In a Windows Phone 7 app, the PhoneApplicationService.Current.State object is declared as an IDictionary, and is implemented as a Dictionary. I was really hoping to get notified when any state changes occur. (I realise I could build my own state collection somewhere else and do whatever I want, but I'm retrofitting this into existing code.)
Is there any way to get that State object set to an ObservableDictionary instead of a Dictionary, so I can attach to it and get notified when the collection changes?
I'm guessing the answer will be 'no' but just want to check I haven't missed something :)
Thanks,
John
You can't change the existing implementation, but you could create a wrapper class which implements IObservable but uses PhoneApplicationService.Current.State internally.
This way, you wouldn't have to build a complete state persistence soution yourself and could implement the ObservableDictionary as best meets your needs.
Related
I'm looking to share an EF Context between "data manager" objects to ensure change tracking occurs under one context as opposed to handling multiple contexts...so I'm looking into named context... but in review of this documentation, I felt it wasn't clear, and I want to ensure my assumption is correct, and if so, update the documentation: here PRISM documents the resolution of named instances via a constructor:
My assumption is that the named typed "carservice" is matched to the named parameter in the constructor to select which concrete class should be reference to that parameter based on the IVehicleService.
Is my assumption correct - either way I'll create a pull request to clarify the documentation..Either way, answering the question here will add reference to clarification/handling of named instances in PRISM.
It seems this is NOT correct assumption, and it's not possible in Unity - I refactored to avoid.
One solution that I didn't try was to simply another interface (came to mind much later), was inheriting from an existing interface, and registers the "new" interface to use a specific constructor. As I'm new to Unity, I thought I would mention. I'm answering my own question, as I can't don't think I can give credit to a comment, and I HATE leaving questions unanswered on this site!
I'm deleting an instance of an entity and depending on the value of an option set in it, I wish to carry our different course of action. The problem is that the field isn't changed, hence, not provided to the plugin's target.
How can I easily tell the stupid plugin to fetch all the fields?
The way I do it now is to use pre-image but I'll be showing the plugin to some rookies and they will definitely not like it. And they won't believe me that's the way to go, for sure, because they're a cocky bunch.
Is there a work-around for that?
Using the pre-image is the suggested way in this scenario, the alternative is to instantiate a service factory in order to get an IOrganizationService and retrieve the entity using the target's Id.
It is part of the IPluginExecutionContext (of which Target is one part.) I think the beginners are confused if they think of Target as anything more than a property of IPluginExecutionContext.
It wouldn't make sense to have these values as part of Target, because then it would cause an update of the field to its current value - if you forced it into Target you would see the update in the audit details.
Thus, CRM has PreEntityImages, Target, and PostEntityImages, if Target was used the way "they" want it would not be able to differentiate between values being updated, previous values, and the final result of the entity.
I have a custom class that exposes an NSString property. In Interface Builder I've bound the title of an NSButton to the property of my custom class.
Is it possible to get a reference to the NSButton instance from within my custom class?
Essentially I'm trying to locate all the user interface elements that are bound to the property in my custom class.
In general, this sounds like an anti-pattern and/or a bad idea. That said, there are a couple of things to bear in mind. Multiple observers could be bound to your property. You can override addObserver:forKeyPath:options:context: and removeObserver:forKeyPath: (and removeObserver:forKeyPath:context:) and then maintain your own array of observers. With that approach I would caution you that you may need to go to extra effort for the array to not retain observers, as traditionally KV observations don't retain the observing object, and you will likely run into leaks/heap growth if you start retaining them by putting them in an NSArray.
The other gotcha with overriding addObserver:... and removeObserver:... is that, without considerable extra work, you wont know if the observation is for a binding or for something else (like, say, a dependent keyPath notification). One possible workaround for that would be to interrogate the observer via infoForBinding: on all exposedBindings on a later runloop pass using performSelector:afterDelay:. (I think I just threw up in my mouth a little bit for suggesting this.)
Relying on private implementation details of the KVO system is not likely to be a good approach, unless your goal is simply to better understand how KVO works, but it sounds like you're actually trying to accomplish something.
Really, this whole approach just feels like a recipe for disaster. It sounds like an MVC violation from the get-go. Why would the model object need to know about the view objects? Whatever you're trying to accomplish here would almost certainly be better accomplished by having the nib be owned by an NSViewController subclass which has IBOutlets for all the UI elements, and properties for the model. That object would then be in a position to more cleanly manage the apparently complex relationship between your view and model objects without runtime trickery. Since you've not elaborated on the ultimate goal of this trickery, it's hard to say what the best approach would be.
In Windows Phone a ListBox support the virtualization of the data, that means it can only load the data needed and not everything. Peter Torr explains the interface you need to implement.
The short version is that you have to create both a method that return the position of an element and another one that return the element in a specific position. The problem is that the example of Peter Torr is rather dumb, he just return an object with the index as a name.
My question is: how do you actually implement this ?
My idea is to create one file that contains a list of an (integer) index and an (integer) id and a file for every object that contains the actual data. It doesn't seem a really elegant idea, but I can't think of anything better, can you ?
UPDATE
It seems that my question is inaccurate. When I say that the example of Peter Torr is "rather dumb" I am not saying that he has done anything wrong; his objective was simply to explain what interface you need to implement. The practical implementation will depend on the specific data.
What I am asking is what choices do I have to implement this ? Should I simply put the data on a web service and query it every time (with a local cache, of course), build a database, create a file the store the indexes and one for the data ? Is there a solution good enough in every case ? What are the downsides and upsides of every choice ?
The article you linked to includes a link to a downloadable project which demonstrates how to implement this.
What more are you after? The general idea is that the ListBox will call into your IList when it needs data. it will ask for an item at a specific index and you pass back an object. it then, presumably, calls ToString() on that object and displays the result in the list.
What that actual object is and where you pull it from is completely up to you. You might be using a really large array in memory. You might be pulling from IsolatedStorage or a web service. You could certainly use it to pull file info, but I don't suspect anyone has a ready-built IList implementation so that's the part that you will have to implement based on your specific project.
There is signal in QStandardItemModel which is emitted when data of an item is changed.
Usually we connect a handler for this signal and do all the work in the handler routine.
Such handle routine only gets pointer to the item.
Using this pointer it is possible to access the data of the item.
However, we do not know what exactly has changed... we only have updated value.
If item data has several roles I want to be able to get exactly which role (data) has been changed and what was the previous value.
In general, QStandardItemModel is for very simple data modeling. If you want to get into more advanced things like you desribe, you should look into subclassing QAbstractItemModel or one of it's abstract derivatives: Model/View classes
It may seem like a lot of work, but use the examples and refernce guides: Model/View programming, Model subclassing and the rewards will be great.
This is not possible with the standard signals of Qt. I suggest to add another signal for that.
For my own models, I usually use this approach: I have a root instance which contains pointers to all parts of my data model. Items in my model use this root instance to send signals like
itemChanged(item, attribute, oldValue, newValue)
for simple properties. The same goes for lists and the like; only here, I have several signals depending on the action, for example:
itemAdded(list, item, index)
[EDIT] The QT signal handling is very basic. Usually, it will only tell "something has changed". There is no support for "what exactly has changed?" since you don't need it most of the time. So if you need that information, you must do it yourself. You can't use a role alone, because roles must be backed by something in your item. What you can do is add change information to your items and read that when the role is requested. But this is not something that is supported "out of the box".