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当ListView在UWP中不包含MVVM项时显示消息

listview

当ListView在UWP中不包含MVVM项时显示消息,listview,winrt-xaml,win-universal-app,windows-10-universal,Listview,Winrt Xaml,Win Universal App,Windows 10 Universal,这是我的第一个MVVM项目，我需要编写代码来操作视图中的控件，但不知何故，代码似乎比实际情况复杂得多 我发现很难完全理解MVVM，也很难决定什么时候可以把东西放在代码后面 基本上，我的问题是，我想显示一条消息，告诉用户listview是空的，而它绑定到的ObservableCollection不包含任何项。其想法是在视图中有一个TextBlock，并且只有在没有要显示的项目时（在用户创建项目之前和删除所有项目之后），才将其visibility属性设置为Visible 我无法使用此解决方案，因为U

这是我的第一个MVVM项目，我需要编写代码来操作视图中的控件，但不知何故，代码似乎比实际情况复杂得多

我发现很难完全理解MVVM，也很难决定什么时候可以把东西放在代码后面

基本上，我的问题是，我想显示一条消息，告诉用户listview是空的，而它绑定到的ObservableCollection不包含任何项。其想法是在视图中有一个TextBlock，并且只有在没有要显示的项目时（在用户创建项目之前和删除所有项目之后），才将其visibility属性设置为Visible

我无法使用此解决方案，因为UWP不支持BooleanToVisibilityConverter：

查看：

<Page
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:EventMaker3000.View"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:ViewModel="using:EventMaker3000.ViewModel"
    xmlns:Interactivity="using:Microsoft.Xaml.Interactivity" xmlns:Core="using:Microsoft.Xaml.Interactions.Core"
    x:Class="EventMaker3000.View.EventPage"
    mc:Ignorable="d">
    <Page.BottomAppBar>
        <CommandBar>
            <CommandBar.Content>
                <Grid/>
            </CommandBar.Content>
            <AppBarButton Icon="Delete" Label="Delete" IsEnabled="{Binding DeletebuttonEnableOrNot}">
                <Interactivity:Interaction.Behaviors>
                    <Core:EventTriggerBehavior EventName="Click">
                        <Core:NavigateToPageAction/>
                        <Core:InvokeCommandAction Command="{Binding DeleteEventCommand}"/>
                    </Core:EventTriggerBehavior>
                </Interactivity:Interaction.Behaviors>
            </AppBarButton>
            <AppBarButton Icon="Add" Label="Add">
                <Interactivity:Interaction.Behaviors>
                    <Core:EventTriggerBehavior EventName="Click">
                        <Core:NavigateToPageAction TargetPage="EventMaker3000.View.CreateEventPage"/>
                    </Core:EventTriggerBehavior>
                </Interactivity:Interaction.Behaviors>
            </AppBarButton>
        </CommandBar>
    </Page.BottomAppBar>

    <Page.DataContext>
        <ViewModel:EventViewModel/>
    </Page.DataContext>

    <Grid Background="WhiteSmoke">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition/>
        </Grid.RowDefinitions>

        <!--Header-->
        <TextBlock 
            Text="Events" 
            Foreground="Black" 
            Margin="0,20,0,0" 
            Style="{ThemeResource HeaderTextBlockStyle}" 
            HorizontalAlignment="center" 
            VerticalAlignment="Center"/>

        <ListView
            ItemsSource="{Binding EventCatalogSingleton.Events, Mode=TwoWay}"
            SelectedItem="{Binding SelectedEvent, Mode=TwoWay}"
            Grid.Row="1"    
            Background="WhiteSmoke"
            Padding="0,30,0,0">
            <Interactivity:Interaction.Behaviors>
                <Core:EventTriggerBehavior EventName="SelectionChanged">
                    <Core:InvokeCommandAction Command="{Binding EnableOrNotCommand}"/>
                </Core:EventTriggerBehavior>
            </Interactivity:Interaction.Behaviors>

