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This tutorial gives an introduction to GUI programming using the Qt cross-platform framework. \image addressbook-tutorial-screenshot.png \omit It doesn't cover everything; the emphasis is on teaching the programming philosophy of GUI programming, and Qt's features are introduced as needed. Some commonly used features are never used in this tutorial. \endomit In the process, we will learn about some basic technologies provided by Qt, such as \list \o Widgets and layout managers \o Container classes \o Signals and slots \o Input and output devices \endlist If you are completely new to Qt, please read \l{How to Learn Qt} if you have not already done so. The tutorial's source code is located in Qt's \c examples/tutorials/addressbook directory. Tutorial chapters: \list 1 \o \l{tutorials/addressbook/part1}{Designing the User Interface} \o \l{tutorials/addressbook/part2}{Adding Addresses} \o \l{tutorials/addressbook/part3}{Navigating between Entries} \o \l{tutorials/addressbook/part4}{Editing and Removing Addresses} \o \l{tutorials/addressbook/part5}{Adding a Find Function} \o \l{tutorials/addressbook/part6}{Loading and Saving} \o \l{tutorials/addressbook/part7}{Additional Features} \endlist Although this little application does not look much like a fully-fledged modern GUI application, it uses many of the basic techniques that are used in more complex applications. After you have worked through it, we recommend checking out the \l{mainwindows/application}{Application} example, which presents a small GUI application, with menus, toolbars, a status bar, and so on. */ /*! \page tutorials-addressbook-part1.html \contentspage {Address Book Tutorial}{Contents} \nextpage {tutorials/addressbook/part2}{Chapter 2} \example tutorials/addressbook/part1 \title Address Book 1 - Designing the User Interface The first part of this tutorial covers the design of the basic graphical user interface (GUI) we use for the Address Book application. The first step to creating a GUI program is to design the user interface. In this chapter, our goal is to set up the labels and input fields needed to implement a basic address book application. The figure below is a screenshot of our expected output. \image addressbook-tutorial-part1-screenshot.png We require two QLabel objects, \c nameLabel and \c addressLabel, as well as two input fields, a QLineEdit object, \c nameLine, and a QTextEdit object, \c addressText, to enable the user to enter a contact's name and address. The widgets used and their positions are shown in the figure below. \image addressbook-tutorial-part1-labeled-screenshot.png There are three files used to implement this address book: \list \o \c{addressbook.h} - the definition file for the \c AddressBook class, \o \c{addressbook.cpp} - the implementation file for the \c AddressBook class, and \o \c{main.cpp} - the file containing a \c main() function, with an instance of \c AddressBook. \endlist \section1 Qt Programming - Subclassing When writing Qt programs, we usually subclass Qt objects to add functionality. This is one of the essential concepts behind creating custom widgets or collections of standard widgets. Subclassing to extend or change the behavior of a widget has the following advantages: \list \o We can write implementations of virtual or pure virtual functions to obtain exactly what we need, falling back on the base class's implementation when necessary. \o It allows us to encapsulate parts of the user interface within a class, so that the other parts of the application don't need to know about the individual widgets in the user interface. \o The subclass can be used to create multiple custom widgets in the same application or library, and the code for the subclass can be reused in other projects. \endlist Since Qt does not provide a specific address book widget, we subclass a standard Qt widget class and add features to it. The \c AddressBook class we create in this tutorial can be reused in situations where a basic address book widget is needed. \section1 Defining the AddressBook Class The \l{tutorials/addressbook/part1/addressbook.h}{\c addressbook.h} file is used to define the \c AddressBook class. We start by defining \c AddressBook as a QWidget subclass and declaring a constructor. We also use the Q_OBJECT macro to indicate that the class uses internationalization and Qt's signals and slots features, even if we do not use all of these features at this stage. \snippet tutorials/addressbook/part1/addressbook.h class definition The class holds declarations of \c nameLine and \c addressText, the private instances of QLineEdit and QTextEdit mentioned earlier. You will see, in the coming chapters, that data stored in \c nameLine and \c addressText is needed for many of the address book's functions. We do not need to include declarations of the QLabel objects we will use because we will not need to reference them once they have been created. The way Qt tracks the ownership of objects is explained in the next section. The