Qt5 Tutorial QStatusBar - 2020

In this tutorial, we will learn about StatusBar.

The QStatusBar class provides a horizontal bar suitable for presenting status information.

Each status indicator falls into one of three categories:

1. Temporary - briefly occupies most of the status bar. Used to explain tool tip texts or menu entries.
2. Normal - occupies part of the status bar and may be hidden by temporary messages. Used to display the page and line number in a word processor.
3. Permanent - is never hidden. Used for important mode indications, for example, some applications put a Caps Lock indicator in the status bar.

Typically, a request for the status bar functionality occurs in relation to a QMainWindow object. QMainWindow provides a main application window, with a menu bar, tool bars, dock widgets and a status bar around a large central widget. The status bar can be retrieved using the QMainWindow::statusBar() function, and replaced using the QMainWindow::setStatusBar() function.

In this example, we'll start from MainWindow class.

We need to add menu actions.

In this example, we'll add just one menu (MyMenuAction) to trigger action.

void MainWindow::on_actionMyMenuAction_triggered()
{
    // showMessage(const QString & message, int timeout = 0)
    ui->statusBar->showMessage("Status");

    // When the action triggered, set the progress bar at 51%
    statusProgressBar->setValue(51);
}

The void QStatusBar::showMessage(const QString & message, int timeout = 0) hides the normal status indications and displays the given message for the specified number of milli-seconds (timeout). If timeout is 0 (default), the message remains displayed until the clearMessage() slot is called or until the showMessage() slot is called again to change the message.

To make the code above to work, the pointer for the ProgressBar should be set in mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QLabel>
#include <QProgressBar>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
    
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
    
private slots:
    void on_actionMyMenuAction_triggered();

private:
    Ui::MainWindow *ui;

    // add references to Label and ProgressBar
    QLabel *statusLabel;
    QProgressBar *statusProgressBar;
};

#endif // MAINWINDOW_H

Here is the implementation file, mainwindow.cpp:

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    // create objects for the label and progress bar
    statusLabel = new QLabel(this);
    statusProgressBar = new QProgressBar(this);

    // set text for the label
    statusLabel->setText("Status Label");

    // make progress bar text invisible
    statusProgressBar->setTextVisible(false);

    // add the two controls to the status bar
    ui->statusBar->addPermanentWidget(statusLabel);
    ui->statusBar->addPermanentWidget(statusProgressBar,1);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_actionMyMenuAction_triggered()
{
    // showMessage(const QString & message, int timeout = 0)
    ui->statusBar->showMessage("Status");
    statusProgressBar->setValue(51);
}

The void QStatusBar::addPermanentWidget(QWidget * widget, int stretch = 0) adds the given widget permanently to this status bar, reparenting the widget if it isn't already a child of this QStatusBar object. The stretch parameter is used to compute a suitable size for the given widget as the status bar grows and shrinks. The default stretch factor is 0, i.e giving the widget a minimum of space.

Permanently means that the widget may not be obscured by temporary messages. It is located at the far right of the status bar.

If we run the code, we get:

If we trigger the action:

This is the final output: