Possible to set a LIstbox.Datasource to a collection?

[nemaroller]

I'm trying to set the datasource value of a listbox to a strongly-typed collection.

.DataSource = myVehicleCollection
.ValueMember = "Item"
.DisplayMember = "ToString"

The Item property in my collection returns a single vehicle.

On load of the form, I keep getting an error stating the ValueMember could not be set.

[Edneeis]

In this case you would either set the DisplayMember to a property of the item (whatever the item type is in the collection) or not at all. If nothing is set then it uses the ToString method by default so there is no need to set it to that. Also the ToString method is a method not a property so I don't think you can set it to that. It has to be a property. So really all you need is:
.DataSource = myVehicleCollection

or
.DataSource = myVehicleCollection
.DisplayMember="VehicleName"

[nemaroller]

Yes... none of that seems to work.


If you look up help in the .Net Ide for .DisplayMember, you will see a simplified example of using a collection for a datasource. However, the State class does not contain any child collections.

Let's pretend that class USState has a child collection of metropolitan areas, and each metro area has a collection of cities....how would one set the Listbox.DisplayMember to point the metro area's city' zipcode property to the Listbox.DisplayMember (or override ToString to point to the State's city suburb's zip code property)

Imports System.Windows.Forms
Imports System.Drawing
Imports System.Collections
 
Public Class USState
 
    Private myShortName As String
    Private myLongName As String
    [color=blue]Private _MetroAreas As New MetroAreaCollection[/color]
 
    Public Sub New(ByVal strlongName As String, ByVal strShortName As String)
        MyBase.New()
        Me.myShortName = strShortName
        Me.myLongName = strLongName
    End Sub
 
    Public ReadOnly Property ShortName() As String
        Get
            Return myShortName
        End Get
    End Property
 
    Public ReadOnly Property LongName() As String
        Get
            Return myLongName
        End Get
    End Property
 
    Public Overrides Function ToString() As String
        Return Me.ShortName & " - " & Me.LongName
    End Function
End Class

State
--MetroArea
----City
-------City.ZipCode

[nemaroller]

I tried putting in the MetoArea class, something like this:

Public Overrides Function ToString() As String
  return _Cities.Item(0).ZipCode
End Function

And I never get anything back. No errors either.

[Edneeis]

Two things: 1) you need to bind directly to the collection that contains the item with the property you want to use in the DisplayMember (i.e USState.MetroAreas(0).Cities) 2) the Displaymember is case sensitive. If it can't find the property in question then it defaults to the ToString method.

Here is an example:

'classes
Public Class USState
 
    Private myShortName As String
    Private myLongName As String
    Private _MetroAreas As New MetroAreaCollection
 
    Public ReadOnly Property MetroAreas() As MetroAreaCollection
        Get
            Return _MetroAreas
        End Get
    End Property
 
    Public Sub New(ByVal strlongName As String, ByVal strShortName As String)
        MyBase.New()
        Me.myShortName = strShortName
        Me.myLongName = strlongName
    End Sub
 
    Public ReadOnly Property ShortName() As String
        Get
            Return myShortName
        End Get
    End Property
 
    Public ReadOnly Property LongName() As String
        Get
            Return myLongName
        End Get
    End Property
 
    Public Overrides Function ToString() As String
        Return Me.ShortName & " - " & Me.LongName
    End Function
 
End Class
 
Public Class MetroAreaCollection
    Inherits CollectionBase
 
    Public Function Add(ByVal item As MetroArea) As Integer
        Return MyBase.List.Add(item)
    End Function
 
    Default Public Property Item(ByVal index As Integer) As MetroArea
        Get
            Return CType(MyBase.List.Item(index), MetroArea)
        End Get
        Set(ByVal Value As MetroArea)
            MyBase.List.Item(index) = Value
        End Set
    End Property
 
End Class
 
Public Class MetroArea
 
    Private _Name As String
    Private _Cities As New CitiesCollection
 
    Public Property Name() As String
        Get
            Return _Name
        End Get
        Set(ByVal Value As String)
            _Name = Value
        End Set
    End Property
 
    Public ReadOnly Property Cities() As CitiesCollection
        Get
            Return _Cities
        End Get
    End Property
 
    Public Sub New(ByVal name As String)
        _Name = name
    End Sub
 
End Class
 
Public Class CitiesCollection
    Inherits CollectionBase
 
    Public Function Add(ByVal item As City) As Integer
        Return MyBase.List.Add(item)
    End Function
 
    Default Public Property Item(ByVal index As Integer) As City
        Get
            Return CType(MyBase.List.Item(index), City)
        End Get
        Set(ByVal Value As City)
            MyBase.List.Item(index) = Value
        End Set
    End Property
 
End Class
 
Public Class City
 
    Private _Name As String
    Private _Zip As String
 
    Public Property Name() As String
        Get
            Return _Name
        End Get
        Set(ByVal Value As String)
            _Name = Value
        End Set
    End Property
 
    Public Property Zip() As String
        Get
            Return _Zip
        End Get
        Set(ByVal Value As String)
            _Zip = Value
        End Set
    End Property
 
    Public Sub New(ByVal name As String, ByVal zip As String)
        _Name = name
        _Zip = Zip
    End Sub
 
End Class
 
'syntax
        Dim test As New USState("California", "CA")
        Dim ma As New MetroArea("Riverside")
        ma.Cities.Add(New City("Riverside", "92501"))
        ma.Cities.Add(New City("Moreno Valley", "92553"))
        test.MetroAreas.Add(ma)
 
        ComboBox1.DataSource = test.MetroAreas(0).Cities
        ComboBox1.DisplayMember = "Zip"

That works for me.

[Edneeis]

Actually you don't have to bind directly to the collection if you put the hierarchy in the DisplayMember as well:

'this also works
        ComboBox1.DataSource = test.MetroAreas
        ComboBox1.DisplayMember = "Cities.Zip"

To expand the example further if you wanted one combo to be a list of metroareas and the other to be the zips of the cities of the selected metroarea then you'd do this:

Dim test As New USState("California", "CA")
        Dim ma As New MetroArea("Riverside")
        ma.Cities.Add(New City("Riverside", "92501"))
        ma.Cities.Add(New City("Moreno Valley", "92553"))
        test.MetroAreas.Add(ma)
        ma = New MetroArea("Orange")
        ma.Cities.Add(New City("Orange", "92525"))
        ma.Cities.Add(New City("Anahiem", "92705"))
        test.MetroAreas.Add(ma)
 
        ComboBox2.DataSource = test.MetroAreas
        ComboBox2.DisplayMember = "Name"
 
        ComboBox1.DataSource = test.MetroAreas
        ComboBox1.DisplayMember = "Cities.Zip"

[nemaroller]

I noticed you defined Cities as a ReadOnly Property. Is that required ? Anyway, thanks for the input, I'm gonna log in and see if I can do something with this.

[Edneeis]

No it is not required I was just lazy and didn't want to type the set part. I'm not sure but a default Item property may be required. Good luck and let me know if you get stuck.

[nemaroller]

Yea... still not getting it to go.

I understand why your above examples work. Let me tell you about my specific situation. I have a LISTBOX, whose DATASOURCE property is set to a _Vehicle collection.

So, you see, trying to have a LISTBOX with a display member such as : _Vehicles.Vehicle.Descriptions.Description

will not work since you have to provide an index, and the index is really a deciding factor here.

[Edneeis]

What is it you are expecting to see in the list? The description of a particular vehicle? How is _Vehicles.Vehicle.Descriptions.Description different than USState.MetroAreas.MetroArea.Cities.City.Zip?