Q_OBJECT macro itself implements some of the more advanced features of Qt. For now, it is useful to think of the Q_OBJECT macro as a shortcut which allows us to use the \l{QObject::}{tr()} and \l{QObject::}{connect()} functions. We have now completed the \c addressbook.h file and we move on to implement the corresponding \c addressbook.cpp file. \section1 Implementing the AddressBook Class The constructor of \c AddressBook accepts a QWidget parameter, \a parent. By convention, we pass this parameter to the base class's constructor. This concept of ownership, where a parent can have one or more children, is useful for grouping widgets in Qt. For example, if you delete a parent, all of its children will be deleted as well. \snippet tutorials/addressbook/part1/addressbook.cpp constructor and input fields Within this constructor, we declare and instantiate two local QLabel objects, \c nameLabel and \c addressLabel, as well as instantiate \c nameLine and \c addressText. The \l{QObject::tr()}{tr()} function returns a translated version of the string, if there is one available; otherwise, it returns the string itself. Think of this function as an \c{} marker to mark QString objects for translation. You will notice, in the coming chapters as well as in the \l{Qt Examples}, that we include it whenever we use a translatable string. When programming with Qt, it is useful to know how layouts work. Qt provides three main layout classes: QHBoxLayout, QVBoxLayout and QGridLayout to handle the positioning of widgets. \image addressbook-tutorial-part1-labeled-layout.png We use a QGridLayout to position our labels and input fields in a structured manner. QGridLayout divides the available space into a grid and places widgets in the cells we specify with row and column numbers. The diagram above shows the layout cells and the position of our widgets, and we specify this arrangement using the following code: \snippet tutorials/addressbook/part1/addressbook.cpp layout Notice that \c addressLabel is positioned using Qt::AlignTop as an additional argument. This is to make sure it is not vertically centered in cell (1,0). For a basic overview on Qt Layouts, refer to the \l{Layout Classes} document. In order to install the layout object onto the widget, we have to invoke the widget's \l{QWidget::setLayout()}{setLayout()} function: \snippet tutorials/addressbook/part1/addressbook.cpp setting the layout Lastly, we set the widget's title to "Simple Address Book". \section1 Running the Application A separate file, \c main.cpp, is used for the \c main() function. Within this function, we instantiate a QApplication object, \c app. QApplication is responsible for various application-wide resources, such as the default font and cursor, and for running an event loop. Hence, there is always one QApplication object in every GUI application using Qt. \snippet tutorials/addressbook/part1/main.cpp main function We construct a new \c AddressBook widget on the stack and invoke its \l{QWidget::show()}{show()} function to display it. However, the widget will not be shown until the application's event loop is started. We start the event loop by calling the application's \l{QApplication::}{exec()} function; the result returned by this function is used as the return value from the \c main() function. At this point, it becomes apparent why we instanciated \c AddressBook on the stack: It will now go out of scope. Therefore, \c AddressBook and all its child widgets will be deleted, thus preventing memory leaks. */ /*! \page tutorials-addressbook-part2.html \previouspage Address Book 1 - Designing the User Interface \contentspage {Address Book Tutorial}{Contents} \nextpage {tutorials/addressbook/part3}{Chapter 3} \example tutorials/addressbook/part2 \title Address Book 2 - Adding Addresses The next step to creating our basic address book application is to allow a little bit of user interaction. \image addressbook-tutorial-part2-add-contact.png We will provide a push button that the user can click to add a new contact. Also, some form of data structure is needed to store these contacts in an organized way. \section1 Defining the AddressBook Class Now that we have the labels and input fields set up, we add push buttons to complete the process of adding a contact. This means that our \c addressbook.h file now has three QPushButton objects declared and three corresponding public slots. \snippet tutorials/addressbook/part2/addressbook.h slots A slot is a function that responds to a particular signal. We will discuss this concept in further detail when implementing the \c AddressBook class. However, for an overview of Qt's signals and slots concept, you can refer to the \l{Signals and Slots} document. Three QPushButton objects: \c addButton, \c submitButton and \c cancelButton, are now included in our private variable declarations, along with \c nameLine and \c addressText from the last chapter. \snippet tutorials/addressbook/part2/addressbook.h pushbutton declaration We need a container to store our address book contacts, so that