Hi I bind collection from Caliburn Micro on ListBox control in view. Here is it.
public BindableCollection<UserInfo> Friends
{
get { return _friends; }
set
{
_friends = value;
NotifyOfPropertyChange(() => Friends);
}
}
ListBox items is type of UserInfo.
Hi I sort and group listbox items, I use CollectioView on this purpose.
When I initialize ListBox I sort and group items with this method.
private ICollectionView _currentView;
//...
private void SortContactList()
{
_currentView = CollectionViewSource.GetDefaultView(Friends);
_currentView.GroupDescriptions.Add(new PropertyGroupDescription("TextStatus"));
_currentView.SortDescriptions.Add(new SortDescription("TextStatus", ListSortDirection.Ascending));
_currentView.SortDescriptions.Add(new SortDescription("Nick", ListSortDirection.Ascending));
}
TextStatus and Nick are properties of userInfo class.
When I update values of item in bindable collection Friend I would like have a way how notify collection view about this change. Because I need move item to right/good group.
for example
Friend[0].TextStatus = "Ofline" -> is in offline group
I change value on online;
Friend[0].TextStatus="Online" -> move in online group
and here I want notify collection view (_currentView) about change on Friends collection.
I had the same issue when I created an application that had a table with the Rating column.
I wondered why row doesn't move up when I change rating, and in the end I used the Refresh method.
For your example:
Friend[0].TextStatus="Online" -> move in online group
_currentView.Refresh();
Fortunately, performance problems didn't occur, so now I use this solution in similar situations.
Related
I have a List bound to a (Telerik) GridView. The selected item is a separate variable of type T which is assigned the object of the selected row in the GridView when the user clicks on a row. T is derived from ObservableObject. This means I am using MVVM Light Toolkit.
I need to deselect the row from my ViewModel in certain situations. On the GridView control this works, if the selected item is set to NULL in the ViewModel. Whenever I do this, MVVM reports a crash (NPE). I debugged it and saw that it is failing in ObservableObject.cs. It calls a method
protected bool Set<T>(
Expression<Func<T>> propertyExpression,
ref T field,
T newValue)
and crashes one line before return when calling RaisePropertyChanged(propertyExpression)
I don't know if this is working as designed or not. My problem is, that I need to set the selected Object to NULL in the ViewModel to deselect a row of my GridView in the View. I CANNOT use CodeBehind for the deselection!
Code I have:
public ObservableCollection<ContractTypeDto> ContractTypes { get; private set; }
public ContractTypeDto SelectedContractType
{
get { return _selectedContractType; }
set
{
Set(() => SelectedContractType, ref _selectedContractType, value);
RaisePropertyChanged(() => SelectedContractType);
}
}
When you click on a row in the grid it opens a new UserControl containing lots of details of this record. This control has its own ViewModel. I store the calling view Model (where the selected item is stored). When the page (control) is closed (destroyed) I have to deselect the row in the grid. I call a method like so:
protected void DeselectCallersSelectedItem()
{
if (CallingObject == typeof(ContractTypeListViewModel))
{
var vm = SimpleIoc.Default.GetInstance<ContractTypeListViewModel>();
vm.SelectedContractType = null;
}
}
Any ideas?
To remove the collection you can either set the SelectedItem property to null or clear the SelectedItems.
gridViewName.SelectedItem = null;
gridViewName.SelectedItems.Clear();
Without showing the code, we cannot precisely help you. A solution I think you can do is to implement the INotifyPropertyChanged interface in your view model and bind the selected item to a property of that type. Also check the output window if there is any binding failure.
May be it's a silly (or more than trivial) kinda question, but it seems i just don't know the answer. Here's the case -
I assigned a UserList as the ItemsSource of a combobox. So what i did essentially is assigning a reference type to another.
I cleared the UserList. So now i get the Count of the ItemsSource 0 as well.
I still get the items present in my combobox. And i also can cast the SelectedItem of the combobox to a User object.
