Getting at the “parent” of a databound object?

问题:

I have an object with two arrays of strings. The object is data bound to a listbox. One list is bound as the list's ItemsSource. The other, which is the thing causing me trouble, needs to be bound to a combobox that's part of a DataTemplate that is set to the list's ItemTemplate. Basically each item on the listbox has the corresponding element of the first list and a combo box that contains the second list. In other words, every item in the list has the same combobox of choices.

The problem comes from the fact that it winds up that the DataTemplate is data bound the first list. I was expecting the DataTemplate to be databound to the object that contains both lists. Now, with that happening, I can't figure out what kind of binding syntax I need to get at the "parent" of the DataContext, if that's even possible.

Can someone point me in the right direction?

Thanks!

回答1:

If I'm understanding you correctly, you can set the DataContext of your ListBox to an instance of a class (in my example I do it in code by: list.DataContext = myclass;) and you want to set the ItemSource of your listbox to a list in the class (ie Items) and the itemssource of your combobox to another list in the class (ie Values). Here's my xaml that seems to work:

<ListBox Name="list" ItemsSource="{Binding Items}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <StackPanel>
                <TextBlock Text="{Binding}"/>
                <ComboBox ItemsSource=
                          "{Binding RelativeSource={RelativeSource FindAncestor, 
                                                    AncestorType={x:Type ListBox}}, 
                                    Path=DataContext.Values}"
                />
            </StackPanel>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

and heres the class that I'm binding to:

public class AClass
{

    protected List<string> _Items;
    public List<string> Items
    {
        get
        {
            if (_Items == null)
            {
                _Items = new List<string>();
            }
            return _Items;
        }
    }


    protected List<string> _Values;
    public List<string> Values
    {
        get
        {
            if (_Values == null)
            {
                _Values = new List<string>();
            }
            return _Values;
        }
    }
}

In code I created an instance of AClass, added Items and Values, and set the instance to the DataContext of the listbox.

回答2:

I don't think you want to do what you are trying to do. You are asking for the pain.

What you'd likely want to do instead is reference a static collection inside each item in your collection that contains the subcollection for your ComboBox. So:

//Pseudocode
TopLevelEntity
{
     SubLevelEntity[] SubItemsForComboBox;
}

This way for each "TopLevelEntity" you'd be prepared with your collection of items for the combo box.

<ListView ItemsSource="{StaticResource MyCollectionOfTopLevelEntities}">
    <ItemTemplate>
        <DataTemplate>
            <ComboBox ItemsSource="{Binding SubItemsForComboBox} />
        </DataTemplate>
    </ItemTemplate>
</ListView>

As is my way, I've not verified this code and it's possible it doesn't even compile, but the theory should be sound.

Let us know what you decide to do.

回答3:

First of all as Anderson suggests I would suggest you to re-design your classes to get Combobox items from some where outside as statically referenced list But here is a workaround for your current scenario. I am assuming that your Main Object of interest('Parent') is the DataContext of the ListBox. which you wanted to reference inside the DataTemplateLevel. Idea is to walk up to the ListBox and get the DataContext

 <Combobox DataContext="{Binding DataContext, RelativeSource={RelativeSource AncestorType={x:Type ListBox}}}" ItemsSource="{Binding YourCollection}" ....