Related
I need to know when inFullscreen of monitor object is set to true, I wanna make sure it's not set to true when window is maximized. I can't find any docs for imports.ui.main nor any imports.ui.*. That's simple (but still annoying) I can hold alt and press F2 and type lg then enter to try it in the repl. But what if I need some info about queueDeferredWork?
Or what if I wanna know if there's a signal like switch-workspace but when the switch is finished (when switch-workspace is triggered it SEEMS that the switch animation just began and at least inFullscreen doesn't return true when I switch to a fullscreen workspace, it just SEEMS so, I can't make sure as I can't find docs for it.)
Is gnome-shell api (except imports.gi.*) not documented? or am I missing something?
There was very similar question asked here: How do I get the monitor of an active window in GNOME?
Sorry I didn't see your question earlier; you should use the tags [gnome-shell-extensions] and [gjs] to ellicit help for more programming related questions.
Updated September 2021
As of, well awhile ago, GJS has its own portal for tutorials, documentation and so on.
https://gjs.guide
Everything below is linked to from this portal, so it's a good bookmark.
There are guides covering all the basics, much of the advanced usage, introductions to core libraries like GLib and GTK, including some specialized tutorials like spawning subprocesses. There is also a dedicated section for extensions, covering creation, translations, preferences and porting guides to get your extension working on the latest release.
Please - do request any documentation you find lacking. It may not always be feasible or quick, but we'll do our best.
https://gjs-docs.gnome.org
This is GJS's official API documentation for the GNOME platform, including all core libraries and all the other libraries like GStreamer and WebKit you expect. If a library is missing, you can request it by opening an issue.
For GNOME Shell extensions, these will be of particular interest (see the Architecture page for more details):
Clutter: The compositor-side toolkit, part of Mutter
Meta: The window manager and/or compositor (aka Mutter)
St: Builds on Clutter to add more complex widgets and CSS
Shell: The internal library of GNOME Shell, providing several classes and functions
Gvc: High-level bindings for PulseAudio. Not strictly a part of GNOME Shell, but used by it and worth noting.
This documentation is still correct, however it is probably best for those familiar with the GNOME platform that just need some hints for GJS.
Modules built into GJS: https://gitlab.gnome.org/GNOME/gjs/blob/master/doc/Modules.md
General API usage in GJS: https://gitlab.gnome.org/GNOME/gjs/blob/master/doc/Mapping.md
As JavaScript is (now) evolving fairly quickly, it is highly advised you familiarize yourself with GNOME Shell's JavaScript source. Aside from being crucial to writing extensions, this is the best way to keep up with new features in JavaScript and GJS, including patterns for using them.
HELP!
discourse.gnome.org using the extensions tag
Matrix: https://matrix.to/#/#extensions:gnome.org
IRC: irc://irc.gnome.org/shell-extensions
Now that TideSDK is effectively dead, I've been looking into alternative 'wrappers' to run HTML/CSS/JS applications as stand-alone desktop applications. The three viable options I have run across so far, are NW.js (formerly node-webkit), brackets-shell, and Electron (formerly atom-shell).
The problem is that there does not appear to be a sufficiently complete comparison between the three in terms of feature set, compatibility, etc. I'm hoping to turn this into a more-or-less canonical thread on the (objective) differences between the three, in particular regarding:
Platform support; operating systems, dependencies, etc.
Language feature support, as far as HTML5, CSS3 and JavaScript are concerned. Think things like "does HTML5 video work, and if yes, what codecs are available?"
Non-standard extra features, such as tray icons, popup notifications, and OS-rendered menu bars.
Extensibility; eg. ability to 'plug in' native code, talk to Node.js, and so on.
Architecture; in particular the architectural differences that affect daily usage as a developer.
Debugging; included development tools, compatibility with commonly used tools like node-inspector, etc.
... and so on.
What are the objective, technical differences that matter when making a choice between them as an application developer?
I did similar research about two months ago, and in the end I went with node-webkit. The biggest upside on node-webkit is node.js and npm. The package management of npm is really nice, and node has well done filesystem access.
