WPF Imported xlsx file will not show in DataGrid

Question

I want to import .xlsx file into my Application to save it in the DataBase then. The .xlsx file can be different so I don't have static ColumnNames.

First I want to Load the content of the .xlsx file in the DataGrid. So I made a Grid with AutoGenerateColumns = true.

<DataGrid x:Name="DataGrid" AutoGenerateColumns="True" IsReadOnly="True" Grid.Row="1" />

Then I created a ImportExcel class for the code-behind.

private void ChooseExcelFile_Click(object sender, RoutedEventArgs e)
    {
        OpenFileDialog openFileDialog = new OpenFileDialog();
        openFileDialog.DefaultExt = ".xlsx";
        openFileDialog.Filter = "(.xlsx)|*.xlsx";
        if (openFileDialog.ShowDialog() == true)
        {
            FilePathTextBox.Text = System.IO.Path.GetFullPath(openFileDialog.FileName);

            string constr = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source = '" + FilePathTextBox.Text + "'" + @";Extended Properties=""Excel 8.0;HDR=YES;IMEX=1;ImportMixedTypes=Text;TypeGuessRows=0""";
            string query = "SELECT * FROM [Sheet1$]";

            OleDbConnection con = new OleDbConnection(constr);
            OleDbDataAdapter dataAdapter = new OleDbDataAdapter(query, con);
            DataTable dataTable = new DataTable();
            dataAdapter.Fill(dataTable);
            DataGrid.DataContext = dataTable;
        }
    }

my problem is, that the DataGrid will not have any content after clicking "OK". What is wrong there ?

I also tried DataGrid.DataContext = dataTable.DefaultView without success. Also, is string query = "SELECT * FROM [Sheet1$]"; always working? Because what is if the name of the sheet is not Sheet1 ?