C++ Programming with Qt 3

Transcription

1 C++ Programming with Qt Developing Applications using Qt Classes...3 Hello Qt! application...3 Classes...3 Code...4 Compiling & Running...4 Quit application (Event handling)...5 Classes...5 Code...5 Compiling & Running...6 Numbers application (Synchronization)...6 Task...6 Arrangement...6 Modularization...7 Classes...7 Definition of the Form class...7 Implementation of the Form class...8 The application s main program...8 Creating custom slots...8 Definition of Custom Slot: sayasword(int)...9 Implementation of Custom Slot: sayasword(int)...10 The application s project file...10 Compiling & Running...11 Memory management, parent-child relationship...11 Layout application (Arrangement)...12 Layout Manager...12 Laying Out of the Form...12 Memory Managament, Parent-Children relationship...12 The Form Class using Layout Manager s Classes...13 Form Class s implementation with Layout Classes...13 The application s main program...14 The Application s Project File...14 Compiling & Running...14 Creating Application Using Qt Designer...15 The.ui file and the generated code...15 Extending the functionality of the form...16 The subclassing approach...16 The ui.h extension approach...16 Construction and destruction...17 Words application (Custom slot)...17 Creating the Words project...17 Creating the Main Window (Form)...17 The Form s Design...18 The Form s Arrangement (Layout)...18 Creating the main program (main.cpp)...18 Inserting Variable into the Project...19 initwords() function...19 init() function...20 CEEPUS H81 Network Page 1

2 Connecting the widgets...20 Creating Custom Slot: sayasword(int)...20 The sayasword(int) function s implementcation...21 The application s project file (words.pro)...21 Compiling & Running...21 Workshop...21 Quiz...21 Exercises...21 Workbook s programs can be downloaded from the people.inf.elte.hu/nacsa/qt/lessons/ site. Examples are created on Qt Prepared by: Rozália Szabó-Nacsa [email protected] home page: people.inf.elte.hu/nacsa Documentations: Jasmin Blanchette, Mark Summerfield: C++ GUI Programming with Qt 3 Daniel Solin: Qt Programming Customizing and Integrating Qt Designer, Quick Start Budapest, April CEEPUS H81 Network Page 2

3 Qt is a complete C++ application development framework. It includes a class library, tools for cross-platform development and internationalization. There are a few different so-called toolkits you can use to create graphical program in Linux, however Qt is one of the more popular ones. Because of Qt s Object-Oriented hierarchy, its good structure, its well-developed widgets, and the fact that it includes many other functions than just for creating graphical interfaces, makes it a good choice for beginners as well as experts. Qt is also the toolkit used by KDE desktop environment. Qt is that it available for UNIX/Linux, but also for Microsoft Windows program as well. Although Qt is made as a multiplatform toolkit, because of its powerful API, many organizations use Qt for single-platform development. For example Adobe Photoshop Album is an example of Windows application written in Qt. The Qt toolkit first became publicly available in May Qt 3.0 was released in 2001, which is available on Windows, Unix, Linux, Embedded Linux, and Mac OS X. The Qt API and tools are consistent across all supported platforms, enabling platform independent application development. Qt developers only have to learn one API to write apps that run almost anywhere. Qt applications run natively, compiled from the same source code, on all supported platforms. Qt has got a very nice online documentation. Qt s reference documentation is an essential tool for any Qt developer. It covers every class and function in Qt. Qt 3.2 includes over 400 public classes and over 6000 functions. Developing Applications using Qt Classes The Qt toolkit is a C++ class library and a set of tools for building multiplatform GUI programs using a write once, compile anywhere approach. Qt tools can be found on : site. Hello Qt! application Task: Make a Hello Qt application using Qt classes. Classes The Hello Qt application on Linux CEEPUS H81 Network Page 3

