[RESOLVED] UserControl Question

[Grifter]

Hi all

Description of problem: I have a simple form with a usercontrol on it. There is a drop down box with a list of departments in it and a button, this is all in the usercontrol. I pick a department then press the button to view the employees in a listview for the department picked. All worked fine until I moved the code for drop down and button into the usercontrol from the form.

The data is taken from oracle database express 10G edition and I am using a cursor package (CP) and I pass parameters from the code to the oracle procedure within the CP. One of these parameters is the selected department from the drop down list (which I have picked) and my code does not seem to be picking up this parameter, it keps saying that the bold bit of code below is nothing:

myCmd.Parameters.Add(New OracleParameter("n_dept", OracleDbType.Varchar2)).Value = usr1.cmbDepartments.SelectedItem

Everything else seems to be fine. Because it is not picking up the selected item then the dr.read (no data by the looks of it) is false and it just falls out without populating any employees for that dept in the listview.

Does anyone care to take a stab at suggesting what might be wrong? Why won't it pick up the selected item in the user control I have just picked it in?

Thanks

G

[minitech]

Because an item isn't selected? That's the only reason SelectedItem would ever be Nothing (unless, of course, you've added Nothing values to your ComboBox). Maybe check SelectedIndex, too.

[Grimfort]

If you moved this code into the usercontrol then surely you dont need to say usr1.cmbDepartments but just cmbDepartments ? Do you have a public instances called usr1 that is not the one in question?

[minitech]

I think he's referencing the ComboBox from the form, not the UserControl. By default, the scope for added controls is Friend in VB.NET, Private in C#.

[Grimfort]

I pick a department then press the button to view the employees in a listview for the department picked.

You sure? the button is on the usercontrol.

[minitech]

That would make the code impossible to build, though - UserControls don't have default instances.

[Grimfort]

Thats why I went for the public instance being declared but not being used in this case hence the nothing

[.paul.]

so is the query within the usercontrol or in the parent form?

[Grifter]

Finding it hard deciding who too respoond to first. What I will do is post the code from the different classes etc and see if anyone can see the issue:

User control class:

Public Class UserControl1
    Dim emp As New employees


    Private Sub btn1_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles btn1.Click
        With cmbDepartments
            If .SelectedItem Is Nothing Then
                MessageBox.Show("Please Pick a Department Before Continuing.", "Pick Department")
                .Focus()
            Else
                Form1.ListView1.Items.Clear()
                Form1.SetListViewColumns()
                emp.getEmployeeDetails() ' Changed 19/05/2010
            End If
        End With
    End Sub

    Private Sub UserControl1_Load(ByVal sender As Object, _
    ByVal e As System.EventArgs) Handles Me.Load
        Dim queryStr1 As String = "Select department_name from departments"
        'Dim queryStr2 As String = "Select department_id from departments"
        Me.connectToOra(queryStr1)
    End Sub

    ' Pass cmbbox, sql query string, table column, and connection string to db, for this function
    ' Use function to dimension array
    ' to dimension count for array
    ' to dimension connection as new oracle connection
    ' Associate parameter function connstr string value with oracle connection object
    ' Fire 'try' statement to firstly connect to DB with error handling
    ' Finish 'try' then dimension a new oracle command object
    ' Associate sql string (sqlstr) to command text
    ' Associate command type text as command type
    ' Associate oracle connection with commmand type connection
    ' Dimension oracle data reader
    ' Start 'try' to read data into array
    ' Use variable table column to read each value in the passed table column to the array
    ' Add count 1 to each value put in the array
    ' once array is populated use combobox parameter to additems to the combo box 
    ' Return the array
    ' Close the connection
    ' Dispose of the connection object
    Public Function populateComboDepts(ByVal cmbBox As ComboBox, _
                                        ByVal sqlStr As String, _
                                        ByVal tableCol As String, _
                                        ByVal connStr As String) As String()

