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502 lines
16 KiB
Plaintext
502 lines
16 KiB
Plaintext
// Copyright (C) 2022 The Qt Company Ltd.
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// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
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/*!
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\example tutorials/notepad
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\title Getting Started Programming with Qt Widgets
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\examplecategory {User Interface Components}
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\brief A tutorial for Qt Widgets based notepad application.
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In this topic, we teach basic Qt knowledge by implementing a simple
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Notepad application using C++ and the \l{Qt Widgets} module. The
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application is a small text editor which allows you to create a text
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file, save it, print it,
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or reopen and edit it again. You can also set the font to be used.
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\image notepad1.png "Notepad application"
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\include examples-run.qdocinc
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\section1 Creating the Notepad Project
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Setting up a new project in Qt Creator is aided by a wizard that
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guides you step-by-step through the project creation process. The
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wizard prompts you to enter the settings needed for that particular
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type of project and creates the project for you.
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\note The UI text in Qt Creator and the contents of the generated files
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depend on the Qt Creator version that you use.
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\image notepad2.png "Qt Creator New Project dialog"
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To create the Notepad project, select \uicontrol File >
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\uicontrol {New Project} > \uicontrol {Application (Qt)} >
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\uicontrol {Qt Widgets Application} > \uicontrol Choose, and follow the
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instructions of the wizard. In the \uicontrol{Class Information} dialog,
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type \e Notepad as the class name and select \uicontrol QMainWindow
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as the base class.
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\image notepad3.png "Class Information Dialog"
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The \uicontrol {Qt Widgets Application} wizard creates a project that contains
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a main source file and a set of files that specify a user interface
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(Notepad widget):
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\list
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\li CMakeLists.txt - the project file.
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\li main.cpp - the main source file for the application.
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\li notepad.cpp - the source file of the notepad class of the
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Notepad widget.
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\li notepad.h - the header file of the notepad class for the
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Notepad widget.
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\li notepad.ui - the UI form for the Notepad widget.
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\endlist
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The files come with the necessary boiler plate code for you to be able to
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build and run the project. We will take a closer look at the file contents
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in the following sections.
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\b{Learn More}
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\table
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\header
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\li About
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\li Here
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\row
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\li Using Qt Creator
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\li \l{Qt Creator Manual}{Qt Creator}
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\row
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\li Creating other kind of applications with Qt Creator
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\li \l{Qt Creator: Tutorials}{Qt Creator Tutorials}
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\endtable
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\section1 Main Source File
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The wizard generates the following code in the main.cpp file:
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\quotefromfile tutorials/notepad/main.cpp
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\skipto "notepad.h"
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\printuntil }
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We will go through the code line by line. The following lines include
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the header files for the Notepad widget and QApplication. All Qt classes
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have a header file named after them.
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\quotefromfile tutorials/notepad/main.cpp
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\skipto notepad.h
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\printuntil QApplication
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The following line defines the main function that is the entry point
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for all C and C++ based applications:
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\printline main
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The following line creates a QApplication object. This object manages
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application-wide resources and is necessary to run any Qt program
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that uses Qt Widgets. It constructs an application object with \c argc
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command line arguments run in \c argv. (For GUI applications that
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do not use Qt Widgets, you can use QGuiApplication instead.)
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\skipuntil {
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\printuntil QApplication
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The following line creates the Notepad object. This is the object for
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which the wizard created the class and the UI file. The user interface
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contains visual elements that are called \c widgets in Qt. Examples
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of widgets are text edits, scroll bars, labels, and radio buttons. A
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widget can also be a container for other widgets; a dialog or a main
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application window, for example.
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\printline Notepad
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The following line shows the Notepad widget on the screen in its own
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window. Widgets can also function as containers. An example of this
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is QMainWindow which often contains several types of widgets. Widgets
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are not visible by default; the function \l{QWidget::}{show()} makes
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the widget visible.
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\printline w.show
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The following line makes the QApplication enter its event loop. When
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a Qt application is running, events are generated and sent to the
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widgets of the application. Examples of events are mouse presses
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and key strokes.
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\printline a.exec
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\b{Learn More}
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\table
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\header
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\li About
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\li Here
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\row
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\li Widgets and Window Geometry
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\li \l{Window and Dialog Widgets}
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\row
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\li Events and event handling
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\li \l{The Event System}
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\endtable
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\section1 Designing a UI
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The wizard generates a user interface definition in XML format: notepad.ui.
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When you open the notepad.ui file in Qt Creator, it automatically
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opens in the integrated Qt Designer.
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When you build the application, Qt Creator launches the Qt
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\l{User Interface Compiler (uic)} that reads the .ui file and creates
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a corresponding C++ header file, ui_notepad.h.
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\section2 Using Qt Designer
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The wizard creates an application that uses a QMainWindow. It has
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its own layout to which you can add a menu bar, dock widgets, toolbars,
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and a status bar. The center area can be occupied by any kind of widget.