4 Code hello.cpp # include <qapplication.h> # include <qlabel.h> int main(int argc,char **argv) QApplication app(argc,argv); QLabel *label = new QLabel("Hello Qt!",0); app.setmainwidget(label); label->show(); return app.exec(); First we inserted the definition of used classes. Then we created a QApplication object (app), which is responsible for managing the application s resources. Having defiined the QApplication object we pass two arguments: argc, argv, because QApplication supports command-line arguments of its own. Then we created a QLabel object to display Hello Qt! and we announced this label as the application s main widget (setmainwidget()). The zero value as the second parameter of the QLabel constructor says, that this widget has no parents. Having prepared the main widget we let show it on the screen (show()). By default created widgets are not shown on the screen in order to avoid flickering. The last statement passes control of the application on to Qt. The program enters kind of stand-by mode, waiting for user actions to which the program can respond. Having closed the main window the main widget will be deleted from the heap and at the same time it disappears from the screen. You are allowed to use HTML-style text in the QLabel constructor, as well. QLabel *label = new QLabel("<h1><i>Hello</i><font color=red> Qt!</font></h1>",0); Compiling & Running We now have a main.cpp containing the main() function. Le us learn to compile, link and run the application. The qmake tool provided with Qt can create Makefile appropriate to our platform based on.pro project file. Qt Designer produces.ui files which are used to generate.h and.cpp files for the compiler to compile. The.ui files are processed by uic. Please do the next steps in order to compile & run the application: 1. Make the hello directory. 2. Enter the above code using your favorite text editor. Save it as hello.cpp in the hello directory. 3. Be in hello directory. 4. Generate the platform independent project file (hello.pro) with the next command: qmake -project 5. Generate the platform dependent make 1 file wih the next command: qmake -o Makefile hello.pro. 6. Build the program: nmake (make in Linux) 7. Run the program. (Linux:./hello; Windows: hello) This program can be downloaded from the people.inf.elte.hu/nacsa/qt/lessons/hello site. 1: Makefile is a script file for compiling, linking and building project s elements. CEEPUS H81 Network Page 4

5 Quit application (Event handling) In this example we illustrate, how to respond to a user action. This application consist of only one button. This button will be the main widget of the application. Clicking on this button (user action) the program closes (responding on an action). Closing the window the main window will be deleted automatically from the memory and from the screen, too. This example is similar to the previous one, except that we are using a button instead of text. Classes The Quit application Code quit.pro # include <qapplication.h> #include <qpushbutton.h> int main(int argc, char *argv[]) QApplication app(argc,argv); QPushButton *button = new QPushButton("Quit",0); QObject::connect(button,SIGNAL(clicked()),&app,SLOT(quit())); app.setmainwidget(button); button->show(); return app.exec(); Qt widgets are visual graphical GUI elements (control elements). They can send a signal (message) when their state have changed or when a user action occurred. We can connect these signals with special functions (slots) in order to respond on a signal. After we have connected a signal and a slot, the slot will be automatically performed whenever this signal is emitted. We can connect more slots to the same signal. In this case the order of performance is undefined. In our example we have connected the button s clicked() signal with the app s quit() slot. Please observe that we referred on the button and app via pointers. CEEPUS H81 Network Page 5

6 Compiling & Running Please do the next steps in order to compile & run the application: 1. Make the quit directory. 2. Enter the above code using any text editor. Save it as quit.cpp in the quit directory. 3. Be in quit directory. 4. Generate the platform independent project file (quit.pro) with the next command: qmake -project 5. Generate the platform dependent make file with the next command: qmake -o Makefile quit.pro. 6. Build the program: nmake (make in Linux) 7. Run the program. (Linux:./quit; Windows: quit) This program can be downloaded from the people.inf.elte.hu/nacsa/qt/lessons/quit site. Numbers application (Synchronization) This task illustrates how to create own main window and how to synchronize communication between widgets (control elements). Task Make an application which has got a Slider, a SpinBox and a TextBox. Whenever you change the value one of the widgets the remainder widgets must automatically change and show this actual value. The Numbers application First we create the Form class which represents the main window. Then we create a form object in the main program (main), and we announce it to be the application s main widget (setmainwidget()).we let to show this widget on the screen (show()) and pass the control on to Qt to start the message loop waiting on a user action (exec()). The main window inherits the QVBox 2 widget. We put on the main window three widgets: a QSpinBox (spinbox), a QSlider(slider) and a QLineEdit (lineedit) widget. Arrangement 2 HBox: Stores elements horizontally. VBox: Stores elements vertically CEEPUS H81 Network Page 6

