Pass index value to collection in XAML binding expression

Question

I am coding in Visual Studio 2017 and using Xamarin.Forms.

I can bind the "Text" properties of labels and buttons to strings, use INotifyPropertyChanged and also implement the Command interface for my buttons, cool, it all works fine and dandy.

I have a collection in my ViewModel which is essentially a class referenced by my View which is a XAML page.

What I am trying to do now is Bind a label to a specific index of my collection of strings.

So I have this in the VM (c# class)

public List<string> MessageCollection;

And this in the View (XAML Content page)

<Label Text="{Binding MessageCollection}"/>

I have googled for a while and checked other questions here on Stack-O but have not found a definitive answer to my question.

What I want to do is something like this:

<Label Text="{Binding MessageCollection[0]}"/>

or

<Label Text="{Binding MessageCollection, Index="0"}"/>

proceeding with

<Label Text="{Binding MessageCollection[0]}"/>
<Label Text="{Binding MessageCollection[1]}"/>
<Label Text="{Binding MessageCollection[2]}"/>

and so on.

The List will be modified at runtime as users can add and remove strings and edit the content of those strings via buttons and entryfields.

What is a good way to reference the collection by index in a binding expression?

Bind a repeating element, eg an ItemsControl to the list instead and add `` in the ItemTemplate [as shown here](https://stackoverflow.com/questions/9391746/how-can-i-data-bind-a-list-of-strings-to-a-listbox-in-wpf-wp7) and [here](https://stackoverflow.com/questions/7688368/wpf-repeating-elements) — Panagiotis Kanavos, Oct 04 '18 at 12:51
Thanks, those examples are for WPF but adapting them to Xamarin.Forms was not that difficult. - I am still working on the solution. — Alex J, Oct 06 '18 at 07:32
XAML ix XAML, no matter what the stack underneath is. There may be differences in features or binding syntax but the concepts are the same - Itemcontrols, composition, data binding — Panagiotis Kanavos, Oct 08 '18 at 07:05
Yes, quite right you are! Thanks for stating it in a such clear manner. Very helpful. — Alex J, Oct 09 '18 at 13:28

score 1 · Answer 1 · answered Dec 09 '20 at 12:48

Try using converter as below...

public class ListToFirstObjectGetter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value is System.Collections.IList list)
            {
                return list[0];
            }
            return null;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

score 0 · Answer 2 · answered Oct 04 '18 at 13:34

0

This syntax should work

<Label Text="{Binding MessageCollection[0]}"/>

However, you can only bind to public properties, so you need to declare MessageCollection with a getter

public List<string> MessageCollection { get; set; }

answered Oct 04 '18 at 13:34

Jason

86,222
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Thanks I will go and try this and come post my results for future reference. – Alex J Oct 06 '18 at 07:33

score 0 · Answer 3 · answered Oct 05 '18 at 07:02

0

you can try in the following formate.

Sample code

List<string> messageCollection;
string message = string.empty;
message = messageCollection.indexOf(your specific index no);

From the above code, you can retrieve the specific string from your message collection. now you can bind 'message' string to your view.

answered Oct 05 '18 at 07:02

sahithi

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Thanks will try it and come post my results. – Alex J Oct 06 '18 at 07:32

Pass index value to collection in XAML binding expression

3 Answers3