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This tutorial gives an introduction to GUI programming using the Qt SDK. \image addressbook-tutorial-screenshot.png 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 All these technologies will be introduced via the Qt Creator Integrated Development Environment (IDE). 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{examples/addressbook-sdk/part1}{Designing the User Interface} \o \l{examples/addressbook-sdk/part2}{Adding Addresses} \o \l{examples/addressbook-sdk/part3}{Navigating between Entries} \o \l{examples/addressbook-sdk/part4}{Editing and Removing Addresses} \o \l{examples/addressbook-sdk/part5}{Adding a Find Function} \o \l{examples/addressbook-sdk/part6}{Loading and Saving} \o \l{examples/addressbook-sdk/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-sdk-part1.html \contentspage {Address Book Tutorial}{Contents} \nextpage {examples/addressbook-sdk/part2}{Chapter 2} \example examples/addressbook-sdk/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 begin by launching Qt Creator and use it to generate a new project. To do this, select \gui{New File or Project...} from the \gui File menu. In the \gui{New...} dialog, select \gui{Projects -> Qt4 Gui Application} and click \gui OK. Set your project name to \bold part1 with the QtCore and QtGui modules checked. Ensure that you select QWidget as your base class and name it \c AddressBook. When you click \gui Next, \e five files will be generated in this \gui{Project}: \list \o \c{main.cpp} - the file containing a \c main() function, with an instance of \c AddressBook, \o \c{addressbook.cpp} - the implementation file for the \c AddressBook class, \o \c{addressbook.h} - the definition file for the \c AddressBook class, \o \c{addressbook.ui} - the user interface file created with \QD, and \o \c{part1.pro} - the project file. \endlist Now that we have all the files we need, click \gui Finish so can start designing the user interface. \table \row \o \bold{Note:} For more details on how to create a \gui Project with Qt Creator, refer to \l{Creating a Project in Qt Creator}. \endtable \section1 Placing Widgets on The Form \image addressbook-tutorial-part1-creator-screenshot.png In the \gui{Projects} sidebar, double-click on the \c{addressbook.ui} file. The \QD plugin will be launched, allowing you to design your program's user interface. \image addressbook-tutorial-part1-designer-screenshot.png We require two \l{QLabel}s to label the input fields as well as a QLineEdit and a QTextEdit for the input fields. So, drag those widgets from the \gui{Widget Box} to your form. In the \gui{Property Editor}, set their \gui{objectName} property to \c nameLabel and \c addressLabel for the \l{QLabel}s, \c nameLine for the QLineEdit and finally, \c addressText for the QTextEdit. Next, we have to position the widgets properly, according to the screenshot earlier. 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. To place the caption of the \c addressLabel on the top, change the vertical alignment property to \c AlignTop. The diagram below shows the layout cells and the position of our widgets. Place your widgets accordingly and save the form by choosing \gui{File -> Save} or using the \key{Ctrl+S} shortcut. \image addressbook-tutorial-part1-labeled-screenshot.png A common mistake when designing user interfaces with \QD is overlooking the top level widget's layout. Unlike sub-layouts, which \QD displays with a red border, top level layouts have no graphical representation. Layouts are necessary for top level widgets, in this case QWidget, to ensure that when the window is resized, the widgets on the form will resize accordingly. You can try this out by pressing \key{Ctrl+Alt+R} now. To correct it, simply click anywhere on the form and select \gui{Lay out Horizontally} or \gui{Lay out Vertically}. The output will be the same. Now your widgets will resize correctly. \table \row \o \bold{Note:} Refer to the \l{Layout Classes} document for more details on Qt's layout management classes. In addition, the \l{Getting to Know Qt Designer} document explains how to use layouts with \QD. \endtable \section1 The AddressBook Class The \l{examples/addressbook-sdk/part1/addressbook.h}{\c addressbook.h} file is used to define the \c AddressBook class. Let's take a look at what is already provided for us by Qt Creator. The \c AddressBook class has been defined as a QWidget subclass with a constructor and destructor.The Q_OBJECT macro is used to indicate that this class uses internationalization as well as Qt's signals and slots features. Although the macro implements some of Qt's more advanced features, for now, it is useful