            <ListView.ItemTemplate>
                <DataTemplate>
                    <Grid VerticalAlignment="Center" Margin="5,0">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="Auto" />
                            <ColumnDefinition Width="*" />
                        </Grid.ColumnDefinitions>

                        <Grid.RowDefinitions>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                        </Grid.RowDefinitions>

                        <TextBlock Grid.Column="0"
                            Grid.Row="0"
                            Margin="5" 
                            Text="{Binding Name, Mode=TwoWay}" 
                            Style="{ThemeResource TitleTextBlockStyle}" Foreground="Black"/>
                        <TextBlock Grid.Column="1"
                            Grid.Row="1"
                            Margin="5" 
                            Text="{Binding Place, Mode=TwoWay}"
                            HorizontalAlignment="Right"
                            Style="{ThemeResource CaptionTextBlockStyle}" Foreground="Black"/>
                        <TextBlock Grid.Column="0"
                            Grid.Row="2"
                            Margin="5" 
                            Text="{Binding Description, Mode=TwoWay}"
                            Style="{ThemeResource BodyTextBlockStyle}" Foreground="Black"/>

                        <TextBlock Grid.Column="0"
                            Grid.Row="1" 
                            Margin="5" 
                            Text="{Binding DateTime, Mode=TwoWay}" 
                            Style="{ThemeResource CaptionTextBlockStyle}" Foreground="Black"/>
                    </Grid>
                </DataTemplate>
            </ListView.ItemTemplate>

            <!--Sets each listview item to stretch-->
            <ListView.ItemContainerStyle>
                <Style TargetType="ListViewItem">
                    <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
                </Style>
            </ListView.ItemContainerStyle>
        </ListView>

        <!-- TextBlock for empty list view-->

        <TextBlock 
            Grid.Row="1"
            Margin="5,5,5,5"  
            VerticalAlignment="Center"  
            HorizontalAlignment="Center"  
            Text="You have no events"  
            Style="{StaticResource BaseTextBlockStyle}"  
            Visibility="{Binding TextBlockVisibility}"/>
    </Grid>
</Page>
Singleton:

<Page
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:EventMaker3000.View"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:ViewModel="using:EventMaker3000.ViewModel"
    xmlns:Interactivity="using:Microsoft.Xaml.Interactivity" xmlns:Core="using:Microsoft.Xaml.Interactions.Core"
    x:Class="EventMaker3000.View.EventPage"
    mc:Ignorable="d">
    <Page.BottomAppBar>
        <CommandBar>
            <CommandBar.Content>
                <Grid/>
            </CommandBar.Content>
            <AppBarButton Icon="Delete" Label="Delete" IsEnabled="{Binding DeletebuttonEnableOrNot}">
                <Interactivity:Interaction.Behaviors>
                    <Core:EventTriggerBehavior EventName="Click">
                        <Core:NavigateToPageAction/>
                        <Core:InvokeCommandAction Command="{Binding DeleteEventCommand}"/>
                    </Core:EventTriggerBehavior>
                </Interactivity:Interaction.Behaviors>
            </AppBarButton>
            <AppBarButton Icon="Add" Label="Add">
                <Interactivity:Interaction.Behaviors>
                    <Core:EventTriggerBehavior EventName="Click">
                        <Core:NavigateToPageAction TargetPage="EventMaker3000.View.CreateEventPage"/>
                    </Core:EventTriggerBehavior>
                </Interactivity:Interaction.Behaviors>
            </AppBarButton>
        </CommandBar>
    </Page.BottomAppBar>

    <Page.DataContext>
        <ViewModel:EventViewModel/>
    </Page.DataContext>

    <Grid Background="WhiteSmoke">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition/>
        </Grid.RowDefinitions>

        <!--Header-->
        <TextBlock 
            Text="Events" 
            Foreground="Black" 
            Margin="0,20,0,0" 
            Style="{ThemeResource HeaderTextBlockStyle}" 
            HorizontalAlignment="center" 
            VerticalAlignment="Center"/>

