My first program in QT

dbzhang800 · wrote on 18 May 2012, 17:19

[quote author="p3aul" date="1337358650"]

[1] Shouldn't QT have taken care of the declaration itself?
[2] If not, where would i have to declare lineEdit and would I also have to declare the pushbutton also?
[/quote]

You can always try to understand the code using your C++ knowledge.

For a Normal C++ application:

Source files:

*.cpp
*.h
can be compiled by your C++ compiler, then linked by your linker.

While a Normal Qt application:

Source files:

x.cpp
x.h
x.h [Contains Q_OBJECT] ==> moc_x.cpp (generated by moc)
x.ui ==> ui_x.h (generated by uic)
x.rcc ==> qrc_x.cpp (generated by rcc)

Then all you get is normal *.cpp and .h files now.

All the *.cpp and *.h files can be compiled by your C++ compiler, then linked by your linker.

dbzhang800 · wrote on 18 May 2012, 17:25

If you are used to C++ builder and Delphi, you can easily solve such issues, do you?

Perhaps you copid some code from network which contains invalid C/C++ characters.
[quote author="p3aul" date="1337361431"]Whew! I got a bunch of errors that time! Here they are:
@/home/owner/qt/first-build-desktop-Desktop_Qt_4_8_1_for_GCC__Qt_SDK__Release/../first/mainwindow.cpp:18: error: stray '\342' in program

/home/owner/qt/first-build-desktop-Desktop_Qt_4_8_1_for_GCC__Qt_SDK__Release/../first/mainwindow.cpp:18: error: stray '\200' in program

/home/owner/qt/first-build-desktop-Desktop_Qt_4_8_1_for_GCC__Qt_SDK__Release/../first/mainwindow.cpp:18: error: stray '\234' in program

/home/owner/qt/first-build-desktop-Desktop_Qt_4_8_1_for_GCC__Qt_SDK__Release/../first/mainwindow.cpp:18: error: stray '\342' in program

/home/owner/qt/first-build-desktop-Desktop_Qt_4_8_1_for_GCC__Qt_SDK__Release/../first/mainwindow.cpp:18: error: stray '\200' in program

/home/owner/qt/first-build-desktop-Desktop_Qt_4_8_1_for_GCC__Qt_SDK__Release/../first/mainwindow.cpp:18: error: stray '\235' in program

And last but not least:

/home/owner/qt/first-build-desktop-Desktop_Qt_4_8_1_for_GCC__Qt_SDK__Release/../first/mainwindow.cpp:-1: In member function 'void MainWindow::on_pushButton_clicked()':
/home/owner/qt/first-build-desktop-Desktop_Qt_4_8_1_for_GCC__Qt_SDK__Release/../first/mainwindow.cpp:18: error: 'Hello' was not declared in this scope@

I think I know why you added the ui: to reference the form?[/quote]

p3aul · wrote on 18 May 2012, 17:57

I just don't understand all this. My C++ builder coding was years ago. but I could do a simple app like this in under a minute. All I had to do was double-click the button, write that code snippet between the {} symbols and choose build project. compile and the choose run. It was that simple.
This is as simple as it gets. one label one pushbutton. why can't I set the property with lineEdit->setText("Hello")? is this even the right syntax?

dbzhang800 · wrote on 18 May 2012, 18:33

[quote author="p3aul" date="1337363837"]
why can't I set the property with lineEdit->setText("Hello")? is this even the right syntax?
[/quote]

As I said before, you can always try to understand the code using your C++ knowledge as this is normal C++ code and there is no magic.

Whether you can use "lineEdit" depends in which way you defined the variable.

Is a global variable
Is a class member variable
Is a member variable inherited from the parent class.
Is a local variable
...

If you find it's hard to understand, maybe a C++ book will be useful for you.