we can traverse and display them. A QMap object, \c contacts, is used for this purpose as it holds a key-value pair: the contact's name as the \e key, and the contact's address as the \e{value}. \snippet tutorials/addressbook/part2/addressbook.h remaining private variables We also declare two private QString objects, \c oldName and \c oldAddress. These objects are needed to hold the name and address of the contact that was last displayed, before the user clicked \gui Add. So, when the user clicks \gui Cancel, we can revert to displaying the details of the last contact. \section1 Implementing the AddressBook Class Within the constructor of \c AddressBook, we set the \c nameLine and \c addressText to read-only, so that we can only display but not edit existing contact details. \dots \snippet tutorials/addressbook/part2/addressbook.cpp setting readonly 1 \dots \snippet tutorials/addressbook/part2/addressbook.cpp setting readonly 2 Then, we instantiate our push buttons: \c addButton, \c submitButton, and \c cancelButton. \snippet tutorials/addressbook/part2/addressbook.cpp pushbutton declaration The \c addButton is displayed by invoking the \l{QPushButton::show()} {show()} function, while the \c submitButton and \c cancelButton are hidden by invoking \l{QPushButton::hide()}{hide()}. These two push buttons will only be displayed when the user clicks \gui Add and this is handled by the \c addContact() function discussed below. \snippet tutorials/addressbook/part2/addressbook.cpp connecting signals and slots We connect the push buttons' \l{QPushButton::clicked()}{clicked()} signal to their respective slots. The figure below illustrates this. \image addressbook-tutorial-part2-signals-and-slots.png Next, we arrange our push buttons neatly to the right of our address book widget, using a QVBoxLayout to line them up vertically. \snippet tutorials/addressbook/part2/addressbook.cpp vertical layout The \l{QBoxLayout::addStretch()}{addStretch()} function is used to ensure the push buttons are not evenly spaced, but arranged closer to the top of the widget. The figure below shows the difference between using \l{QBoxLayout::addStretch()}{addStretch()} and not using it. \image addressbook-tutorial-part2-stretch-effects.png We then add \c buttonLayout1 to \c mainLayout, using \l{QGridLayout::addLayout()}{addLayout()}. This gives us nested layouts as \c buttonLayout1 is now a child of \c mainLayout. \snippet tutorials/addressbook/part2/addressbook.cpp grid layout Our layout coordinates now look like this: \image addressbook-tutorial-part2-labeled-layout.png In the \c addContact() function, we store the last displayed contact details in \c oldName and \c oldAddress. Then we clear these input fields and turn off the read-only mode. The focus is set on \c nameLine and we display \c submitButton and \c cancelButton. \snippet tutorials/addressbook/part2/addressbook.cpp addContact The \c submitContact() function can be divided into three parts: \list 1 \o We extract the contact's details from \c nameLine and \c addressText and store them in QString objects. We also validate to make sure that the user did not click \gui Submit with empty input fields; otherwise, a QMessageBox is displayed to remind the user for a name and address. \snippet tutorials/addressbook/part2/addressbook.cpp submitContact part1 \o We then proceed to check if the contact already exists. If it does not exist, we add the contact to \c contacts and we display a QMessageBox to inform the user that the contact has been added. \snippet tutorials/addressbook/part2/addressbook.cpp submitContact part2 If the contact already exists, again, we display a QMessageBox to inform the user about this, preventing the user from adding duplicate contacts. Our \c contacts object is based on key-value pairs of name and address, hence, we want to ensure that \e key is unique. \o Once we have handled both cases mentioned above, we restore the push buttons to their normal state with the following code: \snippet tutorials/addressbook/part2/addressbook.cpp submitContact part3 \endlist The screenshot below shows the QMessageBox object we use to display information messages to the user. \image addressbook-tutorial-part2-add-successful.png The \c cancel() function restores the last displayed contact details and enables \c addButton, as well as hides \c submitButton and \c cancelButton. \snippet tutorials/addressbook/part2/addressbook.cpp cancel The general idea behind adding a contact is to give the user the flexibility to click \gui Submit or \gui Cancel at any time. The flowchart below further explains this concept: \image addressbook-tutorial-part2-add-flowchart.png */ /*! \page tutorials-addressbook-part3.html \previouspage Address Book 2 - Adding Addresses \contentspage {Address Book Tutorial}{Contents} \nextpage {tutorials/addressbook/part4}{Chapter 4} \example tutorials/addressbook/part3 \title Address Book 3 - Navigating between Entries The address book application is now half complete. We need to add some functions to navigate between contacts. But