Here's the complete code -
public class User
{
public int Id { get; set; }
public string Name { get; set; }
}
public partial class MainWindow : Window
{
private List<User> _userList;
public MainWindow()
{
InitializeComponent();
_userList = new List<User>()
{
new User() {Id = 1, Name = "X"},
new User() {Id = 2, Name = "Y"},
new User() {Id = 3, Name = "Z"}
};
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
this.comboBox1.ItemsSource = _userList;
this.comboBox1.DisplayMemberPath = "Name";
}
private void button1_Click(object sender, RoutedEventArgs e)
{
_userList.Clear();
/* ItemsSource is cleared as well*/
IEnumerable userList = this.comboBox1.ItemsSource;
/*I can still get my User*/
User user = this.comboBox1.SelectedItem as User;
}
}
So, where the items are coming from? What actually happens under-the-hood when i make such binding? Does the control have some kind of cache? It's a royal pain to realize not having such basic ideas. Can anybody explain the behind-the-scene detail?
EDIT : I wrote the code in WPF, but i have the same question for WinForms Combobox.
EDIT : Doesn't a combobox display its items from it's in-memory Datasource? When that datasource contains 0 items, how does it display the items?
When you set an ItemsSource of any ItemsControl it copies the ref to the list into its Items property. Then it subscribes to the OnCollectionChanged event, and creates a CollectionView object. So, on the screen you can see that collectionView.
as I have found in source code ItemCollection holds two lists:
internal void SetItemsSource(IEnumerable value)
{
//checks are missed
this._itemsSource = value;
this.SetCollectionView(CollectionViewSource.GetDefaultCollectionView((object) this._itemsSource, this.ModelParent));
}
How could you get SelectedItem?
This is my assumption from quick look into the source code:
ItemsControl has a collection of "views" and each View sholud store a ref to the item (User instance), because it has to draw data on the screen. So, when you call SelectedItem it returns a saved ref.
Upd about references
Assume there is an User instance. It has the adress 123 in memory. There is a list. It stores references. One of them is 123.
When you set an ItemsSource ItemsControl saves a reference to the list, and creates a Views collection. Each view stores a references to an item. One view stores an address 123.
Then you cleared a list of users. Now list doesn't contains any references to Users. But in memory there is an adrress 123 and there is an instance of User by this adress. Garbage Collector doesn't destroy it, because View has a reference to it.
When you get SelectedItem it returns User instance from the 123 adress.
var user = new User();
var list = new List<User>();
list.Add(user);
list.Clear();
Console.WriteLine(list.Count()); //prints 0 - list is empty
Console.WriteLine(user == null); //prints false. - user instance is sill exists;
In answer to your comment to #GazTheDestroyer ("... why it doesn't get cleared, and how it holds the items?")
In WPF, when you set the ItemsSource property of an ItemsControl, the control will wrap the list of items in a CollectionView, which is a collection type optimised for use by the UI framework. This CollectionView is assigned to the Items property of the control and is what the display-drawing code actually works from. As you see, this collection is entirely separate of the object you originally assigned to ItemsSource, and so there is no propogation of changes from one to the other. This is why the items are still in the control when you clear the original list: the control is ignoring the original list, and has its own list that contains your objects.
It's for this reason that an ItemsSource value needs to raise events - specifically INotifyCollectionChanged.NotifyCollectionChanged - so that the control knows to refresh the Items list. ObservableCollection implements this interface and raises the correct event, and so the functionality works as expected.
It's hugely important to note that this is nothing like what happens in WinForms, which is why I've been pressing you for the clarification.
EDIT: To clarify, there is no "deep copy." The code that is happening is similar in principle to the following:
private List<object> myCopy;
public void SetItemsSource(List<object> yourCopy)
{
myCopy = new List<object>();
foreach (var o in yourCopy)
{
myCopy.Add(o);
}
}
Once this code has run, there's only one copy of every item in your list. But each of the items is in both of the lists. If you change, clear or otherwise manipulate yourCopy, myCopy knows nothing about it. You cannot "destroy" any of the objects that are within the list my clearing yourCopy - all you do is release your own reference to them.
