Qt

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Official (new) website

Wiki

Developer Page

Forum

Uses

Binding with different languages

http://qt-project.org/wiki/Category:LanguageBindings

Qt 5

Transition of code from Qt 4.x to 5.x

To resolve the error invalid use of incomplete type 'class QWidget' or QApplication: No such file or directory ... when compiling the code was written based on Qt 4.

In summary, we need to add the following line to .pro file (Don't understand why qmake from Qt5 cannot automatic do it for us) 

QT += widgets

and change all instances of 

#include <QtGui>

to 

#include <QtWidgets>

What's new in Qt 5

5.0

  • Improved support for Javascript and QML
  • Mobile
  • Amazing Graphics Capability and Performance
  • Qt Quick (qml application)
  • HTML5
  • Multimedia (qml)

5.1 What's New in Qt 5.1

  • Qt for Android, Qt for iOS
  • Qt Quick Controls, Qt Quick Layouts, Qt Quick Dialogs, Qt Sensors, Qt Serial Port

5.2 What's New in Qt 5.2

  • Qt Android Extras
  • Qt Bluetooth
  • Qt Mac Extras
  • Qt NFC
  • Qt Positioning
  • Qt Windows Extras

5.3 What's New in Qt 5.3

  • Enginio - A client-side library for Qt Cloud Services.
  • Qt WebSockets
  • WinRT

5.4 What's New in Qt 5.4

  • Qt WebChannel
  • Qt WebEngine
  • Qt WebEngine Widgets
  • Qt Platform Headers
> ex4  # C:\Qt\4.8.6\examples
 [1] "activeqt"     "animation"    "dbus"         "declarative"  "designer"     "desktop"      "dialogs"      "draganddrop"  "effects"     
[10] "gestures"     "graphicsview" "help"         "helper"       "ipc"          "itemviews"    "ja_JP"        "layouts"      "linguist"    
[19] "mainwindows"  "multimedia"   "network"      "opengl"       "openvg"       "painting"     "phonon"       "qmake"        "qtconcurrent"
[28] "qtestlib"     "qws"          "richtext"     "script"       "sql"          "statemachine" "threads"      "tools"        "touch"       
[37] "tutorials"    "uitools"      "webkit"       "widgets"      "xml"          "xmlpatterns" 
> ex5  # C:\Qt\Examples\Qt-5.4
 [1] "activeqt"          "aggregate"         "androidextras"     "assistant"         "bluetooth"         "corelib"          
 [7] "dbus"              "declarative"       "designer"          "embedded"          "enginio"           "gui"              
[13] "help"              "linguist"          "location"          "macextras"         "multimedia"        "multimediawidgets"
[19] "network"           "nfc"               "opengl"            "positioning"       "qmake"             "qml"              
[25] "qmltest"           "qpa"               "qtconcurrent"      "qtestlib"          "quick"             "script"           
[31] "sensors"           "serialport"        "sql"               "svg"               "touch"             "uitools"          
[37] "wayland"           "webchannel"        "webengine"         "webenginewidgets"  "webkit"            "webkitqml"        
[43] "webkitwidgets"     "websockets"        "widgets"           "winextras"         "xml"               "xmlpatterns"      
> setdiff(ex5, ex4)
 [1] "aggregate"         "androidextras"     "assistant"         "bluetooth"         "corelib"           "embedded"         
 [7] "enginio"           "gui"               "location"          "macextras"         "multimediawidgets" "nfc"              
[13] "positioning"       "qml"               "qmltest"           "qpa"               "quick"             "sensors"          
[19] "serialport"        "svg"               "wayland"           "webchannel"        "webengine"         "webenginewidgets" 
[25] "webkitqml"         "webkitwidgets"     "websockets"        "winextras"

Install precompiled binary Qt on Windows

http://download.qt.io/official_releases/

For example, the source code for 5.0.1 can be downloaded from http://download.qt-project.org/official_releases/qt/5.0/5.0.1/single/

Qt 4.8.5 based on MinGW binary

Got an error of 'Only versions with W32API 3.13 are supported'. See https://bugreports.qt-project.org/browse/QTBUG-26137. I am using MinGW-get-setup.exe to install MinGW. The gcc version is 4.7.2-1.

Some suggestions are to install old versions of GCC. http://qt-project.org/forums/viewthread/22352 and http://wiki.qt.io/MinGW.

Download gcc 4.4.0 (mingw-gcc440_1.zip) from search google. Just unzip it to C:\. There is no need to put 'C:\mingw\bin' in Windows environment variable PATH. At the end, we will have a new folder C:\mingw.

Although Qt can be installed without any errors, when I try some examples, some of them will give an error "The program has unexpectedly finished". Update: the error was caused by previous build residue. Just delete the build directory (Debug/Release) and re-build again. Things works well. However, remember the executable file can only be run through Qt Creator. It does not work by just double clicking the executable file.

The order of installation is

  1. mingw
  2. Qt library
  3. Qt creator

Qt 5.1.1 based on MSVC

I try Qt 5.1.1 for Windows 32bit (VS 2010, OpenGL 504 MB) on my Windows 7 + VS 2010. The <fancybrowser> works fine.

