Collapse ListView Groups by default

[Mano Sadeh]

Hey

Can we initialize RadListView control with Grouping that all groups are collapsed by default?

Thanks,

Mano

[Lance | Senior Manager Technical Support]

Hello Mano,

There's no initialization property that does this, however you can achieve the same effect by programmatically collapsing the groups. See here for more information: Expand and Collapse Groups.

Regards,
Lance | Tech Support Engineer, Sr.
Progress Telerik

[Иван]

I added next code:

lvWorkTasks.PropertyChanged += LvWorkTasks_PropertyChanged;

        private void LvWorkTasks_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
        {
            if (e.PropertyName.Equals("ItemsSource"))
            {
                lvWorkTasks.GetDataView().CollapseAll();
            }
        }

But when CollapseAll method is called then null reference exception appears for Items property.

[Lance | Senior Manager Technical Support]

Hi Ivan,

I see that you opened a support ticket for the same question and my colleague has replied. I will share the reason you're having that problem, along with the solution, here with the community as well.

Problem:
Using the Xamarin.Forms PropertyChanged event handler, to check when ItemsSource has changed, is too soon in the lifecycle because the native control's items haven't had a chance to be populated yet.

Solution:
You can instead use the NativeControlLoaded event, which will fire when the native TKExtendedListView control is ready.

// event subscription (can also be done in XAML)
listView.NativeControlLoaded += listView_NativeControlLoaded;

// event handler
private void listView_NativeControlLoaded(object sender, EventArgs e)
{
    var dataView = this.listView.GetDataView();

    dataView.CollapseAll();
}

Regards,
Lance | Tech Support Engineer, Sr.
Progress Telerik

[Иван]

The same exception in that case
System.NullReferenceException: 'Object reference not set to an instance of an object.' 

[Lance | Senior Manager Technical Support]

Hi Ivan,

If you're continuing to see that behavior, there is likely another factor specific to how your application loads data.

Run the demo we sent you in the ticket to see that it works as expected using the recommendation. Then, update the demo so that it replicates the exception and send it back to Didi in that ticket thread for further investigation. She will be able to investigate directly and provide a more appropriate solution for that scenario.

Regards,
Lance | Tech Support Engineer, Sr.
Progress Telerik

[Parvez]

what work around i did.. because its giving me the count zero , so again i am checking it after full list get loaded. May be this will help you.

public SubSectionEquipmentPage()
        {
            InitializeComponent();
            MyListView.NativeControlLoaded += MyLisView_NativeControlLoaded;
        }

        private void MyLisView_NativeControlLoaded(object sender, System.EventArgs e)
        {
            CollapseList();
        }

        public async void CollapseList()
        {
            var dataView = this.MyListView.GetDataView();
            if (dataView != null && dataView.Items.Count>0)
            {
                dataView.CollapseAll();
            }
            else
            {
                await Task.Delay(2000);
                CollapseList();
            }
        }