        Dim array(0) As String
        Dim cnt As Integer = 0
        Dim conn As New OracleConnection
        conn.ConnectionString = connStr
        Try
            conn.Open()
        Catch ex As Exception
            MessageBox.Show("Error: " & ex.Message)
            MsgBox("Failed connection to Oracle" & ex.Message)
            'Return array
        End Try
        Dim cmd As New OracleCommand
        With cmd
            .CommandText = sqlStr
            .CommandType = CommandType.Text
            .Connection = conn
        End With
        Dim dr As OracleDataReader
        dr = cmd.ExecuteReader
        Try
            While dr.Read
                ReDim Preserve array(cnt)
                array(cnt) = dr.Item(tableCol)
                cnt = cnt + 1
            End While
            'cmbBox.Items.Clear()
            cmbBox.Items.AddRange(array)
            'Return array
        Catch ex As Exception
            MessageBox.Show(ex.Message, "Error")
            'Dim a(0) As String
            'a(0) = 0
            'Return a
        Finally
            conn.Close()
            conn.Dispose()
        End Try
        Return array
    End Function

    Public Sub connectToOra(ByVal queryStr1 As String)
        Try
            Dim xe As String = "Data Source=XE;User Id=hr;Password=hr;"
            Dim conn As New OracleConnection(xe) ' Associate connection string with connection object
            conn.Open()
            Dim sql1 As String = queryStr1
            'Dim sql2 As String = queryStr2
            Dim cmd As New OracleCommand(sql1, conn)
            cmd.CommandType = CommandType.Text
            Dim dr As OracleDataReader = cmd.ExecuteReader
            dr.Read()
            populateComboDepts(Me.cmbDepartments, sql1, "department_name", xe)
            'populateComboDeptID(cmbDeptID, sql2, "department_id", xe)
            conn.Dispose()
        Catch ex As Exception
            MessageBox.Show("Error: " & ex.Message)
        Finally
        End Try
    End Sub
End Class

Employees Class:

Public Class employees
    Private mEmployees As New Collection

    Public Function count() As Long
        count = mEmployees.Count
    End Function


    Public Sub remove(ByVal index As VariantType)
        mEmployees.Remove(index)
    End Sub

    Public Function item(ByVal index As VariantType) As employee
        item = mEmployees.Item(index)
    End Function

    Public Function newenum()
        newenum = mEmployees.GetEnumerator
    End Function

    Public Sub getEmployeeDetails()
        Dim usr1 As UserControl1
        usr1 = New UserControl1
        Dim ds As New DataSet
        Dim xe As String = "Data Source = XE; User id=hr;Password=hr;"
        Dim conn As New OracleConnection(xe)
        conn.Open()
        Dim myCmd As New OracleCommand
        myCmd.Connection = conn
        myCmd.CommandText = "curspkg_emp.emp_details_cursor1"
        myCmd.CommandType = CommandType.StoredProcedure
        myCmd.Parameters.Add(New OracleParameter("n_dept", OracleDbType.Varchar2)).Value = usr1.cmbDepartments.SelectedItem 
        << Here's where it is not picking up the selected item
        myCmd.Parameters.Add(New OracleParameter("io_cursor", OracleDbType.RefCursor)).Direction = ParameterDirection.Output

        Dim dr As OracleDataReader = myCmd.ExecuteReader
        Dim emp As employee
        emp = New employee
        While dr.Read
            With emp
                .EmployeeID = dr.Item("Employee_ID")
                .FirstName = dr.Item("First_Name")
                .LastName = dr.Item("Last_Name")
                .Email = dr.Item("Email")
                .PhoneNumber = dr.Item("Phone_Number")
                .HireDate = dr.Item("Hire_Date")
                .JobID = dr.Item("Job_ID")
                .Salary = dr.Item("Salary").ToString
                If IsDBNull(dr.Item("Commission_PCT")) Then
                    .CommissionPCT = 0
                Else
                    .CommissionPCT = dr.Item("Commission_PCT")
                End If
                If IsDBNull(dr.Item("Manager_ID")) Then
                    .ManagerID = 0
                Else
                    .ManagerID = dr.Item("Manager_ID")
                End If
                .DepartmentID = dr.Item("Department_ID")
            End With
            Dim lst As New ListViewItem
            Form1.ListView1.Items.Add(lst)
            lst.Text = dr.Item("Employee_ID")
            With lst.SubItems
                .Add(dr.Item("First_Name"))
                .Add(dr.Item("Last_Name"))
                .Add(dr.Item("Email"))
                .Add(dr.Item("Phone_Number"))
                .Add(dr.Item("Hire_Date"))
                .Add(dr.Item("Job_ID"))
                .Add(dr.Item("Salary").ToString)
                If IsDBNull(dr.Item("Commission_PCT")) Then
                    .Add(0)
                Else
                    .Add(dr.Item("Commission_PCT"))
                End If
                If IsDBNull(dr.Item("Manager_ID")) Then
                    .Add(0)
                Else
                    .Add(dr.Item("Manager_ID"))
                End If
                .Add(dr.Item("Department_ID"))
                mEmployees.Add(emp)
            End With
            'Print("Hello")
            lst = Nothing
        End While
    End Sub
End Class

