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As you might know, the QtQuick.Controls 1 module has been officially deprecated since Qt 5.11; this had been in the air already since quite some time, given that the development of the module had almost stopped. It looks like The Qt Company is mostly investing on the more performing QtQuick.Controls 2 module, and is inviting developers to switch over to that — at least for new projects.

However, there currently isn't a style available that would make an application using the QtQuick.Controls 2 look native on the desktop. There has been an attempt at it, but it soon turned into a custom style for the KDE desktop environment. So, some time ago I decided to give it a try: I started by forking the project of the KDE guys and as a first step I removed the dependency on the KDE libraries.

A button generated by the QML QQC2 desktop style

A traditional QPushButton

The difference (enhanced in Gimp, or you wouldn't see a thing)

It's a work in progress, and it probably has a long way to go before it's usable for a real world product, but I'm trying my best to turn it into something you can trust: this is a project where Test Driven Development fits very well, because in order to ensure pixel by pixel visual compatibility (that's my goal indeed!) I'm running a test where I create the same widget using the QtWidgets module and with this QQC2 style, and comparing the resulting surfaces for equality. In the pictures above you can see how the Button element looked earlier today (before I fixed it ��), compared to a traditional QPushButton: the test code creates a visual diff of the two images, and the test passes only if the resulting image is pitch black (with a very small tolerance for possible differences in font antialiasing).

For the time being I'm focusing my attention on the visual appearance of the individual widgets and their implicit size, but I'll soon add tests (and code) for layouts and interaction behaviours. I also need to extend the tests: they are currently run in GitLab CI for Linux only (where I can test the Fusion and the Windows styles), but I hope to find a way to run them in AppVeyor and on Mac OS. By the way, if someone knows of a CI service which would allow me to run my graphical tests on a Mac, please let me know in the comments.

This is an early notice that the project exists; if you have some time and energy to spare, you are very welcome to help me with the development.

Among the different cross-distribution application packaging systems available for Linux, the major ones being Flatpak, Snap and AppImage, I've chosen the latter for my own needs for the simple reason that it provides me the easiest way to ship my application and have it work out of the box. Flatpak and Snap will eventually get there, but for the time being universal availability and features like drag and drop are still to come.

However, the AppImage for PhotoTeleport is huge: due to having me ship many Qt5 modules, and especially the enormous QtWebEngine with all of its dependencies, the final package is almost 100 megabytes in size. One way to reduce that would be to require the user system to already have a Qt5 installation available, and therefore remove these libraries from the AppImage file. And if someone ran PhotoTeleport in a system where these libraries are not available, a small wrapper tool (based on xmessage maybe, and whatever Wayland equivalent exists) could inform the user of the problem and invite him to install the missing dependency. And I'm sure you certainly agree that this would be a horrible user experience: since we are so smart to tell that a dependency is missing, why not go the extra mile and install it ourselves?

Unfortunately, this “extra mile” is filled with subtle issues and there's the risk of delivering a solution that works in only a few lucky cases. For this reason, I would like to get the help of other developers and try to find a solution that takes into account all (or most) the subtleties that we need consider for different applications and target distributions. So, what follows is only the result of my initial brainstorming, and could be totally changed (or abandoned, if deemed unfeasible) depending on your welcome feedback.

Requirements

• Smaller size: indeed, this is the whole point of this effort!
• Optional: we don't want to make life harder for all developers: if you are happy with the size of your AppImage file, you should continue to be able to produce it the way you do now, and users should be able to continue to install it in the same way
• Easy but not magic: installing the missing dependencies should be easy, but should not happen without the user's consent. At the very least, we must check that an internet connection is available and make sure that the user is fine with us downloading the extra stuff we need.

The UI problem

No matter how the solution gets implemented, we can be certain of one point: we'll need a way to show some UI to the user. At the very least, this would be a dialog box or a wizard, which would inform the user of what we are doing. We need to find a solution that works both on X11 and Wayland, and that is small enough not to totally destroy the size gain. xmessage is probably present in every Linux distribution, but there doesn't appear to be a Wayland equivalent that is as much available (wlmessage even seems to be unmaintained). Of course, the possibility of shipping whatever tool we need in the AppImage itself always exists and is indeed in the philosophy of AppImage, but then we need to consider how much this costs in term of size.