7 Modularization Classes Definition of the Form class form.h #ifndef FORM_H # define FORM_H # include <qwidget.h> # include <qvbox.h> class QHBox; class QSpinBox; class QSlider; class QLineEdit; class Form: public QVBox public: Form(QWidget *parent=0, const char *name=0); private: QHBox *hbox; QSpinBox *spinbox; QSlider *slider; QLineEdit *lineedit; ; #endif CEEPUS H81 Network Page 7

8 Implementation of the Form class form.cpp # include <qhbox.h> #include <qspinbox.h> #include <qslider.h> #include <qlineedit.h> #include "form.h" Form::Form(QWidget *parent, const char *name) :QVBox(parent,name) setmargin(6); setspacing(6); hbox = new QHBox(this); lineedit = new QLineEdit(this); hbox->setmargin(6); hbox->setspacing(6); spinbox = new QSpinBox(hbox); slider = new QSlider(Qt::Horizontal,hbox); slider->setrange(0,10); // interval spinbox->setrange(0,10); // interval spinbox->setvalue(5); connect(slider,signal(valuechanged(int)),spinbox,slot(setvalue(int))); connect(spinbox,signal(valuechanged(int)),slider,slot(setvalue(int))); It is not obligatory to add the QObject:: reference before the connect function, because QVBox and QHBox inherit the QObject class, so this function definition can be found without this extra prefix. The application s main program main.cpp # include <qapplication.h> #include "form.h" int main(int argc, char *argv[]) QApplication app(argc,argv); Form *form = new Form; app.setmainwidget(form); form->show(); return app.exec(); Creating custom slots We would like to show the number with words in the text box. In order to respond on the Slider s or SpinBox s changes we introduce a new slot. sayasword(int). CEEPUS H81 Network Page 8

9 Definition of Custom Slot: sayasword(int) form.h #ifndef FORM_H # define FORM_H # include <qwidget.h> # include <qvbox.h> class QHBox; class QSpinBox; class QSlider; class QLineEdit; class Form: public QVBox Q_OBJECT public: Form(QWidget *parent=0, const char *name=0); private: QHBox *hbox; QSpinBox *spinbox; QSlider *slider; QLineEdit *lineedit; QString words[11]; void initwords(); public slots: ; #endif void sayasword(int i); We declare an array to store the words of numbers (QString words[11]) and a private function to initialize this array, initwords(). Furthermore we declare a public slot sayasword(int). Please consider, that public slots keyword doesn t exist in standard C++. These elements must be transformed into the standard C++ code using a special precompiler: moc (meta object compiler). Because of using this special keyword (public slots), we have to add an extra macro to the source: Q_OBJECT, which consists of function declarations, used in run time to obtain meta language related information. My notes CEEPUS H81 Network Page 9

10 Implementation of Custom Slot: sayasword(int) form.cpp # include <qhbox.h> #include <qspinbox.h> #include <qslider.h> #include <qlineedit.h> #include "form.h" Form::Form(QWidget *parent, const char *name):qvbox(parent,name) setmargin(6); setspacing(6); hbox = new QHBox(this); lineedit = new QLineEdit(this); hbox->setmargin(6); hbox->setspacing(6); spinbox = new QSpinBox(hbox); slider = new QSlider(Qt::Horizontal,hbox); slider->setrange(0,10); spinbox->setrange(0,10); connect(slider,signal(valuechanged(int)),spinbox,slot(setvalue(int))); connect(spinbox,signal(valuechanged(int)),slider,slot(setvalue(int))); connect(slider,signal(valuechanged(int)),this,slot(sayasword(int))); initwords(); spinbox->setvalue(5); void Form::sayAsWord(int i) lineedit->settext(words[i]); void Form::initWords() words[0] = "null"; words[1] = "one";... words[10] = "ten"; The application s project file numbers.pro TEMPLATE = app INCLUDEPATH +=. # Input HEADERS += form.h SOURCES += form.cpp main.cpp CEEPUS H81 Network Page 10

