/**************************************************************************** ** ** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies). ** All rights reserved. ** Contact: Nokia Corporation (qt-info@nokia.com) ** ** This file is part of the documentation of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:FDL$ ** No Commercial Usage ** This file contains pre-release code and may not be distributed. ** You may use this file in accordance with the terms and conditions ** contained in the Technology Preview License Agreement accompanying ** this package. ** ** GNU Free Documentation License ** Alternatively, this file may be used under the terms of the GNU Free ** Documentation License version 1.3 as published by the Free Software ** Foundation and appearing in the file included in the packaging of this ** file. ** ** If you have questions regarding the use of this file, please contact ** Nokia at qt-info@nokia.com. ** $QT_END_LICENSE$ ** ****************************************************************************/ /*! \page widgets-tutorial.html \title Widgets Tutorial \brief This tutorial covers basic usage of widgets and layouts, showing how they are used to build GUI applications. \section1 Introduction Widgets are the basic building blocks for graphical user interface (GUI) applications built with Qt. Each GUI component (e.g. buttons, labels, text editor) is a \l{QWidget}{widget} that is placed somewhere within a user interface window, or is displayed as an independent window. Each type of widge is provided by a subclass of QWidget, which is itself a subclass of QObject. QWidget is not an abstract class. It can be used as a container for other widgets, and it can be subclassed with minimal effort to create new, custom widgets. QWidget is often used to create a window inside which other \l{QWidget}s are placed. As with \l{QObject}s, \l{QWidget}s can be created with parent objects to indicate ownership, ensuring that objects are deleted when they are no longer used. With widgets, these parent-child relationships have an additional meaning: Each child widget is displayed within the screen area occupied by its parent widget. This means that when you delete a window widget, all the child widgets it contains are also deleted. \section1 Writing a main Function Many of the GUI examples provided with Qt follow the pattern of having a \c{main.cpp} file, which contains the standard code to initialize the application, plus any number of other source/header files that contain the application logic and custom GUI components. A typical \c main() function in \c{main.cpp} looks like this: \snippet doc/src/snippets/widgets-tutorial/template.cpp main.cpp body First, a QApplication object is constructed, which can be configured with arguments passed in from the command line. After the widgets have been created and shown, QApplication::exec() is called to start Qt's event loop. Control passes to Qt until this function returns. Finally, \c{main()} returns the value returned by QApplication::exec(). \section1 Simple widget examples Each of theses simple widget examples is written entirely within the \c main() function. \list \o \l {tutorials/widgets/toplevel} {Creating a window} \o \l {tutorials/widgets/childwidget} {Creating child widgets} \o \l {tutorials/widgets/windowlayout} {Using layouts} \o \l {tutorials/widgets/nestedlayouts} {Nested layouts} \endlist \section1 Real world widget examples In these \l{Widget examples} {more advanced examples}, the code that creates the widgets and layouts is stored in other files. For example, the GUI for a main window may be created in the constructor of a QMainWindow subclass. \section1 Building The Examples If you installed a binary package to get Qt, or if you compiled Qt yourself, the examples described in this tutorial should already be built and ready to run. If you wish to modify and recompile them, follow these steps: \list 1 \o From a command prompt, enter the directory containing the example you have modified. \o Type \c qmake and press \key{Return}. If this doesn't work, make sure that the executable is on your path, or enter its full location. \o On Linux/Unix and Mac OS X, type \c make and press \key{Return}; on Windows with Visual Studio, type \c nmake and press \key{Return}. \endlist An executable file is created in the current directory. On Windows, this file may be located in a \c debug or \c release subdirectory. You can run this executable to see the example code at work. */ /*! \example tutorials/widgets/toplevel \title Widgets Tutorial - Creating a Window If a widget is created without a parent, it is treated as a window, or \e{top-level widget}, when it is shown. Since it has no parent object to ensure that it is deleted when no longer needed, it is up to the developer to keep track of the top-level widgets in an application. In the following example, we use QWidget to create and show a window with a default size: \raw HTML
\endraw \snippet tutorials/widgets/toplevel/main.cpp main program \raw HTML \endraw \inlineimage widgets-tutorial-toplevel.png \raw HTML
\endraw To create a real GUI, we need to place widgets inside the window. To do this, we pass a QWidget instance to a widget's constructor, as we will demonstrate in the next part of this tutorial. */ /*! \example tutorials/widgets/childwidget \title Widgets Tutorial - Child Widgets We can add a child widget to the window created in the previous example by passing \c window as the parent to its constructor. In this case, we add a button to the window and place it in a specific location: \raw HTML
\endraw \snippet tutorials/widgets/childwidget/main.cpp main program \raw HTML \endraw \inlineimage widgets-tutorial-childwidget.png \raw HTML
\endraw The button is now a child of the window and will be deleted when the window is destroyed. Note that hiding or closing the window does not automatically destroy it. It will be destroyed when the example exits. */ /*! \example tutorials/widgets/windowlayout \title Widgets Tutorial - Using Layouts Usually, child widgets are arranged inside a window using layout objects rather than by specifying positions and sizes explicitly. Here, we construct a label and line edit widget that we would like to arrange side-by-side. \raw HTML
\endraw \snippet tutorials/widgets/windowlayout/main.cpp main program \raw HTML \endraw \inlineimage widgets-tutorial-windowlayout.png \raw HTML
\endraw The \c layout object we construct manages the positions and sizes of widgets supplied to it with the \l{QHBoxLayout::}{addWidget()} function. The layout itself is supplied to the window itself in the call to \l{QWidget::}{setLayout()}. Layouts are only visible through the effects they have on the widgets (and other layouts) they are responsible for managing. In the example above, the ownership of each widget is not immediately clear. Since we construct the widgets and the layout without parent objects, we would expect to see an empty window and two separate windows containing a label and a line edit. However, when we tell the layout to manage the label and line edit and set the layout on the window, both the widgets and the layout itself are ''reparented'' to become children of the window. */ /*! \example tutorials/widgets/nestedlayouts \title Widgets Tutorial - Nested Layouts Just as widgets can contain other widgets, layouts can be used to provide different levels of grouping for widgets. Here, we want to display a label alongside a line edit at the top of a window, above a table view showing the results of a query. We achieve this by creating two layouts: \c{queryLayout} is a QHBoxLayout that contains QLabel and QLineEdit widgets placed side-by-side; \c{mainLayout} is a QVBoxLayout that contains \c{queryLayout} and a QTableView arranged vertically. \raw HTML
\endraw \snippet tutorials/widgets/nestedlayouts/main.cpp first part \snippet tutorials/widgets/nestedlayouts/main.cpp last part \raw HTML \endraw \inlineimage widgets-tutorial-nestedlayouts.png \raw HTML
\endraw Note that we call the \c{mainLayout}'s \l{QBoxLayout::}{addLayout()} function to insert the \c{queryLayout} above the \c{resultView} table. We have omitted the code that sets up the model containing the data shown by the QTableView widget, \c resultView. For completeness, we show this below. As well as QHBoxLayout and QVBoxLayout, Qt also provides QGridLayout and QFormLayout classes to help with more complex user interfaces. These can be seen if you run \l{Qt Designer}. \section1 Setting up the Model In the code above, we did not show where the table's data came from because we wanted to concentrate on the use of layouts. Here, we see that the model holds a number of items corresponding to rows, each of which is set up to contain data for two columns. \snippet tutorials/widgets/nestedlayouts/main.cpp set up the model The use of models and views is covered in the \l{Item Views Examples} and in the \l{Model/View Programming} overview. */