recursive loading data when scrolling (virtualCollection)

[nidhal ben hamadou]

Hi,
I use a VirtualCollection binded to a RadGridView (Version 2015.1.225.45    framework 4.5.1 ) 
My scenario is : when i click on the button move last  VirtualCollectionPays.MoveCurrentToLast(); the scrollbar of gridview move to last position and when i click on the button move fist  VirtualCollectionPays.MoveCurrentToFirst(); the scrollbar of gridview move to fist position .

Error :  when i move to the last and come back to first position the loading event in virtual collection make a recursive call and load all Items in the database .
I use a plain wcf services  not rest nether data services .
i use an async methode in the loading event .

public async void LoadData()
       {
           VirtualCollectionPays = new VirtualQueryableCollectionViewExtended<Pay>() { LoadSize = SizePage };
           VirtualCollectionPays.ItemsLoading += VirtualCollectionPays_ItemsLoading;

           PayDataPage datapager = null;

           var slowTask = Task.Run(() =>
           {
               datapager = _dataProvider.GetQueryableLazyPay(SizePage, position, PayFilterDescriptor, PaySortDescriptor, PayGroupDescriptor);
           });

           await slowTask;

           VirtualCollectionPays.VirtualItemCount = datapager.TotalCount;
           VirtualCollectionPays.Load(0, datapager.DataItems);
       }

// ItemsLoading 

async void VirtualCollectionPays_ItemsLoading(object sender, VirtualQueryableCollectionViewItemsLoadingEventArgs e)
        {

            BusyIndicatorGrid = true;
            try
            {
                PayDataPage datapager = null;
                ItemsLoading = Task.Run(() =>
                {
                    datapager = _dataProvider.GetQueryableLazyPay(SizePage, e.StartIndex, PayFilterDescriptor, PaySortDescriptor, PayGroupDescriptor);
                });

                await ItemsLoading;

                VirtualCollectionPays.Load(e.StartIndex, datapager.DataItems);

                BusyIndicatorGrid = false;
            }
            catch (Exception ex)
            {
                string mg = ex.Message;
            }

        }

when selected change of gridView the scrollbar change position 

void radGridViewPay_SelectionChanged(object sender, SelectionChangeEventArgs e)
       {
           var VMListePay = this.DataContext as VMListePay;
           radGridViewPay.ScrollIndexIntoView(VMListePay.VirtualCollectionPays.CurrentPosition);

       }

same problem when i change SelectionChanged (radGridView) with PropertyChanged (VirtualCollection)

void VirtualCollectionPays_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
       {
           var VMListePay = this.DataContext as VMListePay;
           if (e.PropertyName == "CurrentPosition")
           {
               if (VMListePay.VirtualCollectionPays.CurrentPosition >= 0)
               {
                   radGridViewPay.ScrollIndexIntoView(VMListePay.VirtualCollectionPays.CurrentPosition);
               }

           }
       }

[nidhal ben hamadou]

hi ,
Any reply please for this exception

[Dimitrina]

Hi,

This seems to be incorporated with the design of the virtual collection as when you scroll upwards there may be less items needed to be loaded, for example in some cases - only 1. The virtual collection is designed like so in order to have smooth scrolling performance and ensure all requested items are actually loaded into view. 
In case you believe this can be improved, would it be possible for you to isolate the exact case in a demo project illustrating it? You can take a look at this blog post for a reference on how to isolate an issue. That way I can debug it with the source code to confirm whether we may consider it as a bug. 

Regards,
Dimitrina
Telerik

 

 

[nidhal ben hamadou]

hi ,
when i move to the last and come back to first position the loading event in virtual collection make a recursive call and load all Items in the database .
I use a plain wcf services  not rest nether data services but i simulated it with the function GetPays.

I can't attach project so here is the link :
https://drive.google.com/file/d/0B_U5cj9rv7d0cy1wc2VibWZTYmM/view?usp=sharing

[Dimitrina]

Hi,

Thank you for isolating the problem in a sample project. I was able to reproduce the issue and I am going to investigate the case further.

Regards,
Dimitrina
Telerik

 

 

[nidhal ben hamadou]

hi ,
same problem when i do gridView.SelectAll();
it repeat the load process of all the data several times

[Dimitrina]

Hello,

Thank you for pointing this out. I should mention the multiple/extended selection with VirtualQueryableCollectionView is only recommended when the selected items are in the View area. It is not possible to actually select items outside it as the items to be eventually displayed are still not presented. You can find a feedback item on the matter on our Feedback portal here.

Regards,
Dimitrina
Telerik

 

 

[nidhal ben hamadou]

hi, 
What is the solution for the first problem ,it's a bug in VirtualCollection or what exactly ?
Thank you for your reply :)

[Dimitrina]

Hello,

I debugged the solution further with the source codes directly and as it turns out this problem occurs only when you have configured RadGridView with SelectionMode="Extended".  My suggestion would be to keep the default single selection mode.

Regards,
Dimitrina
Telerik

 

 

[nidhal ben hamadou]

any correction of this bug in new version ?? i want to use SelectionMode="Extended" please help .

[Maya]

Hi Nidhal,

We declined the item with an explanation written in the corresponding issue in the portal. Please take a look at it - "Cannot extended select all the items when GridView is bound to VirtualQueryableCollectionView"



Regards,
Maya
Telerik