CollectionView：未显示 EmptyView 内容

Question

我在使用 listview 的页面显示中有一个错误，所以我开始从 listview 迁移到 collectionview，但是... 这是集合视图的 XAML 代码，我不知道为什么当 ItemSource 没有任何数据时，没有显示空视图。

<StackLayout Style="{StaticResource PageLayout}">
        <StackLayout VerticalOptions="CenterAndExpand" IsVisible="{Binding LoadingIndicator}">
            <ActivityIndicator IsRunning="True" VerticalOptions="Center" HorizontalOptions="Center"/>
        </StackLayout>
        <StackLayout VerticalOptions="FillAndExpand" IsVisible="{Binding ShowContent}">
            <CollectionView ItemsSource="{Binding Items}" VerticalOptions="FillAndExpand" SelectionMode="Single" SelectionChanged="CollectionView_SelectionChanged" Style="{StaticResource CollectionViewChecklistDefault}">
                <CollectionView.Header>
                    <StackLayout HeightRequest="5">
                    </StackLayout>
                </CollectionView.Header>
                <CollectionView.ItemTemplate>
                    <DataTemplate>
                            <Grid ColumnSpacing="0" RowSpacing="0" Margin="0" Padding="0">
                                <Grid.RowDefinitions>
                                    <RowDefinition Height="Auto" />
                                    <RowDefinition Height="25" />
                                    <RowDefinition Height="Auto" />
                                    <RowDefinition Height="Auto" />
                                    <RowDefinition Height="Auto" />
                                    <RowDefinition Height="Auto" />
                                    <RowDefinition Height="Auto" />
                                    <RowDefinition Height="40" />
                                    <RowDefinition Height="10" />
                                </Grid.RowDefinitions>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="37*" />
                                    <ColumnDefinition Width="33*" />
                                    <ColumnDefinition Width="30*" />
                                </Grid.ColumnDefinitions>
                                <Label Grid.Row="0" Grid.Column="1" Text="{Binding APP_ID}" IsVisible="False"/>
                                <BoxView Grid.Row="0" Grid.Column="0" Grid.RowSpan="8" Grid.ColumnSpan="3" Style="{StaticResource ListBox}"/>
                                <Image Grid.Row="0" Grid.Column="0" Aspect="AspectFit" Style="{StaticResource ListImage}">
                                    <Image.Source>
                                        <FontImageSource Glyph="&#xf46d;" FontFamily="FontAwesomeSolid" Color="#343a40"></FontImageSource>
                                    </Image.Source>
                                </Image>
                                <Label Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2" Text="{Binding OBSERVATION_TYPE_NAME}" Style="{StaticResource ListLabelBold}"/>
                                <Label Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="3" Style="{StaticResource PreviewLabel}">
                                    <Label.FormattedText>
                                        <FormattedString>
                                        <Span Text="{Binding Traductions[DATE], Source={RelativeSource AncestorType={x:Type viewModel:ObservationCloseListViewModel}}, StringFormat='\{0}:'}"  FontAttributes="Bold" TextTransform="Uppercase" TextColor="DarkGray"/>
                                            <Span Text="{Binding OBSERVATION_DATE, StringFormat=' \{0:dd MMM yyyy}'}"/>
                                        </FormattedString>
                                    </Label.FormattedText>
                                </Label>
                                <Label Grid.Row="2" Grid.Column="0" Grid.ColumnSpan="3" Style="{StaticResource PreviewLabel}">
                                    <Label.FormattedText>
                                        <FormattedString>
                                        <Span Text="{Binding Traductions[COMPANY], Source={RelativeSource AncestorType={x:Type viewModel:ObservationCloseListViewModel}}, StringFormat='\{0}:  '}"  FontAttributes="Bold" TextTransform="Uppercase" TextColor="DarkGray"/>
                                            <Span Text="{Binding COMPANY_NAME, StringFormat=' \{0}'}"/>
                                        </FormattedString>
                                    </Label.FormattedText>
                                </Label>
                                <Label Grid.Row="3" Grid.Column="0" Grid.ColumnSpan="3" Style="{StaticResource PreviewLabel}">
                                    <Label.FormattedText>
                                        <FormattedString>
                                            <Span Text="{Binding Traductions[WORKPLACE], Source={RelativeSource AncestorType={x:Type viewModel:ObservationCloseListViewModel}}, StringFormat='\{0}:  '}"  FontAttributes="Bold" TextTransform="Uppercase" TextColor="DarkGray"/>
                                            <Span Text="{Binding WORKPLACE_NAME, StringFormat=' \{0}'}"/>
                                        </FormattedString>
                                    </Label.FormattedText>
                                </Label>