        <ListView
            ItemsSource="{Binding EventCatalogSingleton.Events, Mode=TwoWay}"
            SelectedItem="{Binding SelectedEvent, Mode=TwoWay}"
            Grid.Row="1"    
            Background="WhiteSmoke"
            Padding="0,30,0,0">
            <Interactivity:Interaction.Behaviors>
                <Core:EventTriggerBehavior EventName="SelectionChanged">
                    <Core:InvokeCommandAction Command="{Binding EnableOrNotCommand}"/>
                </Core:EventTriggerBehavior>
            </Interactivity:Interaction.Behaviors>

            <ListView.ItemTemplate>
                <DataTemplate>
                    <Grid VerticalAlignment="Center" Margin="5,0">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="Auto" />
                            <ColumnDefinition Width="*" />
                        </Grid.ColumnDefinitions>

                        <Grid.RowDefinitions>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                        </Grid.RowDefinitions>

                        <TextBlock Grid.Column="0"
                            Grid.Row="0"
                            Margin="5" 
                            Text="{Binding Name, Mode=TwoWay}" 
                            Style="{ThemeResource TitleTextBlockStyle}" Foreground="Black"/>
                        <TextBlock Grid.Column="1"
                            Grid.Row="1"
                            Margin="5" 
                            Text="{Binding Place, Mode=TwoWay}"
                            HorizontalAlignment="Right"
                            Style="{ThemeResource CaptionTextBlockStyle}" Foreground="Black"/>
                        <TextBlock Grid.Column="0"
                            Grid.Row="2"
                            Margin="5" 
                            Text="{Binding Description, Mode=TwoWay}"
                            Style="{ThemeResource BodyTextBlockStyle}" Foreground="Black"/>

                        <TextBlock Grid.Column="0"
                            Grid.Row="1" 
                            Margin="5" 
                            Text="{Binding DateTime, Mode=TwoWay}" 
                            Style="{ThemeResource CaptionTextBlockStyle}" Foreground="Black"/>
                    </Grid>
                </DataTemplate>
            </ListView.ItemTemplate>

            <!--Sets each listview item to stretch-->
            <ListView.ItemContainerStyle>
                <Style TargetType="ListViewItem">
                    <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
                </Style>
            </ListView.ItemContainerStyle>
        </ListView>

        <!-- TextBlock for empty list view-->

        <TextBlock 
            Grid.Row="1"
            Margin="5,5,5,5"  
            VerticalAlignment="Center"  
            HorizontalAlignment="Center"  
            Text="You have no events"  
            Style="{StaticResource BaseTextBlockStyle}"  
            Visibility="{Binding TextBlockVisibility}"/>
    </Grid>
</Page>
公共类事件目录单例 { 私有静态EventCatalogSingleton\u实例

private EventCatalogSingleton()
{
    Events = new ObservableCollection<Event>();

    // Creates instances of events and adds it to the observable collection.
    LoadEventAsync();
}

//Checks if an instance already exists, if not it will create one. Makes sure we only have one instance
public static EventCatalogSingleton getInstance()
{
    if (_instance != null)
    {
        return _instance;
    }
    else
    {
        _instance = new EventCatalogSingleton();
        return _instance;
    }
}

// Creates the observable collection
public ObservableCollection<Event> Events { get; set; }

public void AddEvent(Event newEvent)
{
    Events.Add(newEvent);
    PersistencyService.SaveEventsAsJsonAsync(Events);
}

public void AddEvent(int id, string name, string description, string place, DateTime date)
{
    Events.Add(new Event(id, name, description, place, date));
    PersistencyService.SaveEventsAsJsonAsync(Events);
}


public void RemoveEvent(Event myEvent)
{
    Events.Remove(myEvent);
    PersistencyService.SaveEventsAsJsonAsync(Events);
}

public async void LoadEventAsync()
{

    var events = await PersistencyService.LoadEventsFromJsonAsync();
    if (events != null)
        foreach (var ev in events)
        {
            Events.Add(ev);
        }