Note that after I install it to "C:\Qt\5.1.1" directory, I will get the following sub-directories "5.1.1" (another one), "Licenses", "Tools", "vcredist" with a few files. The <Qt Creator> cannot be unselect in installation and it is located under "Tools" folder.

How to Build static Qt on Windows

General resource:

Why do we need to

Using the VS2010 version of Qt to build an app has a problem when it is time to distribute the application. In my first example of GUI with button & label, I need to put the following 7 dll files in the same exe directory in order to run the exe file from Windows Command Prompt instead of Qt Creator.

  • icudt49.dll (17MB)
  • icuin49.dll (1.3MB)
  • icuuc49.dll (1MB)
  • Qt5Cored.dll (7MB)
  • Qt5Guid.dll (5.5MB)
  • Qt5Widgets.dll (4MB)
  • Qt5Widgetsd.dll (7.5MB)

Google: how to reploy application on windows, how to build qt contains all dll static on windows

My experience based on Qt 4.x.x

MSVC 2010

  • Download and install Perl (no need for python and ruby unless we want WebKit).
  • Unzip source file in zip format and put it under C:\Qt
  • Rename C:\Qt\qt-everywhere-opensource-src-4.8.4 to C:\Qt\4.8.4
  • Open c:\Qt\4.8.4\mkspecs\win32-msvc2010\qmake.conf and replace
QMAKE_CFLAGS_RELEASE = -O2 -MD
QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO += -O2 -MD -Zi
QMAKE_CFLAGS_DEBUG = -Zi -MDd

with 

QMAKE_CFLAGS_RELEASE = -O2 -MT
QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO += -O2 -MT -Zi
QMAKE_CFLAGS_DEBUG = -Zi -MTd

according to the page 

cd C:\Qt\4.8.4
set PATH=C:\QT\4.8.4\bin;%PATH%
configure -platform win32-msvc2010 -static -opensource -debug-and-release
nmake sub-src

If we need to reconfigure, run make confclean and configure. Some guide also includes '-release' option.

See here when we want to build both release and debug mode applications. If we just specify '-release' in the configure line, we will not be able to create debug program although I still do not know how to use debug program in Qt creator with MSVC.

For mingw, we need to use 'mingw32-make' instead of 'make' or 'nmake'. See Building Qt Desktop for Windows with MinGW.

MinGW

Download and install MinGW-gcc440_1 & ActivePerl.

C:\Perl64\site\bin, C:\Perl64\bin (these 2 were added by ActivePerl installer by default), C:\mingw\bin and C:\Qt\4.8.5-src should be put in the PATH variable.

I have successfully built Qt using MinGW. 

configure 
mingw32-make

When I try to run my program (either Debug or Release version), I get an error The program can't start because QtCore4.dll is missing from your computer. Try reinstalling the program to fix this problem.. Reboot?

For Qheatmap application, we still need to copy 2 dll files: mingwm10.dll(11 KB) and libgcc_s_dw2-1.dll(43 KB) from C:\mingw\bin folder to the same folder as Qheatmap.exe. These 2 files were also mentioned in Building Qt Desktop for Windows with MinGW.

My experience based on Qt 5.x.x

  • See the instruction on Git
  • The directory structure in Qt 5 is quite different from Qt 4. For example, \bin directory is now under \qtbase directory not under the root directory.
  • read ReadME file to download Perl, Python and Ruby. Make sure the executable path in in PATH env variable.
  • Download/Install Windows SDK 7.1 (for Windows 7) or 8 (for Windows 8).
  • OpenGL (NOT optional): DirectX SDK The 6/7/2010 version is about 572MB. This will be installed to C:\Program Files (x86)\Microsoft DirectX SDK(June 2010) directory. (The precompiled Qt is built against ANGLE which provides OpenGL ES 2.0 support. ANGLE allows Windows users to run OpenGL ES 2.0 content by translating OpenGL ES 2.0 API calls to DirectX 9 API calls) I actually got an error of Error code S1023 when I installed DirectX SDK. See the solution here/Basically uninstall x86 & x64 VC2010 Redistr and install DirectX SDK and then re-install x86 & x64 VC2010 Redistr.
  • modify mkspecs by searching qmake.conf. It was found in C:\Qt\qt-everwhere-opensource-src-5.1.1\qtbase\mkspecs\win32-msvc2010
  • run the following
cd c:\qt\5.1.1-src
set PATH=C:\QT\5.1.1-src\qtbase\bin;C:\qt\5.1.1-src\gnuwin32\bin;%PATH%
set QMAKESPEC=win32-msvc2010

configure -debug-and-release -static -opensource -opengl desktop -nomake examples -nomake tests

jom

It works when I tested qtbase\examples\widgets\painting.