Assuming you are using WPF:
List<User> doesn't fire any event that the UI will recognise to refresh itself. If you use ObservableCollection<User> instead, your code will work.
The key difference is that ObservableCollection implements INotifyCollectionChanged, which allows the UI to recognise that the content of the collection has changed, and thus refresh the content of the ComboBox.
(Note that this does not work in WinForms. In WinForms you can set the DataSource property of the control, but the same ObservableCollection trick does not work here.)
When you set a collection reference to ItemsControl, all the combo gets is a reference, that it knows is enumerable.
It will enumerate the reference and display the items. Whether it does a deep copy or shallow copy is irrelevant, all it has is a reference (memory address effectively).
If you change your collection in some way, the combo has no way of knowing unless you tell it somehow. The reference (address) hasn't changed, everything looks the same to the combo. You seem to be thinking that the object is somehow "live" and the combo can watch the memory changing or something? This isn't the case. All it has is a reference that it can enumerate over. The contents can change but without some trigger the combo doesn't know that, and so will sit doing nothing.
ObservableCollection is designed to overcome this. It implements INotifyCollectionChanged that fires events when it changes, so the Combo knows that it must update its display.
I've created a WPF custom ComboBox which has the ability to filter items according to a "search string". The ComboBox ItemsSource is bound to a ObservableCollection.
The ObservableCollection is a collection of "Person" object. It exposes a property "Usage Count".
Now if the "search string" is empty i have to show the Top 30 records from the ObservableCollection. The "UsageCount" property in the "Person" class decides the Top 30 Records(i.e. the the Top 30 records with the maximum UsageCount has to be displayed).
The UsageCount property changes dynamically.
How do i achieve this..
Please help. Thanks in advance :)
To handle your searchable sorted collection, you can build your own object, inheriting from ObverservableCollection, overloading Item default property, adding a (notifying) SearchString property, listening to the changes of your Person entire list, building on change (change in SeachString Or in the UsageCount of a Person) a new private list of person, and using NotifyCollectionChanged event to notify it.
here's an idea, if you need filtering why not bind to a ListCollectionView
in the View
ComboBox ItemsSource="{Binding PersonsView}" //instead of Persons
in your ViewModel:
public ListCollectionView PersonsView
{
get { return _personsView; }
private set
{
_personsView= value;
_personsView.CommitNew();
RaisePropertyChanged(()=>PersonsView);
}
}
once you populate your List
PersonsView= new ListCollectionView(_persons);
somewhere in your view you obviously have a place responding to combobox's change, where you update the filter, you can put apply filter there
_viewModel.PersonsView.Filter = ApplyFilter;
where ApplyFilter is an action that decides what gets displayed
//this will evaluate all items in the collection
private bool ApplyFilter(object item)
{
var person = item as Person;
if(person == null)
{
if(person is in that 30 top percent records)
return false; //don't filter them out
}
return true;
}
//or you can do some other logic to test that Condition that decides which Person is displayed, this is obviously a rough sample
}
I have a ObservableCollection , where MyData is a class with 4 properties i.e. int id, string name, bool IsSelected, string IsVisible.
This ObservableCollection is binded to a combobox with checkboxes(Cities data for example). Now, when the user checks the checkboxes then next time when he opens the drop down - all selections should come on top in ascending order by name.
I have also implemented auto complete when the user types in 3 chars in the combobox, the drop down will open showing all the selections first, then then all the items starting from the 3 chars type in by the user.
I have researched and implemented the following code and it is working fine, but i want to know whether this is the best approach or can i implement this in a better manner, code is :
IEnumerable<MyData> sort;
ObservableCollection<MyData> tempSortedCities = new ObservableCollection<MyData>();
sort = City.OrderByDescending(item => item.IsSelected).ThenBy(item => item.Name.ToUpper()) ;
// City is my observablecollection<MyData> property in my Model binded to combobox in UI
foreach (var item in sort)
tempSortedCities.Add(item);
City.Clear(); // City is my observablecollection<MyData> property in my Model
City = tempSortedCities;
tempSortedCities = null;
sort = null;
Thanks in advance for your time !