11 Compiling & Running The uic tool generates the.h and.cpp files from the.ui file. The QVBox class inherits from QObject, so it requires an additional.cpp file to be generated in order to handle run time meta language information. These files are generated by the moc (meta object compiler) and are named moc_numbers.cpp as the original file was called numbers.cpp. As far as our.cpp file contains the Q_OBJECT macro an another file numbers.moc will be generated which will be included in our.cpp file, normally at the end. Fortunately we do not have to deal with these details, because the qmake tool creates the appropriate Makefile from our project file automatically. 1. Make the numbers directory. 2. Enter the above code using any text editor. Save it as numbers.cpp in the numbers directory. 3. Be in numbers directory. 4. Generate the platform independent project file (numbers.pro) with the next command: qmake - project 5. Generate the platform dependent make file with the next command: qmake -o Makefile numbers.pro. 6. Build the program: nmake (make in Linux) 7. Run the program. (Linux:./ numbers; Windows: numbers) The program can be found on people.inf.elte.hu/nacsa/qt/lessons/numbers site. Memory management, parent-child relationship Observing our program code we can realize, that we have used the new operator, but we have not used the delete to free the occupied memory from the heap. We have learnt that a lot of new without deleting leads to the memory leak. Furthermore in GUI applications we have to handle a lot of widgets and some how we have to control memory management. How does it work in Qt? Qt uses the so called parent-children mechanism to handle this problem. The main rules are: Deleting the main widget results deleting of all its children. Deleted widget automatically is deleted from the screen. Closing main window automatically results deleting the main widget. From these rules follow, that the only objects we have to delete explicitly are the objects we create with new operator and that have no parents. The figure below shows the parent-children relationship of our Form class in Numbers application. After we have closed our main window (e.g. clicking on the cross in the top-right corner) each widget will be deleted from the heap and from the screen. CEEPUS H81 Network Page 11

12 Layout application (Arrangement) In this example we demonstrate how to put the GUI control elements (widgets) on the screen to have the freedom to resize the screen without repositioning of its elements. To gain this aim we have to use the Layout Manager classes. Layout Manager In the previous example we used QVBox and QHBox widgets as a container for storing GUI elements. To handle a more sophisticated surface and to have a flexible arrangement of the screen you may use the Layout Manager s classes. The QHBoxLayout and QVBoxLayout inherit QLayout class. Although layout managers are not widgets, they can have parents and children. The meaning of parent is slightly different for layouts than for widgets. If a layout is constructed with a widget as a parent, the layout automatically installs itself on the widget. If a layout is constructed with no parent the layout must be inserted into another layout using addlayout(). When we insert a layout into another layout the inner layout is automatically made a child of the outer layout, to simplify memory management. In contrast, when we insert a widget into a layout using addwidget() the widget doesn t change parent. The QHBoxLayout horizontally, the QVBoxLayout vertically stores the inserted elements. Laying Out of the Form Memory Managament, Parent-Children relationship CEEPUS H81 Network Page 12

