Question

How should I make my collection for grouped collection in gridview ?

When I create List<List<MyObject>> groups I get grouped data with good count of groups and elements in each group but I have no group titles.
So I’ve created object MyGroupedObject that has two fields

public String Key;
public List<MyObject> items;

so I have grouped that in object. But when I pass it to the grid view (like below) I have nothing. No items, no groups no nothing

 <Page.Resources>
<!--
    Collection of grouped items displayed by this page, bound to a subset
    of the complete item list because items in groups cannot be virtualized
-->
<CollectionViewSource
    x:Name="groupedItemsViewSource"
    IsSourceGrouped="true"
    />

</Page.Resources>

than in gridview i just bind this collection as ItemsSource

this question is based on: how to create gridview from dictionary

I’ve created new cause in the original is to many questions so I want to make it all clear

Answer 1

Have you looked at the Grouping and Semantic Zoom sample? http://code.msdn.microsoft.com/windowsapps/groupedgridview-77c59e8e

You can also look at How to group items in a list or grid…
http://msdn.microsoft.com/en-us/library/windows/apps/xaml/hh780627.aspx

Short explanation is… you can do it one of two ways…

List<Activity> Activities = new List<Activity>(); 
Activities.Add(new Activity() 
    { Name = "Activity 1", Complete = true, 
            DueDate = startDate.AddDays(4), Project = "Project 1" });
Activities.Add(new Activity() 
    { Name = "Activity 2", Complete = true, 
            DueDate = startDate.AddDays(5), Project = "Project 2" });

followed by the following to get the data in your CollectionViewSource

var result = from act in Activities 
             group act by act.Project into grp 
             orderby grp.Key select grp;
cvsActivities.Source = result;

Or you can build a hierarchy using object properties like this…

List<Project> Projects = new List<Project>();

Project newProject = new Project();
newProject.Name = "Project 1";
newProject.Activities.Add(new Activity() 
    { Name = "Activity 1", Complete = true, DueDate = startDate.AddDays(4) });
newProject.Activities.Add(new Activity() 
    { Name = "Activity 2", Complete = true, DueDate = startDate.AddDays(5) });
newProject.Activities.Add(new Activity() 
    { Name = "Activity 3", Complete = false, DueDate = startDate.AddDays(7) });
newProject = new Project();
newProject.Name = "Project 2";
newProject.Activities.Add(new Activity() 
    { Name = "Activity A", Complete = true, DueDate = startDate.AddDays(2) });
newProject.Activities.Add(new Activity() 
    { Name = "Activity B", Complete = false, DueDate = startDate.AddDays(3) });
cvsProjects.Source = Projects;

You cannot bind to a simple list and have the grouping automatically configured for you.