具有DependencyProperty的UWP ValueConverter

Question

我有一个UWP项目，我正试图在我的template<typename Tuple> constexpr auto pop_front(Tuple tuple) { static_assert(std::tuple_size<Tuple>::value > 0, "Cannot pop from an empty tuple"); return std::apply( [](auto, auto... rest) { return std::make_tuple(rest...); }, tuple); } 上设置绑定。

它基于this guide。

我在ValueConverter上创建了DependencyProperty，但始终为ValueConverter，而不是null类型的元素。

有我的代码：

MainPage.xaml中

Vehicle

MainPage.xaml.cs中

<Page
    x:Class="Project.Pages.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"     
    mc:Ignorable="d"
    xmlns:conv="using:Project.Converters"
    >

    <Page.Resources>
        <conv:Item_to_FullItem x:Key="Item_to_FullItem" VehicleItem="{Binding}"/>
    </Page.Resources>

    <Grid>
        <ListView x:Name="ListView_Vehicles" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
            <ListView.ItemTemplate>
                <DataTemplate>
                    <Grid ScrollViewer.VerticalScrollBarVisibility="Auto">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="*"/>
                            <ColumnDefinition Width="*"/>
                            <ColumnDefinition Width="*"/>
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions>
                            <RowDefinition Height="40"/>
                        </Grid.RowDefinitions>

                        <Border Grid.Column="0" BorderThickness="1" BorderBrush="Black">
                            <TextBlock Text="{Binding Path=Category}"/>
                        </Border>
                        <Border Grid.Column="1" BorderThickness="1" BorderBrush="Black">
                            <TextBlock Text="{Binding Item, Converter={StaticResource Item_to_FullItem}}"/>
                        </Border>
                        <Border Grid.Column="2" BorderThickness="1" BorderBrush="Black">
                            <TextBlock Text="{Binding Path=Weight}"/>
                        </Border>
                    </Grid>
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>
    </Grid>

</Page>

转换器

namespace Project.Pages
{
    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            InitializeComponent();

            Fill_Vehicle_List();
            ListView_Vehicles.ItemsSource = VehicleServices.Vehicles;
        }

        public class Vehicle : BindableBase
        {
            private int _Category;
            public int Category
            {
                get { return _Category; }
                set { Set(ref _Category, value); }
            }

            private string _Items;
            public string Items
            {
                get { return _Items; }
                set { Set(ref _Items, value); }
            }           

            private double? _Weight;
            public double? Weight
            {
                get { return _Weight; }
                set { Set(ref _Weight, value); }
            }
        }

        public class Values_Vehicle : ObservableCollection<Vehicle> { }

        public static class VehicleServices
        {
            public static Values_Vehicle Vehicles = new Values_Vehicle();

            static VehicleServices()
            {
            }
        }

        public static void Fill_Vehicle_List()
        {
            VehicleServices.Vehicles.Add(new Vehicle()
            {
                Category = 1,
                Items = "1.0",
                Weight = 1000,
            });
            VehicleServices.Vehicles.Add(new Vehicle()
            {
                Category = 2,
                Items = "1.1",
                Weight = 1600,
            });
            VehicleServices.Vehicles.Add(new Vehicle()
            {
                Category = 8,
                Items = "1.2",
                Weight = 1400,
            });
            VehicleServices.Vehicles.Add(new Vehicle()
            {
                Category = 13,
                Items = "1.3",
                Weight = 1500,
            });
            VehicleServices.Vehicles.Add(new Vehicle()
            {
                Category = 1,
                Items = "2.0",
                Weight = 1100,
            });
        }
    }
}

Answer 1

问题是，当您在{Binding}部分中使用<Page.Resources>时，将会相对于Page {{1}评估绑定}。如果您在DataContext的构造函数中设置DataContext = new Vehicle()，则可以验证这一点。

要解决此问题，您只需将转换器移到Page声明：

中

DataTemplate

这样<DataTemplate> <Grid ScrollViewer.VerticalScrollBarVisibility="Auto"> <Grid.Resources> <converters:Item_to_FullItem x:Key="Item_to_FullItem" VehicleItem="{Binding}"/> </Grid.Resources> <Grid.ColumnDefinitions> <ColumnDefinition Width="*"/> <ColumnDefinition Width="*"/> <ColumnDefinition Width="*"/> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height="40"/> </Grid.RowDefinitions> <Border Grid.Column="0" BorderThickness="1" BorderBrush="Black"> <TextBlock Text="{Binding Path=Category}"/> </Border> <Border Grid.Column="1" BorderThickness="1" BorderBrush="Black"> <TextBlock Text="{Binding Item, Converter={StaticResource Item_to_FullItem}}"/> </Border> <Border Grid.Column="2" BorderThickness="1" BorderBrush="Black"> <TextBlock Text="{Binding Path=Weight}"/> </Border> </Grid> </DataTemplate> 的数据上下文将是当前的Binding项，它应该按预期工作。