Windows Phone 8.1 Listview唯一的第一项和最后一项模板
本文关键字：一项 Phone 最后 Windows Listview 唯一 | 更新日期: 2024-10-18 23:26:25
去年我为Windows Phone 8制作了一个应用程序，其中包含一个带有唯一第一项和最后一项模板的LongListSelector，如下所述：
LongListSelector第一个和最后一个项目的不同项目模板
我最近将该应用程序更新到Windows Phone 8.1应用商店，但此功能已损坏。这是我的课程（与帖子的唯一区别是，我在Windows Phone 8.1 Store中使用ListView而不是LongListSelector，因为LongListSelecter不是Windows Phone 8.1商店框架的一部分）：
public abstract class TemplateSelector : ContentControl
{
public abstract DataTemplate SelectTemplate(object item, int index, int totalCount, DependencyObject container);
protected override void OnContentChanged(object oldContent, object newContent)
{
base.OnContentChanged(oldContent, newContent);
var parent = GetParentByType<ListView>(this);
var index = (parent.ItemsSource as IList).IndexOf(newContent);
var totalCount = (parent.ItemsSource as IList).Count;
ContentTemplate = SelectTemplate(newContent, index, totalCount, this);
}
private static T GetParentByType<T>(DependencyObject element) where T : FrameworkElement
{
T result = null;
DependencyObject parent = VisualTreeHelper.GetParent(element);
while (parent != null)
{
result = parent as T;
if (result != null)
{
return result;
}
parent = VisualTreeHelper.GetParent(parent);
}
return null;
}
}
问题是：
DependencyObject parent = VisualTreeHelper.GetParent(element);
由于某种原因，GetParentByType函数的返回null。有人知道为什么，或者有其他解决方案吗？
下面是我的XAML代码（去掉了一些xmln）。DataTrigger之所以存在，是因为有时一个唯一的第一项模板就足够了（由ViewModel的LoadMore属性控制，该属性是布尔）。
<controls:WP81Page
xmlns:core="using:Microsoft.Xaml.Interactions.Core"
xmlns:interactivity="using:Microsoft.Xaml.Interactivity"
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<controls:WP81Page.Resources>
<DataTemplate x:Key="first">
<Grid HorizontalAlignment="Left" Width="Auto" Height="200">
<Border BorderThickness="1" BorderBrush="Black" Visibility="{Binding NoLargeImage, Converter={StaticResource BoolToVisibilityConverter}}" >
<Image Source="/Images/default-image.png" Stretch="UniformToFill" />
</Border>
<Border BorderThickness="1" BorderBrush="Black" Visibility="{Binding NoLargeImage, Converter={StaticResource BoolToVisibilityConverterReverse}}" >
<Image Source="{Binding LargeImageUrl}" Stretch="UniformToFill" />
</Border>
<StackPanel VerticalAlignment="Bottom" Background="#7F000000" >
<TextBlock Text="{Binding Header}" VerticalAlignment="Center" TextWrapping="Wrap" Foreground="White" FontWeight="Bold" Margin="15,0,15,15"/>
</StackPanel>
</Grid>
</DataTemplate>
<DataTemplate x:Key="default">
<StackPanel Orientation="Horizontal" Margin="0,10,0,0" Height="105" Width="Auto">
<Border BorderThickness="1" BorderBrush="Black" Margin="0,2" Visibility="{Binding NoSmallImage, Converter={StaticResource BoolToVisibilityConverter}}" >
<Image Source="/Images/default-image.png" Width="130" Height="100" Stretch="UniformToFill" />
</Border>
<Border BorderThickness="1" BorderBrush="Black" Margin="0,2" Visibility="{Binding NoSmallImage, Converter={StaticResource BoolToVisibilityConverterReverse}}">
<Image Source="{Binding SmallImageUrl}" Width="130" Height="100" Stretch="UniformToFill"/>
</Border>
<StackPanel Orientation="Vertical" Width="300" Margin="8,0,0,0">
<TextBlock Text="{Binding Header}" TextWrapping="Wrap" FontWeight="Bold" />
<TextBlock Margin="0,3,0,0" Text="{Binding DisplayDate}" TextWrapping="Wrap" Foreground="#FFB9B9B9" FontSize="16" />
</StackPanel>
</StackPanel>
</DataTemplate>
<DataTemplate x:Key="last">
<TextBlock Text="hent flere nyheder" FontSize="25" Margin="0,20" TextWrapping="Wrap" VerticalAlignment="Center" HorizontalAlignment="Center" Height="75" />
