c# - 转换器中的 WPF MultiBinding 失败 ==> DependencyProperty.UnsetValue

Question

我的代码在启动时失败，因为 Multibinding 调用的 Converter 中的值数组 未填充正确的值，但值为 DependencyProperty.UnsetValue。

看看 Convertor 并看看我在哪里出错

public class ButtonColorConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            string val1 = string.Format("  {0}  ", values[0]);
            string val2 = (string)values[1];  **//Here i am getting ==> {DependencyProperty.UnsetValue}** 
            return val1.Equals(val2)
                ? Brushes.NavajoWhite
                : Brushes.White;  
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

您可以下载full code或按照下面查看我的代码片段。

MainWindow.xaml

<Window x:Class="DataPager.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525"
        xmlns:Local="clr-namespace:DataPager.Convertor_For_BackGround">
    <Grid>
        <Grid.Resources>
            <Local:ButtonColorConverter x:Key="currentPageSetter"/>
        </Grid.Resources>
        <Grid.RowDefinitions>
            <RowDefinition Height="36*" />
            <RowDefinition Height="275*" />
        </Grid.RowDefinitions>
        <ItemsControl Name="pageControl" ItemsSource="{Binding Path=PageCollection}" Grid.Row="0">
            <ItemsControl.Template>
                <ControlTemplate TargetType="ItemsControl">
                    <Border >
                        <StackPanel>
                            <ItemsPresenter></ItemsPresenter>
                        </StackPanel>
                    </Border>
                </ControlTemplate>
            </ItemsControl.Template>
            <ItemsControl.ItemsPanel x:Uid="pageItemTemplate">
                <ItemsPanelTemplate>
                    <StackPanel Orientation="Horizontal"/>
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <Button x:Name="pageNumberButton" Margin="3,4" Content="{Binding Path=Page_Number}">
                        <Button.Background>
                            <MultiBinding Converter="{StaticResource currentPageSetter}">
                                <Binding Path="Page_Number" />
                                <Binding Path="CurrentPage.Page_Number" /> **//This Binding not resolves properly**
                            </MultiBinding>
                        </Button.Background>
                    </Button>
                </DataTemplate>
            </ItemsControl.ItemTemplate>

        </ItemsControl>
        <TextBox Text="{Binding Path=CurrentPage.Page_Number,Mode=TwoWay, FallbackValue=asdf}" Grid.Row="1" Height="23"  Margin="79,62,257,0" Name="textBox1" VerticalAlignment="Top" Width="167" />
    </Grid>
</Window>

MainWindow.xaml.cs

 public partial class MainWindow : Window
    {
        public MainWindow()
        {


            MyPageViewModel = new PageViewModel();

            MyPageViewModel.PageCollection.Add(new PageNumberViewModel(string.Format("  {0}  ",0)));
            MyPageViewModel.PageCollection.Add(new PageNumberViewModel(string.Format("  {0}  ",1)));
            MyPageViewModel.PageCollection.Add(new PageNumberViewModel(string.Format("  {0}  ",2)));
            MyPageViewModel.PageCollection.Add(new PageNumberViewModel(string.Format("  {0}  ",3)));

            InitializeComponent();
        }

        public PageViewModel MyPageViewModel
        {
            get
            {
                return this.DataContext as PageViewModel;
            }
            set
            {
                this.DataContext = value;
            }
        }
    }

这是 ViewModel 类。

PageViewModel.cs

public class PageViewModel:ViewModelBase
    {
        private ObservableCollection<PageNumberViewModel> m_pageCollection = new ObservableCollection<PageNumberViewModel>();
        private PageNumberViewModel m_currentPage = new PageNumberViewModel(string.Format("  {0}  ",0));

        public PageViewModel()
        {
            m_currentPage = new PageNumberViewModel(string.Format("  {0}  ", 1000));
        }

        public PageNumberViewModel CurrentPage 
        {
            get
            {
                return this.m_currentPage;
            }
            set
            {
                if (m_currentPage == value)
                    return;
                this.m_currentPage = value;
                base.OnPropertyChanged("CurrentPage");
            }
        }
        public ObservableCollection<PageNumberViewModel> PageCollection
        {
            get
            {
                return this.m_pageCollection;
            }
            set
            {
                if (m_pageCollection == value)
                    return;
                this.m_pageCollection = value;
                base.OnPropertyChanged("PageCollection");
            }
        }
    }

PageNumberViewModel.cs

public class PageNumberViewModel : ViewModelBase
    {
        private string m_pageNumber;

        public PageNumberViewModel()              
        {

        }
        public PageNumberViewModel(string pageNumgerArg)
        {
            this.m_pageNumber = pageNumgerArg;
        }

        public string Page_Number
        {
            get { return m_pageNumber; }
            set
            {
                if (m_pageNumber == value)
                    return;
                m_pageNumber = value;
                OnPropertyChanged("PageNumber");
            }
        }

    }

Answer 1

当您在任何 ItemsSource 中设置列​​表时，DataTemplate 的各个项目的 DataContext 将是列表中的每个项目。

的确，您的 TextBlock 绑定(bind)工作正常，因为 DataContext 设置为您的主要对象:PageViewModel

但在您的 DataTemplate 中，DataContext 将设置为 PageNumberViewModel，因为这些是您集合中的项目。

因此，绑定(bind)到 Path=CurrentPage.Page_Number 将导致 UnsetValue，因为 CurrentPage 不是 PageNumberViewModel 的属性

希望这能澄清事情!

如果您确实希望绑定(bind)到窗口 DataContext 的 CurrentPage 属性，请考虑使用 ElementName 绑定(bind):

给窗口一个名字，绑定(bind)到

<Binding ElementName="name" Path="DataContext.CurrentPage.Page_Number" />

或使用 RelativeSource 绑定(bind):

<Binding RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}" Path="DataContext.CurrentPage.Page_Number" />