to think of it as a shortcut that allows us to use the \l{QObject::}{tr()} and \l{QObject::}{connect()} functions. \snippet examples/addressbook-sdk/part1/addressbook.h class definition Qt Creator's \gui{Project Wizard} provides us with the \c Ui object as a way to access the widgets on our form. The \l{examples/addressbook-sdk/part1/addressbook.cpp}{\c addressbook.cpp} file is used to implement the \c AddressBook class. The constructor sets up the \c ui file; the destructor deletes it. \snippet examples/addressbook-sdk/part1/addressbook.cpp class implementation \section1 The \c{main()} Function The \l{examples/addressbook-sdk/part1/main.cpp}{\c main.cpp} file contains the \c{main()} function It is generated by the \gui{Project Wizard}. Within this function, a QApplication object, \c a, is instantiated. 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 examples/addressbook-sdk/part1/main.cpp main function The code constructs a new \c AddressBook widget on the stack and invokes its \l{QWidget::}{show()} function to display it. However, the widget will not be shown until the application's event loop is started. This is done by calling the application's \l{QApplication::}{exec()} function. Finally, the result returned by \l{QApplication::}{exec()} is used as the \c main() function's return value. \section1 Running the Application To run your application with Qt Creator, simply click on the Play button (image). A bare bones Address Book will be displayed. Click on the X button to close it. \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 do not 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 provided 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 is needed. */ /*! \page tutorials-addressbook-sdk-part2.html \previouspage Address Book 1 - Designing the User Interface \contentspage {Address Book Tutorial}{Contents} \nextpage {examples/addressbook-sdk/part3}{Chapter 3} \example examples/addressbook-sdk/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 Placing Widgets on The Form We shall continue with the form we had from the last chapter; we have the labels and input fields set up, but we need to add push buttons to complete the process of adding a contact. So, we begin by breaking the existing layouts: select \gui{Break Layout} from the context menu. You might have to do a \gui{Select All} with \key{Ctrl+A} first.. Then, we add three push buttons. Double-click on each of them to set their text to "Add", "Submit", and "Cancel". Next, set the \c objectName of the buttons to \c addButton, \c submitButton and \c cancelButton respectively. We now require a vertical spacer to ensure that the push buttons will be laid out neatly; drag one from the \gui{Widget Box}. ## image for button missing Next, lay out these three push buttons and the spacer vertically, by selecting all three of them (using the \key{Ctrl + click}) and choosing \gui{Lay out Vertically} from the context menu. Alternatively you can click on the ... button or use the \key{Ctrl+L} shortcut. We use the spacer as we do not want the buttons to be evenly spaced, but arranged closer to the top of the widget. The figure below shows the difference between using the spacer and not using it. \image addressbook-tutorial-part2-stretch-effects.png Select all the objects on the form (use \key{Ctrl+A}) and lay them out in a grid. Lastly, set the top level widget's layout by right-clicking anywhere on the widget and selecting \gui{Lay out Horizontally} or \gui{Lay out Vertically}. The final design of the form is shown in the screenshot below: ## image \section1 The AddressBook Class To ensure that the Address Book reacts to user interaction, we need to write slots for each push button that we added earlier. A slot is a function that responds to a particular signal. We will discuss this concept in further detail below. However, for an overview of Qt's signals and slots concept, you can refer to the \l{Signals and Slots} document. In the \l{examples/addressbook-sdk/part2/addressbook.h}{\c addressbook.h} file, we add the following code: \snippet examples/addressbook-sdk/part2/addressbook.h slot definition Since the \c AddressBook class is a subclass of QWidget, Qt Creator includes QWidget in the header file. \snippet examples/addressbook-sdk/part2/addressbook.h include 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 examples/addressbook-sdk/part2/addressbook.h members 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. ## this is a bit confusing, as the ctor was not defined by us nor is a slot Let's move on to implementing the slots we defined earlier. Within the constructor of \c AddressBook, we set up our fields by ensuring that \c nameLine