usage of observableCollection in longlistselector - windows-phone-7

Question

I am using the _wordItems as the longlistselector's itemsource in order to dynamically delete items in longlistSelector
private ObservableCollection<Group<WordItem>> _wordItems = new ObservableCollection<Group<WordItem>>();
The Group class is defined as:
public class Group<T> : ObservableCollection<T>
{
public Group(string name, IEnumerable<T> items)
{
this.Key = name;
foreach (T item in items)
{
this.Add(item);
}
}
public override bool Equals(object obj)
{
Group<T> that = obj as Group<T>;
return (that != null) && (this.Key.Equals(that.Key));
}
public string Key
{
get;
set;
}
}
and the WordItem class is defined as:
[Table]
public class WordItem //:INotifyPropertyChanged,INotifyPropertyChanging
{
private int _wordItemId;
[Column(IsPrimaryKey = true, IsDbGenerated = true, DbType = "INT NOT NULL Identity", CanBeNull = false, AutoSync = AutoSync.OnInsert)]
public int WordItemId
{
get
{
return _wordItemId;
}
set
{
if (_wordItemId != value)
{
_wordItemId = value;
}
}
}
private string _word;
[Column(CanBeNull=false)]
public string Word
{
get
{
return _word;
}
set
{
if (_word != value)
{
_word = value;
}
}
}
private string _wordExplains;
[Column]
public string WordExplains
{
get
{
return _wordExplains;
}
set
{
if (_wordExplains != value)
{
_wordExplains = value;
}
}
}
}
when I use the code _wordItems[1].RemoveAt(1);, the _wordItems has been modified, and the longlistselector in the screen has also deleted certain item. But the problem is that when I call _wordItems[1].RemoveAt(1);, the longlistselector just deleted the _wordItems[1][0] item. When I call _wordItems[1].RemoveAt(0);, it just deleted the header of the second group and combined the items in _worditems[1] with the _wordItem[0].
The definition of longlistselector:
<toolkit:LongListSelector x:Name="WordsGroup" Background="Transparent"
Margin="12,0,12,73" ItemTemplate="{StaticResource WordItemTemplate}"
GroupHeaderTemplate="{StaticResource YoudaoGroupHeaderTemplate}"
GroupItemTemplate="{StaticResource YoudaoGroupItemTemplate}"
SelectionChanged="WordsGroup_SelectionChanged"
>
<toolkit:LongListSelector.GroupItemsPanel>
<ItemsPanelTemplate>
<toolkit:WrapPanel/>
</ItemsPanelTemplate>
</toolkit:LongListSelector.GroupItemsPanel>
</toolkit:LongListSelector>
The datatemplate is as:
<DataTemplate x:Key="WordItemTemplate">
<Border BorderBrush="Gray" BorderThickness="0,0,0,0" Margin="0,3,0,5">
<StackPanel >
<toolkit:ContextMenuService.ContextMenu>
<toolkit:ContextMenu Opened="ContextMenu_Opened" >
<toolkit:MenuItem Header="delete this word" Click="DelectWord_Click"/>
<toolkit:MenuItem Header="share this word" Click="SMSShare_Click"/>
</toolkit:ContextMenu>
</toolkit:ContextMenuService.ContextMenu>
<TextBlock Text="{Binding WordItemId}" Style="{StaticResource PhoneTextNormalStyle}" Visibility="Collapsed"/>
<TextBlock Text="{Binding Word}" Style="{StaticResource PhoneTextNormalStyle}" FontSize="25" Foreground="Black" FontWeight="Bold"/>
<TextBlock Text="{Binding WordExplains}" Style="{StaticResource PhoneTextNormalStyle}" Foreground="Black" TextWrapping="Wrap"/>
</StackPanel>
</Border>
</DataTemplate>
<DataTemplate x:Key="YoudaoGroupHeaderTemplate">
<Border Background="#1BA1E2" Margin="0">
<TextBlock Text="{Binding Key}" FontSize="30" Margin="12,0,0,0" Foreground="Black" />
</Border>
</DataTemplate>
<DataTemplate x:Key="YoudaoGroupItemTemplate" >
<Border Background="#1BA1E2" Width="99" Height="99" Margin="6">
<TextBlock Text="{Binding Key}" VerticalAlignment="Center" HorizontalAlignment="Center" FontSize="40" Foreground="{StaticResource PhoneForegroundBrush}"/>
</Border>
</DataTemplate>
Thx in advance.
ps. I am using the linq as
var wordBy4sLetter = from word in wordList
group word by word.Word.ToCharArray()[0].ToString() into s
orderby s.Key
select new Group<WordItem>(s.Key, s);
this._wordItems = wordBy4sLetter.ToObservableCollection();
this.WordsGroup.ItemsSource = this._wordItems;

Answer 1

I think you need another ObservableCollection. Take a look at the accepted answer for this question. Group Listbox for Windows Phone 7?
I have modified the code there and created new Add/Remove methods that will create a group if not there for an add, and remove the group if it's empty on a remove.