Project_Administrator.ProjectAdministratorDataSet projectAdministratorDataSet = ((Project_Administrator.ProjectAdministratorDataSet)(this.FindResource("projectAdministratorDataSet")));
Project_Administrator.ProjectAdministratorDataSetTableAdapters.СustomerTableAdapter projectAdministratorDataSetСustomerTableAdapter = new Project_Administrator.ProjectAdministratorDataSetTableAdapters.СustomerTableAdapter();
projectAdministratorDataSetСustomerTableAdapter.Fill(projectAdministratorDataSet.Сustomer);
System.Windows.Data.CollectionViewSource сustomerViewSource = ((System.Windows.Data.CollectionViewSource)(this.FindResource("сustomerViewSource")));
сustomerViewSource.View.MoveCurrentToFirst();

<DataGrid x:Name="сustomerDataGrid" AutoGenerateColumns="False" EnableRowVirtualization="True" ItemsSource="{Binding}" RowDetailsVisibilityMode="VisibleWhenSelected" LayoutUpdated="DataGrid_LayoutUpdated">
            <DataGrid.Columns>
                <DataGridTextColumn x:Name="idCustomerColumn" Binding="{Binding IdCustomer}" Header="Id Заказчика" Width="Auto" />
                <DataGridTextColumn x:Name="nameColumn" Binding="{Binding Name}" Header="Название организации" Width="Auto"/>
                <DataGridTextColumn x:Name="locationColumn" Binding="{Binding Location}" Header="Местоположение" Width="Auto" />
                <DataGridTextColumn x:Name="addressColumn" Binding="{Binding Address}" Header="Адрес" Width="Auto" CanUserSort="False"/>
                <DataGridTextColumn x:Name="phoneColumn" Binding="{Binding Phone}" Header="Телефон" Width="Auto" CanUserSort="False"/>
                <DataGridTextColumn x:Name="emailColumn" Binding="{Binding Email}" Header="Эл. почта" Width="Auto" CanUserSort="False"/>
                <DataGridTextColumn x:Name="representativeColumn" Binding="{Binding Representative}" Header="Представитель" Width="Auto" CanUserSort="False"/>
            </DataGrid.Columns>
        </DataGrid>

TextBox t = (TextBox)sender;
string filter = t.Text;
ICollectionView viewSource = CollectionViewSource.GetDefaultView(сustomerDataGrid.ItemsSource);
if (filter == "") viewSource.Filter = null;
else
{
    viewSource.Filter = o =>
    {
     КЛАСС p = o as КЛАСС;
     return p.СВОЙСТВО.ToString().Contains(filter);
    };
    сustomerDataGrid.ItemsSource = viewSource;
 }