Wpf how can I save a datagrid to textfile

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C#

WPF

Hi
how can I save the Items of a DataGrid to a text file.

I watched several Tutorials - where to start?

Inotifychange? updateSourceTrigger? rowcolumnEnding? CellColumnEnding?

When I edit a cell in a datagrid a ObservableCollection will not be updated
only when I trigger the Collection with update?

Any help?

What I have tried:

ObservableCollection<observ> GetData()
            {
                using (var writer = new StreamWriter("text.txt"))
                {
                    foreach (observ item in datagrid)
                    {
                        writer.WriteLine(item.ToString());
                    }
                }

               return dglist;
            }