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I've ported an app from Winforms to Gtk-Sharp.

At first, I ran with the Mono reimplementation of Winforms on Linux. That didn't work very well. There are a lot of little incompatibilities, like differences in how keystrokes are translated, and very buggy text boxes.

So I reimplemented the UI in Gtk-Sharp. That was mostly a matter of translating existing Gtk documentation to the OO API presented by the C# wrapper. I could write this in Visual Studio and run using Gtk on Windows to test; Mono itself wasn't actually needed here.

I then ran the app using Mono on Windows. Once all the DLLs were in the right places, it mostly just worked. Running it on Linux - specifically, Ubuntu 12.04 LTS - was a little trickier, as Ubuntu has split out many of the different assemblies into separate packages, and you have to grovel around a bit to get what you want, if you don't want everything. But again, it mostly just worked.

Compiling using Mono took a little bit of figuring out - mainly, finding out I had to use dmcs rather than mcs or gmcs to enable the right language features. But again, once the right assemblies were referenced on the command line, it mostly just worked.

Writing a cross-platform app in Mono? I wouldn't really try that. Having a separate UI layer for each platform gets you a much better experience. Gtk programming itself is extremely clunky compared to Winforms, which itself is quite clunky - albeit in different dimensions - compared either with Delphi's VCL or WPF. But it was the only way I could see to go to get a reasonable experience on Linux.

Don't bother. No one is maintaining the cross platform GTK bindings (or .Net MVC framework) and basically no one cares about it. It's just getting more and more out of date.

Look at an actively maintained solution like Xamarin or Unity; Xamarin lets you write your UI specific code for each platform; Unity lets you share UI across platforms but you won't get a 'native' look and feel on any.

For both of these you won't be able to use the majority of existing .Net infrastructure (nlog, nject, nhibernate, etc) because they are locked into the windows CLR, but there are a few ports and you can often get away with compiling the source from codeplex yourself (the prebuilt DLLs just wont work).

(Unfortunately, porting your existing application is absolutely out of the question in most cases, for the reason above. Perhaps if you've carefully isolated concerns it might be possible...)

FWIW, every pre-built assembly I've used on the CLR has "just worked" on Mono, no recompile necessary. But I don't have a lot of third party dependencies, mostly database drivers and a few bits and pieces.

If you want to write cross platform applications use Qt. End of story, it's the only extremely well supported cross platform GUI framework out there. If you are looking for a smaller framework you can try WxWidgets, but I would stay away from GTK. GTK has been getting less and less support since version 2. Version 3 is only Mac and Linux and the Mac version is terrible, there is a "custom" Windows version by some french guy, but it's just that, not community supported.

You could also take a look at Juce, depending on what you need to do with it.

But, if you don't mind large binaries you could easily embed a chromium or awesomium layer as your frontend and do your frontend in html/css/javascript and use JavaScript to communicate with your backend.

As people as said, the best idea would be to write one backend and three or two frontends. That will give you the best experience on all three platforms, and the native GUI look, something that on Mac Qt still suffers with.

I have been building GUI applications with Java and Swing for some time. I am willing to go on-the-record and state that Swing provides a reliable and thorough cross-platform GUI toolkit. Once you put the work in, you really can build an application that looks native-ish and does the same thing on Windows, Linux/GTK and Mac OSX. Unfortunately the learning curve is quite steep, many things are more complicated then they need to be.

I have just started working on GUI apps with Clojure and the story is much better so far! Seesaw[0] definitely slims up the Swing code, and I've been using Core.Async[1] to remove a lot of the callback handlers. So far, so good. :-) It's definitely worth looking into.

[0] https://github.com/daveray/seesaw

[1] https://github.com/clojure/core.async

>I have been building GUI applications with Java and Swing for some time. I am willing to go on-the-record and state that Swing provides a reliable and thorough cross-platform GUI toolkit.

Swing is used by two kinds of people: developers, because the tools that use it are just too good to go elsewhere (IntelliJ etc) and enterprise users that have it forced upon them.

I don't think anybody is using Swing willingly -- or enjoying it. Besides the "uncanny valley" effect to native widgets, it suffered from the start from the main negative of Java's culture: it was overengineered. On top, it underdelivers in many areas.

It may be over-engineered, but it's easily available, at hand, when you need it.

The only cross-platform GUI toolkit that I loved working with and that does a much better job than Swing is Qt. Unfortunately Qt is C++ and it's not even standard C++. So language bindings are hard to build and (compared with Gtk) working with C++/Qt is not so painful. The bindings for Mono are dead. Trolltech released at some point Qt Jambi, the Java bindings, which were awesome, unfortunately the Java community hasn't been interested in it, so Qt Jambi also died after Nokia acquired Trolltech - for the moment at least (the wonderful thing about open-source stuff is that it can be revived with enough interest). The only well maintained language bindings for Qt is PyQt.