Debao

p3aul · wrote on 18 May 2012, 23:32

From what you said, I guess you know the answer, but for your own reasons don't wish to reveal it. I see by observing parts of code in more complicated examples that my syntax is correct. Unfortunately, QT is not standard C++. If it was there wouldn't be this foolishness of Slots and Signals instead they would use Methods and Events as in standard C++. . I'm either going to have to get some answers either by waiting and hoping someone else will pitch in and help me or by creating another thread. I asked a simple question. Why can't I get a simple, complete answer. Is knowledge of QT hoarded and only given out bit by bit? I have a book by the way. It's just not a book on QT
Thanks,
Paul

Wilk · wrote on 19 May 2012, 00:23

Hello.
The first, Qt instead of QT.
The second, I guess you should read something about Qt. It's not the same as C++ builder.
About your last problems: could you, please, post all code if mainwindow.cpp?

dbzhang800 · wrote on 19 May 2012, 01:13

[quote author="p3aul" date="1337383959"]From what you said, I guess you know the answer, but for your own reasons don't wish to reveal it. I see by observing parts of code in more complicated examples that my syntax is correct.
Paul[/quote]
Sorry.

And Sorry for my poor English.

As C++ builder is a IDE of C++, and you said that you used to C++ builder, so I wrongly thought that you will be very familiar with C++, but seems you not.

Qt is a library of C++, it isn't a good idea to deep into the Qt world before familiar with C++. Perhaps “C++ Primer” is a good book to start with.

bq. Unfortunately, QT is not standard C++. If it was there wouldn’t be this foolishness of Slots and Signals instead they would use Methods and Events as in standard C++.

It depends.

All the “non-standard” sources will be pre-processed by moc, uic, rcc, and then all you get are C++ “standard” files.

No matter what happened, your Qt application will be compiled by a “standard” C++ compiler such as GCC, MSVC, Intel-C++, Clang, ..., even C++ builder.

p3aul · wrote on 19 May 2012, 01:16

Main Window .cpp
@#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}

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

void MainWindow::on_pushButton_clicked()
{
lineEdit->setText("Hello");
}
@

Errors:
/home/owner/qt/newattempt-build-desktop-Desktop_Qt_4_8_1_for_GCC__Qt_SDK__Release/../newattempt/mainwindow.cpp:-1: In member function 'void MainWindow::on_pushButton_clicked()':
/home/owner/qt/newattempt-build-desktop-Desktop_Qt_4_8_1_for_GCC__Qt_SDK__Release/../newattempt/mainwindow.cpp:18: error: 'lineEdit' was not declared in this scope

This error about lineEdit seems to indicate that I need to declare it somewhere in mainwindow.cpp I don't know if this just the tip of the iceberg though. Once that is corrected others may show up. :(

Wilk · wrote on 19 May 2012, 01:22

Well, the simpliest solution is to declare a signal like sendText (QString) and connecting it with slot of your QLineEdit like setText, and then emit it in your on_pushButton_clicked () slot.

p3aul · wrote on 19 May 2012, 01:22

Robot Herder: I have an excellent book that came with C++ builder version 3. The syntax is correct. In Builder I didn't need to add declarations of Components(Widgets) because Builder added them automatically.

dbzhang800 · wrote on 19 May 2012, 01:26

[quote author="Wilk" date="1337390529"]Well, the simpliest solution is to declare a signal like sendText (QString) and connecting it with slot of your QLineEdit like setText, and then emit it in your on_pushButton_clicked () slot.[/quote]
It's an answer, but not the simpliest ;-) .

The right answer have been given by VanDerSam. And I try to given reasons, but failed ;-(

dbzhang800 · wrote on 19 May 2012, 01:32

[quote author="p3aul" date="1337390576"]Robot Herder: I have an excellent book that came with C++ builder version 3. The syntax is correct. In Builder I didn't need to add declarations of Components(Widgets) because Builder added them automatically.[/quote]

If I am right, you never try to see the code behind the drag and drop operation when using C++ builder.

p3aul · wrote on 19 May 2012, 01:32

Wilk:
@Well, the simpliest solution is to declare a signal like sendText (QString) and connecting it with slot of your QLineEdit like setText, and then emit it in your on_pushButton_clicked () slot.@
That's a perfect example of what I'm talking about. What you wrote is NOT C++ it's Qt! I need a book on Qt, not C++!

