Bogus widget in Qt Creator - qt

Question

I'm a Qt newbie, working in Qt Creator 3.1.2 (Ubuntu Linux), Qt 5.3.1.
My program has a form with a button (pushButton) which changes the value of a text field (plainTextEdit) on being pressed. Both pushButton and plainTextEdit have been added in graphical mode. Connection between the button and its slot (on_pushButton_clicked()) has been set up via the graphical interface too.
The problem is, the program produces a bogus plainTextEdit, i.e. a different one, in the upper left corner, where the output goes to, while the "main" one stays clean. The question hence is, how I can avoid it? In general, how should I connect graphical widgets and their counterparts in the code? Here is my program:
mainwindow.h:
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QPushButton>
#include <QPlainTextEdit>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
public slots:
void on_pushButton_clicked();
private:
Ui::MainWindow *ui;
QPushButton *pushButton;
QPlainTextEdit *plainTextEdit;
};
#endif // MAINWINDOW_H
main.cpp:
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
mainwindow.cpp:
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
plainTextEdit = new QPlainTextEdit(this);
// whenever I remove the previous line, I get SIGSEGV
setWindowTitle(tr("My test app..."));
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_pushButton_clicked()
{
plainTextEdit->setPlainText("Some text here");
}

Answer 1

It's the widget you're creating in your constructor that is "bogus". The widgets you created in the forms editor belong to the Ui::MainWindow, you must not re-create them in your main window.
Remove this from your MainWindow:
QPushButton *pushButton;
QPlainTextEdit *plainTextEdit;
Remove the widget creation from the constructor:
plainTextEdit = new QPlainTextEdit(this);
Change your on_pushButtonClicked member to:
ui->plainTextEdit->setPlainText("Some text here");