Build Webkit

Try on Qt 5.1.1 

set PATH=%PATH%;C:\icu\bin64
set INCLUDE=%INCLUDE%;C:\icu\include
set LIB=%LIB%;C:\icu\lib64

perl qtwebkit\Tools\Scripts\build-webkit --qt --release --minimal

The WebKit build was disabled for the following reasons:
    * ICU is required. To build QtWebKit with Qt 5 you need to build Qt 5 with l
ibICU support. Check for ICU support being mentioned in qtbase/config.summary.
  • The static build of WebKit is not successful when I use qt source code. I get the message "Project ERROR: WebKit requires SQLite. Either make it available via pkg-config, set $SQLITE3SRCDIR or build Webkit under qt5.git."
# Open Qt command prompt from Windows Start
cd c:\qt\5.1.1\5.1.1\Src\qtwebkit\
perl Tools\Scripts\build-webkit --qt --release --minimal
  • The static build of WebKit is not successful when I use SVN version. I get the message "Failed to set up build environment using SQLite. Either make it available via pkg-config, set $SQLITE3SRCDIR or build WebKit under qt5.git."
  • Another try according to stackoverflow. First of all, we still need to follow the build instruction for QtWebKit build on Windows to install GNU tools and setup PATH. Open a QT command prompt (The Qt was not from source code but from MSVC binary) and
cd C:\qt\5.1.1\5.1.1\src\qtwebkit
qmake

Open another VS 2010 command prompt and 

set PATH=%PATH%;C:\icu\bin64
set INCLUDE=%INCLUDE%;C:\icu\include
set LIB=%LIB%;C:\icu\lib64
SET SQLITE3SRCDIR=C:\qt\5.1.1\5.1.1\src\qtbase\src\3rdparty\sqlite
cd C:\qt\5.1.1\5.1.1\src\qtwebkit
nmake

Still get errors "LNK2001: unresolved external symbol _u_charType_51 JavaScriptCore.lib(Lexer.obj)" as reported by this case. This is a good reference.

Install Qt on Ubuntu

ArchWiki is useful; see https://wiki.archlinux.org/index.php/Qt.

It is also necessary to follow http://wiki.qt.io/Install_Qt_5_on_Ubuntu to install g++ and OpenGL libraries. Note the last one is what I added to resolve the error of cannot finding -lGL; check Compile Qt 4.7 on Ubuntu 10.10. 

sudo apt-get install build-essential
sudo apt-get install libgl1-mesa-dev

If Qt Creator was installed (eg from binary installer of Qt 5.1.0), then it can be launched by 

~/Qt5.1.0/Tools/QtCreator/bin/qtcreator

Qt 5.x.x (offline)

It is straight forward if we use the binary version installer instead of building from Qt source. Just use 'chmod +x' to make the downloaded file executable and then run the executable file. Note that the installer name may be changed from time to time. 

./qt-linux-opensource-5.1.1-x86_64-offline.run

It is still necessary to install opengl library by executing sudo apt-get install mesa-common-dev and sudo apt-get install libgl1-mesa-dev.

At the end, the qmake program is available under ~/Qt5.1.1/5.1.1/gcc_64/bin/qmake.

The Qt creator is bundled in the installer so we don't have to download it separately.

Q: How to resolve the error <QPrinter> no such file or directory in Qt 5? Ans: Add QT += printsupport according to http://qt-project.org/forums/viewthread/24668.

Q: How to resolve the error /home/brb/Qt5.1.1/5.1.1/gcc/include/QtCore/qobject.h:214: Error no type named 'Object' in 'struct QtPrivate::FunctionPointer<const char*>'

Q: How to uninstall Qt5 that I installed from .run? Ans: run MaintenanceTools program from Qt directory. See this post. A screenshot of the maintenance tool is given below,

Qt MaintenanceTool.png

Qt 5 (online installer)

(tested on 12/25/2014). By default, it will be installed on ~/Qt directory. We can choose what versions of Qt to install. The newest version is Qt 5.4 now. 

chmod +x qt-opensource-linux-x64-1.6.0-7-online.run
./qt-opensource-linux-x64-1.6.0-7-online.run

Build Qt5 from source

The source code for Qt 5 can be obtained from 

git clone git://code.qt.io/qt/qt5.git

Note that for Qt 4 the source code can be obtained 

git clone git://code.qt.io/qt/qt.git
cd qt

Qt 4.x.x

Method 1. Use apt-get install approach. See http://www.wikihow.com/Install-Qt-SDK-on-Ubuntu-Linux. This will install old version of qmake in the system. 

sudo apt-get install qt4-dev-tools

At the time of writing (tested on Linux Mint 15), the qmake is 4.5.2 (the Qt website offers 4.8.5).

Method 2. Manually compile it. First we download Linux/X11 one from qt-project.org (230MB). It is the same as the source code file. The INSTALL file points to http://qt-project.org/doc/qt-4.8/install-x11.html. We also need to do 'apt-get install libxext-dev' to resolve an error that 'basic XLib functionality test failed'. 

tar xzvf qt-everywhere-opensource-src-4.8.5.tar.gz
cd qt-everywhere-opensource-src-4.8.5
./configure -static -debug-and-release
make -j 3
sudo make install

Note that

  • the last step make install is required; if this is skipped, Qt Creator won't let you to add 4.8.5 as a Kit.
  • the directory 'qt-everywhere-opensource-src-4.8.5' is not useful anymore. It can be deleted to save space (7GB).
  • if we want to save compile time, we can add -nomake examples -nomake tests -opensource to configure command.

