Our next example will add a new Push Button. When it is clicked, a built in dialog box will be displayed that allows the user to select a color. <\/p>\n\n\n
\n#include <QtCore>\n#include <QtGui>\n\nint main(int argc, char *argv[])\n{\n QApplication app(argc, argv);\n\n QWidget *mainWindow = new QWidget();\n mainWindow->setMinimumSize(700, 350);\n\n QPushButton *pb_1 = new QPushButton();\n pb_1->setText("Show Colors");\n\n QPushButton *pb_2 = new QPushButton();\n pb_2->setText("Close");\n\n QHBoxLayout *layout = new QHBoxLayout(mainWindow);\n layout->addStretch();\n layout->addWidget(pb_1);\n layout->addSpacing(10);\n layout->addWidget(pb_2);\n layout->addStretch();\n\n QObject::connect(pb_1, &QPushButton::clicked, \n pb_1, []() { QColorDialog::getColor(Qt::green); });\n\n QObject::connect(pb_2, &QPushButton::clicked,\n mainWindow, &QWidget::close);\n\n mainWindow->show();\n\n return app.exec();\n}\n<\/pre><\/div>\n\n\nLines 18 through 22 are expanded in this example to center the two push buttons in the window and add a spacing of 10 pixels between the buttons. If the user widens the application window the buttons will automatically stay relative to each other and centered on the screen. <\/p>\n\n\n\n
Lines 24 and 25 add a new Signal \/ Slot connection for push button 1. The fourth parameter uses a different syntax than the method pointer syntax for push button 2. Although this syntax looks a bit odd, the end result is to call the getColor() method in the QColorDialog class. <\/p>\n\n\n\n
The code shown below is a C++ lambda expression. The syntax requires a set of square brackets, parentheses, and then a block using curly braces. The source code in the curly braces is what will be invoked. <\/p>\n\n\n\n
[]() { QColorDialog::getColor(Qt::green); }<\/code><\/pre>\n\n\n\nThe following video contains more information about Lambda Expressions.
https:\/\/www.youtube.com\/watch?v=ZHw2XHij1is<\/a> <\/p>\n\n\n\nRunning the Example<\/h3>\n\n\n\n
To build and run this example use the same CMake build file and commands as we showed for the first example. The only suggested modification is on line 2 of the CMakeLists.txt file, change “example_1” to say “example_2”. <\/p>\n\n\n\n