RadTreeViewItem unchecks automatically

[Adrian]

I have the folowing use of RadTreeView. I use Telerik_2012_3_1129

I bind RadTreeView hierarchically to ObservableCollection<FilterTreeNode>

public class FilterTreeNode : NotificationObject
{
  private ToggleState _checkState = ToggleState.On;
  protected ObservableCollection<FilterTreeNode> _children;

  public ToggleState CheckState
  {
     get { return _checkState; }
     set
     {
        if (_checkState != value)
        {
           _checkState = value;
           RaisePropertyChanged(()=>CheckState);
        }
     }
  }

  public ObservableCollection<FilterTreeNode> Children
  {
     get { return _children; }
     set
     {
        if (_children != value)
        {
           _children = value;
           RaisePropertyChanged(() => Children);
        }
     }
  }
}

For the RadTreeView ItemContainerStyle I use following style:

<Style x:Key="ItemContainerStyle" TargetType="telerik:RadTreeViewItem">
    <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
    <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
    <Setter Property="CheckState" Value="{Binding CheckState, Mode=TwoWay}" />
    <Setter Property="MinHeight" Value="0"></Setter>
</Style>

 Steps of usage:
 1. I initialize observable collection with few levels, eg. L1, L2, L3 (Items from level L1 are expanded by default). Item1 in L2 contains few items.
 2. I bind this observable collection to the tree. Everything is working correctly.
 3. After a while in separate thread I finds new element that I need to add to the Item1 (from the level L2) which wasn't expanded yet, but it have few items.
 4. I use Application.Current.Dispatcher.Invoke((Action) (AddRecordsFromQueue)) method to add these new elements to the tree in UI thread.
 5. I create FilterTreeNode class for the new element and by default this class have _checkState = ToggleState.On
 6. I add this new element to _children collection of element Item1
 7. AND THAN: suddenly Item1 is unchecked automatically in the tree :(
 
  I tried to investigate this and looked into the RadTreeViewItem code which is invoked in stack trace when its CheckState is changing to ToggleState.Off
 
 So what is happening:
1. MeassureOverride is invoked on RadTreeViewItem related to my Item1.
2. In MeasureOverride the method this.SetCheckStateWithNoPropagation(RadTreeViewItem.CalculateItemCheckState(this));
3. In CalculateItemCheckState the following code is invoked:

...

ToggleState state = ToggleState.Off;
if (item.Items.Count > 0)
{
    if (checkedCount == item.Items.Count)
    {
        state = ToggleState.On;
    }
    else if (checkedCount + indetermCount > 0)
    {
        state = ToggleState.Indeterminate;
    }
}
else
{
    state = item.CheckState;
}

return state;

5. Previous method probably returns ToggleState.Off and set in to the RadTreeViewItem
6. Via binding the CheckState in my Item1 is set to ToggleState.Off


First, the logic in the CalculateItemCheckState is interesting. Why Parent item gets CheckState set to ToggleState.Indeterminate when it contains at least 1 child in ToggleState.Indeterminate state? This is strange behaviour. I think some users (e.g. me) would like to have parent node checked no matter what are the states of its children.

Second, the most important is that before the CheckState in the Item1 was automatically set to ToggleState.Off there was no checking of the CheckState of the child items (I checked it by putting breakpoint in getter). So probably UI children of Item1 weren't created yet or they were created but wasn't binded yet to the underlying FilterTreeNode objects, so RadTreeViewItems had ToggleState.Indeterminate state before binding.
Probably children UI items wasn't created yet if parent wasn't expanded, so in that case the logic in section 3 should return the current CheckState of the item, but somehow it returns ToggleState.Off.

I also tested the case when I have Item1 expanded before this new element is added. In this case the CheckState of Item1 is automatically set to ToggleState.Indeterminate.



So, am I doing something wrong or it is a bug? What can I do to stop getting my tree nodes unchecked automatically? I think that if it is a bug not just my bad usage of this control than it is critical.

I think that this problem is also somehow related to these 2 problems:
http://www.telerik.com/community/forums/wpf/treeview/binding-to-checkstate.aspx
http://www.telerik.com/community/forums/wpf/treeview/databinding-for-checkstate.aspx


Regards,
Adrian

[Hristo]

Hello Adrian,

Thank you for reporting this issue. I have created a sample project and easily reproduced the issue just as you describe it. Also, I have logged an item in our public issue tracking system http://www.telerik.com/support/pits.aspx#/public/silverlight/15328 and increased your Telerik points.

I would like to recommend you to use a check box placed in the items' data template instead the built-in check box support. This way RadTreeView will not be able to set incorrect values and you could easily customize it to fit your needs. Actually, the built-in check box functionality of RadTreeView is quite inappropriate thus we advice our customers to use check boxes defined in the data template.

Please let us know if you need more info on the topic or the suggested approach does not fit your needs.

Regards,
Hristo
Telerik

[Adrian]

Thank you. With custom checkboxes everything works fine.

If built-in check box functionality of RadTreeView is inappropriate than in my opinion it would be better to remove build-in checkboxes in the next versions until it will be implemented correctly. This will stop the users to get confused.

Best regards,
Adrian

[Tina Stancheva]

Hello Adrian,

Thank you for your feedback. We will definitely consider it while further discussing how to proceed and better describe the specifics and limitations of the RadTreeView built-in CheckBox functionality.

Regards,
Tina Stancheva
Telerik

[Steve]

I agree, the checkbox functionality should be removed or marked obsolete. I have just wasted two hours trying to get it working with the CheckState binding as all of your examples point to using this functionality. The checkboxes do not work especially in tri state mode.

[Tina Stancheva]

Hello Steve,

Thank you for this feedback. We will discuss further how to proceed with the RadTreeView CheckBox functionality and will also make sure to update our support resources - documentation and sample projects, accordingly.

Regards,
Tina Stancheva
Telerik