Right now I am coding an application and am thinking that there has to be a better solution to what I am doing right now.
I have a main window which shall handle the settings of the program. Then I have further classes and windows. For example a language handler class and a form that is handling the user input needed for the "main function".
However, until now I always have to pass my main window to each of this classes, because the language handler shall be able to change the main window's strings. And the other form should also be able to pass data to the main Window.
If we imagine there will be much more classes and every class needs a copy of the main window this would consume a lot of resources depending on the main window's "size".
So, is there a better/more efficient way to communicate between these classes.
Common way to do that is to use observer pattern, which in .NET is events system. Simply said, your classes subscribe to each other's events and perform action when event is raised. As noted in comment, passing references is not memory heavy, but it results in tight coupling between different pieces of your code - observer pattern addresses that problem.
Another option is to consider you classes as services. Code them to an interface and then use dependency injection (aka Inversion of Control) to build up the object graph (You tell the IoC container you want a frmSomething and it will determine what services/classes it needs and instantiate them as appropriate).
This means that:
you only ever have to code against an interface not an implementation
your code is loosely coupled (You can swap an OldTranslator for a NewTranslator and as long as they both comply to the same interface, nothing has to be changed except the configuration of the container)
you can develop high-level features which rely on services that haven't been written yet and your code will compile
You can very easily change how your app works, at run-time if needs be, by changing what classes/services are registered in your container.
Have a look at Unity for the MS-Supported DI container. Castle Windsor is a popular alternative but there are many more
It's worth noting that passing a "Copy" of the main window around as you've said is not a bad thing - You're actrually only passing a reference (effectively a pointer) to the main window (since anything more complex than the real primitives are reference types). This means that there's very little overhead whatsoever
I would suggest you to use Galasoft or Prism MVVM implementations. There you can use their messaging service which is quite easy to use. The class that needs info just sends a message to the subscriber and they in turn can send all data needed. I think that this is the easiest way to handle communication.
in addition to the ans given by IVAN.. if we look at a higher level view without all those terminologies then you should probably create a static class which would server as InMemoryStorage and defines fields on it to save information
this what you will have complete control over what is being shared and multiple components can change it
moreover you can defined getters and setters and raise an event whenever the property is changed so that different forms or windows (views) can subscribe to the change and take action accordingly
Related
I'm writing a small text-editor like utility for our in-house staff to use to modify a bunch of company specific files. I want design this in such a way we minimize leaky handlers and would like to ask for opinions.
There are different actions done based on the type of file loaded. I have each in a separate class, I instantiate and pass through the active tab's instance of the richtextbox. The implementation then subscribes to the following:
SelectionChanged
TextChanged
Then depending on the type of file, they'll deal with their specific things. I've noticed that some of our internal devs don't unsubscribe from events and things leak. The control hangs around (It's not a MDI app, a panel + tab control + many richtextboxes).
What's a good way of delegating the resposibility of susbcribing to events to these implementations?
Should I write a proxy (which they all subscribe to) and my Richtextbox basically gets that proxy to call it for me when something happens - and I subscribe/unsubscribe as necessary when the tab changes? Are there any established patterns - maybe a Gang of Four? that may be what I should use?
Yes. just create proxy class based on type call respective class methods
When developping rather large applications using Prism and MEF/Unity I always reach a point where I should choose between using events, a service or maybe both. And I cannot decide what's most usable. Maybe something is wrong with my architecture (as in this decision shouldn't have to be made in the first place) but I don't see what.
Here's a typical example: my application has a main window and a lot of slave windows that are created on demand by modules or user actions. The application decides what a slave window's chrome looks and behaves like, remembers window placement etc while the content itself is created somewhere in the modules. There are also a lot of user actions resulting in hiding/showing/bringing to front of windows. To achieve all this, I currently have a WindowManager service that listens to CreateWindow/SetWindowState/.. events.
