ObservableCollection - Clear has no Result in UI

6 replies. Latest Post by jroedig on May 27, 2009.

(0)

jroedig

Member

1 points

4 Posts

ObservableCollection - Clear has no Result in UI

05-27-2009 9:31 AM |

Hello,

I have a ObservableCollection _userlist with User Data (Firstname, Lastename)...

This ObservableCollection is bound to an ListBox

If I click a Button, the _userlist.Clear Method clears the Collection. But in the User Interface the data are not cleared.

Can me anyone help?

 1    // resultlist of userliste for databinding
2            private ObservableCollection _userlist = new ObservableCollection();
3            
4           void usersearch_UserSearchLoadingComplete(object sender, Silverlight.Model.EventArguments.UserSearchLoadingEventArgs e)
5            {
6                // clear old results
7                _userlist.Clear();
8               
9                // For each User in new Result collection add in _userlist
10               foreach (User u in e.Results)
11               {
12                   // add result user item
13                   _userlist.Add(u);                   
14               }
15            
16               // fire the event to notify UI
17               UserSearchLoadingComplet(this, null);
18   
19           }
20         
21   
22   
23   
24           public ObservableCollection UserResultlist
25           {         
26               get
27               {
28                   return _userlist;
29               }
30           }

<UserControl.Resources>
        <vm:ViewModel x:Key="ViewModel"></vm:ViewModel>
    </UserControl.Resources>

    <Grid x:Name="LayoutRoot" DataContext="{Binding Source={StaticResource ViewModel}}">
       <Grid.RowDefinitions>
           <RowDefinition Height="0.106*"/>
           <RowDefinition Height="0.894*"/>
       </Grid.RowDefinitions>

        <ListBox Margin="15,15,15,15" Name="ListBoxUser" ItemsSource="{Binding Path=UserResultlist}" Grid.RowSpan="1" Grid.Row="1">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Path=Firstname}"></TextBlock>
                </DataTemplate>
            </ListBox.ItemTemplate>

        </ListBox>
        <Button HorizontalAlignment="Center" Margin="0,0,0,0" Content="Button" x:Name="UserButton" Click="UserButton_Click"/>

jay nana...

Contributor

3388 points

624 Posts

Re: ObservableCollection - Clear has no Result in UI

05-27-2009 9:56 AM |

Hi, try to do two way databinding for the ListBox.

Jay K Nanavaty
www.technologyopinion.com
Mark as answer if it helps. It will also help others...

jroedig

Member

1 points

4 Posts

Re: ObservableCollection - Clear has no Result in UI

05-27-2009 10:05 AM |

jay nanavati:
Hi, try to do two way databinding for the ListBox.

Hey,

TwoWay Mode has no other result.

_userlist.Clear(); clears the collection. but in the listbox the items already existing. the Clear() Method clears not the listbox items...

EliteMike

Member

65 points

25 Posts

Re: ObservableCollection - Clear has no Result in UI

05-27-2009 10:09 AM |

it almost seems like the binding is breaking somewhere. You aren't setting the itemsource to anything in code behind are you? One way binding is all you need for this as well.

jroedig

Member

1 points

4 Posts

Re: ObservableCollection - Clear has no Result in UI

05-27-2009 10:19 AM |

no, the itemsource is one time set in xaml code...

the binding works on line 13 _userlist.Add(...). If the add method is called, the useritem is shown in the listbox.

on line 7 the Clear has no result in the listbox

MarkTap

Participant

1442 points

263 Posts

Re: ObservableCollection - Clear has no Result in UI

05-27-2009 10:33 AM |

I was not able to reproduce your issue with a simplified example. Below is my code that seems to work as desired: when the button is clicked, the contents of the list box disappear. Which ObservableCollection are you using? The one I use is a generic which doesn't match your code.

---Page.xaml---

----Page.xaml.cs----

    public partial class Page : UserControl
    {
        ObservableCollection<UserData> _userData;

        public Page()
        {
            InitializeComponent();

            _userData = new ObservableCollection<UserData>();

            _userData.Add(new UserData() { Firstname = "f1", Lastname = "l1" });
            _userData.Add(new UserData() { Firstname = "f2", Lastname = "l2" });
            _userData.Add(new UserData() { Firstname = "f3", Lastname = "l3" });

            DataContext = _userData;
        }

        private void UserButton_Click(object sender, RoutedEventArgs e)
        {
            _userData.Clear();
        }
    }

    public class UserData
    {
        public string Firstname { get; set; }
        public string Lastname { get; set; }
    }