Brackets-shell looked interesting, but other than a nice IDE I didn't really get what made this one as good or better than the rest. They are very clear that "The brackets-shell is only maintained for use by the Brackets project ", that screams run away to me.
https://github.com/adobe/brackets-shell#overview
Atom-shell seems to be recently active, but it seems much like brackets in that they are really writing and editor/IDE that just happens to be attached to a webkit runtime. It also is built on top of node.js. This one has the downside of being difficult to search for stuff online without being reminded of your middle school chemistry.
I really don't want an new editor, and most programmers have their favorite already. For the actual application development, they pretty much work the same, and should, since they all use webkit. You basically write 90-95% of it like a website, and then deal with the native parts, and some config.
These things are true for all three of them
platforms - runs on Windows, Mac, and Linux
language support - HTML5, CSS3 and Javascript : since they run javascript you can download and run nearly any library/framework that you want.
The big caveat on webkit is codec support. Typically you will have problems with non-free video codecs, unless you rebuild the dll/so to support them. For example the shipped node-webkit won't play mp4 video.
I've been playing with Atom-Shell over the last few days, and I am loving it so far.
The best part about it is that it's backed by GitHub.. which should allow you to settle into the platform for the long term, especially if it gains a large following. It's also made possible by direct Node.js improvements courtesy of a contract with StrongLoop, who is a major Node.js contributor (they claim to employ more Node.js core developers than any other company, even Joyent).
I've also found it rather comfortable to get started. It took me about a day to learn the structure and get my first proof of concept running. Very cool.
Bullet Points:
Platform support: Windows, Linux, Mac OSX (More Info Here)
Language feature support: HTML5, CSS3, JS via Chromium - so far, zero issues, but I have not tested video specifically.
Native Features: Native App Menus, Task Tray Support, Global Hotkeys, Protocol Handler Support (that I've seen so far)
Extensibility: Excellent Node.js integration, both the client and server can "require" Node.js modules and natives. I've also successfully tested Bower libraries (incl jQuery) without issue.
Architecture: Covered in the other points, but in general its very smooth.
Update (11/25/14): I've not yet found use case for Atom-Shell in any official capacity, but I have used it to build a few small apps for my own use, the most complex being an app that pulls my time logs from my PM software and creates Paypal invoices.
My opinion of the platform remains positive. It's pretty awesome.
On my time invoicing app I successfully brought in Bootstrap 3's Dashboard Example Template and a few node modules (bluebird, Paypal SDK, Teamwork PM Client) to create a mildly complex app. It took me a few days and does its job well.
I really cannot think of anything negative to say about Atom-Shell, its solid, stable, fast, and easy to code for. I hope this helps someone.
Besides fully support Web standards, NW.js supports a list of non-standard features for native app development including:
Protect JS source code by compiling them into machine code: https://github.com/nwjs/nw.js/wiki/Protect-JavaScript-source-code-with-v8-snapshot
Jailed devtools: https://github.com/nwjs/nw.js/wiki/Devtools-jail-feature
Additional security model with which you can do more in DOM: https://github.com/nwjs/nw.js/wiki/Security https://github.com/nwjs/nw.js/wiki/Changes-to-DOM
enhanced file dialog: https://github.com/nwjs/nw.js/wiki/File-dialogs
kiosk mode: https://github.com/nwjs/nw.js/wiki/The-Kiosk-mode
supports for a growing list of chrome.* API, include chrome.webRequest so you can intercept HTTP requests from DOM: https://github.com/nwjs/nw.js/issues/518
support for rich notifications, print preview, many more chrome.* APIs, Chrome Apps and other Chromium features starting from 0.13.0-alpha0
There is much more to see in the wiki including Menu, Tray, etc.
I've been working with brackets-shell for some time now, here are some of my findings:
brackets-shell is primarily developed as a shell under the brackets IDE project, but the project can run any web application. You just need to point it to your own html page. Clint Berry wrote an excellent tutorial about doing just this: http://clintberry.com/2013/html5-desktop-apps-with-brackets-shell/
The project is backed by Adobe and has a lot of activity
Documentation could be better
platform support They support Windows, Mac and Linux. An installer package can also be created. I only tested it on Win and Mac, it works great.
feature support html5, css3, js. Html5 video does not work out of the box, but is very easy to enable (by default the ffmpegsumo.dll is not copied into the installer, if you change the script to copy it it will work).
native features menu bar, 'open file with', file system access. I am not using any of these, as all I need is the communication with the node process.
extensibility a nodejs is built in, and you can communicate with node from your web application. In this way, you can use node to access the filesystem etc.
architecture The project is well set up, keeping a nice separation between the shell project and your own web app running inside it. In your own application, a global appshell object is available which gives you access to the brackets functionality (filesystem access, communication with node process, ...).