first, we have to decide what sort of a data structure we would like to use to hold these contacts. In Chapter 2, we used a QMap of key-value pairs with the contact's name as the \e key, and the contact's address as the \e value. This works well for our case. However, in order to navigate and display each entry, a little bit of enhancement is needed. We enhance the QMap by making it replicate a data structure similar to a circularly-linked list, where all elements are connected, including the first element and the last element. The figure below illustrates this data structure. \image addressbook-tutorial-part3-linkedlist.png \section1 Defining the AddressBook Class In order to add navigation functions to the address book application, we need to add two more slots to our \c AddressBook class: \c next() and \c previous(). These are added to our \c addressbook.h file: \snippet tutorials/addressbook/part3/addressbook.h navigation functions We also require another two QPushButton objects, so we declare \c nextButton and \c previousButton as private variables: \snippet tutorials/addressbook/part3/addressbook.h navigation pushbuttons \section1 Implementing the AddressBook Class In the \c AddressBook constructor in \c addressbook.cpp, we instantiate \c nextButton and \c previousButton and disable them by default. This is because navigation is only enabled when there is more than one contact in the address book. \snippet tutorials/addressbook/part3/addressbook.cpp navigation pushbuttons We then connect these push buttons to their respective slots: \snippet tutorials/addressbook/part3/addressbook.cpp connecting navigation signals The image below is our expected graphical user interface. Notice that it is getting closer to our final application. \image addressbook-tutorial-part3-screenshot.png We follow basic conventions for \c next() and \c previous() functions by placing the \c nextButton on the right and the \c previousButton on the left. In order to achieve this intuitive layout, we use QHBoxLayout to place the widgets side-by-side: \snippet tutorials/addressbook/part3/addressbook.cpp navigation layout The QHBoxLayout object, \c buttonLayout2, is then added to \c mainLayout. \snippet tutorials/addressbook/part3/addressbook.cpp adding navigation layout The figure below shows the coordinates of the widgets in \c mainLayout. \image addressbook-tutorial-part3-labeled-layout.png Within our \c addContact() function, we have to disable these buttons so that the user does not attempt to navigate while adding a contact. \snippet tutorials/addressbook/part3/addressbook.cpp disabling navigation Also, in our \c submitContact() function, we enable the navigation buttons, \c nextButton and \c previousButton, depending on the size of \c contacts. As mentioned earlier, navigation is only enabled when there is more than one contact in the address book. The following lines of code demonstrates how to do this: \snippet tutorials/addressbook/part3/addressbook.cpp enabling navigation We also include these lines of code in the \c cancel() function. Recall that we intend to emulate a circularly-linked list with our QMap object, \c contacts. So, in the \c next() function, we obtain an iterator for \c contacts and then: \list \o If the iterator is not at the end of \c contacts, we increment it by one. \o If the iterator is at the end of \c contacts, we move it to the beginning of \c contacts. This gives us the illusion that our QMap is working like a circularly-linked list. \endlist \snippet tutorials/addressbook/part3/addressbook.cpp next() function Once we have iterated to the correct object in \c contacts, we display its contents on \c nameLine and \c addressText. Similarly, for the \c previous() function, we obtain an iterator for \c contacts and then: \list \o If the iterator is at the end of \c contacts, we clear the display and return. \o If the iterator is at the beginning of \c contacts, we move it to the end. \o We then decrement the iterator by one. \endlist \snippet tutorials/addressbook/part3/addressbook.cpp previous() function Again, we display the contents of the current object in \c contacts. */ /*! \page tutorials-addressbook-part4.html \previouspage Address Book 3 - Navigating between Entries \contentspage {Address Book Tutorial}{Contents} \nextpage {tutorials/addressbook/part5}{Chapter 5} \example tutorials/addressbook/part4 \title Address Book 4 - Editing and Removing Addresses In this chapter, we look at ways to modify the contents of contacts stored in the address book application. \image addressbook-tutorial-screenshot.png We now have an address book that not only holds contacts in an organized manner, but also allows navigation. It would be convenient to include edit and remove functions so that a contact's details can be changed when needed. However, this requires a little improvement, in the form of enums. In our previous chapters, we had two modes: \c{AddingMode} and \c{NavigationMode} - but they were not defined as enums. Instead, we enabled and disabled the corresponding