嵌套的 CollectionViews 和显示（使用 Visual Studio 2019、Xamarin XPlatform Android）

Question

1. Nested CollectionView with scrolling one inside another: is it officially supported?
2. Display these collections problem

See below my data model and the XAML code (I have no site to put the resulting screen image in)

namespace Notes.Models
{
    public class Note
    {
        public enum NoteStatus { suspended, alive }

        public string       Description { get; set; }
        public NoteStatus   Status { get; set; }
    }

    public class NotesContainer
    {
        public string                       Name { get; set; }
        public DateTime                     LastModified { get; set; }
        public ObservableCollection<Note>   ListOfNotes { get; set; }
    }
}

  <CollectionView x:Name="notesContainers" SelectionMode="Single" EmptyView="No items currently exist !">
    <CollectionView.ItemTemplate>
      <DataTemplate>
        <Frame BorderColor="Red" BackgroundColor="Beige" CornerRadius="3" HasShadow="False" Padding="5">
          <StackLayout BackgroundColor="Aqua" Padding="5">
            <Grid>
              <Grid.RowDefinitions><RowDefinition Height="auto"/><RowDefinition Height="auto"/></Grid.RowDefinitions>
              <Grid.ColumnDefinitions><ColumnDefinition/><ColumnDefinition/></Grid.ColumnDefinitions>
              <Label Grid.RowSpan="2" Text="{Binding Name}" VerticalTextAlignment="Center" FontSize="Large"/>
              <Label Grid.Row="0" Grid.Column="1" Text="{Binding LastModified, StringFormat='\{0:dddd dd}'}" HorizontalTextAlignment="End"/>
              <Label Grid.Row="1" Grid.Column="1" Text="{Binding LastModified, StringFormat='\{0:MMMM yyyy}'}" HorizontalTextAlignment="End"/>
            </Grid>
            <StackLayout BackgroundColor="BlueViolet" Padding="10">
              <CollectionView ItemsSource="{Binding ListOfNotes}" SelectionMode="Single" EmptyView="No items currently exist !">
                <CollectionView.ItemTemplate>
                  <DataTemplate>
            <StackLayout BackgroundColor="Coral" Padding="0,3">
                    <Frame BorderColor="Blue" BackgroundColor="LightBlue" CornerRadius="3" HasShadow="False" Padding="5">
                      <StackLayout Orientation="Horizontal">
                        <Label Text="{Binding Description}" HorizontalOptions="Start" VerticalTextAlignment="Center"/>
                        <Label Text="{Binding Status}" HorizontalOptions="EndAndExpand" VerticalTextAlignment="Center" HorizontalTextAlignment="End"/>
                      </StackLayout>
                    </Frame>
             </StackLayout>
                 </DataTemplate>
                </CollectionView.ItemTemplate>
              </CollectionView>
            </StackLayout>
          </StackLayout>
        </Frame>
      </DataTemplate>
    </CollectionView.ItemTemplate>
  </CollectionView>

snapshot of outer & inner collectionviews:

I accented the colors to better see the layouts not shrinked.

Questions : (I have tried multiple configurations but without solution)

1. how can I shrink the StackLayouts to its contents?
2. why the StackLayouts elongate greater the size of the screen?

Answer 1

Instead of using CollectionView, you should use StackLayout with the BindableLayout. I just had the same issue and finally I resolved using the BindableLayout inside of a StackLayout as follows:

To give a better idea, I have some list of objects inside a parent. Something like this:

Customers (Items in the code)
--- Products
------- Batches
-----------Series

So I had a List of Customers that contains a List of Product where each one contains a List of Batches and finally they have a List of Serials.

