I've been looking into MVVM toolkits, and MVVM light really appeals to me, especially do to it's focus on "blendability". I put forth the proposal to our engineering team that we move to using it as our go to toolkit for all SL development, and although most people agreed that it was nice, they couldn't understand why BaseViewModel doesn't implement the IDataErrorInfo interface.
Is this an intentional decision in mvvm-light, if so, can someone fill me on why?
IDataErrorInfo is not suitable for all places where you might use a view model. For example, if you've chosen to have a menu backed by view model objects, how would you use IDataErrorInfo in conjunction with a view model that represents a menu item?
I use ViewModelBase as the base for my own ViewModelBases that include additional features I need for that particular circumstance. I agree with mike, you dont want that functionality in the Root ViewModelBase because not all viewmodels would benefit from that functionality, unlike INotifyPropertyChanged or Messenger.
Related
I understand that treeview in asp.net comes with checkboxes option for usage. However, in my application, I will require 2 additional checkboxes or radiobutton on the righthand side of each leaf node of my treeview.
However, I seem to be unable to find a solution to this requirement, and i think treeview structure does not support this feature.
I'm new to asp and I'm not sure if there is any other class which i can use upon to implement this feature.
Hope I can have some ideas from you guys to implement this
All help is appreciated
Thanks!
Regards
bernerd
The tree view control is quite limited however I've found this project http://www.codeproject.com/Articles/43057/ASTreeView-Free-ASP-NET-TreeView-Control which has extended its functionality - check out the reference and see if it provides what you need OR use it as a base to extend it as your scope requires!
I am trying to implement a Metro style Grouped Items Page using the MVVM Light framework following the sample in this blog post but using a ViewModelLocator to provide blendability:
http://mikaelkoskinen.net/post/winrt-tutorial-mvvm-gridview-semanticzoom.aspx
I have got this working, unfortunately the grid itself is not showing up in the designer (which is the point of me using MVVM Light). I have bound the title without problem so I know that the viewmodel is bound correctly.
Any ideas please?
I had the same problem. The issue is, if you're using a CollectionViewSource, that it needs to be explicitly, like this:
As MVVM Light injects design-time-services into the viewmodel you'd expect this to pick up your service and push the design-time data through your viewmodel to the UI. But it doesn't.
You need to give it an explicit design-time instance for this to work:
There is a useful article about using CollectionViewSource in design mode that may help.
I'm fairly experienced with Flex 4, but I still haven't needed frameworks yet (I like to do everything myself) and don't want to use them either, I know it's advantages and have learned how to use one of them, but still, no.
How can I dispatch an event in the main application and have a component inside a popupmanager to react to that event? All this dispatching the event within the main app and NOT aiming it to the popupmanager or the component instance, I want to be able to fire the event and not care about who gets it or if anyone reacts to it at all so if that is possible then I wouldn't care about keeping track of said popups.
I already dispatch an event from the component and receive it in the main application by bubbling the event and therefore being agnostic of each other, now I want it backwards.
Note: I have used singletons, but it's not the approach I need this time.
It sounds to me you are in desperate need of RobotLegs, you seem to be asking how to to create/use an event bus system in order to de-couple your components which is exactly what robotlegs is amazing at.
One thing you should definitely also look at is ActionScript 3 Signals. Signals is an approach to make strongly typed events like .NET Framework, instead of the magic strings event system, and is a fantastic easy bolt on addition to any Flash/Flex project.
Another way that is common is a mediator/controller singleton pattern. Let's say this is an automotive application, and we have a service layer that behind the scenes is receiving some data from the server, whilst at the same time our popup is behind displayed. One way we solve this problem is create a singleton based controller for our data like PartsController. It also has some public const Signals like SingalDataUpdated. The popup can now do something like PartsController.SignalDataUpdated.add(OnPartsUpdated). OnPartsUpdated is a local method inside the popup that can now react to the event as necessary and has no coupling to any other UI component. This is typically the approach we take and ensure that no UI component has explicit knowledge of any other UI component, and instead only talk to the controllers. One thing you need to ensure though is when the popup is closed remove the signal lister.
Again though, RobotLegs does most of all these for you and encourages some very great architecural best-pracitces. I would highly recommend you read through their documenation and get familiar with it. It will change your life when you realize how modular and maintainable it helps make your code.
Good luck!
