[WPF] DataGrid Read Only but not for new row

Question

Hi,

I have a DataGrid (called dgSample), where I set IsReadOnly="True".

User can add a new Row, this row must be editable.

So in my model I set a property:

[DefaultValue(false)]

public virtual bool IsNewItem { get; set; }

where user add new row I set this property to true

So in my DataGrid I have:

<DataGrid.RowStyle>

<Style TargetType="DataGridRow">

<Style.Triggers>

<DataTrigger Binding="{Binding Path=IsNewItem}" Value="True">

<Setter Property="IsReadOnly" Value="False"/>

</DataTrigger>

</Style.Triggers>

</Style>

</DataGrid.RowStyle>

but the last Row is not editable, why?

Thanks.