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The wizard places the Notepad widget there.
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To add widgets in Qt Designer:
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\list 1
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\li In the Qt Creator \uicontrol Edit mode, double-click the notepad.ui
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file in the \uicontrol Projects view to launch the file in the integrated
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Qt Designer.
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\li Drag and drop widgets Text Edit (QTextEdit) to the form.
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\li Press \key {Ctrl+A} (or \key {Cmd+A}) to select the widgets and click
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\uicontrol {Lay out Vertically} (or press \key {Ctrl+L}) to apply a vertical
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layout (QVBoxLayout).
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\li Press \key {Ctrl+S} (or \key {Cmd+S}) to save your changes.
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\endlist
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The UI now looks as follows in Qt Designer:
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\image notepad4.png
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You can view the generated XML file in the code editor:
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\quotefromfile tutorials/notepad/notepad.ui
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\printuntil QMenuBar
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\dots
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The following line contains the XML declaration, which specifies the
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XML version and character encoding used in the document:
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\code
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<?xml version="1.0" encoding="UTF-8"?>
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\endcode
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The rest of the file specifies an \c ui element that defines a
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Notepad widget:
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\code
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<ui version="4.0">
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\endcode
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The UI file is used together with the header and source file of the
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Notepad class. We will look at the rest of the UI file in the later
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sections.
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\section2 Notepad Header File
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The wizard generated a header file for the Notepad class that has the
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necessary #includes, a constructor, a destructor, and the Ui object.
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The file looks as follows:
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\quotefromfile tutorials/notepad/notepad.h
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\skipto #include
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\printuntil ~Notepad();
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\skipto private:
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\printuntil };
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The following line includes QMainWindow that provides a main application
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window:
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\quotefromfile tutorials/notepad/notepad.h
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\skipto #include
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\printuntil >
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The following lines declare the Notepad class in the Ui namespace,
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which is the standard namespace for the UI classes generated from
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.ui files by the \c uic tool:
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\skipto Ui {
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\printuntil }
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The class declaration contains the \c Q_OBJECT macro. It must come
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first in the class definition, and declares our class as a QObject.
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Naturally, it must also inherit from QObject. A QObject adds several
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abilities to a normal C++ class. Notably, the class name and slot
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names can be queried at runtime. It is also possible to query a slot's
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parameter types and invoke it.
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\skipto class Notepad
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\printuntil Q_OBJECT
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The following lines declare a constructor that has a default argument
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called \c parent.
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The value 0 indicates that the widget has no parent (it is a top-level
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widget).
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\printuntil explicit
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The following line declares a virtual destructor to free the resources
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that were acquired by the object during its life-cycle. According to
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the C++ naming convention, destructors have the same name as the class
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they are associated with, prefixed with a tilde (~). In QObject,
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destructors are virtual to ensure that the destructors of derived
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classes are invoked properly when an object is deleted through a
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pointer-to-base-class.
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\printuntil ~Notepad();
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The following lines declare a member variable which is a pointer to
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the Notepad UI class. A member variable is associated with a specific
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class, and accessible for all its methods.
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\skipto private:
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\printuntil };
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\section2 Notepad Source File
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The source file that the wizard generated for the Notepad class looks
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as follows:
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\quotefromfile tutorials/notepad/notepad.cpp
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\skipto #include "notepad.h"
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\printuntil ui->setupUi(this);
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\skipto }
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\printuntil }
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The following lines include the Notepad class header file that was
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generated by the wizard and the UI header file that was generated
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by the \c uic tool:
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\quotefromfile tutorials/notepad/notepad.cpp
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\skipto #include "notepad.h"
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\printuntil #include "ui_notepad.h"
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The following line defines the \c {Notepad} constructor:
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\printuntil Notepad::Notepad
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The following line calls the QMainWindow constructor, which is
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the base class for the Notepad class:
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\printuntil QMainWindow
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The following line creates the UI class instance and assigns it to
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the \c ui member:
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\printline ui(new
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The following line sets up the UI:
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\printuntil ui->setupUi(this)
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In the destructor, we delete the \c ui:
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\skipto Notepad::~Notepad
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\printuntil }
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\section2 Project File
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The wizard generates the following project file, \c CMakeLists.txt, for
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us:
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\quotefile tutorials/notepad/CMakeLists.txt
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The project file specifies the source, header, and UI files included in
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the project.
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\b{Learn More}
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\table
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\header
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\li About
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\li Here
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\row
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\li Using Qt Designer
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\li \l{Qt Designer Manual}
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\row
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\li Layouts
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\li \l{Layout Management},
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\l{Widgets and Layouts},
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\l{Layout Examples}
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\row
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\li The widgets that come with Qt
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\li \l{Qt Widget Gallery}
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\row
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\li Main windows and main window classes
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\li \l{Application Main Window},
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\l{Main Window Examples}
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\row
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\li QObjects and the Qt Object model (This is essential to
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understand Qt)
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\li \l{Object Model}
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\row
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\li qmake and the Qt build system
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\li \l{qmake Manual}
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\endtable
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\section1 Adding User Interaction
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To add functionality to the editor, we start by adding menu items
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and buttons on a toolbar.
