Convertor中的WPF MultiBinding失败==>DependencyProperty.UnsetValue [英] WPF MultiBinding in Convertor fails ==> DependencyProperty.UnsetValue
问题描述
我的代码在启动时失败，因为 Multibinding 调用的 Converter 中的values数组未填充正确的值，但具有 DependencyProperty.UnsetValue .
My code fails at at startup because the values array in the Converter that is called by the Multibinding is not filled with proper value but have a value of DependencyProperty.UnsetValue.
看看Convertor，看看我哪里出错了
have a look at Convertor and also see where i getting error
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();
}
}
您可以下载完整代码或请参阅下面的代码段.
You can download full code or see my codes snippet as per below.
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");
}
}
}
推荐答案
在任何ItemsSource中设置一个列表时，单个项目的DataTemplate的DataContext将成为列表中的每个项目.
When you set a list in any ItemsSource, the DataTemplate's DataContext for the individual items will each item of the list.
由于您的DataContext设置为您的主要对象，因此您的TextBlock绑定正确工作: PageViewModel
True that your TextBlock binding is working correctly, because the DataContext is set to your main object: PageViewModel
但是在您的DataTemplate中，DataContext将设置为 PageNumberViewModel ，因为这些是您集合中的项.
But in your DataTemplate the DataContext will be set to PageNumberViewModel, since these are the items in your collection.
因此，绑定到 Path = CurrentPage.Page_Number 的结果将是UnsetValue，因为CurrentPage不是 PageNumberViewModel
Therefor, the binding to Path=CurrentPage.Page_Number will result to UnsetValue, because CurrentPage is not a property of PageNumberViewModel
希望这可以澄清一切！
如果您确实希望绑定到Window的DataContext的CurrentPage属性，请考虑使用ElementName绑定:
If you truly wish to bind to the CurrentPage property of your Window's DataContext, consider using an ElementName binding:
给窗口命名，绑定到
<Binding ElementName="name" Path="DataContext.CurrentPage.Page_Number" />
或使用RelativeSource绑定:
or use a RelativeSource binding:
<Binding RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}" Path="DataContext.CurrentPage.Page_Number" />
这篇关于Convertor中的WPF MultiBinding失败==>DependencyProperty.UnsetValue的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
