I am programming a plug-in that uses a virtual tree-like file-structure. Basically it acts just like a standard filesystem containing files, with the difference that these files do not actually exist in a specific location in the filesystem but rather are mere java objects.
These are currently supported by the navigator (a custom implementation using the Common Navigator Framework) using a SettingProvider, and interaction with these Objects is implemented just like interaction with standard files.
However, it is necessary to stick markers to these Objects now. As I understand the Eclipse framework, markers can be attached to *IResource*s only, so in order to achieve this goal, instead of using *SettingProvider*s, I should create instances of IResource.
However, the standard implementation only allows creation of resources from the filesystem. Since things like virtual folders exist, there must be a possibility to create virtual resources, i.e. resources without an actual location in the filesystem.
But how can I do this? My research seems to be leading nowhere...
Alternatively, is there a possibility to achieve the desired functionality (sticking markers to objects in a CNF navigator) in a different way?
Thanks in advance!
Right, markers can only be attached to resources in the workspace. To implement a custom filesystem, Eclipse provides the EFS-mechanism, to provide a "file-like" structure, for further information see http://wiki.eclipse.org/EFS - on this page you'll also find links to example implementations which should give you an idea how to implement your own filesystem contributor.
BUT: IMHO it is the wrong approach to use Eclipses marker system for your scenario. All stuff is very tight coupled to the workspace model which does not work well with a custom data model. From my experience the best is to
have your own marker-model which fits exactly to your data model,
implement a decorator for your tree (via extension point)
implement something similar like the Problems-view to visualize markers.
Although is sounds a bit odd to implement something similar that is already there it will save you a lot of headaches cause your scenario is not restricted by the boundaries of the workspace model and api.
Related
my first question on here and I cant seem to find a similar question so sorry if this has been asked before.
This is Unity related by the way, and yes I have also posted on Unity3D answers but thought I might also be able to get help from knowledgeable individuals on stack overflow also.
Basically I am wondering if there is a way to make platform dependent objects or components. I know I can wrap code in pre-processor directive commands which I have been doing, but I tend to use a ton of plugins, many of which only function on specific platforms.
However, I have just one project for all my platform dependent versions of the game and wish to continue working this way. So I was wondering if somehow I can make say an object that has the compatible plugin components, that will only be created if a certain platform is being built for.
If not, is there a way to make an object use say a specific plugins component if say on WP8, but then another entirely different component in its place if building for Android?
If these are not possible, how do you guys get around having platform dependant plugins? Do you simply just make separate projects for each platform? (feels like that defeats the point of unity's cross platform-ness though...)
Thanks guys, any help will be greatly appreciated!
Unfortunately, you will be forced to rely on pre-processor directives if you need to run unique code per platform.
However, this can be a lot easier to manage if you apply a facade-based design pattern. Instead of peppering platform-specific details in myriad scripts throughout your project, you can create one or more facade components that expose a more generic, abstract interface. The facades can internally manage prefabs, APIs, or whatever other platform-specific details you need.
As an example, you could write a SaveManager class that manages player save data. On platforms where direct file access is available, the SaveManager instantiates and controls an internal FileSaveManager that uses direct file access. On other platforms such as web builds, the SaveManager instantiates and controls a PlayerPrefsSaveManager that uses Unity's PlayerPrefs system instead. That way, each of those classes contains only the code that it needs, and other classes can just call SaveManager without worrying about those details.
At the moment I'm doing it in a global, singleton ApplicationModel, but I feel that model should be thinner, and a more cohesive set of tasks and properties concerning composition could be relocated, on their own, to a new 'CompositionModel' class. Each of the vertical imported modules has their own MVVM stack and are basically self sustaining, with very little dependency on the core, or shell, application.
Works for me! I'm currently using it in an application where the client needs to be able to configure services by simply dropping plugins into the relevant folders, haven't run into any major issues so far. As far as your resource dictionaries go you may want to look at the answers to this question, paying particular attention to the build settings...you will need to call InitializeComponent() to get the resources to merge correctly.
I do have an iPad application which is customized for different customers in regards to color scheme, logos and other items.