and \c addressText are read-only, so that we can only display but not edit existing contact details. Note that in order to prevent crashes, you need make sure that the autogenerated \c setupUi() call is always first in the constructor. \snippet examples/addressbook-sdk/part2/addressbook.cpp setup fields We also hide both \c submitButton and \c cancelButton as they will only be displayed when the user clicks \gui Add, and this is handled by the \c addContact() function discussed below. \snippet examples/addressbook-sdk/part2/addressbook.cpp signal slot We connect the push buttons' \l{QAbstractButton::}{clicked()} signal to their respective slots. The figure below illustrates this. \image addressbook-tutorial-part2-signals-and-slots.png Finally, we set the window title to "Simple Address Book" using the \l{QWidget::}{setWindowTitle()} function. The tr() method allows us to translate user interface strings. Refer to ###. \snippet examples/addressbook-sdk/part2/addressbook.cpp window title \section2 The \c addContact() Function In this function, we begin by storing 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; but we disable \c addButton. \snippet examples/addressbook-sdk/part2/addressbook.cpp addContact \section2 The \c submitContact() Function This function can be divided into three parts: \list 1 \o We extract the contact's detail from \c nameLine and \c addressText and store them in QString objects. We also validate to ensure 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 examples/addressbook-sdk/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 about this, preventing the user from adding duplicate contacts. Our \c contacts object is based on key-value pairs or name and address, hence, we want to ensure that \e key is unique. \snippet examples/addressbook-sdk/part2/addressbook.cpp submitContact part2 \o Once we have handled both cases mentioned above, we restore the push buttons to their normal state with the following code: \snippet examples/addressbook-sdk/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 \section2 The \c cancel() Function This function restores the last displayed contact details and enables \c addButton, as well as hides \c submitButton and \c cancelButton. \snippet examples/addressbook-sdk/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 \section1 Running the Application Run your application now. You will be able to add as many unique contacts as you like. */ /*! \page tutorials-addressbook-sdk-part3.html \previouspage Address Book 2 - Adding Addresses \contentspage {Address Book Tutorial}{Contents} \nextpage {examples/addressbook-sdk/part4}{Chapter 4} \example examples/addressbook-sdk/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 Placing Widgets on The Form So far, our application allows us to add new contacts. However, we also need to traverse the existing contacts. To do so, we add two push buttons at the bottom of our application and name them: \gui Next and \gui Previous. The buttons' \c objectName should be \c nextButton and \c previousButton, respectively. Then, we break our top level layout. Simply right-click on \c AddressBook in the \gui{Object Inspector} and then select \gui{Lay out|Break Layout}. Place the \gui Next and \gui Previous buttons in a horizontal layout. Now drag and drop the buttons together with their layout into the existing grid layout. The screenshot below illustrates what you will see as the button layout approaches the grid layout; drop it then. \image addressbook-tutorial-part3-drop-in-gridlayout.png Finally, set a top level layout for the widget again. \note 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. \section1 The AddressBook Class Let's move on to the code. 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(). \snippet examples/addressbook-sdk/part3/addressbook.h slot definition In the \c AddressBook constructor, we setup our fields and disable them by default. This is because navigation is only enabled when there is more than one contact in the address book. \snippet examples/addressbook-sdk/part3/addressbook.cpp setup fields Next, we connect the buttons to their respective slots: \snippet examples/addressbook-sdk/part3/addressbook.cpp signal slot The screenshot below is our expected graphical user interface. Notice that it is getting closer to our final application. \image addressbook-tutorial-part3-screenshot.png Within our \c addContact() function, we have to disable the \gui Next and \gui Previous buttons so that the user does not attempt to navigate while adding a contact. \snippet examples/addressbook-sdk/part3/addressbook.cpp disable navigation Also, in our \c submitContact() function, we enable the