03.2 function ‐ 02

Code:

const char* INTERNET_CHECK_URL = "https://snigdha-os.github.io/";  // URL used to verify internet connectivity by sending a network request.

SnigdhaOSBlackbox::SnigdhaOSBlackbox(QWidget *parent, QString state)
    : QMainWindow(parent)  // Calls the constructor of the QMainWindow base class to initialize the main window with the parent widget.
    , ui(new Ui::SnigdhaOSBlackbox)  // Initializes the user interface (UI) for the SnigdhaOSBlackbox window, using the UI class auto-generated by Qt Designer.
{
    // Sets the window icon to the specified file path, ensuring that the application window will display the given icon (SVG format).
    this->setWindowIcon(QIcon("/usr/share/pixmaps/snigdhaos-blackbox.svg"));

    // Initializes the user interface, setting up the UI components (buttons, labels, etc.) in the SnigdhaOSBlackbox window.
    ui->setupUi(this);

    // Modifies the window flags to disable the close button on the window (i.e., the application cannot be closed directly via the window).
    this->setWindowFlags(this->windowFlags() & -Qt::WindowCloseButtonHint);

    // Gets the last modified timestamp of the executable file (the current running application), which is useful for checking when the application was last updated.
    executable_modify_date = QFileInfo(QCoreApplication::applicationFilePath()).lastModified();

    // Updates the application state based on the provided `state` parameter.
    // This can be a state like "WELCOME", "INTERNET", etc., depending on the condition provided by the caller.
    updateState(state);
}

SnigdhaOSBlackbox::~SnigdhaOSBlackbox()
{
    // Frees the memory allocated for the user interface (UI) object.
    // The 'ui' pointer was allocated in the constructor, and it's responsible for managing the UI components of the SnigdhaOSBlackbox window.
    delete ui;
}

This code represents the constructor and destructor for the SnigdhaOSBlackbox class, which is part of a Qt application. The constructor initializes the UI, window properties, and other essential aspects of the application, while the destructor handles clean-up tasks. Let's break down each part of the code in detail.

1. const char* INTERNET_CHECK_URL = "https://snigdha-os.github.io/";

This line defines a constant pointer INTERNET_CHECK_URL, which points to a URL (https://snigdha-os.github.io/) that is used later in the application to check the availability of the internet. The URL is used in a network request to verify whether the system has an active internet connection by trying to reach the URL.

2. Constructor: SnigdhaOSBlackbox::SnigdhaOSBlackbox(QWidget *parent, QString state)

This is the constructor for the SnigdhaOSBlackbox class. It is called when an instance of SnigdhaOSBlackbox is created. Let's break it down:

• QWidget *parent: This parameter specifies the parent widget for the main window. A QWidget in Qt is the base class for all UI elements. This parameter allows you to specify which widget the SnigdhaOSBlackbox window will be a child of. If nullptr is passed, it means the window will be a top-level window with no parent.

• QString state: This parameter indicates the initial state of the application. The state could be something like "WELCOME", "INTERNET", etc., which is used to set the initial behavior of the window (like determining if the app is online or offline).

• Initialization List:

  • QMainWindow(parent): The constructor of the base class QMainWindow is called with parent passed as an argument. QMainWindow is the standard Qt widget for main application windows, and this call ensures that the parent-child relationship is properly established.

  • ui(new Ui::SnigdhaOSBlackbox): This initializes the ui pointer. Ui::SnigdhaOSBlackbox is an auto-generated class (from Qt Designer) that defines the user interface for the window, including all UI components like buttons, labels, and other widgets. This line allocates memory for the ui object, which is responsible for setting up the UI in the window.

3. this->setWindowIcon(QIcon("/usr/share/pixmaps/snigdhaos-blackbox.svg"));

• This line sets the icon of the application window. setWindowIcon is a Qt method that allows you to set an icon that will be displayed in the window's title bar, as well as in the taskbar (or dock on macOS).
• QIcon("/usr/share/pixmaps/snigdhaos-blackbox.svg") creates an QIcon object with the specified file path (/usr/share/pixmaps/snigdhaos-blackbox.svg). The .svg file is an SVG (Scalable Vector Graphics) format icon, which is resolution-independent and suitable for modern UIs.

4. ui->setupUi(this);

• This line initializes the UI by calling the setupUi() method on the ui object.
• setupUi(this) is a method generated by Qt Designer that sets up all UI components (buttons, labels, text fields, etc.) defined in the .ui file for the SnigdhaOSBlackbox window. It ensures that all the UI elements are correctly placed and connected to the window.

5. this->setWindowFlags(this->windowFlags() & -Qt::WindowCloseButtonHint);

• This line modifies the window flags to disable the close button on the window. windowFlags() retrieves the current flags for the window (such as the ability to minimize, maximize, close, etc.).

• & -Qt::WindowCloseButtonHint: This bitwise operation removes the close button hint from the window's flags, effectively disabling the close button on the window. The window will still be resizable and movable, but the close button will not be visible.

6. executable_modify_date = QFileInfo(QCoreApplication::applicationFilePath()).lastModified();

• QFileInfo is used to retrieve metadata about files. In this line, the QCoreApplication::applicationFilePath() method returns the path of the current executable file.
• lastModified() retrieves the last modified timestamp of the executable file. This timestamp is stored in the executable_modify_date variable.
  • This could be useful for checking whether the application has been updated or if certain actions need to be taken when the application was last modified (e.g., checking for updates).

7. updateState(state);

• This function call updates the application's state based on the state parameter provided during object construction.
• The state could represent different conditions or modes in the application (like "WELCOME", "INTERNET", "UPDATE", etc.).
• The updateState() method would likely handle changing the UI or triggering specific actions depending on the passed state. For example, if the state is "INTERNET", the app might check for internet connectivity.

8. Destructor: SnigdhaOSBlackbox::~SnigdhaOSBlackbox()

The destructor is called when the SnigdhaOSBlackbox object is destroyed. The purpose of the destructor is to clean up resources that were allocated during the lifetime of the object.

• delete ui;: This line deletes the ui object, which was dynamically allocated in the constructor with new Ui::SnigdhaOSBlackbox. Since ui is responsible for the UI components (buttons, labels, etc.), calling delete ensures that all the memory allocated for the UI is properly freed when the object is destroyed.

Summary

• The constructor sets up the application window's icon, user interface, and the initial state, while also disabling the close button and retrieving the last modified timestamp of the executable file.
• The destructor ensures that any dynamically allocated memory (like the UI object) is cleaned up when the window is closed.

This constructor and destructor play a crucial role in initializing the window and ensuring that resources are managed effectively throughout the application’s lifecycle.