B4J Question DragAndDrop file types

Sub DropTarget_DragOver(e As DragEvent)
    If IsValidDropEvent(e) Then e.AcceptTransferModes(TransferMode.COPY)
End Sub

Sub IsValidDropEvent(e As DragEvent) As Boolean
    If e.GetDragboard.HasFiles Then
        Dim files As List = e.GetDragboard.GetFiles
        If files.Size = 1 Then
            Dim filename As String = files.Get(0)
            
            ' Copy and read the file here and check if you accept this file.
            ' return true if yes, false if not.
            
            Return filename.EndsWith(".txt")
        End If
    End If
    Return False
End Sub

Sub DropTarget_DragDropped(e As DragEvent)
    Log("drag dropped")
    Dim filename As String = e.GetDragboard.GetFiles.Get(0)
    Try
        TextArea1.Text = File.ReadString(filename, "")
    Catch
        TextArea1.Text = LastException
    End Try
    Label1.Text = filename
    e.SetDropCompleted(True)
End Sub