如何在Qt窗口小部件项目（Qt Creator）中更新图形视图

Question

I have created a Qt Widgets Application using Qt Creator(Windows 7, MinGW).

I have added a GraphicsView (named as graphicsView ) and a push button (named as pbClick ).

The on_pbClick_clicked() function is given below:

void MainWindow::on_pbClick_clicked()
{
    QGraphicsScene scene;
    //adding some text to the scene
    scene.addText("Hello, world!", QFont("Times", 20, QFont::Bold));
    ui->graphicsView->setScene(&scene);
    ui->graphicsView->show();
}

When I click the pbClick button, nothing happens within the graphicsView .

How can I make the "Hello, world!" text be shown inside the graphicsView .

Answer 1

You create your scene on stack, it is a problem, try to create it on heap (use pointers) in this case if there are not any mistakes, all should works fine. As doc said:

The view does not take ownership of scene.

http://qt-project.org/doc/qt-5/qgraphicsview.html#setScene

It means that when you create scene on stack, this scene will be deleted "in the end" of on_pbClick_clicked slot. So your scene does not exist anymore, and you can't see nothing.

    QGraphicsScene *scene = new QGraphicsScene;
    //adding some text to the scene
    scene->addText("Hello, world!", QFont("Times", 20, QFont::Bold));
    ui->graphicsView->setScene(scene);
    ui->graphicsView->show();