Program crashes when i setCentral Widget

[ssoffel]

Can somebody please explain why this simple program crashes on the last line of code

 ui->plainTextEdit->setPlainText(text);

I create a pointer tEdit to an instance of QPlainTextEdit and set it as the central widget using in the constructor.
Then I get a file using QFileDialog and read the file to the textEditor. If I comment out (setCentralWidget(tEdit)) the program works fine. Can someone please explain why?

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
//    tEdit = new QPlainTextEdit(this);
//    setCentralWidget(tEdit);
}

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

void MainWindow::on_actionNew_triggered()
{
    QString filename = QFileDialog::getOpenFileName(this, "File Dialog", "C:/Users/Scott/MyFolder");
    QFile file(filename);
    if(!file.open(QFile::ReadOnly | QFile::Text))
    {
        QMessageBox::warning(this, "Message to User", "File could not open");
    }

    QTextStream in(&file);
    QString text = in.readAll();
    qDebug() << text;
    ui->plainTextEdit->setPlainText(text);
    file.close();
}

[VRonin]

Because when you set a new central widget, the old one (ui->plainTextEdit) gets deleted. either you use tEdit ->setPlainText(text); or leave ui->plainTextEdit as central widget

[ssoffel]

Ok makes a lot of sense, thanks!