One thing to note (if you care), is that the Electron officially does not support Windows Vista. Vista's market share is about halfway between OSX 10.9 and 10.10 (both of which are fully supported by Electron). Vista is also still supported by Microsoft until 2017.
NW.js works fine in Vista, as well as OSX 10.9+. NW.js works on Ubuntu, Debian, Zorin, Manjaro, Arch, and most other Debian based Linux OS's. Electron has refused PR's to fix Ubuntu specific bugs on their platform which is concerning.
NW.js works in XP too. Currently 18% of the market is still on XP. So if you're desktop application is more general purpose or wants to have access to the late adopters still on XP, you're probably better off with NW.js (0.14.7) as Electron only supports Win 7 and up.
If you use NW.js 0.12.3 you can also support OSX 10.6+ and very old versions of Debian based Linux OS's like Ubuntu, and Win XP+. It is recommended that you do special builds just for those legacy systems though and use the newer versions of NW.js for newer OS's.
We're building a web-based application that requires heavy image processing. We'd like this processing load to be on the client as much as possible and we'd like to support as much platforms (even mobiles) as much as possible.
Yeah, I know, wishful thinking
Here's the info:
Image processing is rasterization from some data. Think like creating a PNG image from a PDF file.
We don't have a lot of server power. So client-side processing is a bit of a must.
So, we're considering:
Flash - most widespread, but from what i read has lackluster development tools. (and no iPhone/iPad support for now).
Silverlight - allows us to use .NET CLR, so a big ++ (a lot of code is in .NET). But is not supported for most mobiles ( rumored android support in the future)
HTML5 + Javascript - probably the most "portable" option. The problem is having to rewrite all that image processing code in Javascript.
Any thoughts or architectures that might help?
Clarification: I don't need further ideas on what libraries are available for Silverlight and Javascript. My dilemma is
choosing Silverlight means no support for most mobiles
choosing Flash means we have to redevelop most of our code AND no iPhone/iPad support
HTML5 + Javascript we have to redevelop most of our code and not fully supported yet in all browsers
choosing two (Silverlight + Flash) will be too costly
Any out-of-the-box or bright ideas / alternatives I might be missing?
This is the sort of issue that software architects run up against all the time. As per usual, there is no ideal solution. You need to select which compromise is most acceptable to your business.
To summarise your problem, most of your image processing software is written in .NET. You'd like to run it client-side on mobile devices, but there is limited .NET penetration on mobiles. The alternatives with higher penetration (eg. Flash) would require you to re-write your code, which you can't afford to do. In addition, these alternatives are not supported on the iPhone/iPad.
What you ideally want is a way to run all your .NET code on most existing platforms, including iPhone/iPad. I can say with some confidence that no such solution currently exists - there is no "silver bullet" answer that you have overlooked.
So what will you need to compromise on? It seems to me that even if you redevelop in flash, you are still going to miss out on a major market (iPhone). And redeveloping software is extremely costly anyway.
Here is the best solution to your problem - you need to compromise on your "client side execution" constraint. If you execute server side, you get to keep your existing code, and also get to deploy to just about every mobile client, including the iPhone.
You said your server power is limited, but server processing power is cheap when compared to software development costs. Indeed, it is not all that expensive to outsource your server component and just pay for what you use. It's most likely that your application will only have low penetration to start off with. As the business grows, you will be able to afford to upgrade your server capacity.
I believe this is the best solution to your problem.
Host you image processing on Amazon E2C, Azure, or Google. IIRC E2C has many common image processing problems packaged and all ready to go.
