Why there is no .Net interface for ICollectionView<T>? Looking at ICollectionView it seems quite obvious to expect for ICollectionView<T>.
Am I missing something?
The ICollectionView is only implemented by the CollectionView class. The MSDN-documentation points out that the CollectionView should not even be instantiated in your code, but instead make use of the CollectionViewSource-object to get your collection view.
If you want to have your own collection of T returned in a CollectionView, you need to add your own collection (implementing IEnumerable) to the CollectionViewSource-object and get the CollectionView from there, for instance:
List<MyClass> listToView = new List<MyClass>();
MyClass x1 = new MyClass() { Name = "Fictive Name 1", Description = "Description...", Date = DateTime.Now};
MyClass x2 = new MyClass() { Name = "Fictive Name 2", Description = "Description...", Date = DateTime.Now};
MyClass x3 = new MyClass() { Name = "Fictive Name 3", Description = "Description...", Date = DateTime.Now};
listToView.Add(x1);
listToView.Add(x2);
listToView.Add(x3);
CollectionViewSource collectionViewSource = new CollectionViewSource();
collectionViewSource.Source = listToView;
ICollectionView collectionView = collectionViewSource.View;
The reason why there is no ICollectionView of T is probably because its not designed that way. The documentation points out that the CollectionView has been designed to give a different view on a collection without changing it:
You can think of a collection view as a layer on top of a binding
source collection that allows you to navigate and display the
collection based on sort, filter, and group queries, all without
having to manipulate the underlying source collection itself.
In that regard it makes sense that you can only view the collection, hence the name 'ViewCollection'.
I think it's not so obvious to expect ICollectionView of T as CollectionView's are not even meant to be instantiated in the first place (see the interesting warning below by the way, after adding some sorting abilities).
System.Windows.Data Warning: 52 : Using CollectionView directly is not
fully supported. The basic features work, although with some
inefficiencies, but advanced features may encounter known bugs.
Consider using a derived class to avoid these problems.
I think the architecture has been designed to work on a 'read-only' based level without changing its underlying datasources, as that is what grouping, filtering and navigating a data collection's is mainly focused on.
However, if you want to know exactly why, you'd probably have to speak with someone from Microsoft that worked on this part of the framework.
Related
Using MVVM Light, it is easy to register for certain types of messages:
public MyViewModel()
{
Messaging.Messenger.Default.Register<MyObject>(this,
new Action<MyObject>((o) => DataMember = o));
}
Now, I have multiple document views in my software which implies showing/hiding views when toggling between them. When a view instance is hidden, I want its registered messages to be ignored. Similarly, when a view instance is shown, I want its registered messages to be handled. Hence, a message token per document is required:
public MyViewModel(String documentID)
{
Messaging.Messenger.Default.Register<MyObject>(this,
documentID,
new Action<MyObject>((o) => DataMember = o));
}
The problem is, I cannot figure out where in XAML/code to specify this token!
Sure, I can provide the documentID from the view...
public MyView()
{
InitializeComponent();
DataContext = new MyViewModel("1234");
}
... effectively giving me the same problem. Where would I specify this "1234" value? I read about x:Arguments Directive, hoping that it would let me specify constructor arguments in XAML, but it seems it's only supported in Loose XAML :(
I can think of a couple of solutions, like having a global variable, ActiveDocumentID, that would be used as token when instantiating the viewmodel. Is there a better solution?
I am working on a WPF app using the MVVM patterm, which I am learning. It uses EF4. I am trying to use a similar tabbed document interface style; several combo boxes on these tabs have the same items sources (from a sql db). Since this data almost never changes, it seemed like a good idea to make a repository object to get them when the app starts, and just reuse them for each viewmodel. For whatever reason though, even though I use new in the constructors, the lists are connected.
If I set a bound combo box on one tab, it gets set on another (or set when a new tab is created). I don't want this to happen, but I don't know why does.
The repository object is initialized before anything else, and just holds public lists. The views simply use items source binding onto the ObservableCollection. I am using the ViewModelBase class from the article. Here is the Viewmodel and model code.
