[844] | 1 | /****************************************************************************
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| 2 | **
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| 3 | ** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
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| 4 | ** All rights reserved.
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| 5 | ** Contact: Nokia Corporation ([email protected])
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| 6 | **
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| 7 | ** This file is part of the documentation of the Qt Toolkit.
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| 8 | **
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| 9 | ** $QT_BEGIN_LICENSE:FDL$
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| 10 | ** Commercial Usage
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| 11 | ** Licensees holding valid Qt Commercial licenses may use this file in
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| 12 | ** accordance with the Qt Commercial License Agreement provided with the
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| 13 | ** Software or, alternatively, in accordance with the terms contained in a
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| 14 | ** written agreement between you and Nokia.
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| 15 | **
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| 16 | ** GNU Free Documentation License
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| 17 | ** Alternatively, this file may be used under the terms of the GNU Free
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| 18 | ** Documentation License version 1.3 as published by the Free Software
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| 19 | ** Foundation and appearing in the file included in the packaging of this
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| 20 | ** file.
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| 21 | **
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| 22 | ** If you have questions regarding the use of this file, please contact
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| 23 | ** Nokia at [email protected].
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| 24 | ** $QT_END_LICENSE$
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| 25 | **
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| 26 | ****************************************************************************/
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| 27 |
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| 28 | /*!
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| 29 | \page gettingstartedqt.html
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| 30 |
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| 31 | \title Getting Started Programming with Qt
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| 32 | \ingroup gettingStarted
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| 33 |
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| 34 | Welcome to the world of Qt--the cross-platform GUI toolkit. In
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| 35 | this getting started guide, we teach basic Qt knowledge by
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| 36 | implementing a simple Notepad application. After reading this
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| 37 | guide, you should be ready to delve into our overviews and API
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| 38 | documentation, and find the information you need for the
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| 39 | application you are developing.
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| 40 |
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| 41 | \section1 Hello Notepad
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| 42 |
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| 43 | In this first example, we simply create and show a text edit in a
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| 44 | window frame on the desktop. This represents the simplest possible
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| 45 | Qt program that has a GUI.
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| 46 |
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| 47 | \image gs1.png
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| 48 |
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| 49 | Here is the code:
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| 50 |
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| 51 | \code
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| 52 | 1 #include <QApplication>
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| 53 | 2 #include <QTextEdit>
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| 54 | 3
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| 55 | 4 int main(int argv, char **args)
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| 56 | 5 {
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| 57 | 6 QApplication app(argv, args);
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| 58 | 7
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| 59 | 8 QTextEdit textEdit;
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| 60 | 9 textEdit.show();
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| 61 | 10
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| 62 | 11 return app.exec();
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| 63 | 12 }
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| 64 | \endcode
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| 65 |
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| 66 | Let us go through the code line by line. In the first two lines, we
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| 67 | include the header files for QApplication and QTextEdit, which are
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| 68 | the two classes that we need for this example. All Qt classes have
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| 69 | a header file named after them.
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| 70 |
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| 71 | Line 6 creates a QApplication object. This object manages
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| 72 | application-wide resources and is necessary to run any Qt program
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| 73 | that has a GUI. It needs \c argv and \c args because Qt accepts a
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| 74 | few command line arguments.
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| 75 |
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| 76 | Line 8 creates a QTextEdit object. A text edit is a visual element
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| 77 | in the GUI. In Qt, we call such elements widgets. Examples of
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| 78 | other widgets are scroll bars, labels, and radio buttons. A widget
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| 79 | can also be a container for other widgets; a dialog or a main
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| 80 | application window, for example.
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| 81 |
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| 82 | Line 9 shows the text edit on the screen in its own window frame.
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| 83 | Since widgets also function as containers (for instance a
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| 84 | QMainWindow, which has toolbars, menus, a status bar, and a few
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| 85 | other widgets), it is possible to show a single widget in its own
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| 86 | window. Widgets are not visible by default; the function
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| 87 | \l{QWidget::}{show()} makes the widget visible.
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| 88 |
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| 89 | Line 11 makes the QApplication enter its event loop. When a Qt
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| 90 | application is running, events are generated and sent to the
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| 91 | widgets of the application. Examples of events are mouse presses
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| 92 | and key strokes. When you type text in the text edit widget, it
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| 93 | receives key pressed events and responds by drawing the text
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| 94 | typed.
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| 95 |
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| 96 | To run the application, open a command prompt, and enter the
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| 97 | directory in which you have the \c .cpp file of the program. The
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| 98 | following shell commands build the program.
