Can't Remove Listview Item From Second Form - vb.net

Question

I am having an issue when trying to delete ListView Items from a second form.
For example, if I use the following command on Form1 it works:
Listview1.SelectedItems(0).Remove
However, if I attempt to remove from Form2 like so:
Form1.Listview1.SelectedItems(0).Remove
I get the following error:
"Invalid argument=value of '0' is not valid for 'index'. Parameter name: index"
I then tried to get a count of items from the listview on Form2 and it gives me a return of 0
Form1.Listview1.Items.Count
I'm not sure what my problem is.
Update
I have posted a brief example of my code (using your suggestion as I can understand it):
frmShowMessages
Private Sub ViewMessage()
Dim frm As New frmViewMailMessage
frm.Show()
End Sub
Public Sub DeleteItem(ByVal index As Integer)
lsvReceivedMessages.Items(index).Remove()
End Sub
frmViewMessage
Private instanceForm as frmShowMessages
Private Sub frmViewMailMessage_Load(sender As Object, e As EventArgs) Handles MyBase.Load
instanceForm = New frmShowMessages()
End Sub
Private Sub cmdDelete_Click(sender As Object, e As EventArgs) Handles cmdDelete.Click
instanceForm.DeleteItem(_index)
End Sub
Hopefully my code can help identify where my issue is.

Answer 1

In VB.net usually you get a default Form instance for each of your Form. Probably you are creating an instance of Form1 and then you are trying to access ListView1 of default instance.
E.g.
Sub ButtonClick()
Dim f As New Form1()
f.Show()
' at this point if you access f's ListView you will get correct count
f.ListView1.Items.Count
' however if you try to access default instance it will NOT have any item
Form1.ListView.Items.Count
End Sub
It means your instance f is NOT equal to default Form1 instance.
Solution can be, make the f variable as class level variable and use it everywhere. Or if Form1 will have only 1 instance, then you can use the default instance everywhere.
Personally I would NOT go with direct control accessing over forms. I would create a Public method which should return the data as list to the caller, in this case your Form2.
UPDATED-2:
As per your given scenario, I am simplifying things for you, and doing implementation using Event.
Public Class frmShowMessages
Private Sub btnOpenMessage_Click(sender As System.Object, e As System.EventArgs) Handles btnOpenMessage.Click
Dim frmView As New frmViewMessage(Me.ListView1.SelectedItems(0).Index)
AddHandler frmView.MessageDeleted, AddressOf DeleteMessageHandler
frmView.Show()
End Sub
Private Sub DeleteMessageHandler(sender As Object, e As frmViewMessage.MessageDeletedEventArgs)
Me.ListView1.Items.RemoveAt(e.MessageIndex)
End Sub
End Class
Public Class frmViewMessage
' a class which will be used for Event communication
Public Class MessageDeletedEventArgs
Inherits EventArgs
Public Property MessageIndex As Integer
Public Sub New(ByVal iIndex As Integer)
MyBase.New()
Me.MessageIndex = iIndex
End Sub
End Class
' main event which will alert the parent that a message deletion should be done
Public Event MessageDeleted As EventHandler(Of MessageDeletedEventArgs)
' private variable that will hold the MessageIndex
Private Property MessageIndex As Integer
' method that is responsible to raise event
Protected Overridable Sub OnMessageDeleted()
RaiseEvent MessageDeleted(Me, New MessageDeletedEventArgs(Me.MessageIndex))
End Sub
' we want to create this Form using the MessageIndex of ListView
Public Sub New(ByVal iMessageIndex As Integer)
Me.InitializeComponent()
Me.MessageIndex = iMessageIndex
End Sub
' the delete button will raise the event to indicate parent that
' a deletion of message should be done
Private Sub btnDelete_Click(sender As System.Object, e As System.EventArgs) Handles btnDelete.Click
Me.OnMessageDeleted()
End Sub
End Class