buttons manually, resulting in multiple lines of repeated code. In this chapter, we define the \c Mode enum with three different values: \list \o \c{NavigationMode}, \o \c{AddingMode}, and \o \c{EditingMode}. \endlist \section1 Defining the AddressBook Class The \c addressbook.h file is updated to contain the \c Mode enum: \snippet tutorials/addressbook/part4/addressbook.h Mode enum We also add two new slots, \c editContact() and \c removeContact(), to our current list of public slots. \snippet tutorials/addressbook/part4/addressbook.h edit and remove slots In order to switch between modes, we introduce the \c updateInterface() function to control the enabling and disabling of all QPushButton objects. We also add two new push buttons, \c editButton and \c removeButton, for the edit and remove functions mentioned earlier. \snippet tutorials/addressbook/part4/addressbook.h updateInterface() declaration \dots \snippet tutorials/addressbook/part4/addressbook.h buttons declaration \dots \snippet tutorials/addressbook/part4/addressbook.h mode declaration Lastly, we declare \c currentMode to keep track of the enum's current mode. \section1 Implementing the AddressBook Class We now have to implement the mode-changing features of the address book application. The \c editButton and \c removeButton are instantiated and disabled by default, as the address book starts up with zero contacts in memory. \snippet tutorials/addressbook/part4/addressbook.cpp edit and remove buttons These buttons are then connected to their respective slots, \c editContact() and \c removeContact(), and we add them to \c buttonLayout1. \snippet tutorials/addressbook/part4/addressbook.cpp connecting edit and remove \dots \snippet tutorials/addressbook/part4/addressbook.cpp adding edit and remove to the layout The \c editContact() function stores the contact's old details in \c oldName and \c oldAddress, before switching the mode to \c EditingMode. In this mode, the \c submitButton and \c cancelButton are both enabled, hence, the user can change the contact's details and click either button. \snippet tutorials/addressbook/part4/addressbook.cpp editContact() function The \c submitContact() function has been divided in two with an \c{if-else} statement. We check \c currentMode to see if it's in \c AddingMode. If it is, we proceed with our adding process. \snippet tutorials/addressbook/part4/addressbook.cpp submitContact() function beginning \dots \snippet tutorials/addressbook/part4/addressbook.cpp submitContact() function part1 Otherwise, we check to see if \c currentMode is in \c EditingMode. If it is, we compare \c oldName with \c name. If the name has changed, we remove the old contact from \c contacts and insert the newly updated contact. \snippet tutorials/addressbook/part4/addressbook.cpp submitContact() function part2 If only the address has changed (i.e., \c oldAddress is not the same as \c address), we update the contact's address. Lastly, we set \c currentMode to \c NavigationMode. This is an important step as it re-enables all the disabled push buttons. To remove a contact from the address book, we implement the \c removeContact() function. This function checks to see if the contact exists in \c contacts. \snippet tutorials/addressbook/part4/addressbook.cpp removeContact() function If it does, we display a QMessageBox, to confirm the removal with the user. Once the user has confirmed, we call \c previous() to ensure that the user interface shows another contact, and we remove the contact using \l{QMap}'s \l{QMap::remove()}{remove()} function. As a courtesy, we display a QMessageBox to inform the user. Both the message boxes used in this function are shown below: \image addressbook-tutorial-part4-remove.png \section2 Updating the User Interface We mentioned the \c updateInterface() function earlier as a means to enable and disable the push buttons depending on the current mode. The function updates the current mode according to the \c mode argument passed to it, assigning it to \c currentMode before checking its value. Each of the push buttons is then enabled or disabled, depending on the current mode. The code for \c AddingMode and \c EditingMode is shown below: \snippet tutorials/addressbook/part4/addressbook.cpp update interface() part 1 For \c NavigationMode, however, we include conditions within the parameters of the QPushButton::setEnabled() function. This is to ensure that \c editButton and \c removeButton are enabled when there is at least one contact in the address book; \c nextButton and \c previousButton are only enabled when there is more than one contact in the address book. \snippet tutorials/addressbook/part4/addressbook.cpp update interface() part 2 By performing the task of setting the mode and updating the user interface in the same function, we avoid the possibility of the user interface getting "out of sync" with the internal state of the application. */ /*! \page tutorials-addressbook-part5.html \previouspage Address Book 4 - Editing and Removing Addresses \contentspage {Address