}

private EventCatalogSingleton（）
{
事件=新的ObservableCollection（）；
//创建事件实例并将其添加到可观察集合。
LoadEventAsync（）；
}
//检查实例是否已经存在，如果不存在，它将创建一个。确保我们只有一个实例
公共静态事件目录Singleton getInstance（）
{
如果（_实例！=null）
{
返回_实例；
}
其他的
{
_实例=新的EventCatalogSingleton（）；
返回_实例；
}
}
//创建可观察的集合
公共ObservableCollection事件{get；set；}
公共无效添加事件（事件newEvent）
{
Events.Add（newEvent）；
PersistencyService.SaveEventsAsJsonAsync（事件）；
}
public void AddEvent（int-id、字符串名称、字符串描述、字符串位置、日期时间）
{
添加（新事件（id、名称、描述、地点、日期））；
PersistencyService.SaveEventsAsJsonAsync（事件）；
}
公共无效删除事件（事件myEvent）
{
移除（myEvent）；
PersistencyService.SaveEventsAsJsonAsync（事件）；
}
公共异步void LoadEventAsync（）
{
var events=await PersistencyService.LoadEventsFromJsonAsync（）；
如果（事件！=null）
foreach（事件中的var ev）
{
事件。添加（ev）；
}
}
}

处理程序：

<Page
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:EventMaker3000.View"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:ViewModel="using:EventMaker3000.ViewModel"
    xmlns:Interactivity="using:Microsoft.Xaml.Interactivity" xmlns:Core="using:Microsoft.Xaml.Interactions.Core"
    x:Class="EventMaker3000.View.EventPage"
    mc:Ignorable="d">
    <Page.BottomAppBar>
        <CommandBar>
            <CommandBar.Content>
                <Grid/>
            </CommandBar.Content>
            <AppBarButton Icon="Delete" Label="Delete" IsEnabled="{Binding DeletebuttonEnableOrNot}">
                <Interactivity:Interaction.Behaviors>
                    <Core:EventTriggerBehavior EventName="Click">
                        <Core:NavigateToPageAction/>
                        <Core:InvokeCommandAction Command="{Binding DeleteEventCommand}"/>
                    </Core:EventTriggerBehavior>
                </Interactivity:Interaction.Behaviors>
            </AppBarButton>
            <AppBarButton Icon="Add" Label="Add">
                <Interactivity:Interaction.Behaviors>
                    <Core:EventTriggerBehavior EventName="Click">
                        <Core:NavigateToPageAction TargetPage="EventMaker3000.View.CreateEventPage"/>
                    </Core:EventTriggerBehavior>
                </Interactivity:Interaction.Behaviors>
            </AppBarButton>
        </CommandBar>
    </Page.BottomAppBar>

    <Page.DataContext>
        <ViewModel:EventViewModel/>
    </Page.DataContext>

    <Grid Background="WhiteSmoke">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition/>
        </Grid.RowDefinitions>

        <!--Header-->
        <TextBlock 
            Text="Events" 
            Foreground="Black" 
            Margin="0,20,0,0" 
            Style="{ThemeResource HeaderTextBlockStyle}" 
            HorizontalAlignment="center" 
            VerticalAlignment="Center"/>

        <ListView
            ItemsSource="{Binding EventCatalogSingleton.Events, Mode=TwoWay}"
            SelectedItem="{Binding SelectedEvent, Mode=TwoWay}"
            Grid.Row="1"    
            Background="WhiteSmoke"
            Padding="0,30,0,0">
            <Interactivity:Interaction.Behaviors>
                <Core:EventTriggerBehavior EventName="SelectionChanged">
                    <Core:InvokeCommandAction Command="{Binding EnableOrNotCommand}"/>
                </Core:EventTriggerBehavior>
            </Interactivity:Interaction.Behaviors>