ICollectionView seems to be a perfect fit for this. It was designed specifically for sorting, filtering and grouping of a collection without modifying the original collection.
You can get an instance of ICollectionView for your collection using the following code:
var sortedCities = CollectionViewSource.GetDefaultView(City);
Then you can setup sorting by adding instances of SortDescription type to the ICollectionView.SortDescriptions collection:
sortedCities.SortDescriptions.Add(new SortDescription("IsSelected", ListSortDirection.Descending));
sortedCities.SortDescriptions.Add(new SortDescription("Name", ListSortDirection.Ascending));
Then you can bind your ComboBox directly to the collection view (instead of City collection) and it will display already sorted data.
MVVM pattern is implemented in my Silverlight4 application.
Originally, I worked with ObservableCollection of objects in my ViewModel:
public class SquadViewModel : ViewModelBase<ISquadModel>
{
public SquadViewModel(...) : base(...)
{
SquadPlayers = new ObservableCollection<SquadPlayerViewModel>();
...
_model.DataReceivedEvent += _model_DataReceivedEvent;
_model.RequestData(...);
}
private void _model_DataReceivedEvent(ObservableCollection<TeamPlayerData> allReadyPlayers, ...)
{
foreach (TeamPlayerData tpd in allReadyPlayers)
{
SquadPlayerViewModel sp = new SquadPlayerViewModel(...);
SquadPlayers.Add(sp);
}
}
...
}
Here is a peacie of XAML code for grid displaying:
xmlns:DataControls="clr-namespace:System.Windows.Controls;
assembly=System.Windows.Controls.Data"
...
<DataControls:DataGrid ItemsSource="{Binding SquadPlayers}">
...</DataControls:DataGrid>
and my ViewModel is bound to DataContext property of the view.
This collection (SquadPlayers) is not changed after its creation so I would like to change its type to
List<SquadPlayerViewModel>
. When I did that, I also added
RaisePropertyChanged("SquadPlayers")
in the end of '_model_DataReceivedEvent' method (to notify the grid that list data are changed.
The problem is that on initial displaying grid doesn't show any record... Only when I click on any column header it will do 'sorting' and display all items from the list...
Question1: Why datagrid doesn't contain items initially?
Q2: How to make them displayed automatically?
Thanks.
P.S. Here is a declaration of the new List object in my view-model:
public List<SquadPlayerViewModel> SquadPlayers { get; set; }
You can't use List as a binding source, because List not implement INotifyCollectionChanged it is require for WPF/Silverlight to have knowledge for whether the content of collection is change or not. WPF/Sivlerlight than can take further action.
I don't know why you need List<> on your view model, but If for abstraction reason you can use IList<> instead. but make sure you put instance of ObservableCollection<> on it, not the List<>. No matter what Type you used in your ViewModel Binding Only care about runtime type.
so your code should like this:
//Your declaration
public IList<SquadPlayerViewModel> SquadPlayers { get; set; }
//in your implementation for WPF/Silverlight you should do
SquadPlayers = new ObservableCollection<SquadPlayerViewModel>();
//but for other reason (for non WPF binding) you can do
SquadPlayers = new List<SquadPlayerViewModel>();
I usually used this approach to abstract my "Proxied" Domain Model that returned by NHibernate.
You'll need to have your SquadPlayers List defined something like this:
private ObservableCollection<SquadPlayerViewModel> _SquadPlayers;
public ObservableCollection<SquadPlayerViewModel> SquadPlayers
{
get
{
return _SquadPlayers;
}
set
{
if (_SquadPlayers== value)
{
return;
}
_SquadPlayers= value;
// Update bindings, no broadcast
RaisePropertyChanged("SquadPlayers");
}
}
The problem is that whilst the PropertyChanged event informs the binding of a "change" the value hasn't actually changed, the collection object is still the same object. Some controls save themselves some percieved unnecessary work if they believe the value hasn't really changed.
Try creating a new instance of the ObservableCollection and assigning to the property. In that case the currently assigned object will differ from the new one you create when data is available.