LoadMoreItemsAsync is called a lot of times at startup even if ItemWidth and ItemHeight are set

Question

Hi,

since Windows 8.1 Preview forum has been closed, I post here my previous question:

http://social.msdn.microsoft.com/Forums/windowsapps/en-US/81e5e14a-5580-4c8a-8f42-8cefd9e428b7/loadmoreitemsasync-is-called-a-lot-of-times-at-startup-even-if-itemwidth-and-itemheight-are-set?forum=w81prevwCsharp#3881528a-5443-4e9b-8973-88bc515226d6

It seems these issues are still present inWindows 8.1 final version.

Any workaround?

Answer 1

This issue should be resolved in 8.1.  Are you running 8.1 RTM, and Visual Studio 2013 RTM?  Also, are you using the same repro?

---

Bret Bentzinger (MSFT) @awehellyeah

Answer 2

Hi,

you can find a sample application that reproduce the problem here:

https://skydrive.live.com/redir?resid=9254CCAFCE7EE400!1733&authkey=!AIFRpAqDpjMsFSQ

In the zip file I uploaded to SkyDrive you can find two folders:

- TestIncrementalLoading that contains the Windows 8.1 Preview App
- TestIncrementalLoadingServices that contains the ASP.NET MVC server side application

Since I'm using Express version of VS 2013, I cannot have the two projects in the same solution so you have to open it separately without using the solution file TestIncrementalLoadin.sln.

There were two issues in Windows 8.1 Preview:

1)  LoadMoreItemsAsync was called a lot of times at startup (the first time with count = 1, the second time with count = 1, the third time with count = page size), even if I specify ItemWidth and ItemHeight in ItemsWrapGrid container.

2) Items were scrolled to the beginning of the list after each incremental load.

The first issue seems to be fixed but the second one is still present: each time LoadMoreItemsAsync is called, the list is scrolled to the begin and this is very annoying.

I found also another issue that I'm not able to reproduce in the sample application but in my real application: when I start another Windows Store app and then I switch back to my app before the app is suspended (swiping from the left corner and selecting the app), all items in the list disappears.

Answer 3

The reason it is jumping back to the beginning is because you are sending the Reset Event(see ExtendedObservableCollection.cs):

public void Add(IEnumerable<T> items)

        {

            if (items != null)

            {

                this.SuspendCollectionChangeNotification();

                int index = base.Count;

                try

                {

                    foreach (var i in items)

                    {

                        base.InsertItem(base.Count, i);

                    }

                }

                finally

                {

                    this.ResumeCollectionChangeNotification();

                    var arg = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset);

                    this.OnCollectionChanged(arg);

                }

            }

        }

If you  want to keep the position then you need to raise as many Add events as many items is being loaded.

---

Bret Bentzinger (MSFT) @awehellyeah

Answer 4

Hi,

I tried the standard ObservableCollection instead of my custom ExtendedObservableCollection and it works.
In Windows 8 my custom ExtendedObservableCollection was working and I'm porting it to Windows 8.1 but maybe something is changed in GridView and ListView.

So I'll go with ObservableCollection.

Thank you very much!