On the other hand, AppImage packages already assume that some libraries are present in the target system: the excludelist file in the AppImages project lists those libraries. Among them we find the XCB library (to create surfaces on X11 systems) and FreeFont (to render font glyphs), which should give us the possibility of creating some UI in X11; the wayland client libraries are not included, but on the other hand we are talking of less than 100 kilobytes. The next question is whether we want just rely on these libraries, and therefore do all the drawing ourselves, or make use of some other drawing library which would make our task easier. A simple drawing library such as libcairo is already 1 megabyte in size, and if we move to a more complete solution such as Gtk or QtWidgets, the size grows considerably (something between 10 and 20 MBs, from a quick rough estimation). I don't have an answer to this question, and I'd like to spend some more time investigating other options before jumping to code the installer and drawing it pixel by pixel. :-)

The possibility of having different installers, depending on the UI toolkit used by the application shipped in the AppImage (so that most of the dependencies can be shared), should also be considered. This would of course reduce the size gain — for a Qt application, for example, we would have anyway to ship QtCore and QtWidgets because the installer needs them — and would introduce additional complexity because we'd need to make sure that indeed both the application and the installer can work with the version of the toolkit we are shipping.

The developer story

Let's put the UI issue aside for a while, and think about how this could work from the application developer point of view. We have a bunch of dependencies that we'd like to take out of our AppImage; for example, Qt 5.9 with QtQuick and QtWebEngine, and OpenCV. Ultimately, the information we need to pass to the installer is the exact name of the libraries (like libQt5Core.so.5.9, libQt5Gui.so.5.9, etc.) as well as their soname as used by the application (like libQt5Core.so.5, libQt5Gui.so.5, etc.), possibly an md5 signature for each of them, and the URL where we can get them from, in case they are missing from the user system. Writing this information is boring, so the AppImage project might store some ready-made configuration snippets in its git repository.

An additional simplification could be the creation of “frameworks”: bundles of closely related libraries (for example, have a QtBase framework containing QtCore, QtGui, QtWidgets, etc. with all their dependencies).

The user story

When the user installs our AppImage on his system and launches the application, this will first execute the installer: the installer will check that all the downloadable libraries declared by the developer are present on the system, and if any of them are missing it would show its UI and guide the user to install them (here I figure a wizard-like UI, with progress reporting and asking as few questions as possible). The libraries would be installed somewhere in the user home directory, without requiring admin rights.

The installer story

This is where all the magic would happen, and where all the dragons are hiding. It's hard to describe all the complexity in a coherent text, therefore I'll just write down a bullet list of whatever passes through my mind (it's a brainstorming, after all):

• The downloaded libraries should be stored somewhere under the user's ~/.cache/ directory: the reason is that AppImage does not have an uninstallation procedure, and we've always been telling users that the way to uninstall an AppImage application is just to remove the corresponding binary. So, given that the user will not know that he has to remove all the downloaded libraries, the most polite thing we can do is to put them in the cache directory, and hope that if the system goes short on disk space, somehow the cache directory will be cleaned.
• The installer will add the location where the downloadable libraries are expected to be installed (for example, this could be ~/.cache/appimage/lib/<app-name>/) to the LD_LIBRARY_PATH environment variable.
• The installer will check for the library presence in the directory above, by using their soname; if all libraries are found, it will start the application.
• If some library is not found, the installer will look for it in the parent directory, ~/.cache/appimage/lib/, this time without using the soname but the full name; if found, a symlink will be created in ~/.cache/appimage/lib/<app-name>/ linking the library soname to the actual binary library. For example: ~/.cache/appimage/lib/MyApp/libQt5Core.5 -> ~/.cache/appimage/lib/libQt5Core.5.9.
• If the library is not found there, system locations could explored, too. And again, a symlink would be created in ~/.cache/appimage/lib/<app-name>/. The application developer should be able to configure the installer to skip this step, in case it's known that some target distributions ship a version of the desired library that is somehow incompatible with the app (because the distro has patched it in some unexpected way).
• If a library is not found at all, the installer UI shall appear, to inform the user that some libraries need to be downloaded. As the user agrees to proceed, the installer will download the missing libraries.
• Are either of curl or wget installed by default on every distribution? It would be simpler to use them from a shell script, instead of using libcurl from C.
• The library must be made available online. The developer could do that on his own website, and/or the effort could be coordinated among AppImage developers to create and maintain common repositories for open source libraries.

