Qt connect signals and slots of different windows/ mirror a lineEdit text on two windows-CodePudding

I'm new to any form of programming but have to do a project with Qt for my "programming for engineers" course where we simultaneously learn the basics of c .

I have to display a text from one lineEdit to a lineEdit in another window.

I have a userWindow that opens from the mainWindow and in this userWindow I have a lineEdit widget that displays the current selected user as a QString (from a QDir object with .dirName() ). But now I have to display the same String in a lineEdit in the mainWindow as well.

From what I've read I have to do this with "connect(...)" which I have done before with widgets inside a single .cpp file but now I need to connect a ui object and signal from one window to another and I'm struggling.

My idea /what I could find in the internet was this:

userWindow.cpp

#include "userwindow.h"
#include "ui_userwindow.h"
#include "mainwindow.h"
#include <QDir>
#include <QMessageBox>
#include <QFileDialog>
#include <QFileInfo>


QDir workingUser; //this is the current selected user. I tried defining it in userWindow.h but that wouldn't work how I needed it to but that's a different issue

userWindow::userWindow(QWidget *parent) :               //konstruktor
    QDialog(parent),
    ui(new Ui::userWindow)
{
    ui->setupUi(this);
    QObject::connect(ui->outLineEdit, SIGNAL(textChanged()), mainWindow, SLOT(changeText(workingUser) //I get the error " 'mainWIndow' does not refer to a value "
}

[...]

mainWindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QDir>
#include <QMainWindow>


QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();


public slots:
    void changeText(QDir user);   //this is the declaration of my custom SLOT (so the relevant bit)

private slots:
    void on_userButton_clicked();

    void on_settingsButton_clicked();

private:
    Ui::MainWindow *ui;

};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "userwindow.h"
#include "settingswindow.h"
#include "click_test_target.h"
#include "random_number_generator.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
   [...]
}
[...]
//here I define the slot
void MainWindow::changeText(QDir user)
{
    QString current = user.dirName();

    ui->userLine->insert("The current working directory is: ");    //"userLine" is the lineEdit I want to write the text to
    ui->userLine->insert(current);
}

I know I'm doing something wrong with the object for the SLOT but can't figure out how to do it correctly.

If anyone could help me I would be very grateful.

Alternatively: perhaps there is another way to mirror the text from one lineEdit to another over multiple windows. If anybody could share a way to do this I would be equally grateful. Is there maybe a way to somehow define the variable "QDir workingUser;" in such a way as to be able to access and overwrite it in all of my .cpp files?

Thank you in advance for any help. Regards,

Alexander M.

CodePudding user response：

"I get the error " 'mainWindow' does not refer to a value"

I don't see you having any "mainWindow" named variable anywhere, but you also mentioned that the MainWindow is the parent, which means you could get reference anytime, like:

MainWindow *mainWindow = qobject_cast<MainWindow *>(this->parent());

Also, your signal-handler (changeText(...) slot) should take QString as parameter (instead of QDir), this way you handle how exactly the conversion is handled, in case users type some random text in input-field (text-edit).

CodePudding user response：

You can create new signal (same params as lineEdit's textChanged) to userWindow which is connected to the textChanged signal of the lineEdit. Then connect that signal userWindow to mainWindow's slot.

//In userWindow.h
signals:
    void textChanged(const QString&);

//In userWindow.cpp
connect(ui.lineEdit, &QLineEdit::textChanged, this, &userWindow::textChanged);

//In mainWindow.cpp
connect(userWindow, &userWindow::textChanged, this, &mainWindow::onTextChanged

Then in onTextChanged write the same text to mainWindow's lineEdit