I already created different targets where I defined #ifdef macros accordingly, and most variables are defined in a global.h file for easy maintanance.
Do you have any other useful suggestions I should consider at this time, especially as in the future there will be updates available - but not all new features will be avaialble to all clients?
Firstly, if you don't do that already, use the branching feature of your versioning system to handle different client needs, i.e. if one client wants an additional feature, don't (automatically) contaminate your master code base.
What you can also do is encapsulate all configurable features of your app. A very simple approach would be to create a configuration .plist or other kind of XML where you can easily configure adaptable features.
Mainly, if it's possible, try to extract all customizable features out of the primary code base. Load customizable data from easily editable files like XMLs, to make sure you don't accidently break something while configuring for a client.
You could totally abstract out all of the customizable elements and create a library of the remaining code. Each customer's App would then just instantiate that library and feed in their own customized elements. That way you don't have to change any code when you build the App for a new customer. You also get the benefit of having all the changes between customers located in one area and it also makes the code more testable.
If a customer doesn't get a feature, then you just feed in a null value (or equivalent)
This ideas is basically Inversion of Control
I like to convert reusable components into frameworks. This way you can expose customizable options and hide all of the complex code.
Another option would be to create a workspace. This would allow you to open projects within it and share their assets with the main workspace files.
A repeating theme in my development work has been the use of or creation of an in-house plug-in architecture. I've seen it approached many ways - configuration files (XML, .conf, and so on), inheritance frameworks, database information, libraries, and others. In my experience:
A database isn't a great place to store your configuration information, especially co-mingled with data
Attempting this with an inheritance hierarchy requires knowledge about the plug-ins to be coded in, meaning the plug-in architecture isn't all that dynamic
Configuration files work well for providing simple information, but can't handle more complex behaviors
Libraries seem to work well, but the one-way dependencies have to be carefully created.
As I seek to learn from the various architectures I've worked with, I'm also looking to the community for suggestions. How have you implemented a SOLID plug-in architecture? What was your worst failure (or the worst failure you've seen)? What would you do if you were going to implement a new plug-in architecture? What SDK or open source project that you've worked with has the best example of a good architecture?
A few examples I've been finding on my own:
Perl's Module::Plugable and IOC for dependency injection in Perl
The various Spring frameworks (Java, .NET, Python) for dependency injection.
An SO question with a list for Java (including Service Provider Interfaces)
An SO question for C++ pointing to a Dr. Dobbs article
An SO question regarding a specific plugin idea for ASP.NET MVC
These examples seem to play to various language strengths. Is a good plugin architecture necessarily tied to the language? Is it best to use tools to create a plugin architecture, or to do it on one's own following models?
This is not an answer as much as a bunch of potentially useful remarks/examples.
One effective way to make your application extensible is to expose its internals as a scripting language and write all the top level stuff in that language. This makes it quite modifiable and practically future proof (if your primitives are well chosen and implemented). A success story of this kind of thing is Emacs. I prefer this to the eclipse style plugin system because if I want to extend functionality, I don't have to learn the API and write/compile a separate plugin. I can write a 3 line snippet in the current buffer itself, evaluate it and use it. Very smooth learning curve and very pleasing results.
One application which I've extended a little is Trac. It has a component architecture which in this situation means that tasks are delegated to modules that advertise extension points. You can then implement other components which would fit into these points and change the flow. It's a little like Kalkie's suggestion above.
Another one that's good is py.test. It follows the "best API is no API" philosophy and relies purely on hooks being called at every level. You can override these hooks in files/functions named according to a convention and alter the behaviour. You can see the list of plugins on the site to see how quickly/easily they can be implemented.
A few general points.
Try to keep your non-extensible/non-user-modifiable core as small as possible. Delegate everything you can to a higher layer so that the extensibility increases. Less stuff to correct in the core then in case of bad choices.
Related to the above point is that you shouldn't make too many decisions about the direction of your project at the outset. Implement the smallest needed subset and then start writing plugins.
If you are embedding a scripting language, make sure it's a full one in which you can write general programs and not a toy language just for your application.