ViewModel
TicketModel _ticket;
public TicketViewModel(TableRepository repository)
{
_ticket = new TicketModel(repository);
}
public ObservableCollection<Customer> CustomerList
{
get { return _ticket.CustomerList; }
set
{
if (value == _ticket.CustomerList)
return;
_ticket.CustomerList = value;
//base.OnPropertyChanged("CustomerList");
}
}
Model
public ObservableCollection<Customer> CustomerList { get; set; }
public TicketModel(TableRepository repository)
{
CustomerList = new ObservableCollection<Customer>(repository.Customers);
}
EDIT: I am sure this is the wrong way to do this, I am still working on it. Here is the new model code:
public TicketModel(TableRepository repository)
{
CustomerList = new ObservableCollection<Customer>((from x in repository.Customers
select
new Customer
{
CM_CUSTOMER_ID = x.CM_CUSTOMER_ID,
CM_FULL_NAME = x.CM_FULL_NAME,
CM_COMPANY_ID = x.CM_COMPANY_ID
}).ToList());
}
This causes a new problem. Whenever you change tabs, the selection on the combo box is cleared.
MORE EDITS: This question I ran into when uses Rachels answer indicates that a static repository is bad practice because it leaves the DB connection open for the life of the program. I confirmed a connection remains open, but it looks like one remains open for non-static classes too. Here is the repository code:
using (BT8_Entity db = new BT8_Entity())
{
_companies = (from x in db.Companies where x.CO_INACTIVE == 0 select x).ToList();
_customers = (from x in db.Customers where x.CM_INACTIVE == 0 orderby x.CM_FULL_NAME select x).ToList();
_locations = (from x in db.Locations where x.LC_INACTIVE == 0 select x).ToList();
_departments = (from x in db.Departments where x.DP_INACTIVE == 0 select x).ToList();
_users = (from x in db.Users where x.US_INACTIVE == 0 select x).ToList();
}
_companies.Add(new Company { CO_COMPANY_ID = 0, CO_COMPANY_NAME = "" });
_companies.OrderBy(x => x.CO_COMPANY_NAME);
_departments.Add(new Department { DP_DEPARTMENT_ID = 0, DP_DEPARTMENT_NAME = "" });
_locations.Add(new Location { LC_LOCATION_ID = 0, LC_LOCATION_NAME = "" });
However, now I am back to the ugly code above which does not seem a good solution to copying the collection, as the Customer object needs to be manually recreated property by property in any code that needs its. It seems like this should be a very common thing to do, re-using lists, I feel like it should have a solution.
Custom objects, such as Customer get passed around by reference, not value. So even though you're creating a new ObservableCollection, it is still filled with the Customer objects that exist in your Repository. To make a truly new collection you'll need to create a new copy of each Customer object for your collection.
If you are creating multiple copies of the CustomerList because you want to filter the collection depending on your needs, you can use a CollectionViewSource instead of an ObservableCollection. This allows you to return a filtered view of a collection instead of the full collection itself.
EDIT
If not, have you considered using a static list for your ComboBox items, and just storing the SelectedItem in your model?
For example,
<ComboBox ItemsSource="{Binding Source={x:Static local:Lists.CustomerList}}"
SelectedItem="{Binding Customer}" />
This would fill the ComboBox with the ObservableCollection<Customer> CustomerList property that is found on the Static class Lists, and would bind the SelectedItem to the Model.Customer property
If the SelectedItem does not directly reference an item in the ComboBox's ItemsSource, you need to overwrite the Equals() of the item class to make the two values equal the same if their values are the same. Otherwise, it will compare the hash code of the two objects and decide that the two objects are not equal, even if the data they contain are the same. As an alternative, you can also bind SelectedValue and SelectedValuePath properties on the ComboBox instead of SelectedItem.
RIA Services is returning a list of Entities that won't allow me to add new items. Here are what I believe to be the pertinent details:
I'm using the released versions of Silverlight 4 and RIA Services 1.0 from mid-April of 2010.