This has benefits:
classes using this only know about IEventAggregator (which they already use most of the time anyway for other events) and the events consumed by WindowManager, not WindowManager itself
classes like ViewModels don't deal with windows directly. Instead they refer to them by their title or id and small event classes that encapsulate just what's needed.
no need for a seperate IWindowManager interface just for the purpose of mocking it in a test
And withdrawals:
WindowManager could be used perfectly standalone, but now it needs to subscribe for events. Or probably better, some other class has to take care of that.
extending it to show a modal dialog is somewhat tricky: if a VM fires an event to show a dialog, it's of utter importance that the Publish call only returns after the dialog was closed
WindowManager is available as a service and it's in the CompositionContainer, why not use it as such anyway?
Using the service directly just shifts benefits/withdrawals around and there doesn't seem to be a clear winner.
Question: what would you use as guidance rules to pick one or the other, or would you rather always pick just one, or both? Is there something particularly wrong in my application design that I have to make this decision?
Events and services are used for different things. You don't have to choose between them, you can use them for different purposes. You would typically use event to notify listeners that something has happened. Example: users changes the font size in the application settings. You would send event to all listeners (e.g. viewmodels) so that the views update. Usually event is kind of thing for which you don't get a response (although you could attach e.g. callback function/action that the event listener would call).
What if your viewmodel needs to open new window? Usually the viewmodel shouldn't care how this new window is opened or whether it is modal or not. In this case it would be easy to use a service:
windowManager.ShowDetailsView();
The WindowManager (which you use through IWindowManager interface) is responsible for displaying the details view. Maybe it is a modal view or maybe there is some kind of slide animation. The point is that the viewmodel that uses IWindowManager doesn't care.
In some cases you might need to receive notification if users clicks Ok or Cancel. You can still use the IWindowManager by having method like this:
public void ShowEditView(Action userSavedChanged, Action userCancelled);
Then just call it from the viewmodel
windowManager.ShowEditView(this.SaveChanges, this.CancelChanges);
// in your viewmodel you have the SaveChanges and CancelChanges methods
private void SaveChanges()
{
// save the changes.
}
Hopefully this all makes some sense. After all it is friday :)
I'm not a hater of singletons, but I know they get abused and for that reason I want to learn to avoid using them when not needed.
I'm developing an application to be cross platform (Windows XP/Vista/7, Windows Mobile 6.x, Windows CE5, Windows CE6). As part of the process I am re-factoring out code into separate projects, to reduce code duplication, and hence a chance to fix the mistakes of the inital system.
One such part of the application that is being made separate is quite simple, its a profile manager. This project is responsible for storing Profiles. It has a Profile class that contains some configuration data that is used by all parts of the application. It has a ProfileManager class which contains Profiles. The ProfileManager will read/save Profiles as separate XML files on the harddrive, and allow the application to retrieve and set the "active" Profile. Simple.
On the first internal build, the GUI was the anti-pattern SmartGUI. It was a WinForms implementation without MVC/MVP done because we wanted it working sooner rather than being well engineered. This lead to ProfileManager being a singleton. This was so from anywhere in the application, the GUI could access the active Profile.
This meant I could just go ProfileManager.Instance.ActiveProfile to retrieve the configuration for different parts of the system as needed. Each GUI could also make changes to the profile, so each GUI had a save button, so they all had access to ProfileManager.Instance.SaveActiveProfile() method as well.
I see nothing wrong in using the singleton here, and because I see nothing wrong in it yet know singletons aren't ideal. Is there a better way this should be handled? Should an instance of ProfileManager be passed into every Controller/Presenter? When the ProfileManager is created, should other core components be made and register to events when profiles are changed. The example is quite simple, and probably a common feature in many systems so think this is a great place to learn how to avoid singletons.
P.s. I'm having to build the application against Compact Framework 3.5, which does limit alot of the normal .Net Framework classes which can be used.
One of the reasons singletons are maligned is that they often act as a container for global, shared, and sometimes mutable, state. Singletons are a great abstraction when your application really does need access to global, shared state: your mobile app that needs to access the microphone or audio playback needs to coordinate this, as there's only one set of speakers, for instance.
