Don't fire RelayCommand - wpf

Question

I have a list in and relaycommand viewmodel,
private List<PurchaseInvoiceDetail> detailList = new List<PurchaseInvoiceDetail>();
public RelayCommand AddCommand { get; set; }
ICollectionView _detailCollection;
public ICollectionView DetailCollection
{
get { return _detailCollection; }
set
{
if (value != _detailCollection)
{
_detailCollection = value;
RaisePropertyChanged("DetailCollection");
}
}
}
when i use DetailCollection in constructor,dont fire relaycommand.
public PurchaseInvoiceDetailViewModel(PurchaseInvoice item)
{
if (item != null)
{
Number = item.Number;
CustomerId = item.CustomerId;
Date = new PersianDate((DateTime)item.Date);
_purchaseInvoice = item.Id;
detailList = _db.PurchaseInvoiceDetails.Where(m => m.PurchaseInvoiceId == item.Id).ToList();
CollectionViewSource.GetDefaultView(detailList).Refresh();
DetailCollection = CollectionViewSource.GetDefaultView(detailList);
}
AddCommand=new RelayCommand(() =>
{
var goods = _db.Goods.Find(GoodsId);
detailList.Add(new PurchaseInvoiceDetail(){GoodsId = GoodsId,Goods = goods,Count = Count,Price = Price,Id=0,PurchaseInvoiceId = 0});
CollectionViewSource.GetDefaultView(detailList).Refresh();
DetailCollection = CollectionViewSource.GetDefaultView(detailList);
});
}
but when i comment DetailCollection ,it work ok..
in view
<Button Margin="0 0 5 0 " Width="90" Command="{Binding AddCommand}"
Style="{StaticResource MaterialDesignRaisedButton}" >
<StackPanel Orientation="Horizontal">
<materialDesign:PackIcon Kind="Plus" />
<TextBlock >َAdd</TextBlock>
</StackPanel>
</Button>
<DataGrid CanUserDeleteRows="True" CellStyle="{StaticResource MaterialDesignDataGridCell}" Name="ListView"
IsReadOnly="True" BorderBrush="{DynamicResource MaterialDesignDivider}" VerticalAlignment="Top" BorderThickness="1" Height="200" Margin="0" AutoGenerateColumns="False"
ItemsSource="{Binding Path=DetailCollection}"
>
<DataGrid CanUserDeleteRows="True" CellStyle="{StaticResource MaterialDesignDataGridCell}" Name="ListView"
IsReadOnly="True" BorderBrush="{DynamicResource MaterialDesignDivider}" VerticalAlignment="Top"
BorderThickness="1" Height="200" Margin="0" AutoGenerateColumns="False"
ItemsSource="{Binding Path=DetailCollection}"
>
<DataGrid.Columns>
<DataGridTextColumn Width="100"
Header="کد کالا" Binding="{Binding Path=Goods.Code}"/>
<DataGridTextColumn Header="نام کالا" Binding="{Binding Path=Goods.Name}" Width="200"/>
<DataGridTextColumn Binding="{Binding Path=Count}" Width="150"
dataGridFilterLibrary:DataGridColumnExtensions.IsCaseSensitiveSearch="True"
Header="تعداد"/>
<DataGridTextColumn Header="قیمت" Binding="{Binding Path=Price}" Width="*"/>
</DataGrid.Columns>
<DataGrid.InputBindings>
<KeyBinding
Key="Delete"
Command="{Binding DeleteCommand}" CommandParameter="{Binding SelectedIndex, ElementName=ListView}"/>
</DataGrid.InputBindings>
</DataGrid>