Reduce boilerplate as much as you can. Don't bother with subclassing, complex APIs, plugin registration and stuff like that. Try to keep it simple so that it's easy and not just possible to extend. This will let your plugin API be used more and will encourage end users to write plugins. Not just plugin developers. py.test does this well. Eclipse as far as I know, does not.
In my experience I've found there are really two types of plug-in Architectures.
One follows the Eclipse model which is meant to allow for freedom and is open-ended.
The other usually requires plugins to follow a narrow API because the plugin will fill a specific function.
To state this in a different way, one allows plugins to access your application while the other allows your application to access plugins.
The distinction is subtle, and sometimes there is no distiction... you want both for your application.
I do not have a ton of experience with Eclipse/Opening up your App to plugins model (the article in Kalkie's post is great). I've read a bit on the way eclipse does things, but nothing more than that.
Yegge's properties blog talks a bit about how the use of the properties pattern allows for plugins and extensibility.
Most of the work I've done has used a plugin architecture to allow my app to access plugins, things like time/display/map data, etc.
Years ago I would create factories, plugin managers and config files to manage all of it and let me determine which plugin to use at runtime.
Now I usually just have a DI framework do most of that work.
I still have to write adapters to use third party libraries, but they usually aren't that bad.
One of the best plug-in architectures that I have seen is implemented in Eclipse. Instead of having an application with a plug-in model, everything is a plug-in. The base application itself is the plug-in framework.
http://www.eclipse.org/articles/Article-Plug-in-architecture/plugin_architecture.html
I'll describe a fairly simple technique that I have use in the past. This approach uses C# reflection to help in the plugin loading process. This technique can be modified so it is applicable to C++ but you lose the convenience of being able to use reflection.
An IPlugin interface is used to identify classes that implement plugins. Methods are added to the interface to allow the application to communicate with the plugin. For example the Init method that the application will use to instruct the plugin to initialize.
To find plugins the application scans a plugin folder for .Net assemblies. Each assembly is loaded. Reflection is used to scan for classes that implement IPlugin. An instance of each plugin class is created.
(Alternatively, an Xml file might list the assemblies and classes to load. This might help performance but I never found an issue with performance).
The Init method is called for each plugin object. It is passed a reference to an object that implements the application interface: IApplication (or something else named specific to your app, eg ITextEditorApplication).
IApplication contains methods that allows the plugin to communicate with the application. For instance if you are writing a text editor this interface would have an OpenDocuments property that allows plugins to enumerate the collection of currently open documents.
This plugin system can be extended to scripting languages, eg Lua, by creating a derived plugin class, eg LuaPlugin that forwards IPlugin functions and the application interface to a Lua script.
This technique allows you to iteratively implement your IPlugin, IApplication and other application-specific interfaces during development. When the application is complete and nicely refactored you can document your exposed interfaces and you should have a nice system for which users can write their own plugins.
I once worked on a project that had to be so flexible in the way each customer could setup the system, which the only good design we found was to ship the customer a C# compiler!
If the spec is filled with words like:
Flexible
Plug-In
Customisable
Ask lots of questions about how you will support the system (and how support will be charged for, as each customer will think their case is the normal case and should not need any plug-ins.), as in my experience
The support of customers (or
fount-line support people) writing
Plug-Ins is a lot harder than the
Architecture
Usualy I use MEF. The Managed Extensibility Framework (or MEF for short) simplifies the creation of extensible applications. MEF offers discovery and composition capabilities that you can leverage to load application extensions.
If you are interested read more...
In my experience, the two best ways to create a flexible plugin architecture are scripting languages and libraries. These two concepts are in my mind orthogonal; the two can be mixed in any proportion, rather like functional and object-oriented programming, but find their greatest strengths when balanced. A library is typically responsible for fulfilling a specific interface with dynamic functionality, whereas scripts tend to emphasise functionality with a dynamic interface.
I have found that an architecture based on scripts managing libraries seems to work the best. The scripting language allows high-level manipulation of lower-level libraries, and the libraries are thus freed from any specific interface, leaving all of the application-level interaction in the more flexible hands of the scripting system.