</DataTemplate>
<DataTemplate x:Key="UniqueFirstTemplateSelector">
<common:UniqueFirstTemplateSelector Content="{Binding}" First="{StaticResource first}" Default="{StaticResource default}" HorizontalAlignment="Stretch"/>
</DataTemplate>
<DataTemplate x:Key="UniqueFirstAndLastTemplateSelector">
<common:UniqueFirstAndLastTemplateSelector Content="{Binding}" First="{StaticResource first}" Default="{StaticResource default}" Last="{StaticResource last}" HorizontalAlignment="Stretch"/>
</DataTemplate>
</controls:WP81Page.Resources>
<controls:WP81Page.DataContext>
<viewModels:NewsViewModel/>
</controls:WP81Page.DataContext>
<Grid x:Name="LayoutRoot" Style="{Binding Source={StaticResource Background}}">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<ProgressBar Grid.Row="0" VerticalAlignment="Top" IsIndeterminate="True" Background="Transparent" Foreground="White" Visibility="{Binding IsLoading, Converter={StaticResource BoolToVisibilityConverter}}" />
<StackPanel Grid.Row="0" Margin="12,17,0,28">
<TextBlock Text="NYHEDER" FontSize="35" FontWeight="Bold" Style="{StaticResource PhoneTextNormalStyle}"/>
</StackPanel>
<Grid x:Name="ContentPanel" Grid.Row="1">
<controls:WP81ListView x:Name="listSelector" Margin="22,0" Grid.Row="2" ItemsSource="{Binding News}" Command="{Binding NewsEntrySelectedCommand}" >
<interactivity:Interaction.Behaviors>
<core:DataTriggerBehavior Binding="{Binding LoadMore}" Value="True">
<core:ChangePropertyAction TargetObject="{Binding ElementName=listSelector}"
Value="{StaticResource UniqueFirstAndLastTemplateSelector}"
PropertyName="ItemTemplate" />
</core:DataTriggerBehavior>
<core:DataTriggerBehavior Binding="{Binding LoadMore}" Value="False">
<core:ChangePropertyAction TargetObject="{Binding ElementName=listSelector}"
Value="{StaticResource UniqueFirstTemplateSelector}"
PropertyName="ItemTemplate" />
</core:DataTriggerBehavior>
</interactivity:Interaction.Behaviors>
</controls:WP81ListView>
</Grid>
</Grid>
</controls:WP81Page>
提前谢谢。
编辑
好吧，所以我想要的不是第一件和最后一件一直都是独一无二的。我正在制作一个新闻提要，其中只有当有更多的新闻条目要加载时，最后一个条目才是唯一的（当单击最后一个项目时，会向ListView中添加更多的新闻条目的）。但是，如果到达了新闻条目的末尾，则最后一个条目必须不是唯一的（因此与交互性相结合）。
首先，您的模板选择器的定义。它需要基于DataTemplateSelector和名为SelectTemplateCore的重写方法。它接受一个ListViewItem对象。这时，您可以在VisualTree上获取ListView，并根据索引选择DataTemplate。
public class MyTemplateSelector : DataTemplateSelector
{
public DataTemplate First { get; set; }
public DataTemplate Default { get; set; }
public DataTemplate Last { get; set; }
protected override DataTemplate SelectTemplateCore(object item, DependencyObject container)
{
var listViewItem = container as ListViewItem;
var listView = GetParentByType<ListView>(listViewItem);
var index = (listView.ItemsSource as IList).IndexOf(item);
var totalCount = (listView.ItemsSource as IList).Count;
if (index == 0)
return First;
else if (index == totalCount - 1)
return Last;
else
return Default;
}
private T GetParentByType<T>(DependencyObject element) where T : FrameworkElement
{
T result = null;
DependencyObject parent = VisualTreeHelper.GetParent(element);
while (parent != null)
{
result = parent as T;
if (result != null)
{
return result;
}
parent = VisualTreeHelper.GetParent(parent);
}
return null;
}
}
然后，您需要在静态资源中创建一个实例
<local:MyTemplateSelector x:Key="SelectingTemplate"
First="{StaticResource first}"
Default="{StaticResource default}"
Last="{StaticResource last}" />
使用First、Default和Last DataTemplates，就像以前一样。
最后一步是将它应用于您正在使用的ListView。
<ListView ItemsSource="{Binding SomeItemsSource}"
ItemTemplateSelector="{StaticResource SelectingTemplate}" />
就这样！