I'm using AvalonEdit for displaying formatted text. The application is written in MVVM architecture in C#/WPF.
The problem is that the AvalonEdit control contains a lot of logic, which is accessible only from the control itself. So, say, I want to deal with current selection - for that I have to reach editor.TextArea.Selection - this is not accessible from the viewmodel.
Now my architecture may be shortly described as:
Main view model contains list of DocumentViewModels
DocumentViewModel contains TextDocument
List of DocumentViewModels is bound to DockingManager to be displayed as a list of tabs
DockingManager's DataTemplate is set to my control containing the TextEditor
TextDocument from DocumentViewModel is bound to Document property of TextEditor
Say, that I want to access selected text from the main window's viewmodel. I can reach for DocumentViewModel of the currently active document, but I have no way of accessing the control, which presents it (it's created and managed via the DataTemplate mechanisms of DockingManager)
Usually I solved this kind of problem by passing view to viewmodel via interface - such that viewmodel might have asked view (indirectly) to do something I couldn't bind or pass via commands. But since I have no control over creation of document views, I have no way of using such solution.
How can I access the TextEditor from MainWindowViewModel having its DocumentViewModel only? And how to do that without breaking the MVVM model? (obviously I may try to reach the control via visual tree, but that's hacking and I definitely want to avoid it)
Related
probably a beginner question,
I develop in c # wpf a graphical application with different windows, if I now open a new window with button and there, for example, capture a customer, then how can the other window still remain interactible with the open table?
or how can I run a function in another window that is supposed to update a DataGrid of another window (other .xaml file)?
Because neither window should actually control the access or view of the underlying data, they both interact with it via a intermediary class/object.
For WPF this pattern is commonly MVVM: Model, View, ViewModel. Your WPF Windows/Forms are the Views, and the data interaction will be in the ViewModel and Model.
I've not had to learn this in a while, but LearnMVVM looks to be reasonable starting point.
I suggest you Implement a ViewModel (if youre lazy there is MVVM Lite) with public or internal access mods. Then call the specified method to update the ViewModel.
You can pass a reference from your 2nd Window to your MainWindow by passing it though the constructor if you, for some reason, cant use static constructs.
What are you looking for is MVVM-Design Pattern (or MVC):
Model − It simply holds the data and has nothing to do with any of the business logic.
ViewModel − It acts as the link/connection between the Model and View and makes stuff look pretty.
View − It simply holds the formatted data and essentially delegates everything to the Model.
Wikipedia: MVVM
Tutorialpoint: MVVM-tutorial
I'm creating a WPF program that consumes rest api data. I want to implement lazyloading and infinite scroll on the data and programmatically create and add either custom data templates or listitems very similar to this design
I'm just confused as to which approach to take and what benefits/costs each provides
Easy choices:
Everyone uses MVVM so use MVVM.
Data Templating is a fundamental of wpf and building UI in code is not recommended - so use data templating.
You can dynamically add templates to resources by building xaml as strings. This is the MS recommended way to build any dynamic UI. Those strings can come from flat files, a database directly or a web service and you can build them by manipulating txt files or serialising controls.
A huge plus of this is you have the markup "right there". So when things go pear shaped you can paste into an experimental solution and see the errors light up in the xaml or see what the user is seeing.
If datatype associated templating doesn't suit for some reason then you could write a datatemplateselector and put your logic in there.
I'm not sure how you expect that to scroll exactly but I'd go with a listbox, some datatemplates associated with a type per view. Assuming the items can have different views - you just seem to have that "gilded" button or tag as an option.
Load your data into viewmodels with one per row.
.Add to an Observablecollection which is a public property in a viewmodel.
Bind that to the itemssource of a listbox.
They are then templated into UI.
A listbox has a scroller built in but you could re-template if you wanted to scroll using some other approach.
A StackPanel is a Panel that arranges child elements into a single line that can be oriented either horizontally or vertically.
A ListView is an ItemsControl that you can bind to an IEnumerable of objects and is used to present a collection of items.
What you should do is to create an ItemsControl with an ItemTemplate that corresponds to a scrollable item in the list. There is a basic example available here and you will find a lot more examples online.
Ok, this is going to be a 1000ft long question, but there's a lot to cover so here goes:
I am creating a paged items control, the purpose of which is to display very large collections in a paged format. I've created a repository on GitHub which can be found here. I have removed any styling for simplicity.
Upon starting the application, it looks like this:
This is pretty straightforward really, there's navigation buttons, an items per page selector but that isn't really important. The problem here is when you click the button "Open New Window".