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Click on "Type Here", and add the options New, Open, Save, Save as,
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Print and Exit. This creates 5 lines in the Action Editor below.
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To connect the actions to slots, right-click an action and select
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\uicontrol {Go to slot} > \uicontrol triggered(), and complete the
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code for that given slot.
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If we also want to add the actions to a toolbar, we can assign an
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icon to each QAction, and then drag the QAction to the toolbar. You
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assign an icon by entering an icon name in the Icon property of the
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action concerned. When the QAction has been dragged to the toolbar,
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clicking the icon will launch the associated slot.
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Complete the method \c newDocument():
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\quotefromfile tutorials/notepad/notepad.cpp
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\skipto newDocument()
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\printuntil }
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The \c currentFile variable is a global variable containing the file
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presently being edited, and \c clear() clears the text buffer.
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The \c currentFile variable is defined in the private part of notepad.h:
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\quotefromfile tutorials/notepad/notepad.h
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\skipto private:
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\printuntil currentFile;
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\section2 Opening a file
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In \c notepad.ui, right click on \c actionOpen and select
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\uicontrol {Go to Slot}.
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Complete method \c open().
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\quotefromfile tutorials/notepad/notepad.cpp
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\skipto open()
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\printuntil file.close
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\printuntil }
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\c QFileDialog::getOpenFileName opens a dialog enabling you to select
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a file. QFile object \c myfile has the selected \c file_name as
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parameter. We store the selected file also into the global variable
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\c currentFile for later purposes. We open the file with \c file.open
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as a readonly text file. If it cannot be opened, a warning is issued,
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and the program stops.
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We define a QTextStream \c instream for parameter \c myfile.
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The contents of file \c myfile is copied into QString \c text.
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\c setText(text) fills the buffer of our editor with \c text.
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\section2 Saving a file
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We create the method for saving a file in the same way as for
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\l {Opening a file}, by right clicking on \c actionSave, and
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selecting \uicontrol {Go to Slot}.
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\skipto Notepad::save
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\printuntil file.close
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\printuntil }
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QFile object \c myfile is linked to global variable \c current_file,
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the variable that contains the file we were working with.
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If we cannot open \c myfile, an error message is issued and the
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method stops. We create a QTextStream \c outstream. The contents
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of the editor buffer is converted to plain text, and then written
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to \c outstream.
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\section2 Saving a file under another name
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\skipto Notepad::saveAs
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\printuntil file.close
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\printuntil }
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This is the same procedure as for \l {Saving a file}, the only
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difference being that here you need to enter a new file name for
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the file to be created.
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\section2 Printing a File
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If you want to use print functionalities, you need to add
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\c PrintSupport to the project file:
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\quotefromfile tutorials/notepad/CMakeLists.txt
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\skipto find_package(Qt6
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\printuntil )
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In \c notepad.cpp, we declare a QPrinter object called \c printDev:
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\quotefromfile tutorials/notepad/notepad.cpp
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\skipto void Notepad::print()
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\printuntil }
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We launch a printer dialog box and store the selected printer in
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object \c printDev. If we clicked on \c Cancel and did not select
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a printer, the methods returns. The actual printer command is given
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with \c ui->textEdit->print with our QPrinter object as parameter.
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\section2 Select a Font
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\skipto Notepad::selectFont
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\printuntil }
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We declare a boolean indicating if we did select a font with
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QFontDialog. If so, we set the font with \c ui->textEdit->setFont(myfont).
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\section2 Copy, Cut, Paste, Undo, and Redo
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If you select some text, and want to copy it to the clipboard,
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you call the appropriate method of \c ui->textEdit. The same counts
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for cut, paste, undo, and redo.
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This table shows the method name to use.
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\table
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\header
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\li Task
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\li Method called
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\row
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\li Copy
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\li ui->textEdit->copy()
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\row
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\li Cut
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\li ui->textEdit->cut()
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\row
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\li Paste
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\li ui->textEdit->paste()
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\row
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\li Undo
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\li ui->textEdit->undo()
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\row
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\li Redo
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\li ui->textEdit->redo()
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\endtable
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\b{Learn More}
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\table
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\header
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\li About
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\li Here
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\row
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\li Files and I/O devices
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\li QFile, QIODevice
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\row
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\li tr() and internationalization
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\li \l{Qt Linguist Manual},
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\l{Writing Source Code for Translation},
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\l{Internationalization with Qt}
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\endtable
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\include cli-build-cmake.qdocinc cli-build-cmake
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*/
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