Rasim Labibov
11 KiB
Introduction
This guide aims to create a simple Qt application with Qt Quick graphical user interface. The tutorial uses CMake as the project format and C++ as the language of source code. The application created is simple in design and consists of sole window.
QtQuick is a user interface library that provides ways to create declarative user interface separated from the programming logic. It's framework is implemented as a part of the Qt library set. QML is a user interface specification and programming language.
CMake is the project generator for many platforms and build systems. CMake uses the unified file format and is able to generate makefiles, Visual Studio solutions and projects for many other build systems from the same project file.
Prerequisites
Compiling and running the sample project requires GCC, CMake, GNU Make and Qt development libraries with Qt Quick enabled. This tutorial specifies the way to install pre-compiled packages from the standard repositories.
Environment Setup
Debian-based Systems
The following instructions are applied to these operating systems:
- Ubuntu 16.04
- Debian 9
sudo apt-get install -y \
build-essential \
cmake qtbase5-dev \
qtdeclarative5-dev \
qml-module-qtquick2 \
qtquickcontrols2-5-dev \
qml-module-qtquick-controls
RedHat-based Systems
The following instructions are applied to these operating systems:
- CentOS 7
- Fedora >=22
sudo yum groupinstall -y "Development Tools"
sudo yum install -y \
cmake \
qt5-qtbase-devel \
qt5-qtdeclarative-devel \
qt5-qtquickcontrols \
qt5-qtquickcontrols2-devel
Directory Structure
The directory of the project is laid out as follows.
$ tree
.
├── CMakeLists.txt
└── src
├── CMakeLists.txt
├── main.cpp
├── main.qml
└── qml.qrc
1 directory, 5 files
All source files for the project will go in src and main project specifications
in CMake format are in the CMakeLists.txt file. Larger projects tend to be
organised in sub-directories for modules, executables and libraries, each with
its individual sub-directory and CMakeLists.txt file within.
Main Window GUI File
Start with declarative file for user interface that is specified in the file
src/main.qml. The code creates a small window without any controls.
Necessary modules are imported. The exact version of the QtQuick library is not
the same as the version of the Qt framework used. QtQuick.Controls library
contains some basic controls for the user interface.
import QtQuick 2.0
import QtQuick.Controls 1.0
Main application window is represented with the ApplicationWindow control in the
Qt Quick library.
ApplicationWindow
{
...
}
There are four attributes of the main window that specify the size and title of
the window. The visible attribute is required to specify that the window should
be shown in the screen right after launch.
visible: true
width: 640
height: 480
title: qsTr("Minimal Qml")
QML Resource File
This is the QML resource file for the application that consists of sole QML file
named main.qml. The file is XML with RCC element as root and qresource as
element for group of resources. This project contains only one group that is the
root (i.e. /). Larger projects may contain additional qresource elements for
each resource subgroup (e.g. customControls, customWindows, etc.).
Application Code
The main entry point of the application provides the C++ code for displaying Qt Quick user interface.
Standard object for Qt application is constructed.
QApplication app(argc, argv);
Here the QML parsing object is initiated for the application. This object
receives the string with address of the main QML resource as the construction
parameter. In this case qrc:/main.qml is the address specified in the qml.qrc
file. qrc: is the default prefix for the QML resource, /main.qml stands for
resource named main.qml in the root resource directory (/).
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
The exec method starts Qt application.
return app.exec();
Project Files
This section shows deployment of Qt Quick application using CMake project format.
This is the main project file. The first line sets the minimum version of CMake
for the project. It includes Qt5 framework into the application and concludes
with the further inclusion of the src subdirectory so that CMake would search
for the project file (CMakeLists.txt) there.
This is the project file for the executable.
The header files of the Qt project should be included into the project so that makefiles generated will have them specified in the corresponding compilation commands. There Qt5Widgets stands the header files for the Qt Framework and QtQml invokes special files for QML functions.
include_directories(${Qt5Widgets_INCLUDE_DIRS} ${QtQml_INCLUDE_DIRS})
The definitions as well as Qt include files should be specified in the makefile compilation commands.
add_definitions(${Qt5Widgets_DEFINITIONS} ${QtQml_DEFINITIONS}
${${Qt5Quick_DEFINITIONS}})
The Qt framework requires the code to be created from the Qt resource files.
This is achieved using the special qt5_add_resources command. The QML resource
file path relative to this file is passed as an argument here.
qt5_add_resources(QT_RESOURCES qml.qrc)
For Qt projects with graphical user interface the compiler should receive special parameters for compilcation
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${Qt5Widgets_EXECUTABLE_COMPILE_FLAGS}")
Qt programs require several additional compilation steps for moc, rcc and uic.
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)
set(CMAKE_AUTOUIC ON)
The name of the project that will be used as a name of the compiled executable
is specified using the set command that receives the name of a variable (i.e.
PROJECT) and it's value.
set(PROJECT "MinimalQml")
The project command sets the current project within the CMake file. It receives the value of the variable defined above.
project(${PROJECT})
The compiler flags for compiling C++ sources are set below. These flags stands for very strict compilation rules and help to detect and locate a lot of potential issues during compilation.
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror -std=c++11
-fstrict-aliasing -pedantic-errors -pedantic -Wno-deprecated-declarations
-Wno-unused-variable")
There are conditional commands in the CMake project language. The code below
detects if there are HEADERS in the project. If the header files were not set
before the file(GLOB ... .h) command creates a list of all header files in the
current directory and passes them as header files of the current project. The
same applies to the .cpp sources that will be stored in the SOURCES variable if
it was not defined.
if(NOT DEFINED HEADERS)
file(GLOB HEADERS ${CMAKE_CURRENT_SOURCE_DIR}/*.h)
endif()
if(NOT DEFINED SOURCES)
file(GLOB SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/*.cpp)
endif()
The source_group definition creates a group of files that will be placed in some
build systems (e.g. there will be project sub-directories in Visual Studio
solution).
source_group("Header Files" FILES ${HEADERS})
source_group("Source Files" FILES ${SOURCES})
This command states an executable file is the result of the project. The first parameter receives the name of an executable file that is the same as the name of the project in this case. The rest of the arguments are project sources, headers and compiled Qt resources.
add_executable(${PROJECT} ${HEADERS} ${SOURCES} ${QT_RESOURCES})
The set of libraries that will be linked with the executable above is set with
the target_link_libraries command. Like the command above it receives the name
of project's executable and the list of libraries. In this case the project uses
Qt framework libraries only.
target_link_libraries(${PROJECT}
Qt5::Widgets
Qt5::Qml
Qt5::Quick
)
Building Project
The program is build with the commands below. The cmake required the directory
with the main project's CMakeLists.txt file as an argument. Then the CMake
creates the build files for the GNU make which builds an executable.
cd <PathToProject>
mkdir build && cd build
cmake ..
make
After the successful build the binary MinimalQml will end up in build/src/.
./src/MinimalQml
Working with Project with Qt Creator
Go to the Welcome tab (1) in the main window and select Open Project (2).
In the opened dialog locate the CMakeLists.txt file in the root directory of the
project.
After that select the version of the Qt framework that will be used for compiling the project. In case there are multiple frameworks installed in the system it is possible to select several of them.
After opening the project its directory structure will be visible in the Projects panel in Qt Creator.
The C++ source files are treated as usual by the editor.
QRC resource files are opened as a resource tree.
From the resource tree it is possible to open QML files of the project.
Links
- Qt Documentation
- CMake