I have a DomainService with a query method that returns List<ParentObject>.
ParentObject includes a property called "Children" that is defined as List<ChildObject>.
In the DomainService I have defined CRUD methods for ParentObject with appropriate attributes for the Query, Delete, Insert, and Update functions.
The ParentObject class has an Id property marked with the [Key] attribute. It also has the "Children" property marked with the attributes [Include], [Composition], and [Association("Parent_Child", "Id",
"ParentId")].
The ChildObject class has an Id marked with the [Key] attribute as well as a foreign key, "ParentId", that contains the Id of the parent.
On the client side, data is successfully returned and I assign the results of the query to a PagedCollectionView like this:
_pagedCollectionView = new PagedCollectionView(loadOperation.Entities);
When I try to add a new ParentObject to the PagedCollectionView like this:
ParentObject newParentObject = (ParentObject)_pagedCollectionView.AddNew();
I get the following error:
" 'Add New' is not allowed for this view."
On further investigation, I found that _pagedCollectionView.CanAddNew is "false" and cannot be changed because the property is read-only.
I need to be able to add and edit ParentObjects (with their related children, of course) to the PagedCollectionView. What do I need to do?
I was just playing around with a solution yesterday and feel pretty good about how it works. The reason you can't add is the source collection (op.Entities) is read-only. However, even if you could add to the collection, you'd still want to be adding to the EntitySet as well. I created a intermediate collection that takes care of both these things for me.
public class EntityList<T> : ObservableCollection<T> where T : Entity
{
private EntitySet<T> _entitySet;
public EntityList(IEnumerable<T> source, EntitySet<T> entitySet)
: base(source)
{
if (entitySet == null)
{
throw new ArgumentNullException("entitySet");
}
this._entitySet = entitySet;
}
protected override void InsertItem(int index, T item)
{
base.InsertItem(index, item);
if (!this._entitySet.Contains(item))
{
this._entitySet.Add(item);
}
}
protected override void RemoveItem(int index)
{
T item = this[index];
base.RemoveItem(index);
if (this._entitySet.Contains(item))
{
this._entitySet.Remove(item);
}
}
}
Then, I use it in code like this.
dataGrid.ItemsSource = new EntityList<Entity1>(op.Entities, context.Entity1s);
The only caveat is this collection does not actively update off the EntitySet. If you were binding to op.Entities, though, I assume that's what you'd expect.
[Edit]
A second caveat is this type is designed for binding. For full use of the available List operation (Clear, etc), you'd need to override a few of the other methods to write-though as well.
I'm planning to put together a post that explains this a little more in-depth, but for now, I hope this is enough.
Kyle
Here's a workaround which I am using:
Instead of using the AddNew, on your DomainContext you can retrieve an EntitySet<T> by saying Context.EntityNamePlural (ie: Context.Users = EntitySet<User> )
You can add a new entity to that EntitySet by calling Add() and then Context.SubmitChanges() to send it to the DB. To reflect the changes on the client you will need to Reload (Context.Load())
I just made this work about 15mins ago after having no luck with the PCV so I am sure it could be made to work better, but hopefully this will get you moving forward.
For my particular situation, I believe the best fit is this (Your Mileage May Vary):
Use a PagedCollectionView (PCV) as a wrapper around the context.EntityNamePlural (in my case, context.ParentObjects) which is an EntitySet. (Using loadOperation.Entities doesn't work for me because it is always read-only.)
_pagedCollectionView = new PagedCollectionView(context.ParentObjects);
Then bind to the PCV, but perform add/delete directly against the context.EntityNamePlural EntitySet. The PCV automatically syncs to the changes done to the underlying EntitySet so this approach means I don't need to worry about sync issues.
context.ParentObjects.Add();
(The reason for performing add/delete directly against the EntitySet instead of using the PCV is that PCV's implementation of IEditableCollectionView is incompatible with EntitySet causing IEditableCollectionView.CanAddNew to be "false" even though the underlying EntitySet supports this function.)