The way forward

While this is a lot of work, I don't immediately see a great complexity or any real blockers. The thing that scares me the most is the idea of writing the installer UI without using any comfortable UI toolkit. Do you see some other big issues that I haven't covered?

While I put more thoughts into this, I'm tempted to start an effort to solve this problem for PhotoTeleport only: the easiest way would be to write an installer program with QtWidgets, which is already a dependency I'm shipping, and have the installer take care of downloading QtDeclarative, a few other QML modules and QtWebEngine. I could write it in such a way that it would be reusable at least for other Qt-based AppImages, and on the other hand this could be a proof of concept to tell whether this whole idea is feasible or not.

Just to highlight it: I wrote that I'm tempted to play with this idea; whether I'll do it for real is all another story. :-) I'm still pondering whether the whole thing is worth the effort, given that I haven't received a single complaint from users so far.

I already wrote about PhotoTeleport in my previous post, but since not everyone can comfortably read interlingua, here's the English announcement

I've spent the last few months of my free time to work on a new application, called PhotoTeleport, which is a photo uploader capable of working with multiple photo sharing services at once.

It's an application I myself felt the need for, because as a photographer I keep my portfolio in many websites: I have a couple of pages in Facebook, and VK (a.k.a. "the Russian facebook"), but I also have a profile in other websites such as Flickr and DeviantArt, which I created to further promote my activity, but which alas I failed to keep up-to-date. The harsh reality is that working with multiple profiles is hard: even if you had just two profiles to maintain, it takes a lot of time to upload the photos to both of them and, no matter how convenient their user interface is, entering captions, descriptions and tags here and there is another boring, repetitive and time consuming task.
Then how about automating it? Enter PhotoTeleport, and all photographers rejoice!

The program in itself is very simple: you drag and drop the photos into its window, select which services you want to upload them to, add captions, descriptions and tags (if you like), review and then upload. For those who prefer a feature list in bullet points, here it is:

• Support many photo sharing services: DeviantArt, Facebook, Flickr, Google Photos, VK, etc. (see here for an updated list)
• Album selection, or creation of a new album (if the service supports it)
• Fast editor for captions, descriptions and tags
• Possibility to specify different captions, descriptions and tags for each website
• Read metadata embedded in the image files
• On upload completion, provide a link to the newly uploaded files for additional editing or sharing

This is just a beta version, but more features are planned, including:

• Ability to save and restore session
• Watermark support
• Image scaling
• Support for more plugins (500px, Imgur, Smugsmug, Shutterstock, Photobucket, Pinterest and more)
• Support for uploading to a custom (S)FTP server

You are indeed welcome to suggest new features, just by adding a comment to this blog post, or by creating an issue in the PhotoTeleport bug tracker.

PhotoTeleport is available for Linux, MacOS X and Windows; to get it, please visit PhotoTeleport website.

Only for the geeks and the folks from the IT crowd

Here's some info for those who desire to hack on PhotoTeleport, or just to know more about the technology behind id: PhotoTeleport is an open source project, it's written in C++ and QML using the cross-platform Qt framework. The authentication to the remote servers is handled by libauthentication, a library that I wrote just before starting the work on Phototeleport to provide an easy way for Qt and QML based applications to authenticate and peform authorized requests to remove websites using the OAuth 1.0 and OAuth 2.0 protocols (other protocols can be supported too).

