I'm developing a WPF application using the MVVM pattern and I need to display a list of items in a ListView (with filtering), with the fields of the selected item displayed in a Master/Detail view. I'm torn between the following two ways of doing this:
Exposing a CollectionView in my ViewModel, and binding to this.
Exposing a plain IList in my ViewModel, and using CollectionViewSource to create the CollectionView in XAML.
Is there an accepted way of doing this? Any thoughts on the best way?
I do the former (expose CollectionView from the VM) but what really matters is where your filtering logic is. That should definitely be in the VM so that it can be tested, even if the view has to wire up the CollectionViewSource to the VM. That said, I don't think there's anything particularly nasty or anti-MVVM about exposing a CollectionView from your VM.
I know I'm a bit late answering your question but I just saw it today.
I have created master/detail viewmodels that use the CollectionViewSource and blogged about it.
I wrote about a viewmodel for master/detail tables here that uses :
http://reyntjes.blogspot.com/2009/04/master-detail-viewmodel_24.html
You can also find a viewmodel for the observablecollection class on my blog pages.
Maybe you find it of use to you.
Related
I started playing around with Windows Phone development. I am using MVVM ligth and I am trying to follow good practices. But lately I ran into an issue:
Is it okay to use ViewModel inside a ViewModel as a property?
My scenario is that I am having a MainViewModel which is a Panorama object. This Panorama objects consists of few PanaoramaItems (Notes, Calender and About Controls/Pages).
My question is, if I have for the MainPage.xaml a MainViewModel, is it okay if I put the other ViewModels as properties (NotesViewModel, CalenderViewModel, AboutViewModel) to the MainViewModel, in that case those will inherit from the MainPage the DataContext and I would just bind to a property of the MainViewModel. Or should I rather use the locator pattern to allow the other pages/control to get their own ViewModels and do not inherit the DataContext?
Is it okay, if a control has a ViewModel or should it be rather for pages?
If the Parent and Child ViewModels are related: sure, that is fine, it does not violate the pattern.
This setup allows you to re-use ViewModels and Views across pages and controls.
I am fairly new to WPF and MVVM.
I see that a DataGrid can be bound to a CollectionViewSource or an ObservableCollection or a DataSet.
What is the significance of using one over the other?
CollectionViewSource is the XAML equivalent (can be instanciated in XAML) for CollectionView, which provides functionality for grouping, sorting, filtering, and navigating in any data collection. If you want to provide any of these features in the view (XAML) only and do not want to do this in the viewmodel, use a CollectionViewSource else use the ObservableCollection or CollectionView in your viewmodel. Use a DataSetwhen you have your data already in that form and do not want to go through the hassle of creating a viewmodel.
I mostly use the ObservableCollection in the viewmodel.
I would not recommend you using DataSet. You could sort, group and filter data using CollectionViewSource.
It seems that others have had variations on this question, but from what I can tell it hasnt been addressed for folks using collections in a single view model.
I have a VM that contains an ObservableCollection of objects, not a VM for each object. Therefore I dont think I can use the SelectedItem bool that is often discussed because I dont think I can bind to the property on the collection's objects...just the properties on the VM.
So I've got the whole thing pretty well written with no code-behind and minimal coupling, but when a new item is added to the collection, which is bound to the treeView, I need to select that item.
Ideas?
Thanks!
When thinking about this. You should really build a wrapper for every element of the tree view that has the IsSelected bool on it as well as the IsExpanded bool they make life so much easier for displaying the data. You could even just add them to your class and use them from there.
Josh Smith has an article on CodeProject where he suggests creating a ViewModel object to represent each node of the TreeView, and then autowires them up as needed.
http://www.codeproject.com/KB/WPF/TreeViewWithViewModel.aspx
I got the following example of a WPF DataGrid bound to a ViewModel in a MVVM pattern, but it is read-only:
MVVM example which has buttons that switch the data in the ViewModel
I tried to extend it so that the DataGrid was bound to an observable collection of ViewModels so that editing cells would fire OnPropertyChanged events on the appropriate ViewModels but couldn't get it to work the way I wanted.
Does anyone know of a code example that does this, i.e. binding the DataGrid not to a collection of ViewModels with OnPropertyChanged properties and Delegate Commands, etc.?
Jaime Rodriguez and Karl Schifflett are doing a MVVM training roadshow. They have developed a demo application (which uses a datagrid) maybe you want to look into that applicatoin as well as the docs...
http://blogs.msdn.com/jaimer/archive/2009/02/10/m-v-vm-training-day-sample-application-and-decks.aspx
I'm trying to understand the basic MVVM design approach when using ItemsControl by binding it via DataTemplates to ObservableCollections on the ViewModel.
I've seen examples that bind to ObservableCollections of strings, Views, and ViewModels.
Binding to strings seems to be only for demos, it is the binding to "ViewModels that contain collections of Views that contain collections of ViewModels" that the power of WPF seems to really come out.
For those of use proficient in the MVVM pattern, what is your standard approach to binding ItemsControl, ListView, ListBox to collections in a ViewModel? I'm looking for advice from experience like this:
always use ObservableCollection<...> and never List<...> because...
something better than ItemsControl to display a collection is...
in order to get filtering to work in your ViewModel instead of code-behind, use...
use collections of Views when ... and collections of ViewModels when...
90% of the time I create an ItemsControl and bind it to an ObservableCollection of Views which have their own ViewModels...
I would use an ObservableCollection of ViewModels for the following reasons:
ObservableCollection already has events available for signaling when it has been modified (e.g. when items are added/removed from the collection).
We're at the ViewModel 'layer' so it provides cleaner separation to have a ViewModel contain a collection of ViewModels rather than Views
If it is necessary to modify or get data from items within the collection you can more easily modify/access that data if the items are ViewModels (if they're views you'll frequently be casting the View's DataContext or accessing its UI elements).
I like using an ObservableCollection of ViewModels. The view that binds to the collection can define a DataTemplate that gives the ViewModel its look. This leads to less coupling among the components.
I have the same question, but replace the "view" with "model". :)
I have a MODEL with a collection of other models.
I want my viewmodel to have an observable collection of other viewmodels, but once I instantiate it like that - the connection between the model collection content is lost.
Do I now need to start wiring all the events from the viewmodels observable collection back to the models collection?