ArrayList view in DataGridView

[EricBHK]

Hi,


I have created an ArrayList that I am filling with names of cities that I retrieve from an Acces database. No problem there since I have inserted MsgBoxes to check the progress and I can see each name for each city being stored in the array as the procedure is running.

However, in displaying the ArrayList later on in a DataGridView, instead of getting the names of the cities, I get the number of characters for each city name (column header in DataGridview is also called ‘length’). So e.g. ‘London’ becomes ‘6’.

Anyone who knows where I go wrong or how to fix this ? I looked into the properties for the DataGridView, but there seems to be nothing there that can offer any help.



Thanks !

[MattP]

In the example below you'll see that the first example I give is of an ArrayList containing Person objects. This binds to the DataGridView with no problems.

In the second example I'm using an ArrayList with Strings. If I were to try and bind StringArrayList to the DataGridView you'd get a column named Length with each value showing how long the string is. This is because String is a Reference Type rather than a Value Type. The DataGridView is looking for properties to bind to and since String is a Reference Type the only thing it can see is Length.

The easiest way to get around this is to create a wrapper class around the String with a Value property so the DataGridView can see that.

Public Class Form1

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Dim PersonArrayList As New ArrayList
        With PersonArrayList
            .Add(New Person With {.FirstName = "Jim", .LastName = "Jones"})
            .Add(New Person With {.FirstName = "Peggy", .LastName = "Sue"})
            .Add(New Person With {.FirstName = "John", .LastName = "Smith"})
        End With

        DisplayDataGridView.DataSource = PersonArrayList

        Dim StringArrayList As New ArrayList
        With StringArrayList
            .Add("Test 1")
            .Add("Test 101")
            .Add("Test 10101")
        End With

        Dim StringValueArray = Array.ConvertAll(StringArrayList.ToArray(), AddressOf GetStringValue)

        StringDataGridView.DataSource = StringValueArray
    End Sub

    Private Function GetStringValue(s As String) As StringValue
        Return New StringValue(s)
    End Function

End Class

Public Class Person

    Public Property FirstName As String
    Public Property LastName As String
    Public ReadOnly Property FullName As String
        Get
            Return String.Join(", ", LastName, FirstName)
        End Get
    End Property

End Class

Public Class StringValue
    Public Property Value As String

    Public Sub New(s As String)
        _Value = s
    End Sub
End Class

All of that being said if you have a version of .NET that supports List(Of T) you should use that rather than an ArrayList.

[dunfiddlin]

Er ... ArrayList? Array, yes. Generic List, yes. ArrayList, nah!

[EricBHK]

Hello MattP?



Thanks for helping me out.

I am working with VS 2010, so List(OfT) is available to me but I have no experience with it.

I tried to create the wrapper (several alternatives) as indicated by you, but unfortunately without success. The only thing I keep getting now is an empty DataGridView.

Below is the code.

Can you point me out ?


P.S. this code will give an error message because database NULL values are not handled.



Thanks,



Eric


Dim keywords As New ArrayList

Dim i As Short = 0
Dim j As Short = 11

Do Until i = count - 1

'MsgBox("1. show i = " & i)
'MsgBox("1. Show j = " & j)

Do Until j = 21

keywords.Add(ds.Tables("Bib").Rows(i).Item(j))

'MsgBox("2. show i = " & i)
'MsgBox("2. Show j = " & j & " = " & (keywords(0)))

j = j + 1

'MsgBox("3. show i = " & i)
'MsgBox("3. Show j = " & j)

Loop

j = 11

i = i + 1

'MsgBox("4. show i = " & i)
'MsgBox("4. Show j = " & j)

Loop

'MsgBox("Loops are both successfull")

DataGridView1.DataSource = keywords

[MattP]

The only thing you need to change from my example is

Dim StringArrayList As New ArrayList

should be

Dim StringList As New List(Of String)

The other option is to create a List(Of StringValue) and bind to that.

        Dim StringValueList As New List(Of StringValue)
        With StringValueList
            .Add(New StringValue("Test 1"))
            .Add(New StringValue("Test 101"))
            .Add(New StringValue("Test 10101"))
        End With

        StringDataGridView.DataSource = StringValueList

The issue of loading NULL values from the database is a separate question and I'll ask you to create a new thread for it so in the future users searching the forum can find it.