Update regarding context and singletons
The idea regarding a context is to create a single singleton known as your application's context that stores the instances of what would be your other singletons. Inversion of control (IoC) and RobotLegs just wires things together so it dosen't look like absolute crap to work with, but you can just use a simple IoC injector like Swiz or SwiftSuspenders which RobotLegs is built upon. So, for example, you might hit a particular controller like:
AppContext.Instance.ProductController.SignalProductAdded.add(OnProductAdded);
But that is a bit ridiculous to try to access everything this way. Here comes RobotLegs to the rescue. Instead define injection rules in your RobotLegs context, so if a component asks for a UserController via an inject metadata tag, everything would get the same UserController. Exactly like a singleton, but correctly so in your component define;
[Inject] public var _objProductController:ProductController;
Now your component can work with the controller object as if it was its own, but instead it was injected in by RobotLegs on construction. For me and and most of my products I build a few base objects like GroupBase, PanelBase, PopupPanelBase, etc. that extend the proper component and already have all the controller injection properties so any component derived from these already connect to the proper controllers as needed.
For your simple project, it's like easier to roll your own and just create a single singleton for your context to hold your controllers and communicate with application's context that way. These are all pretty high level architecural decisions and everyone works differently at this level based on their experience, preference, or whatever. The most important thing is that it works for you, and you are comfortable with the architecture. RobotLegs helps make everything very decoupled which has some amazing unforseen benefits later.
Good luck!
If I understand the question:
how can I dispatch an event in the
main application and have a component
inside a popupmanager to react to that
event
Inside your pop up component, you can do something like this:
var app:Application = FlexGlobals.topLevelApplication as Application;
app.addEventListener('myCustomEvent',onMyCustomEvent);
Now any instances of the myCustomEvent that are dispatched by the main Application class will fire the handler in the popup. Also, any instance of the myCustomEvent that bubble up to to the main Application class will fire the handler in the popup.
I'm not sure if this is a good idea. Accessing the topLevelApplication will add external dependencies to your pop up which may reduce re-use of said component in the long term. Accessing the topLevelApplication is not a decision I would take on without thought.
If you were trying to ask a different question; it is unclear to me from your post, which I found kind of confusing.
Looking further into what Flextras.com said (Jeffry Houser I presume), this feat is impossible, events never bubble to children, only to parents.
Therefore, this has to be done in a central event repository approach, which is the way frameworks do it mostly.
This is indeed one of the problems solved by dependencies injection found in some frameworks as robotlegs.
I'm refactoring some Flex code written by another developer and I'm implementing a PresentationModel approach, as I like to separate out the ActionScript from the MXML. One of the problems I've found is that the original ActionScript code adds/removes elements from the MXML.
What happens is the handler function checks the model and if the values are correct will either create or remove a element from the view. What is the best way to get the presentation model to ad elements to the view and still keep this loose coupling that I'm aiming for.
I was thinking of using simple events which the presentation model dispatches and a view can list for passing the details of the element to add. Is there another solution?
Thanks
Stephen
If you're using the presentation model, I'd assume that you have some kind of data of what needs to happen. When items of any sort are being dynamically added/removed, I make sure to make it data-driven for easier manipulation. If you want another item added, add another data model to your dataProvider of choice (List, ComboBox, DataGroup, etc).
By doing this approach, you're abstracting the logic from the presenter to the view. Events should only be used as a way for your view to know when your presenter has accomplished something. Data can be received this way (and it's good practice to do so) OR you can just bind the data within the presenter to your dataProvider. Both are good, I just find binding to be cleaner and simpler.
Every part of code that do some graphical stuff (drawing border, setting style, drag & drop management, animations, ...), should be included in the view, not the presentation model.
For this kind of graphical that stuff should be executed after a property has been changed in the PM, we use the Cairngorm 3 Observer lib. Basically, it listens to some changes in the presentation model and allows you to execute a function in the View.
<cg:ObserveValue
source="{ model.firstName }" value="{ Name.SARA }"
handler="runEffectFunction"/>
See the documentation
I have an application in flex, it has some components out of the box and quite a few of custom components and events.
I want to get all event listeners on a specific component in runtime, I know how to do it with monkey-patching the framework but I do not want to use a monkey patch nor can I rely on this in production.
Is there a way?
The EventDispatcher has a pretty slim public interface:
addEventListener
dispatchEvent
hasEventListener
removeEventListener
willTrigger
This means the list of listeners isn't exposed. You can only tell if there is at least one event listener for a particular type of event.
I would re-examine why you need to do what you want to do. In a typical Observer Pattern the listener list isn't meant to be exposed. I have a strong feeling if you are trying to get that list then you are approaching a higher level problem from the wrong direction.
You can't. You could simply use custom components only and override addEventListener to gather the information. I don't really see why monkey patching wouldn't work. Flex is powerful in features but poor in design and I guess you'll have to just live with that.