This will open a new MainWindow, but on the first window, the collection disappears, as shown below:
The image above shows the old window in front, as you can see, there is no list of content as there is on the new window.
So, after smashing my head against a wall for a couple of hours, I am in need of assistance. I'll provide an overview of how the project is structured.
AnagramPagedItemsControl
The control being used for displaying the content is a custom control called AnagramPagedItemsControl, it is responsible for handling navigation between pages. I think the key property here is the PagedCollection.
The PagedCollection dependency property holds the collection which is bound to the Models property in the TestItemsViewModel.
TestItemsViewModel
This is the DataContext of the MainWindow, each window instance should create it's own view model. The CreateTestItems() method is responsible for creating the list of test items.
LazyPagedCollection
The purpose of this collection is to encapsulate the logic of a paged observable collection, it only loads pages when they are needed, hence the laziness.
It exposes methods like NextPage which are called in the AnagramPagedItemsControl when the user clicks on the various navigation buttons. The view model can also call navigation on the LazyPagedCollection, this allows the view model to call navigation without having to go through the view to do it.
TL;DR
When I create a new Window, the content of the previous window disappears. The problem is almost certainly with the control however I am stuck as to how to fix the problem.
This is quite a large problem to look at so I'd be very grateful for anyone who can look into it. Again, the source code is here, please feel free to suggest alternatives or pick out anything that I may have overlooked.
Had some time to spare, so:
The problem is the setter for the CollectionView property in the style for AnagramPagedItemsControl in generic.xaml.
This does not instantiate a new ListBox every time the style is applied; it will just create the one ListBox, the first time the style is created, and use that value over, and over again. So in effect, every instance of MainWindow shares the same ListBox.
You can see this by setting the Tag property of PART_CollectionView to (for instance) "1" in SetupBindings(ItemsControl PART_CollectionView). When you open a new window, you'll see that PART_CollectionView.Tag contains the same value you previously assigned.
I am required to use the mvvm pattern. I know that the viewmodel should not care about the view from what I been reading. As a result I don't know how to solve this problem:
I have a dll that basically turns a textbox and listview into an autocomplete control:
SomeDll.InitAutocomplete<string>(TextBox1, ListView1, SomeObservableCollection);
anyways I don't know how to call that method from the viewmodel using the mvvm patter. if I reference the controls in the view I will be braking the rules.
I am new to MVVM pattern and my company requires me to follow it. what will be the most appropriate way of solving this problem?
I know I will be able to solve it by passing the entire view to the viewmodel as a constructor parameter but that will totaly break the mvvm pattern just because I need to reference two controls in the view.
What you're doing here is a pure view concern, so I'd recommend doing it in the view (i.e. the code-behind). The view knows about the VM and its observable collection, so why not let the code behind make this call?
(I'd also recommend seeing if you can get a non-code/XAML API for "SomeDll", but I have no idea how much control you might have over that)
There are two things that I'd point out here -
First, this is effectively all View-layer code. As such, using code behind isn't necessarily a violation of MVVM - you're not bridging that View->ViewModel layer by including some code in the code behind, if necessary.
That being said, this is often handled more elegantly in one of two ways -
You could wrap this functionality into a new control - effectively an AutoCompleteTextBox control. This would allow you to include the "textbox" and "listview" visual elements into the control template, and bind to the completion items within Xaml.
You could turn this into an attached property (or Blend behavior), which would allow you to "attach" it to a text box, and add that functionality (all within xaml). The items collection would then become a binding on the attached property (or behavior).
I'm a bit confused as to what a viewmodel's role is beyond databinding. I have a menu built in silverlight. The menu has x number of menu items which is determined at runtime. One of the features I would like to add to this is that each menuitem has a different text colour when hovered over.
Is it the role of the view to have a colour selector method or should the view handle this in it's code behind?
Normally I would keep the coloring/styling in XAML if possible - My view of the ViewModel is that it is responsible for providing all the data (ie. not graphical stuff) from the Model in a manner the View can consume.
If it was complex logic that determined the color and it was to be reused - I might be tempted to put it in the ViewModel tho.
The view model is used by the data binding process as a "safe" way to allow you to sort/filter/group the records as seen by a specific control without (necessarily) making changes to the actual bound data set (that is, unless/until you tell it to). (FMI read Bea's article here.)
I agree with Goblin here, in that the presentation aspects like color might be best kept separate in the XAML, for example in the DataTemplate used by that control.