There is a form1 class but so little in it that's it's pointless posting. Now I think someone mentioned that if the selected item is nothing then it means it is not selected but when I had all the controls on the form it worked fine, all I have done is move the code to a user control.

I think it's something to do with an incorrect instance setting or something but not exactly sure. I also notice that if I press F8 and go right through the code it loops through this bit twice In user control and tries to pick up a collection in employees class which isn't yet available. Is that right that it tries to pick up a collection, even when not there?:

 Dim emp As New employees

I still get a bit mixed up with these instances, does new mean a clean instance with no data or a newly created instance of an existing object or both, that is what gets me sometimes. Sometimes an instance is not declared as new, sometimes it is.

Any ideas?

G

[Grimfort]

Dim usr1 As UserControl1 'You have declared a variable that will hold a reference to an object, currently it does not point to anything
usr1 = New UserControl1 'You have created a brand new usercontrol, assuming you have one on your form, this is then a second copy
As you declared this inside a method you will loose reference to it when the method is complete.

So when you call usr1.xxxx you are using the New copy which you can not see as you have never shown it to the user, and as such will have no values selected.

The way to get around this (the quickest way anyway) is to pass the usercontrol that calls this method as a paramter so:

emp.getEmployeeDetails(Me) 
....
Public Sub getEmployeeDetails(usr1 As UserControl1)
  'remove local declaration
  Dim ds As New DataSet
....

[Grimfort]

I think you are being confused by this:

Form1.ListView1.Items.Clear()

For some reason MS decided to bring back in default instance names for forms, to help those VB6 users who are converting up. When you call Form1.xxx if Form1 has never been created ie Dim Form1 As New Form1, then it will do it for you. You can access it from anywhere and things look much simpler to code, however you have just shot yourself in the foot in the design sense. You call Form1. while inside your UserControl1, which means that your usercontrol can not be placed on any form, only ever the default instance of Form1. The idea of a usercontrol is that you can re-use it, put it on Form2 put it on a different copy of Form1. Controls have the ability to raise events to tell their parents that an action is required.

In your case you could do this

'At top of usercontrol
Public Event SetupSelection()

'Inside your sub instead of
   'Form1.ListView1.Items.Clear()
   'Form1.SetListViewColumns()
RaiseEvent SetupSelection

'Inside your form you can handle the UserControl1_SetupSelection event and add
ListView1.Items.Clear()
SetListViewColumns()

This way the form and usercontrol do not interact with their local objects via anything other than their public interface. If the Form1 changes the ListView1 to a new name or you swap to a swanky new SuperListView1 then the usercontrol does not break.

[Grifter]

Hi

I now have it working ok after doing what you said. This helps me understand the use of instances and user controls as well, which I am still trying to learn.

Thanks for all the replies

G

Dim usr1 As UserControl1 'You have declared a variable that will hold a reference to an object, currently it does not point to anything
usr1 = New UserControl1 'You have created a brand new usercontrol, assuming you have one on your form, this is then a second copy
As you declared this inside a method you will loose reference to it when the method is complete.

So when you call usr1.xxxx you are using the New copy which you can not see as you have never shown it to the user, and as such will have no values selected.

The way to get around this (the quickest way anyway) is to pass the usercontrol that calls this method as a paramter so:

emp.getEmployeeDetails(Me) 
....
Public Sub getEmployeeDetails(usr1 As UserControl1)
  'remove local declaration
  Dim ds As New DataSet
....