WPF之Visibility的基础用法

Visibility有三种用法， 第一个：Visible 元素在窗体中正常显示 第二个：Collaspsed 元素不显示，也不占用空间 第三个：Hidden 元素不显示，但是任然为它保留空间 我用Visibility=“Hidden”来隐藏我的页面 页面在DataGrid中用Visibility=“Hidden”

XAML代码：
  <Grid  HorizontalAlignment="Center" VerticalAlignment="Center"  Height="200" Width="200" Grid.ColumnSpan="8" Grid.RowSpan="6">
                <DataGrid x:Name="DG_SP" IsReadOnly="True" AutoGenerateColumns="False" CanUserResizeColumns="False" CanUserResizeRows="False"  SelectionMode="Single" CanUserReorderColumns="False" AlternationCount="2"  RowHeaderWidth="0" CanUserAddRows="False" VerticalAlignment="Top" Visibility="Hidden" SelectedCellsChanged="DG_SP_SelectedCellsChanged">
                    <DataGrid.Background>
                        <LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
                            <LinearGradientBrush.GradientStops>
                                <GradientStop Color="#FFE6F2F7" Offset="0"/>
                                <GradientStop Color="White" Offset="0.1"/>
                                <GradientStop Color="White" Offset="0.4"/>
                                <GradientStop Color="#FFE6F2F7" Offset="0.81"/>
                            </LinearGradientBrush.GradientStops>
                        </LinearGradientBrush>
                    </DataGrid.Background>
                    <DataGrid.Columns >
                        <DataGridTextColumn Header="行号" Binding="{Binding number}" Width="80" />
                        <DataGridTextColumn Header="编码" Visibility="Collapsed" Binding="{Binding CommodityInforID}"  Width="10"/>
                        <DataGridTextColumn Header="商品条码" Binding="{Binding CommodityCode}" Width="120" />
                        <!--<DataGridTextColumn Header="打开"  Visibility="Collapsed" Binding="{Binding as_passenger_type_id}"  Width="10"  />-->
                        <DataGridTextColumn Header="店内码" Binding="{Binding SecondCode}"  Width="70"  />
                        <DataGridTextColumn Header="商品名称" Binding="{Binding CommodityName}"  Width="80" />
                        <DataGridTextColumn Header="数量" Binding="{Binding ss}"  Width="70"  />
                        <DataGridTextColumn Header="金额" Binding="{Binding ee}"  Width="70"  />
                    </DataGrid.Columns>
                </DataGrid>
            </Grid>

按钮调用代码：
private void BTT_SP_Click(object sender, RoutedEventArgs e)
        {
            DG_SP.Visibility = Visibility.Visible;//显示页面
            DataTable mm = myFrm_MerchandiseInventoryClient.Frm_CommodityInventoryEnquiry().Tables[0];
            DG_SP.ItemsSource = mm.DefaultView;
        }

功能页面：