Connection between classes.

Xilit

Hi guys! I almost finish my project and there is only one thing to do.

So there is the problem.

I have two classes: editBook and mainWindow. When user in form edit some book's information and press the button on_btnEditBook_clicked() then signal emitted with info that user made:

editbook.h

signals:
    void sigEditedBookInfoByUser(QVector<QString>&EditedBookInfoByUserToDB);

editbook.cpp

void EditBook::on_btnEditBook_clicked()
{
    //Here I create vector with user's info
    // ... code

    QVector<QString>editedBookInfoByUser;

    // ... code
    
    // And here is the signal that I want to "catch" in mainWindow:
    emit sigEditedBookInfoByUser(editedBookInfoByUser);
}

And here is mainWindow class.

mainWindow.h

private slots:
void getEditedBookInfoByUserToDB(QVector<QString>&EditedBookInfoByUserToDB);

private:
    Ui::MainWindow *ui;
   /* this is reference that I use in my Windows class when I create edit-book-window  (and this is the reference that I use when I create connect()). */
    EditBook *editBook;

mainWindow.cpp
Constructor

    connect(&editBook, SIGNAL(EditBook::sigEditedBookInfoByUser(QVector<QString>&)), this, SLOT(getEditedBookInfoByUserToDB(QVector<QString>&)));

And realization of slot:

void MainWindow::getEditedBookInfoByUserToDB(QVector<QString> &EditedBookInfoByUserToDB)
{
    /* Here I want to "catch" my QVector with Info from user.*/
}

So I have errors when I try to run my program. How can I correctly connect this two slots?

KroMignon

@Xilit said in Connection between classes.:

connect(&editBook, SIGNAL(EditBook::sigEditedBookInfoByUser(QVector<QString>&)), this, SLOT(getEditedBookInfoByUserToDB(QVector<QString>&)));

As far as I can read from code extract, editBook is already a pointer, so right statement is, I guess:
connect(editBook, &EditBook::sigEditedBookInfoByUser, this, &MainWindow::getEditedBookInfoByUserToDB);

I prefere new connect() syntax to SIGNAL() / SLOT(), because it is checked at compilation time. This eliminate most of the common errors (invalid syntax, invalid signal or slot name).

Xilit

@KroMignon

Hmmm. The program compile now and immediatly crashes.

In application output:

18:54:30: Starting E:\Qt\build-BooksCatalogDBSqlite-Desktop_Qt_5_13_1_MinGW_64_bit-Debug\debug\BooksCatalogDBSqlite.exe ...

ASSERT: "c->sender == q_ptr" in file kernel\qobject.cpp, line 391

18:54:33: The program has unexpectedly finished.

18:54:33: The process was ended forcefully.

18:54:33: E:/Qt/build-BooksCatalogDBSqlite-Desktop_Qt_5_13_1_MinGW_64_bit-Debug/debug/BooksCatalogDBSqlite.exe crashed.

What can it be?

KroMignon

@Xilit Stupid question, but have you initialized editBook? (e.g. editBook = new EditBook();) Of course, before the connect() statement!

Xilit

@KroMignon

I change my code to this:

EditBook *editInfoFromUser;
connect(editInfoFromUser, &EditBook::sigEditedBookInfoByUser, this, &MainWindow::getEditedBookInfoByUserToDB);

I compile correctly, but in my getEditedBookInfoByUserToDB() function I didn't get any vector array.

I emulate function work:

void MainWindow::getEditedBookInfoByUserToDB(QVector<QString> &EditedBookInfoByUserToDB)
{
    QString title = EditedBookInfoByUserToDB[0];
    QMessageBox::information(this,"Test",title);
}

After I press edit-button programm don't show any QMessageBox with info from array. It just crashes.

KroMignon

@Xilit said in Connection between classes.:

EditBook *editInfoFromUser;
connect(editInfoFromUser, &EditBook::sigEditedBookInfoByUser, this, &MainWindow::getEditedBookInfoByUserToDB)

This NOT correct.
You have declared a dangling/uninitialized pointer!!

auto *editInfoFromUser = new EditBook ();
connect(editInfoFromUser, &EditBook::sigEditedBookInfoByUser, this, &MainWindow::getEditedBookInfoByUserToDB);

This is correct and will work!

Xilit

@KroMignon

Thank you, I change it!

But situation the same - after I press edit-button programm crashes.

The good new I guess I understand where the problem is.

Actually I've already opened the editWindow from mainWindow, and now I need to return info back to mainWindow.

So the scheme:

In mainWindow user press button "Edit book" -> editWindow opens ->user make edits and press button "Edit" -> Vector with info comes back to mainWindow.

So in mainWindow I've already have pointer to editBook class in order to open editWindow from mainWindow.

mainWindow.h

private:
Ui::MainWindow *ui;
EditBook *editBook;

mainWindow.cpp
This is button in mainWindow to open editWindow:

void MainWindow::on_btnEditBook_clicked()
{
   //code
    editBook->editBookInfo(editBookInfoVector);
    editBook->show();
}

So as you can see I've already opened editWindow, so I don't need to create new one by doing this:

auto *editInfoFromUser = new EditBook ();

Because it opens a new window without any information, and I want to get info back from already opened editWindow from mainWindow.

So haw can I do my connect() correctly?

Xilit

Thank you guys, I soleve my problem. Finally!

If it's interesting or maybe usefull to anyone, proble was in incorrect place of connect(). I move it to void MainWindow::on_btnEditBook_clicked(){} from I called to editWindow and it is working! Finally I understand how SnS works.:)

Thank you!

Pablo J. Rogina

@Xilit said in Connection between classes.:

I soleve my problem

So please mark your post as such! Thanks

Xilit

@Pablo-J-Rogina

Sure.:)