            <ListView.ItemTemplate>
                <DataTemplate>
                    <Grid VerticalAlignment="Center" Margin="5,0">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="Auto" />
                            <ColumnDefinition Width="*" />
                        </Grid.ColumnDefinitions>

                        <Grid.RowDefinitions>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                        </Grid.RowDefinitions>

                        <TextBlock Grid.Column="0"
                            Grid.Row="0"
                            Margin="5" 
                            Text="{Binding Name, Mode=TwoWay}" 
                            Style="{ThemeResource TitleTextBlockStyle}" Foreground="Black"/>
                        <TextBlock Grid.Column="1"
                            Grid.Row="1"
                            Margin="5" 
                            Text="{Binding Place, Mode=TwoWay}"
                            HorizontalAlignment="Right"
                            Style="{ThemeResource CaptionTextBlockStyle}" Foreground="Black"/>
                        <TextBlock Grid.Column="0"
                            Grid.Row="2"
                            Margin="5" 
                            Text="{Binding Description, Mode=TwoWay}"
                            Style="{ThemeResource BodyTextBlockStyle}" Foreground="Black"/>

                        <TextBlock Grid.Column="0"
                            Grid.Row="1" 
                            Margin="5" 
                            Text="{Binding DateTime, Mode=TwoWay}" 
                            Style="{ThemeResource CaptionTextBlockStyle}" Foreground="Black"/>
                    </Grid>
                </DataTemplate>
            </ListView.ItemTemplate>

            <!--Sets each listview item to stretch-->
            <ListView.ItemContainerStyle>
                <Style TargetType="ListViewItem">
                    <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
                </Style>
            </ListView.ItemContainerStyle>
        </ListView>

        <!-- TextBlock for empty list view-->

        <TextBlock 
            Grid.Row="1"
            Margin="5,5,5,5"  
            VerticalAlignment="Center"  
            HorizontalAlignment="Center"  
            Text="You have no events"  
            Style="{StaticResource BaseTextBlockStyle}"  
            Visibility="{Binding TextBlockVisibility}"/>
    </Grid>
</Page>
公共类事件处理程序 {

public EventViewModel EventViewModel{get；set；}
公共事件处理程序（EventViewModel EventViewModel）
{
EventViewModel=EventViewModel；
}
public void CreateEvent（）
{
EventViewModel.EventCatalogSingleton.AddEvent（EventViewModel.Id，EventViewModel.Name，EventViewModel.Description，EventViewModel.Place，DateTimeConverter.DateTimeOffsetAndTimeSetToDateTime（EventViewModel.Date，EventViewModel.Time））；
}
私有void DeleteEvent（）
{
EventViewModel.EventCatalogSingleton.Events.Remove（EventViewModel.SelectedEvent）；
}
//删除前提示用户的确认框
公共异步void getDeleteConfirmationSync（）
{
MessageDialog msgbox=newmessagedialog（“您确定要永久删除此事件吗？”，“删除事件”）；
msgbox.Commands.Add（新UICommand
{
Label=“是”，
调用=命令=>DeleteEvent（）
}
);
msgbox.Commands.Add（新UICommand
{
Label=“否”，
}
);
msgbox.DefaultCommandIndex=1；
msgbox.CancelCommandIndex=1；
msgbox.Options=MessageDialogOptions.AcceptUserInputAfterDelay；
等待msgbox.ShowAsync（）；
}
public void EnableOrNot（）
{
EventViewModel.DeletebuttonEnableOrNot=EventViewModel.DeletebuttonEnableOrNot=true；
}
public void TextBlockVisibility（）
{
if（EventViewModel.EventCatalogSingleton.Events.Count<1）
{
EventViewModel.TextBlockVisibility=EventViewModel.TextBlockVisibility=“可见”；
}        
}
}