At the end of "./configure", it shows 

Qt is now configured for building. Just run 'make'.
Once everything is built, you must run 'make install'.
Qt will be installed into /usr/local/Trolltech/Qt-4.8.5

To reconfigure, run 'make confclean' and 'configure'.

In .profile (if your shell is bash, ksh, zsh or sh), add the following lines: 

 PATH=/usr/local/Trolltech/Qt-4.8.5/bin:$PATH
 export PATH

If qt-creator was not found in the dash, we can find creator a desktop file and drag&drop it to the launcher. The icon for qt-creator can be found in /usr/share/app-install/icons/qtcreator.png.

Qt Creator

  • Multiple version of Qt library
  • Keyboard shortcuts:
    • Ctrl + Click the symbol - move to the definition or the declaration of a symbol.
    • Click a symbol + Right click + Follow the symbol under cursor - move to the definition
  • The default build directory is parallel to the folder of source code which is a pain if there is a same project name. A better default build directory should be under the source code folder. To change the default setting, go to Tools -> Options -> Build and Run -> Remove "../" from the Default build directory value "../build-%{CurrentProject:Name}-%{CurrentKit:FileSystemName}-%{CurrentBuild:Name}". The project name is determined by Qt project file XXXX.pro.
  • here teaches us how to set warning level when compiling a Qt project. Qt project uses the settting in makefile. We can overwrite it by setting something in .pro file
win32:QMAKE_CXX_FLAGS_WARN_ON += -Wextra

Google: Qt change warning level.

Debug Qt program built with the Microsoft Visual Studio compilers

Qt Tutorial

Books

Code snippets

http://qt-project.org/wiki/Category:Snippets

Simple Test

QWidget

To quickly test whether the Qt was built successfully, we can 

#include <QApplication>
#include <QWidget>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QWidget window;

    window.resize(250, 150);
    window.setWindowTitle("Simple example");
    window.show();

    return app.exec();
}

Go to Windows Command line (The 'nmake' command will be 'make' on Linux OS). 

cd c:\Qt
mkdir example
cd example
notepad test.cpp
set PATH=%PATH%;C:\QT\4.8.4\bin
qmake -project        # Create .pro file
qmake                 # Create Makefile
nmake                 # Run 'make' on Linux

If everything went well, we will obtain the executable file under release folder. That is, we can run the executable file by 

release\example.exe

With Layout

See Listing 1-10 from FOQ. 

#include <QApplication>
#include <QWidget>
#include <QVBoxLayout>
#include <QLabel>
#include <QLineEdit>

int main( int argc, char **argv )
{
  QApplication app( argc, argv );

  QWidget widget;
  QLineEdit *lineEdit = new QLineEdit();
  QLabel *label = new QLabel();

  QVBoxLayout *layout = new QVBoxLayout();
  layout->addWidget( lineEdit );
  layout->addWidget( label );
  widget.setLayout( layout );

//  MyClass *bridge = new MyClass( "", &app );
//  QObject::connect(
//    lineEdit, SIGNAL(textChanged(const QString&)),
//    bridge, SLOT(setText(const QString&)) );
//  QObject::connect(
//    bridge, SIGNAL(textChanged(const QString&)),
//    label, SLOT(setText(const QString&)) );

  widget.show();

  return app.exec();
}

No Layout

See Listing 9-10 from FOQ. 

#include <QApplication>
#include <QMainWindow>

class MainWindow : public QMainWindow
{
public:
  MainWindow();
};

MainWindow::MainWindow() : QMainWindow()
{
  setCentralWidget( new QTextEdit( this ) );
}

int main( int argc, char **argv )
{
  QApplication app( argc, argv );
    
  MainWindow window;
  window.show();
  
  return app.exec();
}

Similarly we can use setCentralWidget() in QMainWindow. See Chapter 4 of 'The Book of Qt4'. 

#include <QApplication>
#include <QMainwindow>
#include <QLabel>
int main(int argc, char *argv[])
{
  QApplication a(argc, argv);

  QMainWindow mainWindow;
  QLabel *label = new QLabel("<center>Central Widget</center>");
  mainWindow.setCentralWidget(label);
  mainWindow.show();

  return a.exec();
}

Qt-Apps.org

http://qt-apps.org/ is a good source to find open source projects based on Qt.

Graphics

Scientific

Sound Application

Qt Widget

  • AnalogWidgets It builds on my Beaglebone black after I edit the file <Flags.pri> to remove lines containing "-march=core2" and "-mfpmath=sse". Just run 'qmake' and 'make' and it'll build successfully. The only problem is the BBB's screen is too small so I have to kill it from another way.
  • Virtual keyboard
  • Image cropper
  • QProgressIndicator
  • QProg

Qt games

C++ basics

See C++ tutorial.