<ScrollView>
    <StackLayout BindableLayout.ItemsSource="{Binding Items}">
        <BindableLayout.ItemTemplate>
            <DataTemplate>
                <StackLayout Orientation="Vertical" HorizontalOptions="FillAndExpand">

                    <StackLayout x:DataType="ms:Customer" Orientation="Vertical">

                        <StackLayout BindableLayout.ItemsSource="{Binding Products}">
                            <BindableLayout.ItemTemplate>
                                <DataTemplate>

                                    <Frame CornerRadius="10" Margin="5, 5, 5, 5" HasShadow="True" BackgroundColor="#5ac8fa">
                                        <StackLayout>

                                            <StackLayout x:DataType="ms:Product" Orientation="Vertical">
                                                <Label Text="{Binding Name}" FontAttributes="Bold" FontSize="Caption" />
                                                <Label Text="{Binding ProductCode}" FontAttributes="Italic" FontSize="Micro" />

                                                <StackLayout BindableLayout.ItemsSource="{Binding Batches}">
                                                    <BindableLayout.ItemTemplate>
                                                        <DataTemplate>
                                                            <StackLayout x:DataType="ms:Batch" Orientation="Vertical" HorizontalOptions="FillAndExpand">

                                                                <Grid Margin="0,10,0,0">
                                                                    <Grid.ColumnDefinitions>
                                                                        <ColumnDefinition Width="2*" />
                                                                        <ColumnDefinition Width="1*" />
                                                                    </Grid.ColumnDefinitions>
                                                                    <Label Grid.Column="0" Text="{Binding Code}" FontAttributes="Bold" FontSize="Caption" />
                                                                    <Label Grid.Column="1" Text="{Binding ExpiredDateFormated}" FontAttributes="Italic" HorizontalTextAlignment="End" FontSize="Micro" />
                                                                </Grid>

                                                                <StackLayout BindableLayout.ItemsSource="{Binding Serials}">
                                                                    <BindableLayout.ItemTemplate>
                                                                        <DataTemplate>
                                                                            <StackLayout x:DataType="ms:Serial" Orientation="Vertical" HorizontalOptions="FillAndExpand">
                                                                                <Frame CornerRadius="10" HasShadow="True">

                                                                                    <StackLayout>
                                                                                        <Label Text="{Binding SerialCode}" FontAttributes="Bold" FontSize="Micro" />
                                                                                    </StackLayout>
                                                                                    <Frame.GestureRecognizers>
                                                                                        <TapGestureRecognizer 
                                                                                                            NumberOfTapsRequired="1" 
                                                                                                            Command="{Binding Source={RelativeSource AncestorType={x:Type vm:SearchSerialsByLocationViewModel}}, Path=SerialTappedCommand}" 
                                                                                                            CommandParameter="{Binding .}" />
                                                                                    </Frame.GestureRecognizers>
                                                                                </Frame>
                                                                            </StackLayout>
                                                                        </DataTemplate>
                                                                    </BindableLayout.ItemTemplate>
                                                                </StackLayout>

                                                            </StackLayout>
                                                        </DataTemplate>
                                                    </BindableLayout.ItemTemplate>
                                                </StackLayout>

                                            </StackLayout>

                                        </StackLayout>
                                    </Frame>

                                </DataTemplate>
                            </BindableLayout.ItemTemplate>
                        </StackLayout>

                    </StackLayout>
                </StackLayout>
            </DataTemplate>
        </BindableLayout.ItemTemplate>
    </StackLayout>
</ScrollView>

It's working really good.

Answer 2

Nested CollectionView with scrolling one inside another : is it officially supported ?

In my knowledge, nested CollectionViews are not supported by all platforms as they have a Scroll in them and Nested ScrollViews are a widely known bad practice.

Display these collections problem

I was not able to understand what exactly did you mean here but if you could clarify, maybe I would be able to help you out.

How can I shrink the StackLayouts to its contents?

By setting the Spacing to 0 would be a good start!

I expect StackLayouts no longer than the size of the screen as it is with the code above and a few data

Is it that your StackLayout taking the whole screen? (The one which is in the ItemTemplate ?)

Answer 3

I was just dealing with this myself, and found this solution: https://docs.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/collectionview/grouping

In short: The idea is to restructure your data in such a way that the parent is a List<child> with additional properties, turn IsGrouping on in your CollectionView , structure the parent element as the CollectionView.GroupHeaderTemplate , and the child as the CollectionView.ItemTemplate .