navigation buttons, depending on the size of \c contacts. Asmentioned 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 examples/addressbook-sdk/part3/addressbook.cpp enable 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 examples/addressbook-sdk/part3/addressbook.cpp next Once we have iterated to the current 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 examples/addressbook-sdk/part3/addressbook.cpp previous Again, we display the contents of the current object in \c contacts. */ /*! \page tutorials-addressbook-sdk-part4.html \previouspage Address Book 3 - Navigating between Entries \contentspage {Address Book Tutorial}{Contents} \nextpage {examples/addressbook-sdk/part5}{Chapter 5} \example examples/addressbook-sdk/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. #screenshot 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 Placing Widgets on The Form To edit and remove contacts, we need two push buttons. Drag them and name them accordingly. Their \c objectName properties should be \c editButton and \c removeButton, respectively. The quickest way to place these two buttons into our existing layout, is to simply drag and drop them. Use the screenshot below as a guide: \image addressbook-tutorial-part4-drop-in-gridlayout.png \section1 The AddressBook Class We update the header file to contain the \c Mode enum: \snippet examples/addressbook-sdk/part4/addressbook.h enum We also add two new slots, \c editContact() and \c removeContact(), to our current list of public slots. \snippet examples/addressbook-sdk/part4/addressbook.h slot definition In order to switch between modes, we introduce the \c updateInterface() function to control the enabling and disabling of all push buttons. \snippet examples/addressbook-sdk/part4/addressbook.h updateInterface Lastly, we declare \c currentMode to keep track of the enum's current mode. \snippet examples/addressbook-sdk/part4/addressbook.h current mode Let's begin by implementing the mode-changing features of the address book application. The \c editButton and \c removeButton are disabled by default, as the address book starts up with zero contacts in memory. \snippet examples/addressbook-sdk/part4/addressbook.cpp extract objects These buttons are then connected to their respective slots, \c editContact() and \c removeContact. \snippet examples/addressbook-sdk/part4/addressbook.cpp signal slot Now we look at the \c editContact() and \c removeContact() functions in detail. \section2 The \c editContact() Function This 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 examples/addressbook-sdk/part4/addressbook.cpp editContact Since we will reuse the \c submitButton for both: adding a new contact and editing an existing contact, we need to modify our existing \c submitContact() function. So, we divide it in two with an \c{if-else} statement. First, we check \c currentMode to see if it is in \c AddingMode. If it is, we proceed with our adding process. \snippet examples/addressbook-sdk/part4/addressbook.cpp submitContact part1 \dots \snippet examples/addressbook-sdk/part4/addressbook.cpp submitContact part2 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 examples/addressbook-sdk/part4/addressbook.cpp submitContact part3 If only the contact's address 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. \snippet examples/addressbook-sdk/part4/addressbook.cpp removeContact This function first checks to see if the contact exists in \c contacts. 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()} function. As a courtesy, we display a QMessageBox to inform the user. Both the message boxes used in this function are shown below: # image \section2 The \c updateInterface() Function We mentioned this 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 examples/addressbook-sdk/part4/addressbook.cpp updateInterface part1 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 examples/addressbook-sdk/part4/addressbook.cpp updateInterface part2 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. To maintain consistency, we need to modify our \c addContact() and \c cancel() functions respectively. Below is the code: \snippet examples/addressbook-sdk/part4/addressbook.cpp addContact \dots \snippet examples/addressbook-sdk/part4/addressbook.cpp cancel */ /*! \page tutorials-addressbook-sdk-part5.html \previouspage Address Book 4 - Editing and Removing Addresses \contentspage {Address Book Tutorial}{Contents} \nextpage {examples/addressbook-sdk/part6}{Chapter 6} \example examples/addressbook-sdk/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, it becomes tedious to navigate them with the \gui Next and \gui Previous buttons. In this case, a \gui Find function would be more efficient in looking up contacts. The screenshot above shows the \gui Find button and its position on the panel of buttons. When the user clicks on the \gui Find button, it is useful to display a dialog prompting the user for a contact's name. Qt provides QDialog, which we subclass in this chapter, to implement a FindDialog class. \section1 Designing The FindDialog \image addressbook-tutorial-part5-finddialog-in-designer.png We begin by adding a new \c{.ui} file and a corresponding class to our project. Right click on your project and select \gui{Add New...