For this to work, the scripting system must have a fairly robust API, with hooks to the application data, logic, and GUI, as well as the base functionality of importing and executing code from libraries. Further, scripts are usually required to be safe in the sense that the application can gracefully recover from a poorly-written script. Using a scripting system as a layer of indirection means that the application can more easily detach itself in case of Something Bad™.
The means of packaging plugins depends largely on personal preference, but you can never go wrong with a compressed archive with a simple interface, say PluginName.ext in the root directory.
I think you need to first answer the question: "What components are expected to be plugins?"
You want to keep this number to an absolute minimum or the number of combinations which you must test explodes. Try to separate your core product (which should not have too much flexibility) from plugin functionality.
I've found that the IOC (Inversion of Control) principal (read springframework) works well for providing a flexible base, which you can add specialization to to make plugin development simpler.
You can scan the container for the "interface as a plugin type advertisement" mechanism.
You can use the container to inject common dependencies which plugins may require (i.e. ResourceLoaderAware or MessageSourceAware).
The Plug-in Pattern is a software pattern for extending the behaviour of a class with a clean interface. Often behaviour of classes is extended by class inheritance, where the derived class overwrites some of the virtual methods of the class. A problem with this solution is that it conflicts with implementation hiding. It also leads to situations where derived class become a gathering places of unrelated behaviour extensions. Also, scripting is used to implement this pattern as mentioned above "Make internals as a scripting language and write all the top level stuff in that language. This makes it quite modifiable and practically future proof". Libraries use script managing libraries. The scripting language allows high-level manipulation of lower level libraries. (Also as mentioned above)
I've noticed in pretty much every company I've worked that they have a common library that is generally shared across a number of projects. More often than not this has been a single companyx-commons project that ends up as a dumping ground for common programs including:
Command Line Parsers
File Utilities
Framework Helpers
etc...
Some of these are well thought out and some duplicate functionality found in Apache commons-lang, commons-io etc..
What are the things you have in your common library and more importantly how do you structure the common libraries to make them easy to improve and incorporate across other projects?
In my experience, the single biggest factor in the success of a common library is user buy-in; users in this case being other developers; and culture of your workplace/team(s) will be a big factor.
Separate libraries (projects/assemblies if you're in .Net) for different application tiers is essential (e.g: there's obviously no point putting UI and data access code together).
Keep things as simple as possible; what you don't put in a common library is often at least as important as what you do. Users of the library won't want to have to think, so usage needs to be super easy.
The golden rule we stuck to was keeping individual functions focused on a single task - do one thing and do it well (or very very well); don't try and provide something that tries to take every possibility into account, the more reusable you think you're making it - the less likely it is to be used. Code Complete (the book) has some excellent content on common libraries.
A good approach to setting/improving a library up is to do regular code reviews and retrospectives; find good candidates that you've already come up with and consider re-factoring them into a library for future projects; a good candidate will be something that more than one developer has had to do on more that one project (for example).
Set-up some sort of simple and clear governance of the libraries - someone who can 'own' a specific library and ensure it's overal quality (such as a senior dev or team lead).
I have so far written most of the common libraries we use at our office.
We have certain button classes that are just slightly more useful to us than the standard buttons
A database management class that does some internal caching and can connect to ODBC, OLEDB, SQL, and Access databases without even the flip of a parameter
Some grid and list controls that are multi threaded so we can add large amounts of data to them without the program slowing and without having to write all the multithreading code every time there is a performance issue with a list box/combo box.
These classes make it easier for all of us to work on each other's code and know how exactly they work since we all use the exact same interfaces throughout our products.
As far as organization goes, all of the DLL's are stored along with their source code on a shared development drive in the office that we all have access to. (We're a pretty small shop)
We split our libraries by function.
Commmon.Ui.dll has base classes for ui elements.
Common.Data.Dll is sort of a wrapper around Enterprise library Data access classes.
Common.Business is a dumping ground for other common classes that don't fit into one of those.
We create other specialized dlls as needs arise.