QListWidget itemActivated signal example

mainwindow.cpp

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

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

    QObject::connect(ui->listWidget, SIGNAL(itemActivated(QListWidgetItem*)),
                     this, SLOT(changeLabelText(QListWidgetItem*)));
}

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

void MainWindow::changeLabelText(QListWidgetItem * item)
{
    ui->label->setText(item->text());
}