获得一个项目的索引在一个ObservableCollection项目内 [英] Getting index of an item in an ObservableCollection inside the item

问题描述

我希望能够从一个DataTemplate中显示的索引值，但我的不要的数据被持久化或由模型视图模型或支持。换句话说，如果在所述OC变化的项目的顺序，不希望有重新计算的索引。该值应本质绑在OC标的指数。如果该指数是基于0（其实，我希望它），这是好的。

I'd like to be able to display an index value from within a DataTemplate, but I don't want the data to be persisted or backed by the model or viewmodel. In other words, if the order of the items in the OC changes, I don't want to have to recalculate the indexes. The value should be intrinsically tied to the underlying index in the OC. It is okay if the index is 0-based (in fact, I'd expect it).

这是其他人使用的一种方法是的 AlternationIndex AP，但这都有自己的缺陷对于某些情况下

One method that others have used is the AlternationIndex AP, but this has its own pitfalls for certain situations.

最后一个想法：我不禁想转换器将是一个最终的解决方案有帮助的。

One last thought: I can't help but think that a converter is going to be helpful in a final solution.

推荐答案

我会用一个转换器来做到这一点。

I would use a converter to do this.

诀窍是给它的源收集，无论是在 ConverterParameter 或依赖项属性。 。在这一点上，转换为使用的IndexOf 简单

The trick is giving it the source collection, either on the ConverterParameter or a Dependency Property. At that point, conversion is as simple as using IndexOf.

下面是一个示例转换器，做到这一点：

Here's a sample converter that does this:

public class ItemToIndexConverter : IValueConverter
{
    public object Convert(...)
    {
        CollectionViewSource itemSource = parameter as CollectionViewSource;
        IEnumerable<object> items = itemSource.Source as IEnumerable<object>;

        return items.IndexOf(value as object);
    }

    public object ConvertBack(...)
    {
        return Binding.DoNothing;
    }
}

您可以强类型的实现，则返回一个格式化字符串作为一个数等的基本格局将是如上虽然。

You can make the implementation strongly typed, return a formatted string as a number, etc. The basic pattern will be as above though.

这实现使用参数的方法，是把一个DP，在我看来较为凌乱。因为你不能绑定 ConverterParameter ，我把它设置为的静态资源的绑定到集合：

This implementation uses the parameter approach, as making a DP is more messy in my view. Because you can't bind ConverterParameter, I have it set to a static resource that is bound to the collection:

<CollectionViewSource x:Key="collectionSource" Source="{Binding Path=MyCollection}" />

...

<TextBlock Text="{Binding Converter={StaticResource ResourceKey=ItemToIndexConverter}, 
               ConverterParameter={StaticResource ResourceKey=collectionSource}}"/>

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