In the case of your application, you have a single, "active" profile, that different parts of the application need to be able to modify. I think you need to decide whether or not the user's profile truly fits into this abstraction. Given that the manifestation of a profile is a single XML file on disk, I think it's fine to have as a singleton.
I do think you should either use dependency injection or a factory pattern to get a hold of a profile manager, though. You only need to write a unit test for a class that requires the use of a profile to understand the need for this; you want to be able to pass in a programatically created profile at runtime, otherwise your code will have a tightly coupled dependency to some XML file on disk somewhere.
One thing to consider is to have an interface for your ProfileManager, and pass an instance of that to the constructor of each view (or anything) that uses it. This way, you can easily have a singleton, or an instance per thread / user / etc, or have an implementation that goes to a database / web service / etc.
Another option would be to have all the things that use the ProfileManager call a factory instead of accessing it directly. Then that factory could return an instance, again it could be a singleton or not (go to database or file or web service, etc, etc) and most of your code doesn't need to know.
Doesn't answer your direct question, but it does make the impact of a change in the future close to zero.
"Singletons" are really only bad if they're essentially used to replace "global" variables. In this case, and if that's what it's being used for, it's not necessarily Singleton anyway.
In the case you describe, it's fine, and in fact ideal so that your application can be sure that the Profile Manager is available to everyone that needs it, and that no other part of the application can instantiate an extra one that will conflict with the existing one. This reduces ugly extra parameters/fields everywhere too, where you're attempting to pass around the one instance, and then maintaining extra unnecessary references to it. As long as it's forced into one and only one instantiation, I see nothing wrong with it.
Singleton was designed to avoid multiple instantiations and single point of "entry". If that's what you want, then that's the way to go. Just make sure it's well documented.
I'm interested in creating a desktop application composed of modules such that the source code to those modules is embedded in the application itself, allowing the user to edit the application as they are running it and have the updated modules put into use without restarting the application. Can anyone suggest a good architecture for this?
I'm looking to use Microsoft.Net and C# for this. DLR is not an option.
Thanks!
It's not easy to suggest a good architecture for this in a short posting.
At first, i'd define a contract (an Interface) every module the user writes/modifies must implement. It should contain at least an Execute method.
Then I'd create a Wrapper-Class for these modules which:
loads the source code from a file
The wrapper compiles the file and also makes sure it implements the contract
Contains an indicator of whether the file could be compiled sucessfully
It should also implement the contract, for easy calling and handling
Then I'd have some kind of shell which contains a collection of all the module-wrappers. Any wrapper that sucessfully compiled would then let the Shell call the Execute method of the module interface.
When it comes to compiling and executing code on the fly, this link should provide all the information you need:
http://www.west-wind.com/presentations/dynamicCode/DynamicCode.htm
Well, a dynamic language certainly would have been the best fit...
You can use the types in the System.Reflection.Emit namespace to dynamically create assemblies.
However, it's going to be really painful because you'd need to load those dynamic assemblies into custom AppDomains because otherwise you'll not be able to unload them again.
This again means that you must address marshalling and assembly resolution issues related to cross-AppDomain communication.
What you are probably looking for is the concept of Dependency Injection.
Dependency Injection means that instead of having module X use module Y directly, module X only relies on an interface, and the application tells module X which implementation should use for it, e.g. using module Y.
There are several ways of implementing Dependency Injection. One is to have references to the interfaces in each of your modules, and explicitly let the application configure each of its modules with the right implementation of the interface.
The second wahy of implementing it (and probably the most useful in your case) is by using a central registry. Define all the interfaces that you want to have in your application. These are the interface for which you want to dynamically change the implementation. Then define identifications for these interfaces. These could be strings or integers or GUID's.
Then make a map in your application that maps the identifications to the interfaces, and fill the map with the correct implementations of the interfaces. In a C++ application (I'm not very skilled in C# yet) this could work like this:
std::map<std::string,IInterface> appInterfaces;
appInterfaces["database"] = new OracleDatabaseModule();
appInterfaces["userinterface"] = new VistaStyleUserInterface();
Make all modules go to this central registry whenever they want to use one of the modules. Make sure they don't access the modules directly, but they only pass via the registry. E.g.
