Question

I have a ViewModel:

public class VM
{
    public ObservableCollction<PersonRole> PersonRoles { get; private set; }
}

public class PersonRole
{
    public int RoleID { get; set; }
    //..
}

In View I have to display three ListBoxes:

• all persons with RoleID == 1
• all persons with RoleID == 2
• all persons with RoleID == 3

How it’s better to do?

• Create 3 properties in ViewModel with filtering:

  Roles1 = CollectionViewSource.GetDefaultView(PersonRoles);
Roles1.Filter = o => ((PersonRole)o).RoleID == 1;

• Some possibilities to do this in XAML? How?

• More options?

Answer 1

Depending on how often you expect the data in the list to change, I would probably go with ICollectionView instances as you suggest. You won’t be able to use CollectionViewSource.GetDefaultView for 3 separate properties, however, as it will return the same object instance every time. Instead, you’ll need to explicitly create new ICollectionViews:

this.Property1 = new ListCollectionView(this.PersonRoles);
this.Property2 = new ListCollectionView(this.PersonRoles);
this.Property3 = new ListCollectionView(this.PersonRoles);
// then set up filters

Alternatively, if the data in the list is only going to change very rarely, it might be better to do the filtering using LINQ when you actually populate the list and actually store 3 collections:

this.Property1 = new ObservableCollection<PersonRole>(dataSource.Where(o => o.RoleID=1);
this.Property2 = new ObservableCollection<PersonRole>(dataSource.Where(o => o.RoleID=2);
//etc

This approach is not particularly good if you expect items to be added to and removed from the overall list with any regularity though, as it will mean that you need to manually keep all 3 lists syncronised all the time.

As a final comment, you can set up collection views in XAML but you will not be able to filter them without some form of code behind.