从另一种形式更新ListView

Question

I tried all methods by users here but none seems to work for me. I want to update a ListView in Form1 from Form2 in vb.net but nothing happens when I launch this method.

Public Sub checkFoundList()
    For Each item In myListView.Items
        If Not File.Exists(item.SubItems(2).Text) Then
            myListView.Items.Remove(item)
        End If
    Next
End Sub

This method is on Form1 and when I launch it here it works fine. But if I call it from Form2, it doesn't.

In Form2 I just call it with:

Form1.checkFoundList()

I tried also to put the modifier Public to myListView but still doesn't work. Also the methods explained by some users like using events doesn't work. Really weird.

Is ListView a special control?

Answer 1

One problem you will have is you are modifying the items in the list as you are enumerating it with a For Each statement. This will cause problems when you delete an item.

Instead enumerate it with a For statement working backwards so the indexes don't shift when you are removing an item:

Public Sub checkFoundList()
    For i = myListView.Items.Count - 1 To 0 Step -1
        Dim item As <TypeTheListViewHolds> = myListView.Items(i)
        If Not File.Exists(item.SubItems(2).Text) Then
            myListView.Items.RemoveAt(i)
        End If
    Next
End Sub

I have just adapted the code you provided (without knowing what myListView holds), but the methodology would be the same regardless of the datatype.

With regards to calling it from Form2 , make sure you are calling checkFoundList from an instance of Form1 . Something like:

' Class variable in Form2 which has an instance of Form1.
Private _form1 As Form1

' New Form2 method.
' Pass an instance of Form1 to the constructor of Form2.
' This way this instance of Form2 will "know" about a Form1 object.
Public Sub New(form1Object As Form1)
   ' Initialization code.

   ' Set the reference to Form1 in Form2
   _form1 = form1Object
End Sub

Public Sub Form2Method()
    _form1.checkFoundList
End Sub

Answer 2

As mentioned, it would be helpful to see the error you are getting. But it is most likely because Form2 doesn't have a reference to Form1. One of many ways to fix this is to set Form2's owner to Form1.

In Form1 when you create Form2 set its owner:

Dim f2 As Form2 = New Form2()
f2.Owner = Me
f2.ShowDialog()

In Form2 get a reference to Form1 and access the list box, in this case I access a simple text box:

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim f1 As Form1 = DirectCast(Me.Owner, Form1)
    f1.TextBox1.Text = "Hello World"
End Sub