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| 99 |
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| 100 | \code
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| 101 | qmake -project
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| 102 | qmake
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| 103 | make
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| 104 | \endcode
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| 105 |
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| 106 | This will leave an executable in the \c part1 directory (note that
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| 107 | on Windows, you may have to use \c nmake instead of \c make. Also,
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| 108 | the executable will be placed in part1/debug or part1/release). \c
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| 109 | qmake is Qt's build tool, which takes a configuration file. \c
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| 110 | qmake generates this for us when given the \c{-project} argument.
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| 111 | Given the configuration file (suffixed .pro), \c qmake produces a
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| 112 | \c make file that will build the program for you. We will look
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| 113 | into writing our own \c .pro files later.
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| 114 |
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| 115 | \section2 Learn More
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| 116 |
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| 117 | \table
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| 118 | \header
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| 119 | \o About
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| 120 | \o Here
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| 121 | \row
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| 122 | \o Widgets and Window Geometry
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| 123 | \o \l{Window and Dialog Widgets}
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| 124 | \row
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| 125 | \o Events and event handling
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| 126 | \o \l{The Event System}
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| 127 | \endtable
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| 128 |
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| 129 | \section1 Adding a Quit Button
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| 130 |
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| 131 | In a real application, you will normally need more than one
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| 132 | widget. We will now introduce a QPushButton beneath the text edit.
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| 133 | The button will exit the Notepad application when pushed (i.e.,
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| 134 | clicked on with the mouse).
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| 135 |
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| 136 | \image gs2.png
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| 137 |
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| 138 | Let us take a look at the code.
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| 139 |
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| 140 | \code
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| 141 | 1 #include <QtGui>
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| 142 | 2
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| 143 | 3 int main(int argv, char **args)
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| 144 | 4 {
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| 145 | 5 QApplication app(argv, args);
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| 146 | 6
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| 147 | 7 QTextEdit textEdit;
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| 148 | 8 QPushButton quitButton("Quit");
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| 149 | 9
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| 150 | 10 QObject::connect(&quitButton, SIGNAL(clicked()), qApp, SLOT(quit()));
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| 151 | 11
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| 152 | 12 QVBoxLayout layout;
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| 153 | 13 layout.addWidget(&textEdit);
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| 154 | 14 layout.addWidget(&quitButton);
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| 155 | 15
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| 156 | 16 QWidget window;
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| 157 | 17 window.setLayout(&layout);
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| 158 | 18
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| 159 | 19 window.show();
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| 160 | 20
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| 161 | 21 return app.exec();
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| 162 | 22 }
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| 163 | \endcode
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| 164 |
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| 165 | Line 1 includes QtGui, which contains all of Qt's GUI classes.
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| 166 |
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| 167 | Line 10 uses Qt's Signals and Slots mechanism to make the
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| 168 | application exit when the \gui {Quit button} is pushed. A slot is
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| 169 | a function that can be invoked at runtime using its name (as a
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| 170 | literal string). A signal is a function that when called will
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| 171 | invoke slots registered with it; we call that to connect the slot
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| 172 | to the signal and to emit the signal.
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| 173 |
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| 174 | \l{QApplication::}{quit()} is a slot of QApplication that exits
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| 175 | the application. \l{QPushButton::}{clicked()} is a signal that
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| 176 | QPushButton emits when it is pushed. The static
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| 177 | QObject::connect() function takes care of connecting the slot to
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| 178 | the signal. SIGNAL() and SLOT() are two macros that take the
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| 179 | function signatures of the signal and slot to connect. We also
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| 180 | need to give pointers to the objects that should send and receive
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| 181 | the signal.
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| 182 |
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| 183 | Line 12 creates a QVBoxLayout. As mentioned, widgets can contain
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| 184 | other widgets. It is possible to set the bounds (the location and
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| 185 | size) of child widgets directly, but it is usually easier to use a
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| 186 | layout. A layout manages the bounds of a widget's children.
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| 187 | QVBoxLayout, for instance, places the children in a vertical row.
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| 188 |
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| 189 | Line 13 and 14 adds the text edit and button to the layout. In
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| 190 | line 17, we set the layout on a widget.