Linux users might ask me why I chose to ship PhotoTeleport as an AppImage package, rather than using Flatpak, Snap or a native distribution package like deb or rpm. This might deserve a blog post of its own, but in brief:

• deb> or rpm: they require root permissions to be installed, moreover PhotoTeleport uses Qt 5.9 which is not available in all distributions, so if I have to bundle Qt with my package, I don't see many advantages over shipping an AppImage;
• Snap: they require root permission to be installed, and the support for desktop applications is still incomplete;
• FlatPak: there's no runtime for Qt applications (and no, I don't want to force users to install the whole KDE runtime!), and drag & drop is not supported yet.

That said, it's just a matter of making the best out of my little spare time. I can reach every Linux user with the AppImage format, so that's the first option I took. I'm certainly open to the idea of using also other formats in the future (I might make debs after Ubuntu 18.04 is released with Qt 5.9) and I'll happily accept any contribution that can make PhotoTeleport available in Snap, Flatpak or other formats. But I don't have the time pioneering that right now :-)

I decided to blog about my experience of transitioning from being a GLib and GObject enthusiast to a Qt (and QML) fanboy. :-) I'm not writing this with any specific goals, other than sharing my own experience and hopefully making the life of those developers who are forced to learn and use Qt less painful and a bit more rosy; in particular, I'm not trying to be a Qt evangelist here and convince you, hardcore GObject developer, to switch to Qt: I'm indeed sure that if my current self tried to talk my 3 years younger self into Qt, it would be a useless and tiresome (and maybe violent ;-)) discussion.

Just a bit of background on myself: I've been developing on Linux and Unix for more than 10 years now, mostly using GObject based libraries, such as Gtk+. I had a short encounter with Qt in about 2004, just for a few weeks, which left me with a bad impression (mostly because of the uic). Other than that, I was simply not interested in Qt, mostly because I hate C++ and love C and anyway all my needs were perfectly met by GLib, GObject and Gtk+. I remember that the first time when I read about GObject, I was fascinated: the power of OO programming on top of my favorite language, all open source and hackable. In autumn 2006 I started a new job in Nokia, in the maemo team, working on a middleware component in the Telepathy VoIP framework; I enjoyed it a lot, and (if possible) grew even more fond of GObject and GLib. On early 2008, the big news: Nokia acquires Trolltech (the SW house developing Qt); for me, as for most of the people working in the maemo team, this came as a complete surprise, and not as a really good one. Indeed, we were afraid that we would have to abandon the C/Gtk+ work and switch to C++/Qt — perhaps not coincidentally, several GNOME developers working in Nokia even left the company around that time. Luckily though, nothing really changed for us for more than one year, and even later, when more people joined to work on Qt-related stuff and I moved to another project, I could still avoid touching Qt code and continue using only my beloved GObject. However, like all good dreams, this also came to an end: eventually, I had to refresh my C++ knowledge and change my most typed character from "g" to the hated "q".
So, here my Q story begins.

The first prolonged exposure to Qt

It was painful. My first task was to create Qt-bindings for the GLib-based library I was developing. There was no UI involved, so on the tools front the experience was not as bad as I remembered; but on the pure programming side, I was horrified: I felt extremely limited, many programming paradigms I was used too couldn't be applied, or I was just told (by people more expert in Qt) that “you shouldn't do like that, it's not the Qt way!”. Urgh.

The biggest issues I had were the lack of reference counting in QObject (!!) and the veto on using C-style function callbacks for asynchronous operations (you should use Qt slots, and in order to have a slot you must have a receiving QObject). How could I take Qt seriously? Sure, there were also a few nice things about it, like the fact that QObject comes with child-parent lifetime handling out of the box (when a parent object dies, all of its children are automatically deleted), and that signal connections are automatically broken when either the emitter or the receiver object dies (yay, no more explicit signal disconnections — or random crashes!). But still, this could in no way compensate for the lack of the other low-level features I was used to.

I cannot really say that I enjoyed the first months of using Qt. I was still trying to work as much as possible on the GLib-based parts of the project, and twisting my head around to figure out what was “the Qt way” of doing all the things that I was used to do almost instinctively with GLib/GObject.