}. In the \gui{New File} dialog, select \gui{Qt Designer Form Class}. In the \gui{Qt Designer Form Class} dialog, select \e{Dialog without buttons}. Name the class \c{FindDialog} and add the files it to your project. Open your new form in the \QD form editor within Qt Creator by double-clicking on the \c{finddialog.ui} file in the \gui{Project Sidebar}. To replicate the screenshot above, we need a label, a line edit, and a push button. Drag these onto your form. Set their text accordingly and name them \c label, \c lineEdit, and \c findButton, respectively. Place these widgets in a horizontal layout. Then set a top level layout - either horizontal or vertical. \section1 Implementing The FindDialog Class Let's look at \c{FindDialog}'s header file. We define a public function, \c findText(), to be used by classes that instantiate \c FindDialog. This function allows the these classes to obtain the search string entered by the user. A public slot, \c findClicked(), is also defined to handle the search string when the user clicks the \gui Find button. \snippet examples/addressbook-sdk/part5/finddialog.h findText \dots \snippet examples/addressbook-sdk/part5/finddialog.h findClicked Now, lets look at our constructor in the \c{finddialog.cpp} file. \snippet examples/addressbook-sdk/part5/finddialog.cpp constructor In \c findClicked(), we validate 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 examples/addressbook-sdk/part5/finddialog.cpp findClicked \c findText() is public, which makes it easy for classes instantiating and using \c FindDialog to access the search string that the user has entered and accepted. \snippet examples/addressbook-sdk/part5/finddialog.cpp findText Finally, we connect our signals to their respective slots. Notice that \c{findButton}'s \l{QPushButton::}{clicked()} signal is connected to \c findClicked(), which calls \l{QDialog::}{accept()} or \l{QDialog::}{reject()}. The \l{QDialog::}{accept()} slot provided by QDialog hides the dialog and sets the result code to \l{QDialog::}{Accepted}, while \l{QDialog::}{reject()} sets it to \l{QDialog::}{Rejected} accordingly. We use this function to help \c{AddressBook}'s \c findContact() function know when the \c FindDialog object has been closed. We will explain this logic in further detail when discussing the \c findContact() function. \image addressbook-tutorial-part5-signals-and-slots.png \section1 The AddressBook Class To ensure that we can use \c FindDialog from within our \c AddressBook class, we include \c finddialog.h in the \c addressbook.h file. \snippet examples/addressbook-sdk/part5/addressbook.h include So far, all our address book features have a QPushButton and a corresponding slot. Similarly, for the \gui Find feature, we have \c{ui->findButton} and \c findContact(). \snippet examples/addressbook-sdk/part5/addressbook.h slot definition Once we have instantiated a dialog, we might 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. Within the \c AddressBook class's constructor, we connect the \c{findButton}'s \l{QPushButton::}{clicked()} signal to \c findContact(). \snippet examples/addressbook-sdk/part5/addressbook.cpp signal slot Now, all that is left is the code for our \c findContact() function: \snippet examples/addressbook-sdk/part5/addressbook.cpp findContact 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 either QDialog::Accepted or QDialog::Rejected by the FindDialog's \c findClicked() method. This ensures that we only search for a contact if the user typed something in the FindDialog's line edit. We then proceed to extract the search string, which in this case is \c contactName, using \c{FindDialog}'s \c findText() 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-dialogbox.png The concept behind finding a contact only applies for cases where we have more than two contacts in our address book. Hence, we implement this behavior by modifying our \c{Navigation Mode} within our \c updateInterface() function, by only enabling the \gui Find button when we have more than two contacts. \snippet examples/addressbook-sdk/part5/addressbook.cpp