And yes, building the UI using the platforms native stuff yields better results, but it's also more expensive to do so. We're all moving in that direction anyway, given the emerging mobile platforms. Sometimes I'm thinking that for desktop apps it's just better to embed a web browser and build the UI with HTML/CSS and JS.

>It may be over-engineered, but it's easily available, at hand, when you need it. The only cross-platform GUI toolkit that I loved working with and that does a much better job than Swing is Qt.

Both statements I agree with!

I think it's a sad state of affairs, that the tens of billion s IT industry, and the whole OSS community, cann't produce, and maintain, a decent, cross platform UI, based on C with hooks for various languages.

GTK has dropped the ball even on Linux (Mac/Windows support is crap, and the library is essentially what it was 10 years ago content wise).

wXWidgets is at the same level more or less.

QT is nice, but is C++, so you either by into the whole thing or you face the not so good support and bindings to other languages (Python has the best support, but even that is mediocre).

Mozilla's XUL was never wrapped and maintained properly (as once promised), to be use to use for cross platform development.

SWT needs Java, and is too tailored to Eclipse's needs.

I, for one, don't need native look in all apps -- I could do with something like the cross platform widget library Adobe built for Lightroom -- that and a webkit view.

>I don't think anybody is using Swing willingly -- or enjoying it. Besides the "uncanny valley" effect to native widgets, it suffered from the start from the main negative of Java's culture: it was overengineered. On top, it underdelivers in many areas.

Just out of curiosity, what other gui tool kits have you used that you compare Swing too? I always wonder what gui toolkits those who decry Swing have experience with.

Myself, I've used Win 32 api, MFC, SWT, and gtk. Imo, Swing is by far the best of those; relatively consistent api, a wide variety of widgets, customizable, ... True it can be very complex (ie editor kits) and some things are/were missing for a long time (close buttons in tabbed panes). Also true that it doesn't look 'native' on all platform, but no gui tool kit can. I have not used Qt, but it seems to be equivalent to, or surpass Swing in all those areas.

>Just out of curiosity, what other gui tool kits have you used that you compare Swing too? I always wonder what gui toolkits those who decry Swing have experience with.

I've used Cocoa, GTK on Linux, and Windows Forms (or whatever .NET v1 and v2 had called) in Windows. Have also used Swing.

Quality of results wise, Cocoa beats them all down, but single platform unfortunately. The .NET solution was also nice, but limited to a single platform too. (I know of, but don't care for small-time hacks to make Cocoa/.NET play on other platforms, only for officially supported projects).

Swing had been a pain in the ass to create UIs with, overengineered, with missing functionality (how long did we have to wait for a HTML control?) and ugly too boot.

Swing has one thing going for it: it does work on all platforms. I just wish it was better designed (API wise), more complete, and less uncanny valey-ish.

Swing is also fully rendered on the GPU.

Seesaw is the only reason why I'm still bothering with Swing too, it actually makes the thing fun to use!

I'm in the market of cross-platform desktop application as well and I've been monitoring Mono/Ximian for a while until last night when I was searching for a .NET Oauth 2.0 library and came across of a project called DotNetOAuth which after further digging does not work on Mono.

I'm a Java developer and I would write the software using Java if only Java isn't stigmatized by "bad software" in the desktop market. It's too bad because so far only Java that provide some of the solutions for me in a few areas to tackle in the cross-platform desktop market, namely: dealing with dependencies, rich 3rd-party libraries (and most of them are FOSS) and a packaging tool for Mac App-Store!.

I wouldn't mind writing 3 different UI code as long as I can share the back-end part and that shareable code works consistently across platform (i.e.: something that communicate with an embedded database like SQLite).

Can anyone share their experience using Mono for cross-platform desktop application that requires DB connection and potentially deal with Service API (i.e.: Twitter, Dropbox, etc)?

My requirements are as follow:

1. Installer/Packager

Something that can help me to generate installer for Windows 7, Mac AppStore, Ubuntu software center (or .deb). RPM would be nice but I can live with writing shell script.

2. Build+Dependency management (don't know if NuGet works flawlessly or not in Linux/Mac)

Maven spoiled me (people who dislike Maven please close your eyes...). I've read that Mono has xbuild but the documentation seems... lacking.

3. Unit-testing

Something where I can run unit-tests through the IDE so I can debug directly from my unit-tests when bugs are found.

4. Good enough 3rd-party libraries

I'm down writing missing libraries if needed but my first priority is the app itself.

I recently worked on a small-ish desktop app that shuttled data between a HID USB device and a web service. We targeted Windows and OSX. The UI portion of the application was very simple and I still found the Xamarin/GtkSharp combination buggy and frustrating.