From hate to love

Now that I think back and try to find the moment of time when I finally started liking Qt (or just not dislike it too much), I cannot really point out a definite time. It was a very slow process, that surely wouldn't have completed if I hadn't been forced to use Qt because of my work. But indeed, the moment when I realized that Qt was not so bad after all is when I started writing new original code with it. In retrospection, I would say that my experience with Qt was so bad because I started with a completely wrong task: as an inexperienced Qt developer, creating binding for a GObject-based library couldn't possibly make me appreciate Qt; I was just bound to notice all the GObject features that were not present in Qt, and suffer their absence. And I wouldn't notice almost any of the niceties that Qt offers to application developers, because there is not much code you can write in a wrapper library other than some trivial glue code.
So, my first suggestion for those GObject developers who start using Qt is: do not write a Qt wrapper to your favorite GObject library!, you are going to hate it. Leave it to someone who is more experienced than you in Qt; it can be a very pedagogic task, indeed, but chances are that it will be the last time you are going to use Qt. If you can, start with writing new code.

That said, there is a big difference between not disliking something and loving it. But again, I cannot tell when I started loving Qt. What I surely can tell is when I realized that I loved it: and that was when I started porting some GObject-based code to Qt (not as a line-by-line port, but more like a functional rewrite) and found out that the resulting code was not only more compact and easier to write, but — and especially — easier to read. And of course, when I realized that my enthusiasm was not the same as before, whenever I had to do some programming in C+GObject.

What I find cute in Qt

Let me begin with a couple of statements which could dispel some myths or anyway clarify some doubts that the Qt-virgin might hold:

• It's not C++. This is a bold (and false) statement, but it's probably the most effective to convey the idea: if you — like me — hate C++, you won't necessarily hate Qt. Qt's C++ is a subset of C++: although you can use whatever C++ feature you might like, developing with Qt does not involve using exceptions, templates, RTTI and the STL. In a similar way to how GLib and GObject “extend” the C language, Qt uses a preprocessor (called moc) to add its own run-time type information (think of GType) and implement the signals/slots mechanism. In the end, you don't need to know all the details of C++ to develop Qt; instead, it's somehow similar to developing Vala code — it's like a programming language of its own.
• It's not just GUI. As you might have noticed, this post is not about Qt vs. Gtk+, not at all. There are many other articles on the web where you can find comparisons and opinions of the two, but what I'm focusing on here is my experience with Qt programming and GNOME programming, and not just at the UI level. So, yes, the point is that you can develop whatever code with Qt (except maybe kernel drivers): I've personally written D-Bus services, command line tools and embedded software using just Qt.
• There really is a Qt way. My disappointment about the lack of reference counting in QObject is now history: apart from the fact that indeed there is one class in Qt which lets you implement reference counting for QObjects, I cannot recall any case where reference counting would have been useful. I know, coming from GObject this might sound hard to believe (especially to my three years younger self, who used to mess up with cross references everywhere in the code), but it's a fact: after some initial struggle, I always managed to design the software with clear ownership of objects, so that the reference counting ended up to be totally superfluous. And in fact, my code is designed better now. The same can be said of any other feature that I initially missed: if it's not there, you can do without it: just restructure your code in a different way — the Qt way — and there's a good chance that while reworking your classes you'll clear up some mess. :-)

That said, here's a list of things that I came to like about Qt; I'm obviously not mentioning those things that are also in GLib/GObject, unless there are significant differences.