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| 191 |
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| 192 | \section2 Learn More
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| 193 |
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| 194 | \table
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| 195 | \header
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| 196 | \o About
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| 197 | \o Here
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| 198 | \row
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| 199 | \o Signals and slots
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| 200 | \o \l{Signals & Slots}
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| 201 | \row
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| 202 | \o Layouts
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| 203 | \o \l{Layout Management},
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| 204 | \l{Widgets and Layouts},
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| 205 | \l{Layout Examples}
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| 206 | \row
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| 207 | \o The widgets that come with Qt
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| 208 | \o \l{Qt Widget Gallery},
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| 209 | \l{Widget Examples}
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| 210 | \endtable
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| 211 |
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| 212 | \section1 Subclassing QWidget
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| 213 |
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| 214 | When the user wants to quit an application, you might want to
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| 215 | pop-up a dialog that asks whether he/she really wants to quit. In
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| 216 | this example, we subclass QWidget, and add a slot that we connect
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| 217 | to the \gui {Quit button}.
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| 218 |
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| 219 | \image gs3.png
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| 220 |
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| 221 | Let us look at the code:
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| 222 |
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| 223 | \code
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| 224 | 5 class Notepad : public QWidget
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| 225 | 6 {
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| 226 | 7 Q_OBJECT
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| 227 | 8
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| 228 | 9 public:
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| 229 | 10 Notepad();
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| 230 | 11
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| 231 | 12 private slots:
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| 232 | 13 void quit();
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| 233 | 14
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| 234 | 15 private:
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| 235 | 16 QTextEdit *textEdit;
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| 236 | 17 QPushButton *quitButton;
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| 237 | 18 };
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| 238 | \endcode
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| 239 |
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| 240 | The \c Q_OBJECT macro must be first in the class definition, and
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| 241 | declares our class as a \c QObject (Naturally, it must also
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| 242 | inherit from QObject). A \l{QObject} adds several abilities to a
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| 243 | normal C++ class. Notably, the class name and slot names can be
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| 244 | queried at run-time. It is also possible to query a slot's
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| 245 | parameter types and invoke it.
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| 246 |
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| 247 | Line 13 declares the slot \c quit(). This is easy using the \c
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| 248 | slots macro. The \c quit() slot can now be connected to signals
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| 249 | with a matching signature (any signal that takes no parameters).
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| 250 |
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| 251 | Instead of setting up the GUI and connecting the slot in the \c
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| 252 | main() function, we now use \c{Notepad}'s constructor.
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| 253 |
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| 254 | \code
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| 255 | Notepad::Notepad()
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| 256 | {
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| 257 | textEdit = new QTextEdit;
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| 258 | quitButton = new QPushButton(tr("Quit"));
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| 259 |
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| 260 | connect(quitButton, SIGNAL(clicked()), this, SLOT(quit()));
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| 261 |
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| 262 | QVBoxLayout *layout = new QVBoxLayout;
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| 263 | layout->addWidget(textEdit);
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| 264 | layout->addWidget(quitButton);
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| 265 |
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| 266 | setLayout(layout);
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| 267 |
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| 268 | setWindowTitle(tr("Notepad"));
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| 269 | }
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| 270 | \endcode
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| 271 |
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| 272 | As you saw in the class definition, we use pointers to our \l
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| 273 | {QObject}s (\c textEdit and \c quitButton). As a rule, you should
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| 274 | always allocate \l{QObject}s on the heap and never copy them.
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| 275 |
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| 276 | We now use the function \l{QObject::}{tr()} around our user
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| 277 | visible strings. This function is necessary when you want to
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| 278 | provide your application in more than one language (e.g. English
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| 279 | and Chinese). We will not go into details here, but you can follow
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| 280 | the \c {Qt Linguist} link from the learn more table.
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| 281 |
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| 282 | \section2 Learn More
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| 283 |
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| 284 | \table
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| 285 | \header
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| 286 | \o About
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| 287 | \o Here
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| 288 | \row
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| 289 | \o tr() and internationalization
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| 290 | \o \l{Qt Linguist Manual},
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| 291 | \l{Writing Source Code for Translation},
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| 292 | \l{Hello tr() Example},
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| 293 | \l{Internationalization with Qt}
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| 294 | \row
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| 295 | \o QObjects and the Qt Object model (This is essential to understand Qt)
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| 296 | \o \l{Object Model}
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| 297 | \row
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| 298 | \o qmake and the Qt build system
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| 299 | \o \l{qmake Manual}
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| 300 | \endtable
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| 301 |
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| 302 | \section2 Creating a .pro file
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| 303 |
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| 304 | For this example, we write our own \c .pro file instead of
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| 305 | using \c qmake's \c -project option.
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| 306 |
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| 307 | \code
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| 308 | HEADERS = notepad.h
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| 309 | SOURCES = notepad.cpp \
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| 310 | main.cpp
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| 311 | \endcode
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| 312 |
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| 313 | The following shell commands build the example.
