Qt Quick vs. Qt Widget [closed]

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I am new to Qt and don't quite understand the difference between a Qt Quick Project and a Qt Widget Project.

I am hoping to create a program that draws a lattice of hexagons that the user can rotate and shear, as well as pan around and zoom in and out of. It will eventually be a MIDI controller. Which type of project would be better for this, and why?

I am hoping for this to work on both desktop and mobile platforms.

Cobblestone answered 24/12, 2011 at 19:4 Comment(2)

Spend a bit of time on the Qt Quick website and look around the examples. If that's what you need, use it. If not, got for normal Qt widget project, but mobile platforms will possibly be an issue. – Laundrywoman 24/12, 2011 at 20:1

Updated link for Ayxan Haqverdili's comment doc.qt.io/qt-6/qtquick-index.html – Amoebaean 24/3, 2022 at 15:32

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Note: Qt Widgets have been replaced with QML Widgets; this answer responds to the question as asked, which is now strictly a historical question about the old Qt Widgets.

Qt Quick is a declarative, smartphone-style user interface with support for a lot of the cool animation transitions that are common in smartphone apps. Quick is also a good choice for rapidly developing a prototype. Qt Widget is the traditional desktop-oriented UI model.

Right now (pre-Qt5), Qt Quick support for desktop system features is lacking (but improving). There's not as much support for menus, toolbars, dialogs, and other standard desktop behaviors in Quick, while Widget supports those elements extremely well.

Do you want your app to look and feel native on desktop and tablet platforms, or are you building a simple application around your own custom UI widget? As Mat said, if Qt Quick supports the features you want, that will probably be your fastest approach. If you want to build full-featured desktop versions, Qt Widget is probably your best bet.

Piemonte answered 31/1, 2012 at 21:25 Comment(9)

I'd like both. :) Using Qt Widget for now. – Cobblestone 2/2, 2012 at 2:48

This answer should be either removed, edited or downvoted as we are now in a post Qt 5.0, we are even approaching 6.0 and Qt Widgets were superseded by QML Widgets. – Crier 5/2, 2018 at 20:55

The answer, or the question? Seems like you're saying that the question is no longer relevant. – Piemonte 8/2, 2018 at 16:49

QML is NOT a replacement for Qt Widgets, even now in 2019, at least until it replace projects like Qwt, QCustomPlot and bunch of others which seems is not the case. Until when it is just another way of implementation, no more no less. – Buatti 26/1, 2019 at 13:6

@Ariel M. Qt Widgets is not superseded and can not be, at least until everything is rewrited, which is not the case. – Buatti 26/1, 2019 at 13:8

Qwt and QCustomPlot are third party projects, and not part of QtWidgets so it's irrelevant if they are or aren't ported. Furthermore, Anthony is a newbie and was asking about creating a MIDI controller where a heavily customized UI would be needed (see Arena, Lemur PS Elements and similar software). QML is the way to go. – Crier 27/1, 2019 at 22:12

@Ariel M. You said about QML supersede something which is not a supersede at all. It is a way to write new code, but not a way to replace existed code. – Buatti 2/2, 2019 at 14:14

"Supercede" as in "replace in the long run" then, like a tracktor replaced a plow, the world has mostly moved to fluid uI's and simpler languages with simpler tooling. – Crier 3/2, 2019 at 20:49

Where did you get that Qt Widgets have been replaced with QML Widgets from?! They're just two different ways to achieve what you what. Where each of which has its advantages and disadvantages over the other, by NO means one is a replacement for the other!! – Burgoo 18/9, 2021 at 7:0

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^{Note: In this answer, "Qt Widgets" refers to a Qt Widgets Application, selectable when creating a new Qt application.}

This is seven years after the question was first posted... but here's my "objective" two cents to neutralise any developments since then.

A Refresher

Language

Qt Quick projects use QML and JavaScript. The latter carries the brunt of program logic: event actions (Component.onCompleted, onClicked, etc.), math, etc.

Qt Widgets projects use C++ code. (PyQt and PySide, Python bindings for Qt, uses Python.)

Performance and Coding

As such, Qt Widgets could be considered low-level compared to Qt Quick. But this implies that in the long run, a Qt Widgets project will run faster and have better performance. Being low-level can be good though, as Qt Widgets is more exposed to native API (the QtCore module, etc). That said, it is often used for desktop development.

Qt Quick caters to both desktop and mobile development. It has ready-to-use popups, animations, tabs and layouts, flickables, drawers, and the usual controls; all ubiquitous in mobile development.

Look-and-Feel

As mentioned before, Qt Widgets is more in touch with the native look-and-feel, so styling defaults to the native look-and-feel. You can use Qt Style Sheets to enhance your widgets, but these are still limited.

Qt Quick is more flexible in terms of styling. One interesting case study is MuseScore. In the migration from version 3 to 4, MuseScore changed many UI components from Qt Widgets to Qt Quick/QML. Why? Because of ambitious UI/UX designs. Pop-ups (among other things) were more convenient to implement with Qt Quick. (Source: Tantacrul on MuseScore 4, 8:08-9:30)

UI Design

Both have ui files which work with QtDesigner, providing a high-level view for setting layouts and creating interfaces. This also enables designers with little knowledge of programming to do their magic. (In Qt Quick, extensions are .ui.qml. In Qt Widgets, they are .ui.) It's not necessary to use .ui files; you can still choose to programmatically design your UI using QML/JS or C++/Python.

Learning

If you're completely new to programming, I suggest having a look at Qt Quick first. Personally, I think Qt Quick has a gentler learning curve and is easier to work with to accomplish myriads of projects. It's called "Qt Quick" for a reason. (Don't look down on Qt Widgets though, they have some nice modules that outdo QtQuick.)

However, if you've been programming with C++ or Python before, I would suggest taking a look at Qt Widgets first, to get used to their signals and slot mechanism and modules that might interest you (e.g. sql, network, gui) alongside programming designs (e.g. model/view programming for displaying data).

Especially with C++, most non-Qt libraries that do event-handling use while-loops, this is not the case with Qt. They use signals and slots.

In the end, even if you're mainly using Qt Widgets, you might want to look at Qt Quick as it offers a high-level declarative language to work with and allows you to set things up more quickly. (Especially for mobile development.)

Qt provides examples in abundance for both Qt Quick and Qt Widget projects, along with a forum. You shouldn't worry about getting help in the long run. (Don't forget StackOverflow!)

Qt Quick + Qt Widget

So far we've been treating them like separate entities. But it is possible to integrate QML into C++. This allows you to take advantage of Qt Widget, C++, and other modules. For example, QtQuick provides a TreeView but not a TreeModel, which can/should be registered into QML from C++. Often there is a separation of concerns pitch, where Qt recommends separating programs into UI and logic into QML and C++ respectively.

This also comes in handy, if say, you need a backend for intense SQL queries, algorithms, or asynchronous http/xml requests. Isn't that cool? QML/JS frontend plus a C++ backend. Fullstack Qt'er. :-)

Domenic answered 12/11, 2018 at 11:27 Comment(2)

Qt Quick allows hot reload, see qhot or Hot reload QML when using ApplicationWindow or felgo live – Crapshooter 18/2, 2023 at 10:6

qtdeclarative (for Qt Quick) is a large dependency -> runtime size, bundle size – Crapshooter 19/2, 2023 at 13:50