• QObject automatic destruction of children. I already mentioned it before, but it's worth expanding a bit. Quite often I had to use reference counting in my GObject subclasses to keep track of the child-parent relationships; QObject already does that for you: whenever you create a QObject, you can specify one parent object which will “watch” its lifetime and destroy it in its destructor. This leads to a nice programming paradigm where you can create all the objects that your class needs and just use the this pointer as parent object: then you don't need to remember destroying them explicitly in your destructor.
• Automatic disconnection of signals when receiver object dies. I also mentioned this before, but repetita iuvant: if you are an experienced C + GObject developer, you must have seen at least once in your programming career one crash due to a signal callback invoked when the objects it operated on had already been destroyed. Of course I know that it never happened to you personally, but you surely saw this in someone else's software. ;-) Well, in Qt this is very unlikely to happen, because (at least till Qt4) it's impossible to bind signals to C callbacks: you must bind them to a QObject method (called “slot”), and the QObject system takes care of disconnecting the signal for you when either the emitter or the receiver object are destroyed.
• QString. I'm sometimes a bit maniacal with micro-optimizations, and one thing I was always trying to optimize in my early GLib days was avoiding string allocations. It really hurts me to write a g_strdup() in a library method's implementation when I could rather write "Please, don't destroy or change @string_param while this object is still alive" in the documentation string for the method. But that's not the GLib way (and indeed, not my way anymore when I write GLib code): you can never know what happens with the string, so it's way safer to incur the small penalty of a g_strdup() than run the risk of a crash which is likely to be very hard to debug. So, C/GLib code is often full with g_strdup() and g_free() (not to speak about valac-generated code!). Enter QString! QString is not only a class that provides a ton of useful string methods, it is an implicitly shared class. That means that the QString structure itself is very small (size of a pointer?), and that the string data is reference counted; then if/when you modify a string which has a reference count higher than 1, the string data is copied and your QString is now pointing at the modified copy. So you never have to worry about copying strings! How cool is that? :-)
• Awesome container classes. Qt comes with a few container classes which you'll surely get to like: QMap, QList are those that you'll use the most, but then there's also QSet, QQueue, QHash, QVector and others. These are template classes, so you can write QMap<QString,QVariant> and get the equivalent of a GHashtable whose keys are strings and values are GValues. Inserting items is as easy as writing

  QMap<QString,QVariant> map;
  map.insert("string", "string value");
  map.insert("integer", 12);
  

  while to iterate the values you have the handy foreach macro, which lets you write

  foreach (const QVariant &value, map) {
      QDebug() << "Value:" << value;
  }
  

  And if you remember what I wrote above about QString: Qt container classes are implicitly shared too!
• Reduced usage of pointers. This follows in part from the above: QString handles all string pointers for you, and the ease of implementing implicit sharing of container classes makes it so that you will be often passing them by value or by reference. Also, implementing implicit sharing for your own data structures is very easy, and you might prefer investing a little time doing that rather than using raw pointers.
• Class and API offering. Even excluding the GUI classes, the functionality provided by the Qt classes will satisfy the most demanding developer: whether you want to deal with date/time, with network resources, with graphics/images, HTML (webkit), SQL databases, D-Bus, plugins, regular expressions, etc., it's all there, and everything works perfectly together. The APIs are intuitive and clean: you won't find duplicate classes offering the same functionality (unless one is deprecated), and the documentation is excellent.
• Compact and clean code. Qt application code is likely to be much mode compact and clean than GObject code. Just like Vala, imagine removing all GObject casts and using class namespaces to shorten your method names and fit your code in a 80 chars wide editor. :-) Use const effectively to mark your class methods and finally be able to pass constant objects and structures around your code, minimizing the risk of incorrect usage.
• QML. This would deserve a chapter on its own, but since there has been quite a lot of buzz around it on the internet I won't spend many words on describing it. Instead, I'll focus on how I came to like it so much. As it often happens with new things, my first impression was not so great; sure, all the QML demos you can find in the internet are extremely captivating, and it's impressive how much you can achieve with very little code — which doesn't even look like real code, but more like a static description. And this was indeed my first doubt: what is the limit of QML? It's a nice language for moving graphics items around, but does it let me do anything more than that? Or: if it really allows me to write complex UIs for big applications, won't the code become a horrible mess to maintain? Again, time and hands-on experience is what changed my mind. I'm porting one map application from Gtk+/Clutter to Qt and of course the map widget and its animations has been my first item in the list. Clutter is a fantastic toolkit for producing animated UIs in the GNOME world; the Qt equivalent is QGraphicsView, whose APIs luckily match very close the Clutter ones; so, the porting wasn't that difficult at all, and it didn't took long until I had my widget working. However, for implementing the animations (zoom, panning and rotation of the map) I didn't use the Qt Animation Framework, which would be the natural equivalent to Clutter animation classes, but instead went for QML: exposing the map properties to QML enables implementing animations in a much easier and enjoyable way. QML property bindings, together with property animation descriptions, empower your application to any kind of smooth animations with almost no effort on your side. You don't have to take care of starting/stopping animations, changing the direction of animations while they are running, or combining zooming/panning/rotation at overlapping moments: no matter how crazily the user plays with your UI, all animations happen as expected, without any need for you to special code them. I couldn't help falling in love with QML. :-)
  So, my answers to the above questions are that, first of all, QML is a language especially designed for developing UIs and UI logics. There's not much else that you can do beside that; in order to write algorithms and implement the rest of application (all what is non-UI) you have to resort to either Javascript or C++ (or Python, etc.); the only difference on how you use these languages is that it's possible to write the Javascript code in the .qml file itself, which is very convenient but also, in my humble opinion, something that you shouldn't do. So, while you could say that it is possible to write an entire application in QML, I heartily discourage you from doing so; if you really like Javascript (why would you, by the way?) and want to write your application with it and QML, it's much better to write the code of your application logic in a .js file and import that from QML. About QML code becoming a maze when writing complex applications, I disagree; of course, it's possible, but it's the same in all other languages (which I know of). If you split your code into smaller QML files (per UI component or groups of components) and avoid creating cross dependencies between components, everything will go smoothly — my golden rule when writing QML code is that a .qml file should never refer to identifiers which are not defined in the file itself. The reason why I'm getting so down in technicalities here is that, if you are a developer who has some experience with QML but finds it messy, you should go and check your code against this rule. :-) Indeed, QML is not a panacea which let everyone who is not a developer write über-complex applications; it's easier and more effective than all other languages (which I know of, again), but the rules of good software development still apply.