  • Use dot (.) to refer to any public member of a class.
  • Use the arrow operator (->) to refer to a member of an object pointed by a pointer. The label below is a pointer rather than an object but *label is an object.
QLabel *label = new QLabel("ABCDE");
label->show();
// (*label).show();
  • Use the operator of scope (::) to set a definition of a class's member function or call a function from some class. For example,
QObject::connect();

means to use connect() function from QObject class.

  • The this pointer passed on to the EditDialog sets the parent of the dlg to the list dialog.
EditDialog dlg( this );

Here explains: The keyword this identifies a special type of pointer. Suppose that you create an object named x of class A, and class A has a nonstatic member function f(). If you call the function x.f(), the keyword this in the body of f() stores the address of x..

Qt Basic

QWidget vs QDialog

  • If a class's parent is QWidget, the class will be shown at the top-left corner of the screen.
  • If a class's parent is QDialog, the class will be shown at the center of the screen (seems better).

QWidget vs QDialog vs QMainWindow

http://stackoverflow.com/questions/3298792/whats-the-difference-between-qmainwindow-and-qwidget-and-qdialog

  • A QWidget is the base class for all drawable classes in Qt. Any QWidget-based class can be shown as a window by showing it when it has no parent. A simple example of QWidget class can be found on zetcode.com.
  • A QMainWindow is based on QWidget and is designed around common needs for a main window to have. It has predefined places for a menu bar, a status bar, a toolbar, and other widgets. It does not have any built-in allowances for buttons like QDialog does. QMainWindow examples can be found at http://doc.qt.io/qt-4.8/examples-mainwindow.html.

The following table shows the differences of show method and layout management of these classes.

class show method layout
QApplication .exec()
QWidget .show() layout
QMainWindow .show() centralwidget
QDialog .exec() layout

Q_OBJECT

This macro is required if a class contains SIGNAL/SLOT.

tr()

tr() means translation; the characters were auto translated depending on system's locale. See http://qt-project.org/doc/qt-4.8/linguist-hellotr.html

Run Qt from Command Line

I use 

# Open command prompt from Visual Studio 2010
set PATH=C:\Qt\Qt5.0.2\5.0.2\msvc2010_opengl\bin;%PATH%

Now we can build the project by for example 

cd C:\Qt\FQD\Chapter01\plain-cpp
qmake -project
qmake
nmake

The executable will be located under release subfolder.

From C++ to Qt

See Chap 1 of Foundation of Qt Development book.

No Qt Qt
Class List 1.1 
#include <string>
using std::string;
class MyClass
{
public:
  MyClass (const string & text);
  const string& text() const;
  void setText (const string& text);
  int getLengthOfText() const;
private:
  string m_text
}
List 1.2 
#include <QObject>
#include <string>
using std::string;
class MyClass : public QObject
{
public:
  MyClass (const string& text, QObject *parent = 0);
...
}
Main List 1.3 
#include <iostream>
int main(int argc, char **argv)
{
  MyClass *a, *b, *c;
  a = new MyClass ("foo");
  b = new MyClass("ba-a-ar");
  c = new MyClass("baz");
  std::cout << a->text() << "(" << a->getLengthOfText() << ")" << std::endl;
  a->setText( b-> text() );
  std::cout << a->text()  << "(" << a->getLengthOfText() << ")" << std::endl;
  int result = a->getLengthOfText() - c ->getLengthOfText();
  delete a;
  delete b;
  delete c;
  return result;
}
List 1.4 
#include <QtDebug>
int main (int argc, char **argv)
{
  QObject parent;
  MyClass *a, *b, *c;
  a = new MyClass ("foo", &parent); // Or a = new MyClass("foo", this);
  b = new MyClass("ba-a-ar", &parent);
  c = new MyClass ("baz", &parent);
  qDebug() << QString::fromStdString(a->text()) << "(" << a->getLengthOfText() << ")";
  a -> setText( b-> text());
  qDebug() << QString::fromStdString(a->text()) << "(" << a->getLengthOfText() << ")";
  return a->getLengthOfText() - c->getLengthOfText();
}
File Output 
const char *filename="/home/brb/file";
string filename2;
std::ofstream myfile
myfile.open(filename, ios::out | ios::app);
myfile.open(filename); // Error
myfile.open(filename.c_str());
if (!myfile.is_open()) return;
myfile << "ABC\n";
myfile.close();

Qstring filename;
QFile file(filename)
if (!file.open(QFile::WriteOnly | QFile::Text)) return;
QTextStream  out(&file);
out << "ABC\n";
file.flush();
file.close();

Forward Declaration

The forward declarations of the Qt classes tells the C++ compiler that a class exists, without giving all the detail that a class definition provides. 

// <finddialog.h>
class QCheckBox;

On the other hand, we can simply include QtGui in the cpp file. That saves us to include every class we need individually. 

// <finddialog.cpp>
#include <QtGui>
#include "finddialog.h"
FindDialog::FindDialog(QWidget *parent) : QDialog(parent)
{
 ...
}

Subclass and Parent in constructor

The QDialog in the class definition shows the base class for FindDialog class.