                                <Label Grid.Row="4" Grid.Column="0" Grid.ColumnSpan="3" Style="{StaticResource PreviewLabel}">
                                    <Label.FormattedText>
                                        <FormattedString>
                                            <Span Text="{Binding Traductions[SECTOR], Source={RelativeSource AncestorType={x:Type viewModel:ObservationCloseListViewModel}}, StringFormat='\{0}:  '}"  FontAttributes="Bold" TextTransform="Uppercase" TextColor="DarkGray"/>
                                            <Span Text="{Binding SECTOR_NAME, StringFormat=' \{0}'}"/>
                                        </FormattedString>
                                    </Label.FormattedText>
                                </Label>

                                <Label Grid.Row="5" Grid.Column="0" Grid.ColumnSpan="3" Style="{StaticResource PreviewLabel}">
                                    <Label.FormattedText>
                                        <FormattedString>
                                            <Span Text="{Binding Traductions[FOLLOW_UP_DEPARTMENT], Source={RelativeSource AncestorType={x:Type viewModel:ObservationCloseListViewModel}}, StringFormat='\{0}:  '}"  FontAttributes="Bold" TextTransform="Uppercase" TextColor="DarkGray"/>
                                            <Span Text="{Binding FOLLOW_DEPARTMENT_NAME, StringFormat=' \{0}'}"/>
                                        </FormattedString>
                                    </Label.FormattedText>
                                </Label>
                                <Label Grid.Row="6" Grid.Column="0" Grid.ColumnSpan="3" Style="{StaticResource PreviewLabel}">
                                    <Label.FormattedText>
                                        <FormattedString>
                                            <Span Text="{Binding Traductions[DESCRIPTION], Source={RelativeSource AncestorType={x:Type viewModel:ObservationCloseListViewModel}}, StringFormat='\{0}:  '}"  FontAttributes="Bold" TextTransform="Uppercase" TextColor="DarkGray"/>
                                            <Span Text="{Binding OBSERVATION_DESCRIPTION, StringFormat=' \{0}'}"/>
                                        </FormattedString>
                                    </Label.FormattedText>
                                </Label>
                                <Label Grid.Row="7" Grid.Column="0" Grid.ColumnSpan="3"  Text="{Binding Traductions[CLOSE_OBSERVATION], Source={RelativeSource AncestorType={x:Type viewModel:ObservationCloseListViewModel}}}" Style="{StaticResource ListValueGreenEnd}" />
                                <Image Grid.Row="7" Grid.Column="2" Aspect="AspectFit" Style="{StaticResource ListImageArrow}">
                                    <Image.Source>
                                        <FontImageSource Glyph="&#xf138;" FontFamily="FontAwesomeSolid" Color="#7ca04b"></FontImageSource>
                                    </Image.Source>
                                </Image>
                            </Grid>
                    </DataTemplate>
                </CollectionView.ItemTemplate>
                <CollectionView.EmptyView>
                        <StackLayout VerticalOptions="CenterAndExpand">
                            <Label Text="{Binding Traductions[THERE_ARE_NO_OBSERVATIONS], Source={RelativeSource AncestorType={x:Type viewModel:ObservationCloseListViewModel}}}" Style="{StaticResource ListNotItemsFound}"/>
                            <Label Text="TEST"/>
                        </StackLayout>
                </CollectionView.EmptyView>
            </CollectionView>
        </StackLayout>
    </StackLayout>

这是它在集合视图（空）中的显示方式。我在 TEST 上贴了一个额外的标签

这是必须的

Answer 1

我做了一些实验。出现此症状的唯一方法是 {Binding ShowContent} 未能 return True。

我相信问题不在于 CollectionView。它是周围 StackLayout 的可见性。

验证：

将IsVisible="{Binding ShowContent}"替换为IsVisible="True"。

如果这导致 EmptyView 出现，请检查这些可能的原因：

绑定上下文。（在评论中，您展示了看起来正确的代码。仔细检查。）
正确声明 ShowContent，通知 XAML 更改：

    // Start "true", so InitializeComponent will begin with it there.
    private bool _showContent = true;
    public bool ShowContent {
        get => _showContent;
        set {
            _showContent = value;
            OnPropertyChanged();
        }
    }

如果您有设置 ShowContent 的代码，请确认您已将其设置为 true。

Answer 2

您遇到的问题的根本原因在于 CollectionView.Header 的使用。但这不是你的错。这是CollectionView的一个bug：使用Header时没有出现EmptyView。它已经报告给 Xamarin.Forms 开发人员。您可以跟踪进度 here.

CollectionView：未显示 EmptyView 内容

CollectionView: EmptyView content not shown

xamarin.forms