enable */ /*! \page tutorials-addressbook-sdk-part6.html \previouspage Address Book 5 - Adding a Find Function \contentspage {Address Book Tutorial}{Contents} \nextpage {examples/addressbook-sdk/part7}{Chapter 7} \example examples/addressbook-sdk/part6 \title Address Book 6 - Loading and Saving This chapter covers the file handling features of Qt that we used 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 ready for use until we can save 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 isa 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 Placing Widgets on The Form To load and save files containing contact details, we need two push buttons. Drag them and name them accordingly. Their \c objectName properties should be \c loadButton and \c saveButton, respectively. Then, similar to \l{Address Book 5 - Adding a Find Function}{Chapter 5}, we place these buttons in our layout simply by dragging and dropping them. The \c text property of our push buttons are \gui{Load...} and \gui{Save...} respectively. Ideally, it would be more user-friendly to set the push buttons' labels to \gui{Load contacts from file} and \gui{Save contacts to file}. However, due to the size of our push buttons, we set the labels to \gui{Load...} and \gui{Save...} instead. Fortunately, Qt Creator's \QD plugin provides a simple way to set tooltips with the \c toolTip property. So, we set our buttons' tooltips to \gui{Load contacts from file} and \gui{Save contacts to file} respectively. To test your tooltip, use \key{Ctrl+Alt+R} and hover your mouse cursor on the push buttons. \image addressbook-tutorial-part6-propertyeditor.png \section1 The AddressBook Class We declare two public slots, \c saveToFile() and \c loadFromFile(). \snippet examples/addressbook-sdk/part6/addressbook.h slot definition Now lets look at the \c saveToFile() and \c loadFromFile() functions in detail. \section2 The \c saveToFile() Function To save a contact, 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 examples/addressbook-sdk/part6/addressbook.cpp saveToFile part1 The file dialog that pops up is displayed in the screenshot below: \image addressbook-tutorial-part6-savedialog.png If \c fileName is not empty, we create a QFile object, \c file, with \c fileName. The QFile object 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 examples/addressbook-sdk/part6/addressbook.cpp saveToFile 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 version introduced with Qt 4.5 before serializing the data into \c file. \snippet examples/addressbook-sdk/part6/addressbook.cpp saveToFile part3 \section2 The \c loadFromFile() Function To load a contact, 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 examples/addressbook-sdk/part6/addressbook.cpp loadFromFile part1 On Windows, for example, this function pops up a native file dialog, as shown in the following screenshot. \image addressbook-tutorial-part6-opendialog.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. Similar to our implementation of \c saveToFile(), if this attempt is unsuccessful, we display a QMessageBox to inform the user. \snippet examples/addressbook-sdk/part6/addressbook.cpp loadFromFile part2 Otherwise, we instantiate a QDataStream object, \c in, set its version as above and read the serialized data into hte \c contacts data structure. The \c contacs object is emptied before data is read into it to simplify the file reading process. A more advanced method would be to read the contacts into a temporary QMap object, and copy over non-duplicate contacts into \c contacts. \snippet examples/addressbook-sdk/part6/addressbook.cpp loadFromFile 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 connect the \c clicked() signal of the push buttons with the \c loadFromFile() and \c saveToFile(): \snippet examples/addressbook-sdk/part6/addressbook.cpp connectSlots */ /*! \page tutorials-addressbook-sdk-part7.html \previouspage Address Book 6 - Loading and Saving \contentspage {Address Book Tutorial}{Contents} \example examples/addressbook-sdk/part7 \title Address Book 7 - Additional Features Although our address book application is useful in its own right, it would be useful it 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 Placing Widgets on The Form We add a push button into our layout by dragging and dropping it in, with \c exportButton as its \c objectName. The \c toolTip property is set to \gui{Export as vCard}. \image addressbook-tutorial-part7-screenshot.png \section1 The AddressBook Class We declare a public slot, \c exportAsVCard(), in our header file. Within the \c AddressBook constructor, we connect \c{exportButton}'s \l{QPushButton::}{clicked()} signal to \c exportAsVCard(). */