Azure probably more familiar ground in term of sharing code as a web service
You just pay for CPU cycles and transfers/storage etc
I'm sure there will be Silverlight and JS people posting examples. Here are some image editors written in actionscript:
Phoenix
PhotoshopExpress
There is an ImageProcessing library to start with.
Plus PixelBender is available in Flash Player 10, it's fast, it runs in a separate thread
and people do some pretty mad things with it.
HTH
Some help for the Silverlight part:
There is an Silverlight image editor called Thumba.
And Nokola recently made one called EasyPainter and he will also provide the source code in the furure.
For the image conversion I would recommend the open source library ImageTools that also includes some basic effects.
Silverlight has a class for pixel manipulation of bitmaps called WriteableBitmap. The open source library WriteableBitmapEx is a collection of extension methods for Silverlight's WriteableBitmap. The WriteableBitmap API is very minimalistic and there's only the raw Pixels array for such operations. The WriteableBitmapEx library tries to compensate that with extensions methods that are easy to use like built in methods.
Pixel Shaders can also be used to make some fast and advanced effects. Although they are limited by Shader Model 2 shaders can be used for fast bluring, tinting and such things.
DISCLAIMER: I consider myself as an advocate of the Flash platform. I admire Silverlights huge potential as a technology to deploy almost any .NET content through the browser, but it has low penetration, is horribly marketed and -although perceived as such by many (mostly people who don't know either Flash or Silverlight)- is no competitor of Flash, as much as Flash is no competitor of Sliverlight. The idealist in me loves the idea of doing everything in HTML+JS using a standard, instead of relying on 3rd party proprietary software. But the truth is, JS is slow and the API is limited, and implementations of JS, HTML and CSS are terribly inconsistent accross browsers.
If you really wanna stick to .NET and are so interested in targeting the iPhone and its siblings, then you might wanna check out MonoTouch.
Still, even though this may surprise you, I am going to tell you to use Flash. :)
Why? The image processing bit is the smallest part of your application. Whatever it is you are writing, I am very sure of that. I don't know about Silverlight, but in Flash the filters used by "Thumba" and "EasyPainter" can be created within a day, most of them simply using ConvolutionFilter, ColorMatrixFilter, DisplacementMapFilter and BitmapData::paletteMap or even simply by applying one of the other filters Flash offers out of the box. Any additional things can be created using PixelBender, which was pointed out by George. The kernel language is a subset of C, so porting classic filters shouldn't be too time consuming. Also alchemy (an LLVM backend targeting Flash Player 10) would be an option worth investigating, although it's not very stable yet.
The biggest part of your app will be a lot of GUI design, GUI implementation, Business Logics etc. Flash is really great when it comes to simple, yet reasonably fast image manipulation and with the Flex framework and MXML you have a powerful tool to productively create the GUI of your app, that can interoperate very well with a multitude of server solutions for virtually any platform.
Also, Flash has a great and active community, offering tons of tutorials, code snippets, libraries and frameworks, and a big ecosystem, with cross-compilation tools to deliver flash content to other platforms (including the upcoming Flash CS5, or the mentioned Elips). I don't understand, where you got the impression, that the Flash platform lacks developement tools. The difference to the .NET suite is that they are provided by a multitude of vendors. The upcoming Flash Player 10.1 was already pointed out by George, but never the less, I wanted to stress, that this makes many of the cross-plattform considerations obsolete.
Last but not least, I'd like to point out Haxe. It allows compiling to SWF, but also to C++, using the very same API provided by NME, to target the iPhone. Also there's work in progress on an android backend. If you're aren't playing to launch within the next 4-5 months, then this is definitely an option.
Your issue is a perfect target for the Haxe programming language. Haxe is written for the web and can compile to JavaScript, Flash and Objective-C (possibly Java/.NET soon).
So you do not choose which platform you are going to invest in but in which language. Haxe is easily adoptable for an AcitonScript programmer.
It makes no sense to run your imageprocessing algorithms in a JavaScript sandbox when Flash is available because it will be much faster. It makes also no sense to run heavy image processing algorithms on a mobile device like the iPhone with JavaScript. I would only support JavaScript as the worst fallback solution.
