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How to detect is the form is open or not ?????

Why don't you alter your derived class so that it provides a public boolean, that will tell you if its open or not.

how are you opening your form?

If , for example, FP is the form you want to check and IF I undertood well what you need, perhaps it could be useful for you (I tested it for 5 seconds, only!!!):

VB Code:

Private Sub BtnTestaFP_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnTestaFP.Click
        If FP Is Nothing Then
            MessageBox.Show("E' chiuso!")
        Else
            If FP.CanSelect Then
                MessageBox.Show("E' aperto!")
            Else
                MessageBox.Show("E' chiuso!")
            End If
        End If
    End Sub

Good job:) :wave: