WPF binding to child collection
I have the following objects:
public class User
{
public User()
{
Roles = new ObservableCollection<Role>();
}
public int UserId { get; set; }
public string Name { get; set; }
public DateTime DateOfBirth { get; set; }
public virtual ICollection<Role> Roles { get; set; }
}
public class Role
{
public int RoleId { get; set; }
public string Name { get; set; }
public virtual User User { get; set; }
}
With this ViewModel:
public class UserManagerViewModel : ObservableObject
{
public ObservableCollection<Role> AllRoles { get; set; }
public UserViewModel()
{
AllRoles = new ObservableCollection<Role>(RoleRepository.GetAll());
}
private User _selectedUser;
public User SelectedUser
{
get { return _selectedUser; }
set
{
if (_selectedUser != value)
{
_selectedUser = value;
RaisePropertyChanged();
}
}
}
...
}
I want to show roles SelectedUser
like this (or something similar):
<Window.DataContext>
<vm:UserManagerViewModel/>
</Window.DataContext>
<ListBox ItemsSource="{Binding AllRoles}">
<ListBox.ItemTemplate>
<DataTemplate>
<CheckBox Content="{Binding Name}" IsChecked="{Binding ???}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Why do I need to set a property IsChecked
to CheckBox
represent roles SelectedUser
?
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Assuming you want to "check" the roles it SelectedUser
has.
First we answer the question: "What data does it depend on?" The answer is quite simple, it depends on the role itself, so we write:
<CheckBox Content="{Binding Name}" IsChecked="{Binding .}"/>
It is now clear that this is not a bool; so we will need to write a converter for it that checks the collection. We could do a MultiValueConverter here (as in @Moji's answer), but it's probably easier to expose the collection via the Dependency Property and bind when creating the converter.
<Window.Resources>
<local:CollectionContainsConverter Collection="{Binding SelectedUser.Roles}"/>
</Window.Resources>
<CheckBox Content="{Binding Name}" IsChecked="{Binding Path=., Converter={StaticResource CollectionContainsConverter}"/>
And the converter:
public class CollectionContainsConverter : IValueConverter
{
public IEnumerable<object> Collection { get; set; } //This is actually a DP
public object Convert(...)
{
return Collection.Contains(value);
// or possibly, to allow for the Object.Equals override
return Collection.Any(o => o.Equals(value));
}
public object ConvertBack(...)
{
return Binding.DoNothing;
}
}
Without testing this, you might need to use a second return so that it doesn't compare references and use Object.Equals
(or another comparator of your choice) to figure out if the item is in the list.
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you can use MultipleBinding and MultipleValueVonverter as below
<Grid>
<Grid.Resources>
<local:RoleValueConverter x:Key="converter"></local:RoleValueConverter>
</Grid.Resources>
<ListBox ItemsSource="{Binding AllRoles}" >
<ListBox.ItemTemplate>
<DataTemplate>
<CheckBox Content="{Binding Name}" >
<CheckBox.IsChecked>
<MultiBinding Converter="{StaticResource converter}">
<Binding Path="."></Binding>
<Binding RelativeSource="{RelativeSource AncestorType={x:Type ListBox}}" Path="DataContext"></Binding>
</MultiBinding>
</CheckBox.IsChecked>
</CheckBox>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</Grid>
public class RoleValueConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
//values[0] is Role object
//value[1] is UserManagerViewModel
// then you can see if Selected user had Role object return true else return false
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
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