Incompatibility between the IDE and the book I read to learn Qt5

SGaist

Hi,

lineEdit is not initialized nor is okButton and on_LineEdit_TextChanged uses the format for automatic connection used by the widgets built with designer. The error message means that your Designer based UI doesn't contain any QLineEdit matching the name LineEdit.

eureka

I've been working through this tutorial .. I note that you have misnamed "cancelButton" to "cancleButton" in Qt Creator screenshot.

Ni.Sumi

Hi @tomy
Rename your slot (//on_LineEdit_TextChanged()//), it works.

This is because, when you create setupUI() function, which was created at the time of Dialog/window using QtDesinger. And it does the search function/slot basing on name like "on_widgetName_eventNaeme()" . But if you make some own slot/function similar like this starting with" on_" prefix like what you did in your case "on_LineEdit_TextChanged()" ,which is not related directly to widgetname with valid event name, connect() fails.

So when you make own connection or slot, you shouldn't USE the "on_" prefix for the slot's name (to avoid confusion)because connectSlotsByName is also called at the end of setupUi which would again throw the warning/error that there is nNo matching signal for on_LineEdit_TextChanged()/slot.

tomy

Hi SGaist, thanks for your explanation.

lineEdit is not initialized nor is okButton

But I used them and even changed their properties in the design mode!

and on_LineEdit_TextChanged uses the format for automatic connection used by the widgets built with designer.

I don't exactly know what "the format for automatic connection" means but I think you meant, since I haven't initialize, say, the lineEdit (this way:lineEdit = new QLineEdit;), so the program uses the one I made with the designer. If so, OK, this is what I want. That is, I want the works I have done on the designer mode to be used not useless.

The error message means that your Designer based UI doesn't contain any QLineEdit matching the name LineEdit.

Why should it match the name LineEdit please?
I haven't used the name LineEdit in my codes. I've used lineEdit which exists in designer form. If you meant that I have used LineEdit in theon_LineEdit_TextChanged()function/slot, according to my experience on C++, the names of the user defined functions has nothing to do with the works they do.

PS: I even changed the name of that slot to on_lineEdit_TextChanged(). The same result.

@eureka said:

I've been working through this tutorial .. I note that you have misnamed "cancelButton" to "cancleButton" in Qt Creator screenshot.

I corrected it, thanks. :-)

@Ni.Sumi said:

Hi @tomy
Rename your slot (//on_LineEdit_TextChanged()//), it works.

Thank you for your explanations. I tried to understand them.
Please read my comment on the name of functions/slots above. And that, I even changed the name of that slot.

SGaist

So lineEdit belongs to the UI created with Designer, you should access it using ui->lineEdit. What you are currently using is a raw pointer pointing to nothing.

The automatic connection and function naming scheme has nothing to do with core C++ principles. You should take a look at the Designer manual. Things like automatic connection and how it works is explained there (what @Ni-Sumi already wrote with a bit more practical examples)

JordanHarris

There are some great guides on what's new in Qt5 and how to transition to Qt5. I suggest finding those and reading them over. There's really not too much you need to know. The most important thing to do first IMO is to learn the newer Signal and Slot syntax. I find it to be much more powerful than the old way, plus it's much more efficient. You should make a habit of replacing the old Signal and Slot code with the new style. Here is a guide for transitioning from Qt4 to Qt5. You should get the hang of it after a while. I managed to do so using the resources available to me. It's not ideal to learn an older framework and adapt it to the newer one, but that's just what you'll have to do for now. Luckily, there's all kinds of resources (like examples and tutorials) all over the Web using Qt5, so it's not too hard to pick it up. Good luck on your Qt journey. I've only been using it for a few months and I've grown to like it more than any other framework. It starts to grow on you and things just start making sense. It's so consistent that you'll be using classes without ever reading the documentation.

tomy

@SGaist said:

So lineEdit belongs to the UI created with Designer, you should access it using ui->lineEdit. What you are currently using is a raw pointer pointing to nothing.

The automatic connection and function naming scheme has nothing to do with core C++ principles. You should take a look at the Designer manual. Things like automatic connection and how it works is explained there (what @Ni-Sumi already wrote with a bit more practical examples)

I found this in Designer manual which seems to be fine and useful (especially for a beginner), but, and just as usual, there are imperfect parts in it!
I was precisely reading the explanations until arrived at the Calculator Form point. But neither there nor in Calculator Form's page, the explanations are complete!

For example, please look at the that Calculator Form's page:

It doesn't specify what type of the forms I need to create using the Qt creator!
(I guess I should create one from File -> New File or Project -> Qt -> Qt Designer Form -> Widget)
In the next part, it says:
"To ensure that the example can use this file, we need to include a FORMS declaration in the example's project file:
FORMS = calculatorform.ui"

I think it means that I should type the above statement inside a project file (here, the calculatorform .pro). But creating a form using the way I mentioned just create a .ui file, "form.ui", and not any other file (for example, a .pro file)!

Seemingly, if I can create such a .pro file and put that statement into it, I should do some action (building it using the Build button), so that the program will produce a header file, then, for proceeding the track.

kshegunov

@JordanHarris
Hello,

The most important thing to do first IMO is to learn the newer Signal and Slot syntax. I find it to be much more powerful than the old way, plus it's much more efficient.

Indeed, this:

connect(mySpinBox, static_cast<void (QSpinBox::*)(int)>(&QSpinBox::valueChanged), mySlider, &QSlider::setValue);

instead of this:

connect(mySpinBox, SIGNAL(valueChanged(int)), mySlider, SLOT(setValue(int));

is really simpler and much more beautiful ...

