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++ // Copyright (C) 2016 The Qt Company Ltd.
++ // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
++
++ /*!
++ \example calculatorbuilder
++ \examplecategory {Desktop}
++ \meta tags {widgets,designer}
++ \ingroup examples-designer
++ \title Calculator Builder
++
++ \brief Creating a user interface from a \QD form at run-time.
++
++ \image calculatorbuilder-example.webp {Screenshot showing a calculator
++ application that adds two numbers and outputs the sum}
++
++ We use the form created in the \l{calculatorform}{Calculator Form}
++ example to show that the same user interface can be generated when the
++ application is executed or defined when the application is built.
++
++ \section1 Preparation
++
++ The \l{calculatorform}{Calculator Form} example defines a user
++ interface that we can use without modification. In this example, we use a
++ \l{The Qt Resource System}{resource file} to contain the \c{calculatorform.ui}
++ file created in the previous example, but it could be stored on disk instead.
++
++ To generate a form at run time, we need to link the example against the
++ \c QtUiTools module library. The project file we use contains all the
++ necessary information to do this:
++
++ \snippet calculatorbuilder/CMakeLists.txt 0
++
++ The UI file is loaded from a resource:
++
++ \snippet calculatorbuilder/CMakeLists.txt 1
++
++ For \c qmake:
++
++ \snippet calculatorbuilder/calculatorbuilder.pro 0
++
++ All the other necessary files are declared as usual.
++
++ \section1 Loading the Calculator Form
++
++ We will need to use the QUiLoader class that is provided by the
++ \c libQtUiTools library, so we first ensure that we include the header
++ file for the class:
++
++ \snippet calculatorbuilder/main.cpp 0
++
++ We create a static helper function that creates a top level
++ widget and loads the user interface that we retrieve,
++ via a QFile object, from the example's resources:
++
++ \snippet calculatorbuilder/main.cpp 1
++
++ By including the user interface in the example's resources, we ensure
++ that it will be present when the example is run. The \l{QUiLoader::load()}
++ function takes the user interface description contained in the file
++ and constructs the form widget as a child widget of the \c{CalculatorForm}.
++
++ We are interested in three widgets in the generated user interface:
++ two spin boxes and a label. For convenience, we retrieve pointers to
++ these widgets from the widget that was constructed by the \c FormBuilder,
++ and we record them for later use. The \c findChild() template function
++ allows us to query widgets in order to find named child widgets.
++
++ \snippet calculatorbuilder/main.cpp 2
++
++ The slot that modifies the output widget provided by the form is defined
++ in a similar way to that in the
++ \l{calculatorform}{Calculator Form} example, except that we use a
++ lambda, capturing the widgets found:
++
++ \snippet calculatorbuilder/main.cpp 3
++
++ The form widget is added to a layout, and the window title is set:
++
++ \snippet calculatorbuilder/main.cpp 4
++
++ The advantage of this approach is that we can replace the form when the
++ application is run, but we can still manipulate the widgets it contains
++ as long as they are given appropriate names.
++
++ However, loading a form at runtime incurs a runtime cost compared
++ to converting it to C++ code using the \l {User Interface Compiler (uic)}
++ tool.
++ */