Clearing Temporary Messages on Qt Status Bar with QStatusBar::clearMessage()

Purpose

• Removes any temporary message currently displayed on the status bar.

Context

• It can show two types of messages:
  • Temporary messages
    Short-lived messages that disappear after a certain time or when explicitly cleared.
  • Permanent messages
    Messages that remain visible until removed using other methods (like removeWidget()).
• QStatusBar is a widget used in Qt applications to display informative text messages at the bottom of the window.

Usage

• This function is typically used after the temporary message has served its purpose or when you want to clear the status bar for a new message.
• Call clearMessage() on a QStatusBar object to remove any temporary message that's currently being displayed.

Example

#include <QtWidgets>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QMainWindow window;
    QStatusBar *statusBar = window.statusBar();

    statusBar->showMessage("Loading..."); // Display a temporary message

    // Perform some operation (e.g., simulate loading)
    QThread::sleep(2); // Simulate a 2-second loading process

    statusBar->clearMessage(); // Clear the temporary message

    window.show();

    return app.exec();
}

Key Points

• It doesn't affect permanent messages or widgets added using addWidget() or addPermanentWidget().
• It's a member function of the QStatusBar class.
• clearMessage() has no arguments.

• If you want a temporary message to disappear automatically after a certain time, you can use a timer along with showMessage().
• You can combine clearMessage() with showMessage() to control the display of temporary messages dynamically.

---

Clearing a Temporary Message After User Interaction

#include <QtWidgets>

class MyWindow : public QWidget {
    Q_OBJECT

public:
    MyWindow(QWidget *parent = nullptr) : QWidget(parent) {
        statusBar = new QStatusBar(this);
        setStatusBar(statusBar);
    }

public slots:
    void onButtonClicked() {
        statusBar->showMessage("Button clicked!");

        // Clear the message after 1 second
        QTimer::singleShot(1000, this, SLOT(clearMessageAfterDelay()));
    }

private slots:
    void clearMessageAfterDelay() {
        statusBar->clearMessage();
    }

private:
    QStatusBar *statusBar;
};

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    MyWindow window;
    QPushButton button("Click Me");
    QObject::connect(&button, &QPushButton::clicked, &window, &MyWindow::onButtonClicked);

    window.resize(400, 300);
    window.show();

    return app.exec();
}

In this example, clicking the button displays a temporary message on the status bar. After a 1-second delay using QTimer::singleShot(), the message is cleared using clearMessage().

Clearing a Message Before Displaying a New One

#include <QtWidgets>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QMainWindow window;
    QStatusBar *statusBar = window.statusBar();

    statusBar->showMessage("Operation in progress...");

    // Perform some operation
    QThread::sleep(3);

    statusBar->clearMessage(); // Clear the old message
    statusBar->showMessage("Operation completed successfully!");

    window.show();

    return app.exec();
}

Here, the status bar displays "Operation in progress..." while an operation is running. After the operation finishes, clearMessage() is called to remove it, and a success message is displayed.

#include <QtWidgets>

class MyWindow : public QWidget {
    Q_OBJECT

public:
    MyWindow(QWidget *parent = nullptr) : QWidget(parent) {
        statusBar = new QStatusBar(this);
        setStatusBar(statusBar);

        // Add a permanent widget to the status bar
        QLabel *label = new QLabel("Ready");
        statusBar->addPermanentWidget(label);
    }

public slots:
    void onButtonClicked() {
        statusBar->showMessage("Temporary message");

        // Clear the temporary message without affecting the permanent widget
        QTimer::singleShot(2000, this, SLOT(clearMessageAfterDelay()));
    }

private slots:
    void clearMessageAfterDelay() {
        statusBar->clearMessage();
    }

private:
    QStatusBar *statusBar;
};

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    MyWindow window;
    QPushButton button("Show Temporary Message");
    QObject::connect(&button, &QPushButton::clicked, &window, &MyWindow::onButtonClicked);

    window.resize(400, 300);
    window.show();

    return app.exec();
}

---

Using showMessage() with a timeout

• If timeout is set to a positive value (in milliseconds), the message will automatically disappear after that time.
• Instead of clearing a temporary message later, you can specify a timeout when displaying it using the showMessage(const QString &message, int timeout = 0) overload of QStatusBar::showMessage().

statusBar->showMessage("Loading...", 2000); // Message disappears after 2 seconds

Replacing the Temporary Message

• The old message will be overwritten by the new one.
• If you don't need to explicitly clear the message but want to replace it with another one, you can simply call showMessage() again with the new message.

statusBar->showMessage("Operation in progress...");
// Perform some operation

statusBar->showMessage("Operation completed!");

Using a Timer with Custom Logic

• Inside the slot, you can implement the desired behavior for clearing, replacing, or updating the message based on your application logic.
• If you have more complex requirements for managing temporary messages, you can create a QTimer and connect its timeout() signal to a custom slot.

Choosing the Right Approach

• The best alternative depends on your specific needs:
  • If you simply want a temporary message to disappear after a set time, use showMessage() with a timeout.
  • If you want to replace the message with a new one immediately, use another showMessage() call.
  • For more complex scenarios, use a timer for custom control over the message display.

• QStatusBar::clearMessage() remains a valid option for situations where you need to explicitly remove a temporary message without relying on timers or automatic replacement.