MyModule::someMethod()
{
IDatabaseInterface *dbInterface = dynamic_cast<IDatabaseInterface *>(appInterfaces["database"]);
dbInterface->executeQuery(...);
}
If you now want to change the implementation for an interface in the application, you can simply change the entry in the registry, like this:
IInterface *iface = appInterfaces["database"];
if (iface) delete iface;
appInterface["database"] = new SqlServerDatabaseInterface();
We've been using the MVP pattern and Winforms with a fair amount of success. However, a question always pops-up about MVP:
What is a good granularity for presenters?
What I mean by that is: With Winforms, a fine-granularity usually works quite well for user controls. That way, it's easy to reuse user controls and use them as building blocks while designing more complex GUIs. However, having the same (fine-)granularity with presenters seems to be a problem.
On one hand, having coarse-grained presenters hinders the ability to use "plug-in" controls and it sorts of violate the DRY principle: Multiple presenters often need to implement the same logic (populate a list of customers, for instance), which is used by multiple, more complex, controls.
On the other hand, fine-grained presenters seem to limit the ability to reuse controls in different situations. For instance, an editing view might sometimes need to save the customer right away; sometimes it needs to link it to something else; sometimes is just needs to validate it; and so on. It often depends on the more complex control. But there's also a fair amount of shared behaviour.
Note that, in both cases, 1-presenter-1-view is achievable. What is considered "1-view" changes.
What is usually considered best-practices for presenter granularity using MVP and Winforms?
Fine-grained presenters and customizable behaviour through options or something of that nature?
Coarse-grained presenters and low presenter reusability?
Something else?
Disclaimer: We mainly use Supervising Controller but I think it also applies to Passive View. Sorry for the long question, too.
We use MVP at all of our clients and this is definitely a conversation that comes up in more than one occasion. How clean should our code behind classes and presenters be? Having said that, we have chosen to use the coarse-grained presenter approach. Basically, every form would have its own presenter and would only get and set properties of any of the controls on a particular form using its view. Populating controls-a call to a db to populate a combobox for example-is located in a public service class. Any validation of user inputted data is located in a BO class which can be reused by any and/or all of the presenters. I hope this helps.
In my CAD-CAM system my presenters don't use user controls. User controls reside in the view which reside in a EXE assembly that implement the view interfaces the presenter use.
If want to display a list of customers I hand it off to the view which has a DisplayCustomerList and it uses whatever combination of user controls it needs to display the customer list. If multiple views show the customer list in the same way then in the ExE/View assembly they share a user control or class for doing that. That class doesn't go outside of that assembly.
Our software is adapted to run many different types of metal cutting machine. So we place a lot of emphasis on being able to rip off the UI and replace it with a completely different UI (corresponding to a different machine). All of these UIs reference the same set of core assemblies.
The hierarchy looks like this
View EXE
Presenter Implementation
Command Assembly - commands are executed by the presenter that modify the model
Presenter Interfaces
Model Assemblies
Off to the side are loadable assemblies that define dynamic content like what file types can be loaded, reports, cutting device drivers, etc. These implement various interfaces found in the model assemblies
One thing I do is that I don't impelment a view presenter for every dialog. If the dialog is tightly bound with a command then it is defined, created, and used along side the command class. Occasionally a group of related commands will share a dialog (File handling for example).
The essential question I ask when using MVP is "What happens if want to completely replace the forms with something else?". The answers to that question will identify where you are too dependent on a particular user control or form engine.
The biggest problem (and one that I haven't got a good answer for) of my setup is that current IDEs and langauges make it very easy to tie user controls to database records. It is so productive compared any other setup it tends to dominate the design. I haven't had to deal with the issue much in my CAD-CAM application so I don't have any answer other than passing the dataset to the view and let it handle it. This site has some patterns that may be of use in this situation.