If you do not like to use Haxe I would go with Flash. You can deploy your Flash application for the iPhone aswell if that is your problem. This is also very great because you get native ARM code. There are actually great tools for professional Flash development available. FDT and IntelliJ IDEA are two of them. The best Haxe IDE is probably FlashDevelop at the moment of writing.
So I would definitly not use JavaScript as the only solution. Haxe is perfect for what you try to achieve. If you do not trust or do not want to invest in Haxe you can use Flash because of the iPhone/iPad export.
Depending on your usecase I would also encourage you to look at cloud hosting like Amazon EC2 and Google AppEngine for instance. Hosting costs are cheap and scaling will be easy for your task. The experience will be much better when it comes to complex operations that can take even a lot of time on a desktop system.
In addition to other answers, another option may be a hybrid solution. For example, use Flash/Silverlight for the majority of your target audience and use server-side processing for those that don't support it (or you could create a native app for iP[hone|ad])
You may have to do something like this anyway as the mobiles you are targetting may have insufficient processing power depending how complex your image processing gets.
Of course you still have the option of upgrading your server which, although you've currently discounted, is probably far cheaper than spending development time creating/deploying/testing a client-side solution.
You can use Silverlight for all Silverlight enabled clients and for non Silverlight clients, do the image processing server side. Since the Silverlight code is C#, you can double compile it to make (mostly)the same code work as Silverlight and non-Silverlight (i.e. server). This gets you the best of both worlds.
You don't say what language "all that code" you'd have to rewrite is in. Might a semiautomated translation to Javascript be practical?
Perhaps you could start out server-side, as CraigS suggests, and then move functions into the client over time instead of rewriting all at once.
Have you checked the editor of Pixlr.com ?
Take a look at their API as well..
The best solution is to use silverlight (so you already have the code ready). If the client can't run it (mobile phones, etc) then process it server-side.
It's the best compromise.
Depends on the type of image processing and the end user experience you are targeting.
As you are looking to target mobile phones your image processing will need to take into consideration the type of handset the user or the receipient has (if messaging via SMS/MMS), as different handsets have different resolution screens and handle different image formats for main images and thumbnails.
I'd suggest that you consider a hybrid cloud architecture as was mentioned in the Microsoft PDC keynotes this year. This would enable you to have your own server(s) to support your application, but if you require additional capacity due you scale out into the cloud using AppFabric.
Additionally, to maximise the market availability of your product pulling the image processing to a common reusable infrastructure allows you to target different platforms, exploiting the positives in each.
I have worked on a solution that hosted its image processing and delivery infrastructure server side and then built different UI offerings allowing sales via desktops, MNOs and AppStores. It can work and from a business perspective can offer economies of scale benefits.
Why not mention Java Applet ?
Good sides are:
almost all browser support ?
need install JRE ?
all OS support
Java provide Java Advanced Image kits, but if c++ dll can be called, that is best (JNI can call c++ dll )
In Python, one of the most popular libraries for image processing is pillow. Through the pyodide project (python running inside browser via emscripten), it's possible to use libraries like pillow and numpy for image (or matrix) processing, and convert the output to a base64 string (via Python standard library). This can then be passed to your <img> html element, either native JS document or with a library like React.
The way I see it, there's no one solution that meets all of your needs. Your best option, imo, is to go with Flash and hope that Adobe sets an agreement with Apple to get Flash on the iPhone/iPad. The major downside, of course, is you'll have to rewrite much of your code.
If the mobile sector isn't absolutely critical, then choose the Silverlight option for reasons you mentioned already. You could also use Silverlight in an out-of-browser mode to work as a desktop application.
I've been dwelling on this topic for a long time now. I just wondered if anyone else out there shared my opinion. Isn't it essentially a bad idea integrating preview versions of programming frameworks into your project code before they are at release candidate level?!
I had a situation a few months ago where my boss insisted on using the Managed Extensibility Framework to handle dependency injection in a huge internal system we were building. We built the code around a preview version of this framework and then Microsoft released another version of it. We updated and everything broke, huge amounts of code had to be re-understood and changed...total pain!
...I'm getting the feeling that Ria Services could present us with a similar problem (or any other framework chosen to be implemented into a projects source code prior to full release state).
Opinions welcome.
