So it seems like what I want to do should be straightforward, but I haven't been able to find a way to do it...
I need to display a list of objects that represent custom elements for entering data. Exactly how each object is displayed depends on the parameters of the object - so it could be a grid containing a name, description, and text box. It could be a grid with a couple labels and a dropdown. It could be an expander that contains multiple sub-objects. It could be something new that hasn't been built yet (so it needs to be extensible). Right now, I am populating this list by creating the FrameworkElement for each object and then adding it to a Grid by hand.
I would like to switch to keeping my objects in an ObservableCollection, and then binding that collection to a ListBox (or similar). That way, when new objects are added or removed from the list, the UI would automatically update itself accordingly. What I can't figure out is, is there a way to point it to my C# method for creating the custom-configured FrameworkElement for each object, so that when new objects are added the appropriate elements will be added to the UI?
Well, you're on the right track as far as wanting to use an ObservableCollection<T> and a ListBox control. Though, I'd venture to say you might want to simply use an ItemsControl since you probably don't care about selecting a particular item, but merely displaying an enumeration of items, and the ListBox would allow you to actually select one of those items.
Your problem is that you want each item in the list to display differently depending on certain criteria. For this you'll want to look at the DataTemplate and DataTemplateSelector classes.
Basically, a DataTemplate is a way of saying "I want my item to look like this.", and a DataTemplateSelector is a way of saying "I want to select this specific DataTemplate based on this criteria."
Here are a few examples on how to use the DataTemplate/DataTemplateSelector classes:
http://tech.pro/tutorial/807/wpf-tutorial-how-to-use-a-datatemplateselector
http://mikestedman.blogspot.com/2009/04/datatemplateselector.html
http://wpftutorial.net/DataTemplates.html
Seperating the presentation from the model is always a good idea. It seems like you are on the right track.
Foreach object type, you should create a DataTemplate and then use ItemTemplateSelector to select the correct template for each object type.
Good luck
Related
I have an ObservableCollection that is wrapped by a ListCollectionView.
The ListCollectionView is displayed in a grid (XamDataGrid).
When I add items to my observable collection those items are exposed by the ListViewCollection sorted in the order defined by the SortDescriptions property.
Here's the problem. I would like new items to appear at the bottom of my grid even though the existing ones are currently sorted. Next time the user sorts (by clicking at the column header) the new items should be sorted.
I'm struggling to find a solution to this problem. Anyone's had a similar issue?
Solution A: Manage the sorting yourself behind the scenes
Easiest thing to do here is sort the data behind the scenes (you can use LINQ for that), then assign it to the grid without the sort descriptions. Then as you add items, they'll just appear at the end of the collection. When you click on a header, intercept that and sort yourself accordingly.
Solution B: Add another SortDescription
Another approach is to add another property to your data and create a primary sort on that field first, then by what you actually want to sort on. For instance, you could add a boolean called existedBeforeSort. If you can't modify your model, you can do it via an extension where you store the actual value in a dictionary keyed on the object itself. (That's sort of how DependencyProperties work, but this can be for any object since you're managing the storage.)
Now, in the grid, as you click a sort header, the first thing you do is set the existedBeforeSort property on all items to true. Since your first SortDescription is based on that field, followed by the sort descriptions generated by clicking on the headers, all newly added items will appear at the bottom as you wanted.
The trick to this second approach is making sure as you click on sort headers, you manually make sure your SortDescription based on your existedBeforeSort property is always inserted first. In essence, you're hijacking the implied SortDescriptions and injecting yours to supersede theirs. Shouldn't be too difficult though.
Hope this helps!
I apologize for the crappy title, I wasn't quite sure how to summarize what I'm trying to do.
My scenario:
I am refactoring an existing WinForms application to WPF and MVVM. I'm currently working on a module that provides search functionality for a database comprised of many different tables such as Contact, User, Case, Product, etc. In code-behind there are classes which provide an Object for each. I have written wrapper classes for each of the searchable table Objects that expose only the properties a user would want/need to see in the search results for each type of Object, for binding to a DataGrid.
Once these search results exist, they need to be displayed in a combination of Tab Controls and Data Grids, like so:
Because of some use cases, I need to be able to create an individual display Tab+DataGrid for the results of every single search that is performed. I cannot have a single tab for each type of search that is shown/hidden as needed.