The parent parameter in FindDialog constructor specifies the parent widget (QWidget). The default is a null pointer, meaning that the dialog has no parent.

The private variable is a pointer declared in the header file. So the compiler does not need the full class definition. We could have included the header file <QCheckBox> in the header file, but using forward declarations will makes compiling faster. 

// <finddialog.h>
class FindDialog : public QDialog
{
   Q_OBJECT
  public:
    FindDialog(QWidget *parent = 0);
  private;
    QCheckBox *caseCheckBox;
}

Naming Convention

  • Class name starts with an uppercase letter and the words are divided using Camel-Casing.
  • The names of the methods all start with a lowercase letter, and the words are again divided by using CamelCasing.

Memory Management

Parent is on heap. So it has to be deleted manually. 

#include <QtGui>
#include "addressbook.h"
//...every needed header

int main(...) {
   //QApplication app ....
   QWidget *parent = new QWidget; //a parent for your addressbook 
   AddressBook *myAddressBook = new AddressBook(parent); //pass a pointer to parent widget when you construct an AddressBook object
   //... other code, maybe some layout if necessary...
   parent->show(); //will show the chidren widgets too
   
   int returnValue = app.exec();
   delete parent; //this will delete the parent children too
   return returnValue;
}

OR creating parent on the stack 

int main(...) {
   //QApplication app ....
   QWidget parent; //a parent for your addressbook - parent is created on stack
   AddressBook *myAddressBook = new AddressBook(&parent); //pass a pointer to parent widget when you construct an AddressBook object
   //... other code, maybe some layout if necessary...
   parent.show(); //will show the chidren widgets too

   return app.exec();
}

Bundle a file in app

Check out The Qt Resource System

Scientific Plot

http://www.qcustomplot.com/

QSettings

If QSettings object does not specify a file, the default location is defined here.

For example in my main.cpp, 

    QApplication app(argc, argv);
    app.setOrganizationName("Trolltech");
    app.setApplicationName("Recent Files Example");

then the ini file is saved in "/home/brb/.config/Trolltech/Recent Files Example.conf" as indicated by 

    QSettings settings;
    qDebug() << settings.fileName();

To set or retrieve a key from the setting, use 

settings.setValue("bowtie", inputBowtie);
settings.setValue("recentFiles", recentFiles);

inputBowtie = settings.value("bowtie", "").toString();
recentFiles = settings.value("recentFiles").toStringList();

There are different locations we can use to save the parameter file.

  • The following way will create an entry <testSettings> under <Computer\HKey_CURRENT_USER\Software\ArrayTools> on Windows registry on Windows OS (NativeFormat will be used).
    QSettings settings("ArrayTools", "testSettings");
  • The following way will create a folder name <ArrayTools> and a file <Heatmap.ini> in %AppData% folder (C:\Users\USERNAME\AppData\Roaming) on Windows OS.
QSettings settings(QSettings::IniFormat, QSettings::UserScope, "ArrayTools", "Heatmap"); // %APPDATA%
  • The following way will create a file <test.ini> under a desired folder on Windows OS. Note that if we omit the QSettings::IniFormat option, the parameter file will not be working (read/write).
QSettings settings(QString("C:/Qt/examples/BRCA/test.ini"), QSettings::IniFormat);
  • The following way will create a file <.BDGE.ini> under %HOME% directory on Linux OS.
QString m_sSettingsFile = "/home/" + QString(getenv("USER")) + "/.BDGE.ini";
QSettings settings(m_sSettingsFile, QSettings::NativeFormat);

.pri file, subprojects

Misc

  • If we want to create a new class member to be used in class method, we should declare it in the header file. For example, look at the variable 'label' below. Of course, variables only used locally have not this rule.
class MyButton : public QWidget
{
   Q_OBJECT
public:
    MyButton(QWidget *parent = 0);
    QLabel *label;
private slots:
    void showText();
};

MyButton::MyButton(QWidget *parent)
    : QWidget(parent)
{
  label = new QLabel(); // NOT QLabel *label = new QLabel();
}

void MyButton::showText()
{
  label->setText("My Text!");
}

Qt Quick

Documentation using Doxygen

sudo apt-get install doxygen doxygen-gui

Then run 

doxywizard

from a terminal. The rest should be trivial: enter project directory (nothing will be generated here actually), source code directory and output directory. Click Next. Click 'Run' tab to create HTML file. Click 'x' to quit and choose the default name 'Doxyfile' for the doxy file (> 900 lines). We can click 'Open HTML output' button to see the output or go to the output folder and select html/index.html or html/annotated.html file to view the result.

Note that the input and output (absolute path) values will be written to 'Doxyfile'.

If the source code was changed, we just need to run the following command to update files in the doxy output folder. 

doxygen

We can also create Doxyfile from scratch by running 

doxygen -g

and then generate (default) output files by running 

doxygen Doxyfile  # Or just doxygen

A better practice is to create a project folder and then create subfolders like 

MyProject/
         |--doc/
         |-->Doxyfile 
         |--src/

doxywizard

DoxyWizard.png

Qt Tricks

C++11 support

Add the following to the .pro file. 