How you can start liking Qt

No way you will. ;-) Joke aside, there is some truth in that answer: first of all, you will never like Qt until you try it; and you won't try it unless you are forced to, or have some very good reasons to start looking into it. In my case, in fact, I was forced to, and — at that time — I had absolutely no reason to try Qt on my own: I already had some bad memories with it, I didn't like KDE, the skype Linux client and, most importantly, I was totally happy and satisfied with coding C and GObject.

However, I believe that nowadays there might be two reasons why even a hardcore GNOME developer could, in an unforgivable moment of weakness, decide to try programming with Qt: QML and application portability. QML is the new cool stuff (it was not there when I started with Qt), there are plenty of nice demos and examples out there, and they do pretty amazing things. Especially given that setting up the environment is an easy task (just install the Qt packages from your Linux distribution) and running the demos is in most cases just a matter of typing qmlviewer <file>.qml, and that you are a very curious geek, it's not so unlikely that you'll want to have a closer look to the demos; and since the source code consists in most cases of just a few lines of JSON-like text, it won't take long for you to understand it and maybe start playing with it. Especially because I still believe that GNOME developers deserve something as cool as QML. :-)
The other reason why trying Qt nowadays is not so absurd as it might seem is portability. Yes, Qt has always made portability his flag, but who does really care about Windows and Mac? However, what you might care about is Android! What has changed here in the last couple of years is that Qt and QML run on Android, with GL acceleration and multitouch support, enabling you to develop modern applications which can be run on millions of devices; you can also target the best smartphone ever, Symbian smartphones and whatever devices Nokia will come up with for the next billion.

I don't think there is much more I can write to stimulate you to try out Qt or, if you have already started using it, to support your efforts to master it. What I can tell you, with no fear of being contradicted, is that eventually you will like it; there is no way that this won't happen, if you continue learning it. At some point you will realize that going back to C (or even Vala) and GObject is not going to make your programming more productive, or even more enjoyable than how it has become with Qt. It's just a matter of enduring the difficulties and unpleasantness for a long enough time; which can be even several full months if you are, like me, one who takes technologies, programming languages and libraries next to your heart.