Xamarin.Forms. Collectionview adds a lot of extra white space after its content - xaml

Question

I would like there to be no empty space after the content of the collection view.
I tried to put my button in footer but then i ran into problem that property isenabled = false is not being applied to it in my code behind.
Here is my xaml file:
<ContentPage.Content>
<RefreshView x:DataType="local:QuestionViewModel" Command="{Binding LoadCommand}" IsRefreshing="{Binding IsBusy, Mode=TwoWay}">
<ScrollView>
<StackLayout>
<views:MyTextView LaTeX="{Binding Formulation}" HorizontalOptions="Center" Margin="15, 10, 15, 0"/>
<!--<RefreshView x:DataType="local:QuestionViewModel" Command="{Binding LoadCommand}" IsRefreshing="{Binding IsBusy, Mode=TwoWay}">-->
<CollectionView
ItemsSource="{Binding Answers, Mode=TwoWay}"
SelectedItems="{Binding SelectedAnswers, Mode=TwoWay}"
SelectionMode="Multiple"
x:Name="collectionView"
SelectionChanged="collectionView_SelectionChanged"
>
<CollectionView.ItemsLayout>
<LinearItemsLayout Orientation="Vertical"/>
</CollectionView.ItemsLayout>
<CollectionView.ItemTemplate>
<DataTemplate x:DataType="model:Answer">
<StackLayout Padding="10">
<VisualStateManager.VisualStateGroups>
<VisualStateGroup Name="CommonStates">
<VisualState Name="Normal">
<VisualState.Setters>
<Setter TargetName="frame" Property="Frame.BackgroundColor" Value="{Binding AnswerColor}"/>
</VisualState.Setters>
</VisualState>
<VisualState Name="Selected">
<VisualState.Setters>
<Setter TargetName="frame" Property="Frame.BackgroundColor" Value="{DynamicResource MainColor}"/>
<Setter TargetName="label" Property="views:MyTextView.TextColor" Value="White"/>
</VisualState.Setters>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<Frame CornerRadius="10" HasShadow="True" x:Name="frame" BackgroundColor="{Binding AnswerColor}">
<views:MyTextView x:Name="label" LaTeX="{Binding Content}" />
</Frame>
</StackLayout>
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>
<!--</RefreshView>-->
<StackLayout>
<Label x:Name="conditionLabel" TextColor="{DynamicResource AnswerColor}"/>
<Button x:Name="checkButton" Text="Проверить ответы" CornerRadius="10" Margin="10"
Command="{Binding CheckAnswersCommand}"/>
</StackLayout>
</StackLayout>
</ScrollView>
</RefreshView>
</ContentPage.Content>
Result:
1 part of screen
2 part of screen

Answer 1

You shouldn't use Listview/Collection View with in Scrollview as described in official documentation.
There is an alternative to listview within Scrollview. Look at following code:
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:ScrollViewDemos"
x:Class="ScrollViewDemos.Views.ColorListPage"
Title="ScrollView demo">
<ScrollView>
<StackLayout BindableLayout.ItemsSource="{x:Static local:NamedColor.All}">
<BindableLayout.ItemTemplate>
<DataTemplate>
<StackLayout Orientation="Horizontal">
<BoxView Color="{Binding Color}"
HeightRequest="32"
WidthRequest="32"
VerticalOptions="Center" />
<Label Text="{Binding FriendlyName}"
FontSize="24"
VerticalOptions="Center" />
</StackLayout>
</DataTemplate>
</BindableLayout.ItemTemplate>
</StackLayout>
</ScrollView>
</ContentPage>
Follow Documentation for more support:
https://learn.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/layouts/scrollview

Answer 2

Unfortunately, this is a known problem, and an open issue.
See that thread for possible work-arounds. And to track any progress on fixing it.
Bottom line: you have to manually specify/calculate height. There are multiple ways to do so, of various difficulty. Thread mentions some. You would need to Google for more details.
One quick-and-dirty solution I like, when acceptable, is to wrap CollectionView in Grid, and then use RowDefinitions to force how much height is given to row containing CollectionView, how much to everything else. Something like:
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="1*" />
<RowDefinition Height="2*" />
</Grid.RowDefinitions>
<CollectionView Grid.Row="0" ...>
...
</CollectionView>
<StackLayout Grid.Row = "1" ...>
... everything that is below the CV ...
</StackLayout>
</Grid>
This would restrict row 0 (which contains CollectionView) to top 1/3 of screen.