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| 314 |
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| 315 | \code
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| 316 | qmake
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| 317 | make
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| 318 | \endcode
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| 319 |
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| 320 | \section1 Using a QMainWindow
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| 321 |
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| 322 | Many applications will benefit from using a QMainWindow, which has
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| 323 | its own layout to which you can add a menu bar, dock widgets, tool
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| 324 | bars, and a status bar. QMainWindow has a center area that can be
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| 325 | occupied by any kind of widget. In our case, we will place our
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| 326 | text edit there.
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| 327 |
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| 328 | \image gs4.png
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| 329 |
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| 330 | Let us look at the new \c Notepad class definition.
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| 331 |
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| 332 | \code
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| 333 | #include <QtGui>
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| 334 |
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| 335 | class Notepad : public QMainWindow
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| 336 | {
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| 337 | Q_OBJECT
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| 338 |
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| 339 | public:
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| 340 | Notepad();
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| 341 |
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| 342 | private slots:
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| 343 | void open();
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| 344 | void save();
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| 345 | void quit();
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| 346 |
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| 347 | private:
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| 348 | QTextEdit *textEdit;
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| 349 |
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| 350 | QAction *openAction;
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| 351 | QAction *saveAction;
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| 352 | QAction *exitAction;
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| 353 |
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| 354 | QMenu *fileMenu;
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| 355 | };
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| 356 | \endcode
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| 357 |
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| 358 | We include two more slots that can save and open a document. We
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| 359 | will implement these in the next section.
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| 360 |
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| 361 | Often, in a main window, the same slot should be invoked by
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| 362 | several widgets. Examples are menu items and buttons on a tool
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| 363 | bar. To make this easier, Qt provides QAction, which can be given
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| 364 | to several widgets, and be connected to a slot. For instance, both
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| 365 | QMenu and QToolBar can create menu items and tool buttons from the
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| 366 | same \l{QAction}s. We will see how this works shortly.
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| 367 |
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| 368 | As before, we use the \c {Notepad}s constructor to set up the
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| 369 | GUI.
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| 370 |
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| 371 | \code
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| 372 | Notepad::Notepad()
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| 373 | {
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| 374 | saveAction = new QAction(tr("&Open"), this);
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| 375 | saveAction = new QAction(tr("&Save"), this);
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| 376 | exitAction = new QAction(tr("E&xit"), this);
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| 377 |
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| 378 | connect(openAction, SIGNAL(triggered()), this, SLOT(open()));
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| 379 | connect(saveAction, SIGNAL(triggered()), this, SLOT(save()));
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| 380 | connect(exitAction, SIGNAL(triggered()), qApp, SLOT(quit()));
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| 381 |
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| 382 | fileMenu = menuBar()->addMenu(tr("&File"));
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| 383 | fileMenu->addAction(openAction);
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| 384 | fileMenu->addAction(saveAction);
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| 385 | fileMenu->addSeparator();
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| 386 | fileMenu->addAction(exitAction);
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| 387 |
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| 388 | textEdit = new QTextEdit;
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| 389 | setCentralWidget(textEdit);
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| 390 |
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| 391 | setWindowTitle(tr("Notepad"));
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| 392 | }
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| 393 | \endcode
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| 394 |
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| 395 | \l{QAction}s are created with the text that should appear on the
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| 396 | widgets that we add them to (in our case, menu items). If we also
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| 397 | wanted to add them to a tool bar, we could have given
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| 398 | \l{QIcon}{icons} to the actions.
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| 399 |
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| 400 | When a menu item is clicked now, the item will trigger the action,
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| 401 | and the respective slot will be invoked.
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| 402 |
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| 403 | \section2 Learn More
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| 404 |
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| 405 | \table
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| 406 | \header
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| 407 | \o About
|
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| 408 | \o Here
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| 409 | \row
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| 410 | \o Main windows and main window classes
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| 411 | \o \l{Application Main Window},
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| 412 | \l{Main Window Examples}
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| 413 | \row
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| 414 | \o MDI applications
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| 415 | \o QMdiArea,
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| 416 | \l{MDI Example}
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| 417 | \endtable
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| 418 |
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| 419 | \section1 Saving and Loading
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| 420 |
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| 421 | In this example, we will implement the functionality of the \c
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| 422 | open() and \c save() slots that we added in the previous example.