13 The Form Class using Layout Manager s Classes form.h #ifndef FORM_H # define FORM_H # include <qwidget.h> class QSpinBox; class QSlider; class QLineEdit; class Form: public QWidget Q_OBJECT public: Form(QWidget *parent=0, const char *name=0); private: QSpinBox *spinbox; QSlider *slider; QLineEdit *lineedit; QString words[11]; void initwords(); public slots: void sayasword(int i); void slottextchanged ( const QString & ); ; #endif Form Class s implementation with Layout Classes form.cpp #include <qlayout.h> #include <qspinbox.h> #include <qslider.h> #include <qlineedit.h> #include "form.h" Form::Form(QWidget *parent, const char *name):qwidget(parent,name) spinbox = new QSpinBox(this); slider = new QSlider(Qt::Horizontal,this); slider->setrange(0,10); spinbox->setrange(0,10); lineedit = new QLineEdit(this); QHBoxLayout *toplayout = new QHBoxLayout; //no parents toplayout->addwidget(spinbox); toplayout->addwidget(slider); QVBoxLayout *mainlayout = new QVBoxLayout(this); CEEPUS H81 Network Page 13

14 mainlayout->addlayout(toplayout); mainlayout->addwidget(lineedit); mainlayout->setmargin(11); mainlayout->setspacing(6); connect(slider,signal(valuechanged(int)),spinbox,slot(setvalue(int))); connect(spinbox,signal(valuechanged(int)),slider,slot(setvalue(int))); connect(slider,signal(valuechanged(int)),this,slot(sayasword(int))); initwords(); spinbox->setvalue(5); void Form::sayAsWord(int i) lineedit->settext(words[i]); void Form::initWords() words[0] = "null";... words[10] = "ten"; The application s main program The main.cpp remains unchangeable. The Application s Project File layout.pro TEMPLATE = app INCLUDEPATH +=. # Input HEADERS += form.h SOURCES += form.cpp main.cpp Compiling & Running 1. Make the layout directory. 2. Enter the above code using any text editor. Save it as layout.cpp in the layout directory. 3. Be in layout directory. 4. Generate the platform independent project file (layout.pro) with the next command: qmake -project 5. Generate the platform dependent make file with the next command: qmake -o Makefile layout.pro. 6. Build the program: nmake (make in Linux) 7. Run the program. (Linux:./ layout; Windows: layout) The program can be found on people.inf.elte.hu/nacsa/qt/lessons/layout site. CEEPUS H81 Network Page 14

15 Creating Application Using Qt Designer The.ui file and the generated code The Qt Designer which can be run with designer command is a non integrated, visual tool to support of designing the graphical user interface. Qt Designer reads and writes an XML like.ui file, (form.ui) which contains the definition of the user interface. The user interface compiler, uic, creates both a header file (form.h), and an implementation file (form.cpp), from the.ui file (form.ui). Then the application code in main.cpp includes form.h. Typically main.cpp is used to instantiate the QApplication object and start off the event loop. Qt designer form.ui UIC form.h Reads and writes Reading Generates #includes Tool Generated source file Revision controlled source file form.cpp main.cpp It is a simple approach, but it isn t sufficient for more complex dialogs having a lot of logic attached to the form s widgets, which can t be expressed with predefined signals and slots. Adding code to the generated form.cpp doesn t solve this problem, as this file gets recreated by the uic whenever the form changes. There are two different possibilities to extend form s functionality in Qt. CEEPUS H81 Network Page 15