它包含了很多代码，我知道——我不知道应该省略什么。 我包括了当我在listview中选择了一个项目时启用删除按钮的代码——这很好

为什么删除listview中的所有项目后视图中的TextBlock不显示？为了更改视图中控件的外观和其他内容，我真的需要在viewmodel中添加属性和ICommand吗？

我已经成功地在StackPanel中为我这样的项目添加了可见性绑定

cs型

    Visibility showPanel = Visibility.Collapsed;
    public Visibility ShowPanel
    {
        get
        {
            return showPanel;
        }

        set
        {
            showPanel = value;
            NotifyPropertyChanged("ShowPanel");
        }
    }
XAML

首先，您希望尽最大努力在视图和视图模型之间保持清晰的关注点分离。因此，尽量不要包含特定于UI的类型，如
可见性
和
消息对话框
。您可以为负责显示对话框的
MessageDialog
创建一个界面，然后将其传递给视图模型

其次，您应该准备编写自己的值转换器（
BooleanToVisibilityConverter
），如下所示：

public sealed class BooleanToVisibilityConverter : IValueConverter
{
    public object Convert(object value, 
        Type targetType, object parameter, string language)
    {
        bool isVisible = (bool)value;
        return isVisible ? Visibility.Visible : Visibility.Collapsed;
    }

    public object ConvertBack(object value, 
           Type targetType, object parameter, string language)
    {
        return (Visibility)value == Visibility.Visible;
    }
}
并在您的视图中这样使用它：

<Page
   xmlns:converters="using:MyApp.Whatever">
    <Page.Resources>
        <converters:BooleanToVisibilityConverter x:Key="converter"/>
    </Page.Resources>
    <TextBlock
    Visibility="{Binding HasNoItems, Mode=TwoWay, 
        Converter={StaticResource converter}}">
    </TextBlock>
</Page>
有趣的是，我和Daren May刚刚在微软虚拟学院专门教授了一门免费课程。这对你来说可能是一个很好的资源。看视频#2@13分钟

看看这个简单的方法：

使用此代码：

class VisibleWhenZeroConverter : IValueConverter
{
    public object Convert(object v, Type t, object p, string l) =>
        Equals(0d, (double)v) ? Visibility.Visible : Visibility.Collapsed;

    public object ConvertBack(object v, Type t, object p, string l) => null;
}
这个XAML：

    <StackPanel.Resources>
        <cvt:VisibleWhenZeroConverter x:Name="VisibleWhenZeroConverter" />
    </StackPanel.Resources>

    <ListView ItemsSource="{x:Bind Items}" x:Name="MyList">
        <ListView.Header>
            <TextBlock Visibility="{Binding Items.Count, ElementName=MyList, 
                       Converter={StaticResource VisibleWhenZeroConverter}}">
                <Run Text="There are no items." />
            </TextBlock>
        </ListView.Header>
    </ListView>
有道理吗？我希望如此

附：这正好回答了你问题的标题。希望能有帮助

祝你好运

您是否正确实现了INotifyProperty更改？ 
public bool HasNoItems
{
    get { return this.hasNoItems; }
    set { this.hasNoItems = value; OnPropertyChanged(); }
}

class VisibleWhenZeroConverter : IValueConverter
{
    public object Convert(object v, Type t, object p, string l) =>
        Equals(0d, (double)v) ? Visibility.Visible : Visibility.Collapsed;

    public object ConvertBack(object v, Type t, object p, string l) => null;
}

    <StackPanel.Resources>
        <cvt:VisibleWhenZeroConverter x:Name="VisibleWhenZeroConverter" />
    </StackPanel.Resources>

    <ListView ItemsSource="{x:Bind Items}" x:Name="MyList">
        <ListView.Header>
            <TextBlock Visibility="{Binding Items.Count, ElementName=MyList, 
                       Converter={StaticResource VisibleWhenZeroConverter}}">
                <Run Text="There are no items." />
            </TextBlock>
        </ListView.Header>
    </ListView>