why my listview cant scroll till the end of list items? i have 26 items but cant scroll after 13.

<c:BasePage.Content>

<Grid.RowDefinitions>

</Grid.RowDefinitions>

    <ScrollView>
        <StackLayout>
            <ListView HorizontalOptions="FillAndExpand" SelectionMode="None" HasUnevenRows="True" SeparatorVisibility="None" BackgroundColor="Transparent" ItemsSource="{Binding Data}">
                <ListView.ItemTemplate>
                    <DataTemplate>
                        <ViewCell>
                            <Grid >


                            </Grid>
                        </ViewCell>
                    </DataTemplate>
                </ListView.ItemTemplate>
            </ListView>
        </StackLayout>
    </ScrollView>
</Grid>

</c:BasePage.Content>