If that's the simplest solution than I need to go back to windows and CodeGear or Visual C++

Wilk · wrote on 19 May 2012, 01:36

The fact is that VanDerSam's solution makes your program dependent on UI and actual names of it's components, while you can change UI itself and/or it elements and/or names of UI elements. While my solution makes your application dependent only on interface of class.

p3aul · wrote on 19 May 2012, 01:38

Robot Hearder:
@If I am right, you never try to see the code behind the drag and drop operation when using C++ builder.@

Well yes, except for the code snippets you write your self. Let's face it, I'm no purist! I just want to get the job done, and Qt, like C++ builder is a RAD tool. Otherwise you would all just use a text editor and code it all for the fun of it.

Wilk · wrote on 19 May 2012, 01:41

[quote author="p3aul" date="1337391158"]Wilk:
@Well, the simpliest solution is to declare a signal like sendText (QString) and connecting it with slot of your QLineEdit like setText, and then emit it in your on_pushButton_clicked () slot.@
That's a perfect example of what I'm talking about. What you wrote is NOT C++ it's Qt! I need a book on Qt, not C++!

If that's the simplest solution than I need to go back to windows and CodeGear or Visual C++ [/quote]

You're free do do what you want, but Qt is better at least because it's cross platform. If you don't want to learn something new it totally your problem.
P.S. Use "quote" function instead of code blocks highlighting for quotes.

dbzhang800 · wrote on 19 May 2012, 01:44

;-) Seems you don't know which problem encountered and complained by p3aul.

What he need is a C++ book, no matter which GUI library he want to use.

Qt
MFC
wxWidgets
...

And which C++ IDE he want to selected

Visual Studio
C++ builder
Ellipse
Qt Creator
...

And which C++ compiler he want to choose

cl.exe (MSVC)
g++.exe
clang.exe
....

[quote author="Wilk" date="1337391395"]The fact is that VanDerSam's solution makes your program dependent on UI and actual names of it's components, while you can change UI itself and/or it elements and/or names of UI elements. While my solution makes your application dependent only on interface of class.[/quote]

p3aul · wrote on 19 May 2012, 01:55

I'm using the code format rather than the quote format because that's the only that I can figure out hon this forum. I guess I need a book on Qt forums also? Every one insists that i don't know C++ while I have proven that my syntax is correct. It's just a dead horse you're trying to beat. I know enough to know that I'll will never get an answer here because you are all die-hard loyalists to Qt who can't even accept its deficiencies. Well i guess this post will get me thrown off the forum, but it's just as well. Qt being what it is, i guess ya'll just love java!

Robot Hearder:
@If I am right, you never try to see the code behind the drag and drop operation when using C++ builder.@

Well yes, except for the code snippets you write your self. Let's face it, I'm no purist! I just want to get the job done, and Qt, like C++ builder is a RAD tool. Otherwise you would all just use a text editor and code it all for the fun of it.

@The right answer have been given by VanDerSam. And I try to given reasons, but failed ;-(@

VanDerSam suggested that I use:

ui->lineEdit->setText(“Hello”); and I tried it and came up with about 13 errors. I know I copied and pasted it to replace the code I had written so I know that I used his syntax. Now what is it about that line that makes it the best solution?
Thanks,
Paul

Wilk · wrote on 19 May 2012, 02:04

@1+1=2
If p3aul needs some book about C++ why than he started a thread here?
@p3aul
You've mentioned that events are from standard C++... AFAIK they are not. Furthermore, if you think that signals and slots are foolishness, then you just don't understand the idea of them.
And I didn't tell that you don't know C++.

p3aul · wrote on 19 May 2012, 02:15

Wilk:
Mia culpa! you are right Events are a MS windows thing. C++ in the windows environment just makes use of them. Methods though are C++ (and Pascal/delphi which calls them functions) I guess I can sorta see why Qt would choose Slots and Signals I just wish they had chosen something a little more descriptive and a little less arcane! ;)

Well it's not like I'm trying for a career as a professional programmer. I'm 70 years old and nobody would hire me anyway! But I used to Program! I learned on an NCR with 64K of memory. A lot back then!
I guess I'll stick with web programming Since the scripts are easier and I can even use them on my Linux machine, I guess I'll stick with that.