primer/Pages/ChangedWindow.xaml

<Window x:Class="Namordnik.Pages.ChangedWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Namordnik.Pages"
        mc:Ignorable="d"
        Title="ChangedWindow" SizeToContent="WidthAndHeight">
    <Grid>
        <StackPanel>
            <TextBox Name="SrCost"></TextBox>
            <Button Name="BTChange" Click="BTChange_Click">Изменить</Button>
        </StackPanel>
        
    </Grid>
</Window>