Prefixing ListBoxItem index in DataTemplate

Dominick Marciano

I have a class called Steps and one of the properties is called Text (but it has several others as well). When a user types text in a text box (called txtText) and click the button (called btnAddEntry), and new Steps class is created and added to the list box. My issue is how to format the entries in the list box. I would like the list box to show the value of the Text property of the Step just added, but I would also like the index of the item just added to be prefixed to the text. The XAML for me list box is:

So if I type the entries "First Item", "Second Item", "Third Item" into txtText and click the btnAddEntry the list box will show

First Item
Second Item
Third Item

However I want the list box to show:

1. First Item
2. Second Item
3. Third Item

I've attempted this by modifying the ListBox.ItemTemplate in various ways, but just can't seem to figure it out. I have tried things like the following:

As well as using RelativeSource to Self, but I can never get the list box item to prefix it's index within the list box. I really want this down in XAML because there are buttons to move items up and down the list box after they are added (so the user can reorder items instead of deleting them and re-entering them) and if I using bindings in the item template, these numbers should auto-update. Any help with this will is greatly appreciated. Thanks in advance for any help.

A black hole is where God tried to divide by zero. There are 10 kinds of people in the world; those who understand binary and those who don't.

SledgeHammer01

You did not include an ItemsSource in your XAML, so I'm hoping you just left it out (although you included other stuff)? Please tell me you aren't manually creating ListViewItems and inserting those :). Anyways, assuming you are doing it "the right way" and using an ObservableCollection as your ItemsSource, I would write a MultiConverter that takes the ItemsSource and the item itself and returns the index of the item + 1. Then in your XAML, you would just use StringFormat with a multi-binding to format '{0}. {1}' on a single label.

Dominick Marciano

I am not creating ListViewItems and inserting those. I'm creating new instances of the Steps class and inserting those. The Steps class as a property called Text which is what I want displayed in the list box which is why I'm binding to (). However I wanted the index number prefixed to it, so I was hoping there was some XAML multi-binding expression to add it, without creating an ObservableCollection. However, if I'm understanding you correctly your saying that I should binding the list box to an ObservableCollection, and when a user clicks btnAddEntry the new Steps instance is added to the ObservableCollection, and use the MultiConverter to present the data for the XAML multi-binding expression?

A black hole is where God tried to divide by zero. There are 10 kinds of people in the world; those who understand binary and those who don't.

SledgeHammer01

Well ListViewItem / Potato. I meant that you are inserting stuff into the Items (type ItemCollection) rather then a bound collection. Which it sounds like you are. ItemCollection doesn't have an IndexOf method while pretty much every other list collection does. Doesn't have to be an ObservableCollection, but since you have an add / delete / move-up / move-down. I don't know why you wouldn't use ObservableCollection. It does half the work for you. If you are writing WPF code, it would SERIOUSLY behoove you to get into the habit of NOT operating on the controls themselves and operating on bound objects. That's what WPF was intended for and you can take advantage of a lot of features that you can't take advantage of when operating on the controls themselves. EDIT: Almost forgot to answer your question lol... Yes. Your label would use StringFormat on a multi-binding expression (expression 1 would be the return from your MultiValueConverter and expression 2 would be Path=Text). The MultiValueConverter would be Path=ItemsSource and {Binding} (which is the item itself). The MultiValueConverter would return ((ObservableCollection)values[0]).IndexOf(values[1]) + 1;