how get value of datagrid in wpf

Let's assume we have data grid like this:

<DataGrid Name="DataGrid1" SelectionMode="Single"
          SelectionChanged="DataGrid1_SelectionChanged">
</DataGrid>

and event handler in code behind (xaml.cs file):

private void DataGrid1_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    var item = DataGrid1.SelectedItem/* as YourBusinessObject*/;

    if (item != null)
    {
        // Your code here
    }
}

You should cast selected item to type of your business object.
If you are using anonymous types, you can use combination of the Selector.SelectedValuePath Property[^] and Selector.SelectedValue Property[^].