Unable to retrieve the checked rows from datagrid

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XAML

GUI

I am trying to create a simple Datagrid using WPF such that each row has a checkbox. I am having a tough time while retrieving the data. I am getting only 1 result. What can I fix in the below XAML

<DataGrid x:Name="details" x:Uid="MyDataGrid" AutoGenerateColumns="False" AlternationCount="1" SelectionMode="Single" IsReadOnly="True" HeadersVisibility="Column" Margin="0,0,10,2" HorizontalAlignment="Right" Width="410" Grid.Column="1" Grid.Row="1" >
           <DataGrid.Columns>
               <DataGridTemplateColumn>
                   <DataGridTemplateColumn.Header>
                       <CheckBox Content=" Select All" x:Name="headerCheckBox" />
                   </DataGridTemplateColumn.Header>
                   <DataGridTemplateColumn.CellTemplate>
                       <DataTemplate>
                           <CheckBox Name="chkDiscontinue"  IsChecked="{Binding Path=IsChecked,ElementName=headerCheckBox,Mode=OneWay}"   Margin="45 2 0 0"  />
                       </DataTemplate>
                   </DataGridTemplateColumn.CellTemplate>
               </DataGridTemplateColumn>
               <DataGridTextColumn Binding="{Binding Path=file_name}" Header="File Name" Width="2*" IsReadOnly="True" />
               <DataGridTextColumn Binding="{Binding Path=file_path}" Header="File Path" Width="0.9*"/>
          </DataGrid.Columns> </DataGrid>

What I have tried:

Have been expreimenting with above XML from last 2 days