Pass data type variable to another window

[Iamguy84]

Hi developer,
I am written codes in WPF as below:

MainWindows.xaml:

string[] fileName = null;
        private void btnOpenFiles_Click(object sender, RoutedEventArgs e)
        {
            OpenFileDialog openFileDialog = new OpenFileDialog();
            openFileDialog.Multiselect = true;
            openFileDialog.Filter = "Text files (*.txt)|*.txt|All files (*.*)|*.*";

            Nullable<bool> result = openFileDialog.ShowDialog();

            if (result == true)
            {
                fileName = openFileDialog.FileNames;

                foreach (string item in fileName)
                {
                    lbFiles.Items.Add(System.IO.Path.GetFullPath(item));

                }
            }
        }

Windows1.xaml:

 private void Export_Button(object sender, RoutedEventArgs e)
        {
                foreach (var inputfile in fileName) ???????
                .......
                ........

How to pass the data type variable(From mainwindow) to another window (Window1)?
I am waiting for your response.
Thanks