We used Wix for the Windows installer and the included OSX tools to make the Mac installer (http://s.sudre.free.fr/Stuff/PackageMaker_Howto.html was helpful).

A TeamCity build system using NuGet worked fine for building both flavors, though the Mac build was really just a shell script that TeamCity launched. We used the Xamarin compiler for Mac.

In hindsight I wish we had taken (found?) the time to go all the way and write separate OSX specific UI code and not used GtkSharp. And not require the install of the Mono framework for Mac users-- that really kills the experience. Supposedly you can bundle in Mono with the Xamarin .Mac product but we haven't found the time to get that far yet.

*EDIT: I failed to mention explicitly this was C#/Mono. Also for those interested I used http://www.signal11.us/oss/hidapi/ as a wrapper around the Mac HID USB APIs and it worked fine.

> Does anyone have any recommendations for the easiest way to write cross-platform GUI apps that can run without an internet connection?

Granted, for many people, it's about as hip as Rails is to a newly converted node.js fan, but Tcl and Tk are still a pretty good way of writing smaller apps that run cross platform. Like someone else says, if you want a native GUI, you really need to write that separately for each platform. But that's a big investment, and for some systems, it might not be worthwhile.

A webapp doesn't necessarily have to be hosted on the internet. You can try with embedded server - Java + Jetty + GWT.

If you want to use C#, the easiest way is probably using GtkSharp. I don't know if there's a way to use the VS GUI designer, but MonoDevelop has a built in GUI designer that works with GtkSharp -- and MonoDevelop runs on Windows too.

Might be worth trying out. You can still run your application on Microsoft's .NET stack on Windows, GtkSharp supports it just fine, and because it uses GTK it will look native on all of the supported platforms.

Disclaimer: I haven't actually tried any of the above.

If python is the language that you are gonna use, you would try Kivy cross-platform framework to make GUI for desktop and mobile.

I just tried Kivy. Thanks for telling me about it! Kivy is pretty awesome: very easy to use, and it Just Works on all platforms, even mobile. It's also painless to deploy Kivy apps to users, which is great.

It's hardware accelerated, so I can write my own custom GLSL shaders for the UI, which is pretty cool. I bet I could even implement a Mario-style game using Kivy. The main application window is just a GL context, and all the UI widget rendering is done via GL.

Unfortunately the Kivy UI seems to be riddled with bugs, and the UI widgets themselves are very alien. For example, the Kivy file browser widget seems to be incomplete (it lacks basic features) and confusing (it behaves nothing like a native file selector). So Kivy is probably too jarring of an experience for users... if I use Kivy in its current form, all my users would balk at the unintuitive UI, since Kivy's widgets don't look or feel anything like native platform widgets. And since users would also be fighting Kivy's UI bugs, I predict every user would immediately ragequit my app. (E.g. drag-selecting text within multiline textboxes seems to be broken, etc.)

That said, Kivy is very close to being an effective way to effortlessly write crossplatform GUI apps. The main reason to use Kivy is because it's so easy to write useful apps with it. I wrote one in about 15 minutes from start to finish. The API is a pleasure to use, and the data binding design is especially brilliant.

Kivy seems pretty fantastic for writing internal tools. Data visualization via Python is now a cinch thanks to Kivy. For example, it'd be easy to write an app that shows the current status of all your server instances. And of course at that point it'd be easy to extend your app's functionality with features like "right click on a server instance to spawn an SSH session into it". Stuff like that is a breeze thanks to Kivy.

Time to try out everyone else's suggestions. Up next: Clojure + Seesaw. (This thread has been incredibly helpful... So many interesting ideas. Thanks, everyone!)

Kivy excels at a lot of things, but I'd say that its real value shows when you want to quickly make a cross-platform mobile app that also happens to run on desktop OSes. The widgets and markup language (KV) are designed to be used in a multitouch environment, and they seem pretty alien when used with a mouse and keyboard. They are pretty intuitive when used on a tablet or phone, though -- I recommend you try compiling your app for Android before giving up on the framework.

That being said, even when compiling for PC it's worked very well for me when a client wants an internal tool and is willing to give up a native feel in exchange for fast (cheap!) development. I wrote this for UCLA a few months ago, and I think the whole thing only took me about 20 hours: https://github.com/sbrother/wassum-lab-lick-program/

I have had similar experiences with Kivy. I previously developed a simple game with PyMT[0] relatively easily, so I was very excited when Kivy came out. I had another project requiring multitouch support on a PC recently and decided to use Kivy and it immediately crashed my window manager every time I tried to run it which turned me off pretty quickly.

I ended up doing the multi-touch UI in JavaScript and HTML instead. It felt much clunkier to work with, but I wasn't comfortable with wrangling Kivy's instability for the rest of the project.

[0] http://cleichner.blogspot.com/2011/02/multitouch-project.htm...