Well, what else can be said? You're right - using something not even marked as release candidate for core functionality in your app is a considerable risk.
To alleviate the risk you could try creating a compatibility layer that you could adjust to "translate" to new versions of the framework - but that involves a lot of guesswork that may not work out.
And of course you can just stick with the preview version, if it already does everything you need. But that will bring its own headaches down the road.
All in all, I'd avoid it unless the newfangled thing in question definitely enables you to do something important that would otherwise be impossible, or yields massive productivity gains.
Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 6 years ago.
Improve this question
I need some resources that talk about how to design your software to be extensible, i.e. so that other people can write add-ons/plug-ins that adds functionality to it.
What do you recommend? Any books out there that discuss the subject?
I would prefer something that's short and to the point; a bit of theory and a bunch of concrete examples.
I'm not targeting a specific language, I want to be able to understand the core idea so that I can implement it in any language.
And for the same reason, I prefer not to do it using a framework that someone else built (unless the framework is not very high-level, i.e. doesn't hide too much), at the moment I only want to educate myself on the subject and experiment with various ways to implement it. Plus, a framework usually assumes user's knowledge about the subject.
UPDATE
I'm not asking about OOP or allowing my classes to be inherited. I'm talking about designing an application that will be deployed on a system, such that it can be extended by third-party add-ons AFTER its been deployed.
For example, Notepad++ has a plug-in architecture where you can place a .dll file in the plugins folder, and it adds functionality to the application that wasn't there, such as color-picking, or snippet insertion, or many other things (a wide range of functionality).
IF we're talking .NET, try Scripting .NET applications with VBScript over on CodeProject. Lots of concrete examples there.
Below are sites implementing various application extension techniques
ClearScript - Makes V8, VBScript and JScript available to .NET apps
CS-Script - The C# Script Engine
Plugin Architecture using C#
Opinio plugin architecture
Notes on the Eclipse Plug-in Architecture
Plug-in Architecture Framework for Beginners
Gecko plugin architecture
Fungimol plugin architecture
OSGI is a good practical example of a technical framework allowing to do what you are after.
The theory is here.
The (free!) book is there.
Extensibility and the ability to write plugin must deal with service lifecycle
adding / removing service/plugin on the spot
managing dependencies between services
managing states of services (declared, installed, started, stopped,...)
What is OSGI for ?
One of the main functions of a module is as a unit of deployment… something that we can either build or download and install to extend the functionality of our application.
You will find a good introduction here, on the central notion of service (which is related to your question, and which explain some problems around services, key component for extensibility).
Extract:
Why are services then so important if so many applications can be built without them? Well, services are the best known way to decouple software components from each other.
One of the most important aspects of services is that they significantly minimize class loading problems because they work with instances of objects, not with class names. Instances that are created by the provider, not the consumer. The reduction of the complexity is quite surprising
Not only do services minimize configuration, they also significantly reduce the number of shared packages.
Implement SOLID principles in your application.
1. Single responsibility principle: A class should have only a single responsibility (i.e. only one potential change in the software's specification should be able to affect the specification of the class
2.Open/closed principle: Software entities … should be open for extension, but closed for modification
3. Liskov substitution principle: Objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program
4. Interface segregation principle: Many client-specific interfaces are better than one general-purpose interface
5. Dependency inversion principle: One should Depend upon Abstractions. Do not depend upon concretions
Stackoverflow questions:
Example of Single Responsibility Principle
Is the Open/Closed Principle a good idea?
What is the Liskov Substitution Principle?
Interface Segregation Principle- Program to an interface
What is the Dependency Inversion Principle and why is it important?
You try to reach two competing goals:
The components of your software must expose a lot of themselves, so they can be reused
The components of your software must expose very little of themselves, so they can be reused
Explanation: To encourage code reuse, you should be able to extend existing classes and call their methods. This isn't possible when the methods are declared "private" and the classes are "final" (and can't be extended). So to meet this goal, everything should be public and accessible. No private data or methods.
When you release the second version of your software, you will find that many of the ideas of version 1 were plain wrong. You need to change many interfaces or your code, method names, delete methods, break the API. If you do this, many people will turn away. So in order to be able to evolve your software, the components must not expose anything that is not absolutely necessary - at the cost of code reuse.