16 Extending the functionality of the form The subclassing approach One way to implement custom slots for generated forms is via C++ inheritance as shown in the next figure. Qt designer form.ui Inheritance UIC formbase.h form.h Reads and writes Reading Generates #includes Tool Generated source file Revision controlled source file formbase.cpp form.cpp main.cpp In this approach Form inherits the Qt Designer s form FormBase class. Form is split into the header file (form.h) and the implementation file (form.cpp). The header file includes the uic generated form.h and re-implements all the custom slots. This is possible because uic generated custom slots are virtual. In addition to implementing custom slots, this approach gives the user a natural way to do extra initialization work in the constructor of the subclass, and extra cleanups in the destructor. The ui.h extension approach In this approach addition to the.ui file (form.ui), Qt Designer reads and writes another associated.ui.h file (form.ui.h). This.ui.h file is an ordinary C++ source file that contains implementations of custom slots. The file gets included from the generated form s implementation file (form.cpp) and thus can totally ignored by other user code. (The reason of using.h extension for this file even though it contains C++ code is because it is always included, and because it is easier to integrate into the build process with.h extension.) This file can be read and write by both the user and Qt Designer. Qt Designer s responsibility is to keep the file in sync with custom slot definitions: Whenever the user adds a new slot to the form, Qt Designer adds a stub to the.ui.h file. Whenever the user changes a custom slot s signature, Qt Designer updates the corresponding implementation. Whenever the user removes a custom slot, Qt Designer removes it from the.ui.h file. You can edit the implementations of the slots either within Qt Designer or using your own editor. CEEPUS H81 Network Page 16

17 Qt designer form.ui form.ui form.ui.h UIC form.h Reads and writes Reading Generates #includes Tool Generated source file Revision controlled source file form.cpp main.cpp Construction and destruction With this approach objects are entirely constructed and destructed inside the generated form.cpp code, therefore it is not possible to do further form initializations or cleanups you would do within the constructor and destructor functions of a C++ class, but if you add a slot Form::init() to your form, this slot will be called automatically at the end of the generated form constructor and if you add a slot Form::destroy() to your form, the slot will automatically invoked by the destructor before any form controls get deleted. Words application (Custom slot) In this application we demonstrate how to create a project using Qt Designer. We invent our program by using ui.h extension approach. Creating the Words project Start the Qt Designer and make a new project. The name of the project is words and we will save it into the words directory. Start Qt Designer File/New/C++ project/ok Project file: (brows into the appropriate directory) words.pro OK Creating the Main Window (Form) Create a widget, named Form, representing the main window. File/New/Widget/OK name: Form caption: Form File/Save As : form.ui CEEPUS H81 Network Page 17

18 The Form s Design Type Name Properties QSpinBox spinbox minvalue = 0, maxvalue = 10 QSlider slider minvalue = 0, maxvalue = 10 QLineEdit lineedit The Form s Arrangement (Layout) 1. Keep pressing the Shift button select the spinbox and the slider widgets on the form, then give the command Layout / Lay Out Horizontally. The red box around the two selected widgets shows they have to be laid out together. Using the Layout/ Break Layout command you can break this coherence. It is worth to find the related buttons in the toolbar, too. 2. Now, let us select the lineedit widget and the previously created red box and give the command Layout/ Lay Out Verically. 3. Click on the Fom (MainForm) and give the command Layout/Lay Out in Grid. You can preview the Form s behaviour with the Ctrl+T command. Try to resize the application s window and observe, what is happening. Creating the main program (main.cpp) Now, that we have entered some of the code let s try to build and run the application. To do this we need to create a main() function. We can ask Qt Designer to create this file for us. 1. Click File/New to invoke the New File dialog. 2. Click C++ Main-File, then click OK 3. The Configure Main-File dialog appears, listing the forms in the project. We ve only one for, MainForm, so it is already highlighted. 4. Click OK to create a main.cpp file that loads MainForm. 5. Save As into the project s directory. CEEPUS H81 Network Page 18

19 The generated main program is given below. main.cpp # include <qapplication.h> #include "form.h" int main( int argc, char ** argv ) QApplication a( argc, argv ); Form w; w.show(); a.connect( &a, SIGNAL( lastwindowclosed() ), &a, SLOT( quit() ) ); return a.exec(); We store the QApplication object on the stack, so it will be deleted when the application ended. (All other widgets of this application will be deleted as well, as far as all of them are children of this widget.) Inserting Variable into the Project Let us insert an array of number-words into our project using Qt Designer. Object Explorer/Members/Class Varibles/Private/Double Click/Add Variable: QString words[11] Access: private The variable description will be stored in the.ui, XML style file and the tool uic will generate the appropriate C++ code for it and put it into the form.h. The related fragment in the form.ui file is given below. form.ui <variables> <variable access="private">qstring words[11];</variable> </variables> initwords() function We create a new private function to initialize the words array. Select Form in Project Overview window. Edit/Slots... / New Function Function: initwords() Return type: void Specifier: non virtual Access: private Type: function The function s description is stored in the XML-style.ui file. The uic tool generates from it the appropriate C++ code and writes it into the form.h file. The related fragment in the form.ui file is given below. form.ui <functions> <function access="private" specifier="non virtual">initwords()</function> </functions> CEEPUS H81 Network Page 19