I'm not sure how to proceed from where I currently am to the goal pictured and described above. Thanks for any help anyone can provide.
Not sure I entirely understand your question, but it looks to me that it might be a candidate for datatemplateselector.
Basically, you use an ItemsControl bound to your result collection and then - using a datatemplateselector - you swap in the appropriate template to display the item based upon a code inspection.
That will let you present all the results in a single list.
If you want to display your results in a tabs, I would present a collection of each result type in your viewmodel. So you have a Users collection and a seperate Products collection. Then you can bind individual data grids to each template.
If you want to then hide the tabs when no results are present, add a data trigger using the expression.interactivity namespace to trigger the visibility of each tab page based on its respective collection count.
One more thing, if you want to create tab items dynamically, i.e. One tab for each search - the tab control has an ItemSource property. If you group each search result into an object an expose an observable collection of that object, you can bind that to your tab control and have it create tab items for each search result. Just make that object contain a collection of actual results and you should be able to create a itemscontrol as mentioned here already.
Sorry if this appears a bit of a mind dump, but like I said - not sure if I entirely get the question :)
Rather then chuck a load of code snippets in, there a plenty of samples just a google away if anything sounds helpful.
I currently have a GridView populated with ItemsSource binding to an ObservableCollection.
It's showing the items as I intended but I'd like to manually add one more item at the end that looks and behaves differently. Is there a way I can do it without modifying the ObservableCollection the ItemsSource is bound to?
There are two approaches to this:
Using MVVM the original collection would be pulled up from the model layer and the additional item would be added in the view-model. It works as you can consider the additional item required only for the view, e.g. for example a list of poll options where you need to add an 'all of the above'.
Have two collections, separate, and then concatenate/join them together using an IValueConverter when you bind the ItemsSource. This approach is more tricky and only really useful when you need both collections separate and combined, e.g. a list of items in one collection and a list of item categories in another but also combined.
I have successfully used both approaches in a large widely-used WPF application.
Edit: Reading the comment on the question, if you did mean that you want a different visual or behaviour of the additional item you can achieve that using an Selector DataTemplateSelector and/or ItemContainerStyleSelector. I recently used a combination of option #2 and template selecting successfully.
Some options:
Use a CompositeCollection, you can define this is xaml. Not sure if it would solve the issue, you might need to play around with it a bit
Create a new collection behind the scenes that is populated with the items from your collection + the extra item.
Write a converter than creates a new collection (or returns an IEnumerable) with the new item added.
I guess all of these options have a common theme in that they are all a new collection. You basically can't bind directly to the original collection because it doesn't have the extra item, so you have to bind to something else in some form.
I am trying to build a generic interface that can accept a List of objects and then based on the users selection of how they want to view the objects will select different ways of display the object. Currently, the user has a dropdown that allows them to choose the view type such as "Details, Previews, etc" much like explorer and then based off the selection the display should change. My first attempt at this was to create UserControls that will accept the bound object and display it, however I dont know how to convert my listitems into the user controls. My question is, is should I be using IValueConverter to convert the listitem into the type of user control I want to display, or should I be using DataTemplates and a TemplateSelector to define my different views?
Why not just use ListView and GridView? Your use case is exactly why they're there.
MSDN has a nice little sample for how to switch views in a ListView at runtime right here.
While working in WPF i have the need for a Dynamic Grid. By this i mean a grid that contains only one kind of object, has a template for that object etc. But unlike a similar ItemsControl like a Listbox, i want the grid to be given a Maximum Columns property. This should act as a delimiter which will then calculate the number of rows needed based on the number of objects within the grid. To do this, i thought of inherriting a Grid to make use of its Row and Column properties, but i have a problem... I dont know how to implement an ItemsSource property outside of inherriting the ItemsSource from an ItemsControl...
so my question comes in two parts...
Am i pursuing this the right way? should i be inherriting ItemsControl and trying to re-implement the Grid behavior
if this is the right way to do it, how do i implement an ItemsSource property with its corresponding ItemTemplate
Perhaps a better way would be to use a ListView? Here is an example how to achieve 3-column output: http://kristofmattei.be/2010/03/16/multi-column-listview/
Do you want something like UniformGrid? If you set the Columns property (and don't set the Rows property), it will automatically figure out how many rows to create to hold its items.