Book Tutorial}{Contents} \nextpage {tutorials/addressbook/part6}{Chapter 6} \example tutorials/addressbook/part5 \title Address Book 5 - Adding a Find Function In this chapter, we look at ways to locate contacts and addresses in the address book application. \image addressbook-tutorial-part5-screenshot.png As we keep adding contacts to our address book application, it becomes tedious to navigate them with the \e Next and \e Previous buttons. In this case, a \e Find function would be more efficient in looking up contacts. The screenshot above shows the \e Find button and its position on the panel of buttons. When the user clicks on the \e Find button, it is useful to display a dialog that can prompt the user for a contact's name. Qt provides QDialog, which we subclass in this chapter, to implement a \c FindDialog class. \section1 Defining the FindDialog Class \image addressbook-tutorial-part5-finddialog.png In order to subclass QDialog, we first include the header for QDialog in the \c finddialog.h file. Also, we use forward declaration to declare QLineEdit and QPushButton since we will be using those widgets in our dialog class. As in our \c AddressBook class, the \c FindDialog class includes the Q_OBJECT macro and its constructor is defined to accept a parent QWidget, even though the dialog will be opened as a separate window. \snippet tutorials/addressbook/part5/finddialog.h FindDialog header We define a public function, \c getFindText() for use by classes that instantiate \c FindDialog, which allows them to obtain the text entered by the user. A public slot, \c findClicked(), is defined to handle the search string when the user clicks the \gui Find button. Lastly, we define the private variables, \c findButton, \c lineEdit and \c findText, corresponding to the \gui Find button, the line edit into which the user types the search string, and an internal string used to store the search string for later use. \section1 Implementing the FindDialog Class Within the constructor of \c FindDialog, we set up the private variables, \c lineEdit, \c findButton and \c findText. We use a QHBoxLayout to position the widgets. \snippet tutorials/addressbook/part5/finddialog.cpp constructor We set the layout and window title, as well as connect the signals to their respective slots. Notice that \c{findButton}'s \l{QPushButton::clicked()}{clicked()} signal is connected to to \c findClicked() and \l{QDialog::accept()}{accept()}. The \l{QDialog::accept()}{accept()} slot provided by QDialog hides the dialog and sets the result code to \l{QDialog::}{Accepted}. We use this function to help \c{AddressBook}'s \c findContact() function know when the \c FindDialog object has been closed. This will be further explained when discussing the \c findContact() function. \image addressbook-tutorial-part5-signals-and-slots.png In \c findClicked(), we validate \c lineEdit to ensure that the user did not click the \gui Find button without entering a contact's name. Then, we set \c findText to the search string, extracted from \c lineEdit. After that, we clear the contents of \c lineEdit and hide the dialog. \snippet tutorials/addressbook/part5/finddialog.cpp findClicked() function The \c findText variable has a public getter function, \c getFindText(), associated with it. Since we only ever set \c findText directly in both the constructor and in the \c findClicked() function, we do not create a setter function to accompany \c getFindText(). Because \c getFindText() is public, classes instantiating and using \c FindDialog can always access the search string that the user has entered and accepted. \snippet tutorials/addressbook/part5/finddialog.cpp getFindText() function \section1 Defining the AddressBook Class To ensure we can use \c FindDialog from within our \c AddressBook class, we include \c finddialog.h in the \c addressbook.h file. \snippet tutorials/addressbook/part5/addressbook.h include finddialog's header So far, all our address book features have a QPushButton and a corresponding slot. Similarly, for the \gui Find feature we have \c findButton and \c findContact(). The \c findButton is declared as a private variable and the \c findContact() function is declared as a public slot. \snippet tutorials/addressbook/part5/addressbook.h findContact() declaration \dots \snippet tutorials/addressbook/part5/addressbook.h findButton declaration Lastly, we declare the private variable, \c dialog, which we will use to refer to an instance of \c FindDialog. \snippet tutorials/addressbook/part5/addressbook.h FindDialog declaration Once we have instantiated a dialog, we will want to use it more than once; using a private variable allows us to refer to it from more than one place in the class. \section1 Implementing the AddressBook Class Within the \c AddressBook class's constructor, we instantiate our private objects, \c findButton and \c findDialog: \snippet tutorials/addressbook/part5/addressbook.cpp instantiating findButton \dots \snippet tutorials/addressbook/part5/addressbook.cpp instantiating FindDialog