nothing
Public Function retrieveQuestion() As Question
Dim questionResult As Question = Nothing
......
Using drResult As SqlClient.SqlDataReader = cmdQuery.ExecuteReader()
if drResult.Read() then
questionResult = New Question(drResult("Question_ID"), _
drResult("Question_Text")))
End if
End Using
....
return questionResult
End Function
Dim question = retrieveQuestion()
if question IsNot Nothing then
txtExistingQuestion.Text = question.QuestionText
loaded = True
End If
However, all the comments about string and integer conversion happening automatically on your code are really an alarm bell. You should strive to avoid this kind of conversion because they render your code weak and prone to misterious errors. Switch to Option Strinct On on your project properties and prepare yourself to a lot of conversion fixing.