20 The implementation of initwords() is given in the form.ui.h file. form.ui.h void Form::initWords() words[0] = "null";... words[10] = "ten"; init() function It has no meaning to add code to the generated form.cpp. In order to carry out some initialization of our form, instead of modifying the generated constructor we can add a special init() function, which will be performed immediately after the constructor have run. Select Form in Project Overview window. Edit/Slots... / New Function Function: init() Return type: void Specifier: virtual Access: protected Type: function The init() function s implementation is given below. form.ui.h void Form::init() spinbox->setmaxvalue(10); //You can set it with Qt Designer, too slider->setmaxvalue(10); //You can set it with Qt Designer, too initwords(); spinbox->setvalue(5); Connecting the widgets Let s connect the slider s valuechanged(int) signal to the spinbox s setvalue(int) slot and the spinbox s valuechanged(int) signal to the slider s setvalue(int) slot. Edit/Connections/New Sender: slider Signal: valuechanged(int) Receiver: spinbox Slot: setvalue(int) Edit/Connections/New Sender: spinbox Signal: valuechanged(int) Receiver: slider Slot: setvalue(int) Creating Custom Slot: sayasword(int) Select Form in Project Overview window. Edit/Slots... / New Function Function: sayasword(int) Return type: void Specifier: virtual Access: public Type: slot CEEPUS H81 Network Page 20

21 Let us observe that on the Object Explorer s Member tab among the public slots has appeared the newly defined slot. Clicking on the form.ui.h implementation file in the Project Overview window a text editor containing the implementation file pops up and shows the tube of this newly defined slot. The sayasword(int) function s implementcation. form.ui.h void Form::sayAsWord( int i) lineedit->settext(words[i]); The application s project file (words.pro) Please observe that there are no form.h and form.cpp files in the project file. These files are generated by uic. words.pro TEMPLATE = app INCLUDEPATH +=. # Input HEADERS += form.ui.h INTERFACES += form.ui SOURCES += main.cpp Compiling & Running Using Qt Designer you don t have to generate project file, because it is managed by Qt Designer. 1. Be in words directory. 2. Generate the platform dependent make file with the next command: qmake -o Makefile words.pro. 3. Build the program: nmake (make in Linux) 4. Run the program. (Linux:./words; Windows: words) This program can be downloaded from the people.inf.elte.hu/nacsa/qt/lessons/words site. Workshop You are encouraged to work through this workbook on your own and make exercises to help you to retain what you have learned in this lesson. By completing these exercises you will understand the basics of Qt programming and you ll ensure that understand how signals and slots work and how implement them in your program. Quiz 1. What is a slot? 2. What is a signal? 3. How do you connect a signal to a slot? 4. Can you connect multiple slots to one signal? Exercises 1. Write a Greeting program. Ask user s name then pressing the Greeting button program pops up a message box and greets him or her. 2. Write a new Qt class based on QWidget. Make it 400 pixels wide and 300 pixels high. Add a button to the upper-left corner of the window. Connect the button s clicked() signal to qapp s quit() slot. Make sure it works. 3. Search the Qt Reference Documentation for other signals included QPushButton. Also, look up which slots are included in QApplication. 4. Write a program with two QPushButton objects and one radio button. Connect the three objects so that the two QPushButton objects can control whether the radio button is checked. CEEPUS H81 Network Page 21