将WPF绑定到由属性指定的数组的元素 [英] Binding in WPF to element of array specified by property

问题描述

说我在我的UI上有一些TextBlocks，如下所示：

 < StackPanel Orientation =Vertical > 
< TextBlock Text ={Binding DessertIndex}/> 
< TextBlock Text ={Binding Food [2]}/> 
< TextBlock Text ={Binding Food [{Binding DessertIndex}]}/> 
< / StackPanel> 
  

在我的代码背后我有这样的东西：

  public partial class MainWindow：Window 
 {
 public int DessertIndex 
 {
 get {return 2; } 
} 
 
 public object [] Food 
 {
 get 
 {
 return new object [] {liver，spam ，蛋糕，大蒜}; 
} 
} 
 
 public MainWindow（）
 {
 InitializeComponent（）; 
 DataContext = this; 
} 
} 
  

前两个TextBlock对我来说显示正常，显示2和蛋糕。第三个没有完成我想要的，即使用DessertIndex属性索引到该数组中，并显示cake。我在这里做了一个类似的问题，但没有找到一个。最终，我不想在.xaml文件中指定像2这样的值，并且希望依赖于一个属性，而不是索引到该数组中。这可能吗？如果是这样，我在这里做错什么？

---

编辑：

所以我更密切的是数据是这些对象的列表[]的情况，我使用上面的StackPanel作为ListBox的DataTemplate的一部分。所以，正如马克·希思（Mark Heath）在下面的建议，使用一个取消引用数组的属性看起来不像我想要的那样工作。想法？

解决方案

另一个替代方法是使用MultiBinding转换器：

 < Window x：Class =WpfApplication1.MainWindow
 xmlns =http://schemas.microsoft.com/winfx/2006/xaml/presentation
 xmlns：x =http://schemas.microsoft.com/winfx/2006/xaml
 xmlns：local =clr-namespace：WpfApplication1
 Title =MainWindowHeight = 350宽度=525> 
< StackPanel Orientation =Vertical> 
< StackPanel.Resources> 
< local：FoodIndexConverter x：Key =foodIndexConverter/> 
< /StackPanel.Resources> 
< TextBlock Text ={Binding DessertIndex}/> 
< TextBlock Text ={Binding Food [2]}/> 
< TextBlock> 
< TextBlock.Text> 
< MultiBinding Converter ={StaticResource foodIndexConverter}> 
< Binding Path =DessertIndex/> 
< Binding Path =食物/> 
< / MultiBinding> 
< /TextBlock.Text> 
< / TextBlock> 
< / StackPanel> 
< / Window> 
  

然后在代码隐藏中，转换器定义如下：

 命名空间WpfApplication1 
 {
 public class FoodIndexConverter：IMultiValueConverter 
 {
 public object Convert值，类型targetType，对象参数，System.Globalization.CultureInfo文化）
 {
 if（values == null || values.Length！= 2）
返回null; 
 
 int？ idx = values [0] as int？; 
 object [] food = values [1] as object []; 
 
 if（！idx.HasValue || food == null）
 return null; 
 
返回食物[idx.Value]; 
} 
 
 public object [] ConvertBack（object value，Type [] targetTypes，object parameter，System.Globalization.CultureInfo culture）
 {
 throw new NotImplementedException ）; 
} 
} 
} 
  

Say I've got some TextBlocks on my UI, something like so:

<StackPanel Orientation="Vertical">
    <TextBlock Text="{Binding DessertIndex}" />
    <TextBlock Text="{Binding Food[2]}" />
    <TextBlock Text="{Binding Food[{Binding DessertIndex}]}" />
</StackPanel>

and in my code behind I've got something like this:

public partial class MainWindow : Window
{
    public int DessertIndex
    {
        get { return 2; }
    }

    public object[] Food
    {
        get
        {
            return new object[]{"liver", "spam", "cake", "garlic" };
        }
    }

    public MainWindow()
    {
        InitializeComponent();
        DataContext = this;
    }
}

The first two TextBlocks display fine for me, displaying 2 and 'cake' respectively. The third one doesn't accomplish what I'd like, namely use the DessertIndex property to index into that array and also display 'cake'. I did a little searching here on SO for a similar question but didn't find one. Ultimately, I don't want to specify values like 2 in my .xaml file and would like to rely upon a property instead for indexing into that array. Is this possible? If so, what am I doing wrong here?

---

EDIT:

So what I more closely have is a situation where the data is a List of these object[] and I'm using the above StackPanel as part of a DataTemplate for a ListBox. So the idea, as Mark Heath suggests below, of using a property that dereferences the array doesn't seem to work as I'd want. Ideas?

解决方案

Another alternative is to use MultiBinding with a converter:

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="350" Width="525">
    <StackPanel Orientation="Vertical">
        <StackPanel.Resources>
            <local:FoodIndexConverter x:Key="foodIndexConverter" />
        </StackPanel.Resources>
        <TextBlock Text="{Binding DessertIndex}" />
        <TextBlock Text="{Binding Food[2]}" />
        <TextBlock>
                <TextBlock.Text>
                    <MultiBinding Converter="{StaticResource foodIndexConverter}">
                        <Binding Path="DessertIndex" />
                        <Binding Path="Food"/>
                    </MultiBinding>
                </TextBlock.Text>
        </TextBlock>
    </StackPanel>
</Window>

Then in the code-behind, the converter is defined something like this:

namespace WpfApplication1
{
    public class FoodIndexConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (values == null || values.Length != 2)
                return null;

            int? idx = values[0] as int?;
            object[] food = values[1] as object[];

            if (!idx.HasValue || food == null)
                return null;

            return food[idx.Value];
        }

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

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