Next, we connect the \c{findButton}'s \l{QPushButton::clicked()}{clicked()} signal to \c findContact(). \snippet tutorials/addressbook/part5/addressbook.cpp signals and slots for find Now all that is left is the code for our \c findContact() function: \snippet tutorials/addressbook/part5/addressbook.cpp findContact() function We start out by displaying the \c FindDialog instance, \c dialog. This is when the user enters a contact name to look up. Once the user clicks the dialog's \c findButton, the dialog is hidden and the result code is set to QDialog::Accepted. This ensures that our \c if statement is always true. We then proceed to extract the search string, which in this case is \c contactName, using \c{FindDialog}'s \c getFindText() function. If the contact exists in our address book, we display it immediately. Otherwise, we display the QMessageBox shown below to indicate that their search failed. \image addressbook-tutorial-part5-notfound.png */ /*! \page tutorials-addressbook-part6.html \previouspage Address Book 5 - Adding a Find Function \contentspage {Address Book Tutorial}{Contents} \nextpage {tutorials/addressbook/part7}{Chapter 7} \example tutorials/addressbook/part6 \title Address Book 6 - Loading and Saving This chapter covers the file handling features of Qt that we use to write loading and saving routines for the address book application. \image addressbook-tutorial-part6-screenshot.png Although browsing and searching for contacts are useful features, our address book is not really fully ready for use until we can saving existing contacts and load them again at a later time. Qt provides a number of classes for \l{Input/Output and Networking}{input and output}, but we have chosen to use two which are simple to use in combination: QFile and QDataStream. A QFile object represents a file on disk that can be read from and written to. QFile is a subclass of the more general QIODevice class which represents many different kinds of devices. A QDataStream object is used to serialize binary data so that it can be stored in a QIODevice and retrieved again later. Reading from a QIODevice and writing to it is as simple as opening the stream - with the respective device as a parameter - and reading from or writing to it. \section1 Defining the AddressBook Class We declare two public slots, \c saveToFile() and \c loadFromFile(), as well as two QPushButton objects, \c loadButton and \c saveButton. \snippet tutorials/addressbook/part6/addressbook.h save and load functions declaration \dots \snippet tutorials/addressbook/part6/addressbook.h save and load buttons declaration \section1 Implementing the AddressBook Class In our constructor, we instantiate \c loadButton and \c saveButton. Ideally, it would be more user-friendly to set the push buttons' labels to "Load contacts from a file" and "Save contacts to a file". However, due to the size of our other push buttons, we set the labels to \gui{Load...} and \gui{Save...}. Fortunately, Qt provides a simple way to set tooltips with \l{QWidget::setToolTip()}{setToolTip()} and we use it in the following way for our push buttons: \snippet tutorials/addressbook/part6/addressbook.cpp tooltip 1 \dots \snippet tutorials/addressbook/part6/addressbook.cpp tooltip 2 Although it is not shown here, just like the other features we implemented, we add the push buttons to the layout panel on the right, \c button1Layout, and we connect the push buttons' \l{QPushButton::clicked()}{clicked()} signals to their respective slots. For the saving feature, we first obtain \c fileName using QFileDialog::getSaveFileName(). This is a convenience function provided by QFileDialog, which pops up a modal file dialog and allows the user to enter a file name or select any existing \c{.abk} file. The \c{.abk} file is our Address Book extension that we create when we save contacts. \snippet tutorials/addressbook/part6/addressbook.cpp saveToFile() function part1 The file dialog that pops up is displayed in the screenshot below: \image addressbook-tutorial-part6-save.png If \c fileName is not empty, we create a QFile object, \c file with \c fileName. QFile works with QDataStream as QFile is a QIODevice. Next, we attempt to open the file in \l{QIODevice::}{WriteOnly} mode. If this is unsuccessful, we display a QMessageBox to inform the user. \snippet tutorials/addressbook/part6/addressbook.cpp saveToFile() function part2 Otherwise, we instantiate a QDataStream object, \c out, to write the open file. QDataStream requires that the same version of the stream is used for reading and writing. We ensure that this is the case by setting the version used to the \l{QDataStream::Qt_4_5}{version introduced with Qt 4.5} before serializing the data to \c file. \snippet tutorials/addressbook/part6/addressbook.cpp saveToFile() function part3 For the loading feature, we also obtain \c fileName using QFileDialog::getOpenFileName(). This function, the counterpart to QFileDialog::getSaveFileName(), also pops up the modal file dialog and allows the user to enter a file name or select any