I think Kyle McClellan's approach (see his answer) may be preferred by some because it encapsulates the changes to the EntitySet, but I found that for my purposes it was unneccessary to add the ObservableCollection wrapper around loadOperation.Entities.
Many thanks to to Dallas Kinzel for his tips along the way!
I have implemented Linq-To-Sql..
Add necessary table in it...
after that linq class will automatically set property for field..
I implemented one class using ObservableCollection class.. and pass datacontextclass object in its constructor...
so after getting all data how to filter it?
public class BindBookIssueDetails : ObservableCollection
{
public BindBookIssueDetails(DataClasses1DataContext dataDC)
{
foreach (Resource_Allocation_View res in dataDC.Resource_Allocation_Views)
{
this.Add(res);
}
}
}
private BindBookIssueDetails bResource;
bResource = new BindBookIssueDetails(db);
_cmbResource.ItemSource=bResource;
Please Help me.
You can use CollectionViewSource and filter it. So that it affect only at the View(.XAML) side
ICollectionView collectionView = CollectionViewSource.GetDefaultView(bResource);
collectionView.Filter = new Predicate<object>(YourFilterFunction);
Check out this blog for more details. http://bea.stollnitz.com/blog/?p=31
I tried to use #Jobi's solution but for some reason I got an exception trying to fire FilterFunction.
So I used a slightly different approach. I cast CollectionViewSource's DefaultView to a BindingListCollectionView
myVS=(BindingListCollectionView)CollectionViewSource.GetDefaultView(sourceofdata);
and now I can construct an SQL-like filter string and apply it like that:
myVS.CustomFilter=myfilterstring;
I will still try to resolve my problem (I presume #Jobi's solution is more flexible).
I have a problem with Linq and ObservableCollections in my WPF application.
Context of the problem:
I've created a very simple SQL database with two tables: User and BankAccounts.
The User Table has an one-to-many relationship with the BankAccounts Table. Next I've created Linq-to-SQL dataclasses, which worked fine ==> the assosiation between the two tables was detected as well.
Next I've created a function to retreive all Users which works fine:
DataClassesDataContext dc = new DataClassesDataContext
var query = from u in dc.Users
select u;
Now suppose I want to add a new BankAccount to each user (not very likely but still).
I could add the following code
for each(User u in query)
{
u.BankAccounts.Add(New BankAccount());
}
The above works all fine. The BankAccounts property is automaticly part of the User class, due to the assosiation in the database and Linq DataClasses.
However, in my application I first add the query results to an ObservableCollection. Hereby I could use all sorts off databinding and changenotification. This is accomplished by the following code;
ObservableCollection<User> oUsers = new ObservableCollection<User>(query);
Problem: Within the ObservableCollection I can't do anyting with the users BankAccounts property because it is now of type EntitySet<>. So I can't do the following statement anymore.
for each(User u in oUsers)
{
u.BankAccounts.Add(New BankAccount());
}
Somehow, when queryresults are added to an observablecollection It is not possible to acces the user.BankAccounts properties anymore. However, it is possible to bind the BankAccounts Property to any control, like a listbox, and it contains the correct data.
Does someone now how I can create an observableCollction (or similar collection) from wich I can access these "assosiated" properties? I'm realy looking forward for to a solution.
Thanks in advance!
Best regards,
Bas Zweeris
E: Bas.Zweeris#Capgemini.com
Keep track of the original query which will implement IQueryable, you can run any further queries you need against that.
The ObservableCollection should just be for WPF to have something to bind to - its very useful if you want to add a new collection item but not have it pushed to the database before the user has had chance to edit it.
eg.
// Create a new blank client type
var ct = new ClientType()
{
IsArchived = false,
Description = "<new client type>",
Code = "CT000",
CanLoginOnline = true
};
// Tell the data source to keep track of this object
db.ClientTypes.InsertOnSubmit(ct);
// Also add the object to the observable collection so that it can immediately be shown in the UI and editted without hitting the db
clienttypes.Add(ct);