Example: I wanted to observe the position of the cursor (caret) in an SWT StyledText. The caret is not meant to be extended. If you do it, you'll find that the code contains checks like "is this class in the package org.eclipse.swt" and a lot of methods are private and final and whatnot. I had to copy about 28 classes out of SWT into my project just to implement this feature because everything is locked down.
SWT is a nice framework to use and hell to extend.
Of course there is the famous Open Closed Principle - http://en.wikipedia.org/wiki/Open/closed_principle
Well it depends on the language.
In C/C++ I'm pretty sure there is a loadlibrary function that allows you to open a library at runtime and invoke it's exported functions. This is typically how it's done in C/C++.
In .NET, there is Reflection, which is offers similar (but more broad) to loadlibrary. There is also entire libraries built on Reflection like Managed Extension Framework, or Mono.Addins that does most of the heavy lifting for you already.
In Java, there is also Reflection. And there is the JPF (Java Plugin Framework) which is used in stuff like Eclipse IIRC.
Depending on what language you use I could recommend some tutorial/books. I hope this was helpful.
Plugin architecture is becoming very popular for its extensibility and thus flexibility.
For c++, Apache httpd server is actually plugin based, but a concept of module is used instead. Most of apache features are implemented as modules, like cache, rewrite, load balancing, and even threading model. It is a very modular software I ever saw.
And for java, Eclipse is definitely plugin based. The core of Eclipse is an OSGI module system which manage bundles, another concept for plugin. Bundle can provide extension points on which we can build modules with less efforts. The most intricate thing in OSGI is its dynamic characteristic, which means bundles can be installed or uninstalled at runtime. No stop-the-world syndrome any more!
Since I dont have enough rep points to leave a comment, I am posting this as an answer. SharpDevelop is an IDE for developing applications in C#/VB.NET/Boo. It has a pretty impressive architecture that allows itself to be extended in a number of ways - right from new menu items to development support for whole new languages.
It uses a bit of XML configuration to act as a glue layer between a core of the IDE and the plugin implementation. It handles locating, loading and versioning of plugins out of the box. Deploying new plugins is matter of simply copying in the new xml configuration file and the required assemblies (DLLs) and restarting the application. You can read more on this in the book "Dissecting a csharp application" by the original author(s) - Christian Holm, Mike Krüger, Bernhard Spuida of the application from here. The book doesnt seem to be available on that site, but i found a copy that might still be around here
Also found a related question here
Checkout "CAB" - Microsoft's Composition Application Building blocks Framework. I think they've got a "web version" of that too...
I have just started to develop a smart client application. These are two options I am considering.
Using Microsoft's System.AddIn namespace. Looks very promising, however it may be a little complex for our end solution.
Or the Smart Client - Composite UI Application Block from Microsoft
Recently, i have looked at taking components both the Composite UI Application Block and the System.AddIn namespace to build my own. Since source code is available for the CAB it is easy to extend. I think our end solution will be a light weight version of the CAB, definatly using the Unity Application Block
If you work with .Net, our research yielded two approaches: scripting and composition.
Scripting
You extend the functionality of what your classes can do by orchestrating them using scripts. That means exposing what is compiled in your favorite .Net language in a dynamic language.
Some options we found worth exploring:
IronPython
IronRuby
JavaScript: Jint, Jurassic and JavaScript .Net are good starting points.
Script.Net -> this one was the first one to call our attention.
Composition
If you start a project with .Net 4 or above, you must take a good look at the Managed Extensibility Framework (MEF). It allows you to extend the functionality of your apps in a plugin way.
The Managed Extensibility Framework (MEF) is a composition layer for
.NET that improves the flexibility, maintainability and testability of
large applications. MEF can be used for third-party plugin
extensibility, or it can bring the benefits of a loosely-coupled
plugin-like architecture to regular applications.
Managed Add-in Framework is also a good read.
MSDN: http://msdn.microsoft.com/en-us/library/dd460648.aspx
Codeplex: http://mef.codeplex.com/
Rather than re-inventing the wheel, use the frameworks in hand. Eclipse and Netbeans both support plugin based extensions. You have to work in Java though.