Regarding efficiency, well that point is simply moot. Quite irrelevant, if I may add, unless you can prove that the bottelneck for an application are the signal-slot invocations, which I don't believe you can.

Kind regards.

tomy

If I can, I state my opinion upon the other subjects later. But what is important for me at this point is to move forward along the Qt's path. Please read my previous post. You all have experienced these cases and are able to cube with them.
If possible, please guide me on what are questions for me.

kshegunov

@tomy
Right, sorry for the sarcasm put and the somewhat off-topic-ish comment, as it doesn't really relate to your question. I don't really auto-connect my signals and slots and I believe it to be a terrible idea in the first place. This tutorial seems somewhat useful. Taking it from the top:

The .pro file is the definition of your project encapsulating the names of the source files to be compiled, the headers, the resources, forms, linker flags and compiler flags and other Qt (and non-Qt) related stuff. The file is needed by qmake, which will read the file and retranslate it into a makefile that the compiler can use to build your project.
The .ui file is an XML file that is created by the designer (integrated into QtCreator) and which contains the definitions of your forms. When qmake is preparing your project for building, it will run uic (the user interface compiler) to read the form and create a form header that you can include in your source to access the form.

Suppose you have a form that is for a widget (it's pretty much the same for a dialog or a main window).
Designer view

The user interface compiler will create the file "ui_moduletoolboxpage.h" from the "moduletoolboxpage.ui" file. This header contains:

/********************************************************************************
** Form generated from reading UI file 'moduletoolboxpage.ui'
**
** Created by: Qt User Interface Compiler version 5.3.0
**
** WARNING! All changes made in this file will be lost when recompiling UI file!
********************************************************************************/

#ifndef UI_MODULETOOLBOXPAGE_H
#define UI_MODULETOOLBOXPAGE_H

#include <QtCore/QVariant>
#include <QtWidgets/QAction>
#include <QtWidgets/QApplication>
#include <QtWidgets/QButtonGroup>
#include <QtWidgets/QHeaderView>
#include <QtWidgets/QVBoxLayout>
#include <QtWidgets/QWidget>

QT_BEGIN_NAMESPACE

class Ui_ModuleToolboxPage
{
public:
    QVBoxLayout *verticalLayout;

    void setupUi(QWidget *ModuleToolboxPage)
    {
        if (ModuleToolboxPage->objectName().isEmpty())
            ModuleToolboxPage->setObjectName(QStringLiteral("ModuleToolboxPage"));
        ModuleToolboxPage->resize(719, 384);
        verticalLayout = new QVBoxLayout(ModuleToolboxPage);
        verticalLayout->setObjectName(QStringLiteral("verticalLayout"));

        retranslateUi(ModuleToolboxPage);

        QMetaObject::connectSlotsByName(ModuleToolboxPage);
    } // setupUi

    void retranslateUi(QWidget *ModuleToolboxPage)
    {
        ModuleToolboxPage->setWindowTitle(QApplication::translate("ModuleToolboxPage", "Form", 0));
    } // retranslateUi

};

namespace Ui {
    class ModuleToolboxPage: public Ui_ModuleToolboxPage {};
} // namespace Ui

QT_END_NAMESPACE

#endif // UI_MODULETOOLBOXPAGE_H

The class name comes from the object name: class Ui_ModuleToolboxPage is named after the root object, which in my case (see the picture) is named ModuleToolboxPage. And this line:

QMetaObject::connectSlotsByName(ModuleToolboxPage);

connects slots automatically depending on the slot's name.

To use that form, you include this generated header (remember, it's generated automatically from qmake/uic when the form file is registered in the project file like this: FORM += moduletoolboxpage.ui, and this is done automatically as well when you create it in QtCreator). So suppose I have a dialog I want to initialize with this form, I'd do something like this:

#include "ui_moduletoolboxpage.h"  //< Note that you're including the generated header

class MyDialog : public QDialog
{
    Q_OBJECT

public:
    MyDialog(QWidget * parent = NULL);

private:
    Ui::ModuleToolboxPage ui; //< This is the object that represents the form created in the designer
}

MyDialog::MyDialog(QWidget * parent)
    : QDialog(parent)
{
    ui.setupUi(this);  //< This line creates all the objects described in the form and attaches them to my dialog. It initializes my dialog with my form
}

Well this got a bit out of hand with all the code and the image, but I hope it's helpful.

Kind regards.

tomy

Thank you very much for you comprehensive reply.

Before doing them, are those tutorials applicable on my Qt Creator 3.6.0?
What is I face incompatibilities between them?

As you may know, I'm reading the book C++ GUI Programming With Qt 4 2nd Edition but since that book was confusing me I had to get helps here in forums.
Do you suggest that I finish these tuts and then get back to the book?

kshegunov

@tomy
Hello,

Before doing them, are those tutorials applicable on my Qt Creator 3.6.0?

I don't see a reason why they wouldn't be. The screenshot and the generated header I've taken from my own project, and I'm using QtCreator 3.6, so they're very up to date.

Do you suggest that I finish these tuts and then get back to the book?

No, I've sourced them as "further reading" that should help you with your book and your projects.

Kind regards.

tomy

Hello dear kshegunov and thanks for your talks.

I appreciate your suggestions and I will certainly try to do them in near future, but what I need now is something else.

Please read my above post (the one that I've bookmarked it) and try to answer my questions there.
After that part and the other, I understand some main topics and then continue to reading my book and also I do the tuts you helped me by introducing them.
Thanks again.

koahnig

@tomy
You might be the only one seeing the bookmark, AFAIK it is local.
Therefore probably nobody is going find and answer your specific question.

Even though it is not strongly encouraged in this forum, I suggest that you are starting a new thread with a title already giving an understanding of your problems.