CONFIG += c++11

A simple C++ code that uses a range-based for loops is: 

 int my_array[5] = {1, 2, 3, 4, 5};
for(int &x : my_array)
{
  x *= 3;
}

Break long text

Set Windows initial posiiton

Set main window initial position

Get the current working path

Use QCoreApplication::applicationDirPath() to get the current working path or QFile::absolutePath() to get the absolute path from relative one.

Pop up a help file

  • QMessageBox: no maximize button on top-right corner. Cannot resize (old Qheatmap)
  • QTextBrowser: the html file cannot be part of C++ (Qtextbrowser)
  • QLabel: No scroll bar (Qt07_BasicApplication)
  • QTextEdit: Good (used in Qheatmap)
  • QWebkit
  • QTextDocument: no scroll bar (Qt79_drawText)

Convert QString to std::string

http://stackoverflow.com/questions/4214369/how-to-convert-qstring-to-stdstring 

.toStdString()

Convert QString to const char*

in C++03, ofstream::open takes const char* parameter.

If OutputFileName is std::string. 

ofstream CSVFile;
CSVFile.open(OutputFileName.c_str());

If outputFileName is Qstring 

CSVFile.open(OutputFileName.toStdString().c_str());

See QString::toStdString reference

Custom Plots

CPU/RAM real-time performance widget

https://www.youtube.com/watch?v=eSHTXQbPquk and https://github.com/giordi91/performanceWidget

Use boost libraries with an example

http://stackoverflow.com/questions/16998326/using-boost-libraries-in-qt

On Windows OS, we can add the following to the .pro file 

INCLUDEPATH += C:/boost/boost_1_53_0/
LIBS += "-LC:/boost/boost_1_53_0/stage/lib/"

On Ubuntu OS, I can use (the first line Qt += widgets is only necessary on Qt 5) 

QT += widgets
INCLUDEPATH += /home/brb/Downloads/boost_1_55_0/
LIBS += "-L/home/brb/Downloads/boost_1_55_0/stage/lib/"

The following is an example to compute the 95% percentile from the T distribution (df=195) is 

#include <QApplication>
#include <QLabel>

#include <boost/math/distributions/students_t.hpp>

using namespace std;
using boost::math::students_t;

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    int df = 195;
    double alpha = .1;
    students_t dist(df);
    double T = quantile(complement(dist, alpha / 2));

    QLabel *label = new QLabel("T(.95, df=195)=" + QString::number(T));
    label->show();

    return a.exec();
}

Home directory

QDir::homePath()

Qt Designer

From C++ GUI Programming with Qt book Chapter 2:

In the constructor, we call setupUi() to initialize the form. Thanks to multiple inheritance, we can access Ui::GoToCellDialog's members directly. After creating the user interface, setupUi() will also automatically connect any slots that follow the naming convention on_objectName_signalName() to the corresponding objectName's signalName() signal. In our example, this means that setupUi() will establish the following signal–slot connection: 

connect(lineEdit, SIGNAL(textChanged(const QString &)),
        this, SLOT(on_lineEdit_textChanged()));

However, just like the GUI created in VBA, the text in the QLabel can be cut. So it is best not to use Qt Designer from my opinion.

Cross compile Windows app on Linux

http://stackoverflow.com/questions/10934683/how-do-i-configure-qt-for-cross-compilation-from-linux-to-windows-target

Snchronous processing of QProcess (without freezing the gui)

Google: Qprocess synchronous use. http://stackoverflow.com/questions/11191988/qt-synchronous-processing-of-qprocess-without-freezing-the-gui 

[...]
ui->status->setText("Do something with program 1");
proc1.setReadChannelMode(QProcess::SeparateChannels);
proc1.start("program 1 -args", QIODevice::ReadWrite);
connect(proc1, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(finishedProc1()))
[...]

void finishedProc1()
{
   ui->status->setText("Do something with program 2");
   proc2.setReadChannelMode(QProcess::SeparateChannels);
   proc2.start("program 2 -args", QIODevice::ReadWrite);
   connect(proc2, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(finishedProc2()))
}

void finishedProc2()
{
  [...]
}

Reading the system() command output

Use QProcess. See this post. 

