Question

Is that even possible? I have two ObservableCollections. I want to bind and populate a listbox with one of them. For example let’s say that we have 2 buttons – one for Twitter and one for Facebook. Clicking on a Facebook button it will populate listbox with friend’s names from facebook observable collection and it will bind it. Clicking on Twitter it will populate listbox with Twitter followers and populate listbox and bind it.

How to choose which collection will be populated in listbox?

Answer 1

I would just use one observable collection and fill based on the users choice. You could also fill it with the names from both sources and have a filter to filter out one or the other (apparently you need a wrapper object where you can indicate whether the name is a facebook friend or twitter follower).

Edit: Here is some quick code example of how you can do it:

public interface ISocialContact
{
    string Name { get; }
}

public class FacebookContact : ISocialContact
{
    public string Name { get; set; }
    public string FacebookPage { get; set; }
}

public class TwitterContact : ISocialContact
{
    public string Name { get; set; }
    public string TwitterAccount { get; set; }
}

Then in your data context:

public ObservableCollection<ISocialContact> Contacts { get; set; }

...

Contacts = new ObservableCollection<ISocialContact> {
                    new FacebookContact { Name = "Face", FacebookPage = "book" },
                    new TwitterContact { Name = "Twit", TwitterAccount = "ter" } 
           };

And in your xaml:

<Grid>
    <Grid.Resources>
        <DataTemplate DataType="{x:Type local:FacebookContact}">
            <TextBlock Text="{Binding FacebookPage}"/>
        </DataTemplate>
        <DataTemplate DataType="{x:Type local:TwitterContact}">
            <TextBlock Text="{Binding TwitterAccount}"/>
        </DataTemplate>
    </Grid.Resources>
    <ListBox ItemsSource="{Binding Contacts}" Width="100" Height="100"/>
</Grid>

This will apply the appropriate template to each object in your collection. So you can have collection with just facebook contacts or just twitter contacts or mixed.

Also note: You do not need the common interface. It will also work if you just make your ObservableCollection of type object. But given that they are being displayed by the same app in the same list box indicates that you can find some kind of common base and either can create a comon interface or base class.