existing \c{.abk} file to load it into the address book. \snippet tutorials/addressbook/part6/addressbook.cpp loadFromFile() function part1 On Windows, for example, this function pops up a native file dialog, as shown in the following screenshot. \image addressbook-tutorial-part6-load.png If \c fileName is not empty, again, we use a QFile object, \c file, and attempt to open it in \l{QIODevice::}{ReadOnly} mode. In a similar way to our implementation of \c saveToFile(), if this attempt is unsuccessful, we display a QMessageBox to inform the user. \snippet tutorials/addressbook/part6/addressbook.cpp loadFromFile() function part2 Otherwise, we instantiate a QDataStream object, \c in, set its version as above and read the serialized data into the \c contacts data structure. Note that we empty \c contacts before reading data into it to simplify the file reading process. A more advanced method would be to read the contacts into temporary QMap object, and copy only the contacts that do not already exist in \c contacts. \snippet tutorials/addressbook/part6/addressbook.cpp loadFromFile() function part3 To display the contacts that have been read from the file, we must first validate the data obtained to ensure that the file we read from actually contains address book contacts. If it does, we display the first contact; otherwise, we display a QMessageBox to inform the user about the problem. Lastly, we update the interface to enable and disable the push buttons accordingly. */ /*! \page tutorials-addressbook-part7.html \previouspage Address Book 6 - Loading and Saving \contentspage {Address Book Tutorial}{Contents} \example tutorials/addressbook/part7 \title Address Book 7 - Additional Features This chapter covers some additional features that make the address book application more convenient for everyday use. \image addressbook-tutorial-part7-screenshot.png Although our address book application is useful in its own right, it would be useful if we could exchange contact data with other applications. The vCard format is a popular file format that can be used for this purpose. In this chapter, we extend our address book client to allow contacts to be exported to vCard \c{.vcf} files. \section1 Defining the AddressBook Class We add a QPushButton object, \c exportButton, and a corresponding public slot, \c exportAsVCard() to our \c AddressBook class in the \c addressbook.h file. \snippet tutorials/addressbook/part7/addressbook.h exportAsVCard() declaration \dots \snippet tutorials/addressbook/part7/addressbook.h exportButton declaration \section1 Implementing the AddressBook Class Within the \c AddressBook constructor, we connect \c{exportButton}'s \l{QPushButton::clicked()}{clicked()} signal to \c exportAsVCard(). We also add this button to our \c buttonLayout1, the layout responsible for our panel of buttons on the right. In our \c exportAsVCard() function, we start by extracting the contact's name into \c name. We declare \c firstName, \c lastName and \c nameList. Next, we look for the index of the first white space in \c name. If there is a white space, we split the contact's name into \c firstName and \c lastName. Then, we replace the space with an underscore ("_"). Alternately, if there is no white space, we assume that the contact only has a first name. \snippet tutorials/addressbook/part7/addressbook.cpp export function part1 As with the \c saveToFile() function, we open a file dialog to let the user choose a location for the file. Using the file name chosen, we create an instance of QFile to write to. We attempt to open the file in \l{QIODevice::}{WriteOnly} mode. If this process fails, we display a QMessageBox to inform the user about the problem and return. Otherwise, we pass the file as a parameter to a QTextStream object, \c out. Like QDataStream, the QTextStream class provides functionality to read and write plain text to files. As a result, the \c{.vcf} file generated can be opened for editing in a text editor. \snippet tutorials/addressbook/part7/addressbook.cpp export function part2 We then write out a vCard file with the \c{BEGIN:VCARD} tag, followed by the \c{VERSION:2.1} tag. The contact's name is written with the \c{N:} tag. For the \c{FN:} tag, which fills in the "File as" property of a vCard, we have to check whether the contact has a last name or not. If the contact does, we use the details in \c nameList to fill it. Otherwise, we write \c firstName only. \snippet tutorials/addressbook/part7/addressbook.cpp export function part3 We proceed to write the contact's address. The semicolons in the address are escaped with "\\", the newlines are replaced with semicolons, and the commas are replaced with spaces. Lastly, we write the \c{ADR;HOME:;} tag, followed by \c address and then the \c{END:VCARD} tag. \snippet tutorials/addressbook/part7/addressbook.cpp export function part4 In the end, a QMessageBox is displayed to inform the user that the vCard has been successfully exported. \e{vCard is a trademark of the \l{http://www.imc.org} {Internet Mail Consortium}}. */