QProcess process;
process.start(/* command line stuff */);
process.waitForFinished(-1); // will wait forever until finished

QString stdout = process.readAllStandardOutput();
QString stderr = process.readAllStandardError();

Show table text file in QTableWidget

http://qt-project.org/forums/viewthread/31706 

#include <QApplication>
#include <QMainWindow>
#include <QTableWidget>
#include <QTableWidgetItem>
#include <QFile>
#include <QString>
#include <QStringList>
#include <QTextStream>
#include <QMessageBox>
#include <QDebug>

int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    QMainWindow *window = new QMainWindow();
    QMessageBox msg;

    QFile file("Data.txt");
    if(!file.open(QIODevice::ReadOnly))
    msg.information(0,"Error!","Error opening file!",0);

    QTextStream in(&file);
    QStringList *loadCsv;
    QTableWidget *myTable=new QTableWidget();

    int rowsCount = 1;

    while(!in.atEnd())
    {
        loadCsv = new QStringList(in.readLine().split(";"));
        myTable->setRowCount(rowsCount);
        myTable->setColumnCount(loadCsv->size());
        for(int col = 0; col < loadCsv->size(); ++col)
        {
            QTableWidgetItem *items= new QTableWidgetItem(loadCsv->at(col));
            myTable->setItem((rowsCount - 1), col, items);
        }
        rowsCount++;
        delete loadCsv;
    }
    window->setCentralWidget(myTable);
    window->show();
    return app.exec();
}

and the Data.txt file 

bq. John Kl;34;1335532;CA;0444344
Kuma jo;54;44432;NY;0322355
Lebal ho;24;44022;NY;0110004

Creating spinning image/progress spinner

Adding a child to QMainWindow

This is related to the error message Attempting to set QLayout "" on MainWindow "", which already has a layout. See

Shape-Changing Dialogs

Extension Dialogs

Multi-page dialogs

QTabWidget and QToolBox

Place widget in the center of screen

#include <QDesktopWidget>
...
Widget w;
w.move(QApplication::desktop()->screen()->rect().center() - w.rect().center());
w.show();

Create resource file

For example, if we want to include an image as a background for QTextEdit, then we can do put the following in <main.cpp> 

#include <QtGui>

int main(int argc, char **argv)
{
     QApplication app(argc, argv);

     QTextEdit* edit = new QTextEdit();
     edit->setWindowTitle("QTextEdit Background Image");

     edit->setStyleSheet("background-image: url(:/image/cherryblossom_pink.jpg)");

     // the following 4 lines are playing with font       
     edit->setTextColor(QColor("white"));
     edit->setFont (QFont ("Courier", 20));
     edit->setText("Can you see me?");
     edit->setGeometry(100,100, 480, 272);

     edit->show();
     return app.exec();
}

The image file <cherryblossom_pink.jpg> can be (not necessary) in the source directory.

To add a resource file

  1. right click project name and choose 'add new'
  2. choose 'Qt resource file'. Enter 'resource' for the resource file name (Qt will add .qrc as ext name)
  3. click 'Add Prefix'. Type '/image' for instance.
  4. click 'Add file'. It will open a file explorer for us to browse files we want.
  5. We can refer to this image file by adding colon, prefix and file name such as the above example.

The image file will part of executable file. We can access the file at run time. We can add any files in the resource file. The prefix mechanism is just a way to organize these files when we want to refer them in our code.

Search files in a directory (QDir and QStringList)

#include <QApplication>
#include <QStringList>
#include <QDir>
#include <QtDebug>
int main(int argv, char **args)
{
   QApplication app(argv, args);

   QStringList nameFilter("*.fastq");
   QDir directory("/home/brb/Anders2013small");
   QStringList files = directory.entryList(nameFilter);
   for (int i = 0; i < files.size(); ++i)
       qDebug() << files.at(i) ;

   return app.exec();
}

QRegExp

#include <QApplication>
#include <QString>
#include <QStringList>
#include <QRegExp>
#include <QDebug>
int main(int argc, char *argv[])
{
   QString str;
   str = QString("-o Serum") ;
   QStringList strlist;
   strlist = str.split(" ");
   QRegExp rx("Ser");
   foreach (const QString &str, strlist) {
       qDebug() << "str " << str ;
       qDebug() << "indexIn " << rx.indexIn(str);
        }
   qDebug() << "strlist.indexOf('Serum')" << strlist.indexOf("Serum");

   if (strlist.indexOf("-p") < 0 && strlist.indexOf("--num-threads")) strlist << "-p 5";
   foreach (const QString &str, strlist) {
       qDebug() << str ;
        }
   qDebug() << strlist.join(" ");
}

gives an output 

str  "-o" 
indexIn  -1 
str  "Serum" 
indexIn  0 
strlist.indexOf('Serum') 1 
"-o" 
"Serum" 
"-p 5" 
"-o Serum -p 5"

Query number of threads in CPU

#include <QThread>
....
qDebug() << QThread::idealThreadCount();

Sockets

Some application examples

  • Sending images (FOQ, Chapter 14)
  • Trip planner (C++GUIQt4, Chapter 15)
  • (TBQt4, Chapter 11.5)
  • (DesignPatters, not covering)
  • (AQtPr, not covering)
  • Trip palnner

Trouble Shooting

Undefined reference to vtable

Close the project in Qt-Creator. Open a terminal, cd to the project directory and run 

qmake -project
qmake
make

Gtk-CRITICAL **: IA__gtk_widget_style_get: assertion `GTK_IS_WIDGET (widget)' failed

See this post from stackoverflow.com.

Couldn't register with accessibility bus:

Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.

One solution is to open a terminal, run the following line 

export NO_AT_BRIDGE=1

and finally run the application from the same terminal.

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