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| 423 |
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| 424 | \image gs5.png
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| 425 |
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| 426 | We will start with the \c open() slot:
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| 427 |
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| 428 | \code
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| 429 | QString fileName = QFileDialog::getOpenFileName(this, tr("Open File"), "",
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| 430 | tr("Text Files (*.txt);;C++ Files (*.cpp *.h)"));
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| 431 |
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| 432 | if (fileName != "") {
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| 433 | QFile file(fileName);
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| 434 | if (!file.open(QIODevice::ReadOnly)) {
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| 435 | QMessageBox::critical(this, tr("Error"),
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| 436 | tr("Could not open file"));
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| 437 | return;
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| 438 | }
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| 439 | QString contents = file.readAll().constData();
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| 440 | textEdit->setPlainText(contents);
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| 441 | file.close();
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| 442 | }
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| 443 | \endcode
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| 444 |
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| 445 | The first step is asking the user for the name of the file to
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| 446 | open. Qt comes with QFileDialog, which is a dialog from which the
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| 447 | user can select a file. The image above shows the dialog on
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| 448 | Kubuntu. The static \l{QFileDialog::}{getOpenFileName()} function
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| 449 | displays a modal file dialog, and does not return until the user
|
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| 450 | has selected a file. It returns the file path of the file
|
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| 451 | selected, or an empty string if the user canceled the dialog.
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| 452 |
|
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| 453 | If we have a file name, we try to open the file with
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| 454 | \l{QIODevice::}{open()}, which returns true if the file could be
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| 455 | opened. We will not go into error handling here, but you can follow
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| 456 | the links from the learn more section. If the file could not be
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| 457 | opened, we use QMessageBox to display a dialog with an error
|
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| 458 | message (see the QMessageBox class description for further
|
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| 459 | details).
|
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| 460 |
|
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| 461 | Actually reading in the data is trivial using the
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| 462 | \l{QIODevice::}{readAll()} function, which returns all data in the
|
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| 463 | file in a QByteArray. The \l{QByteArray::}{constData()} returns all
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| 464 | data in the array as a const char*, which QString has a
|
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| 465 | constructor for. The contents can then be displayed in the text
|
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| 466 | edit. We then \l{QIODevice::}{close()} the file to return the file
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| 467 | descriptor back to the operating system.
|
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| 468 |
|
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| 469 | Now, let us move on to the the \c save() slot.
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| 470 |
|
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| 471 | \code
|
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| 472 | QString fileName = QFileDialog::getSaveFileName(this, tr("Save File"), "",
|
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| 473 | tr("Text Files (*.txt);;C++ Files (*.cpp *.h)"));
|
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| 474 |
|
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| 475 | if (fileName != "") {
|
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| 476 | QFile file(fileName);
|
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| 477 | if (!file.open(QIODevice::WriteOnly)) {
|
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| 478 | // error message
|
---|
| 479 | } else {
|
---|
| 480 | QTextStream stream(&file);
|
---|
| 481 | stream << textEdit->toPlainText();
|
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| 482 | stream.flush();
|
---|
| 483 | file.close();
|
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| 484 | }
|
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| 485 | }
|
---|
| 486 | \endcode
|
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| 487 |
|
---|
| 488 | When we write the contents of the text edit to the file, we use
|
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| 489 | the QTextStream class, which wraps the QFile object. The text
|
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| 490 | stream can write QStrings directly to the file; QFile only accepts
|
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| 491 | raw data (char*) with the \l{QIODevice::}{write()} functions of
|
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| 492 | QIODevice.
|
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| 493 |
|
---|
| 494 | \section2 Learn More
|
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| 495 |
|
---|
| 496 | \table
|
---|
| 497 | \header
|
---|
| 498 | \o About
|
---|
| 499 | \o Here
|
---|
| 500 | \row
|
---|
| 501 | \o Files and I/O devices
|
---|
| 502 | \o QFile, QIODevice
|
---|
| 503 | \endtable
|
---|
| 504 |
|
---|
| 505 | \omit
|
---|
| 506 | \section1 Moving On
|
---|
| 507 |
|
---|
| 508 | This may not be true for the first release.
|
---|
| 509 | The Qt documentation comes with three getting started guides. You
|
---|
| 510 | have come to the end of the first, which concerns itself with
|
---|
| 511 | basic Qt concepts. We also have guides covering intermediate and
|
---|
| 512 | advanced topics. They are found here: You may also have noticed that the learn more sections in
|
---|
| 513 | this guide frequently linked to them.
|
---|
| 514 | Basic Qt Architecture
|
---|
| 515 | \endomit
|
---|
| 516 | */
|
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| 517 |
|
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