[Qt-interest] statusBar()

[Scott Aron Bloom]

Denton.. Alex is absolutely correct... 

It was clear from Sujan's post that he did nto read the basic
documentation on signals and slots nor did he have a basic understanding
of C++..

And btw...  It is NOT generally a good idea to communicate upwards from
child to parent in a type specific manner...

Why?

1) You have now created a child widget that ONLY works with that 1 type
of parent.  This makes sense for paired child/parent relationships
(TreeWidget/TreeWidgetItem or QMidArea/QMdiAreaSubWindow) but is a VERY
VERY poor technique otherwise
2) Your child now has 2 other depencencies in this case.  1 on
QMainWindow and 1 on Qstatusbar.. neither is necessary
3) You had to create a local method and another layer of possible buggy
code (every line of code is a possible bug) to do something you simply
don't need...

Now.. look at the QStatusBar::showMessage method.. You will notice, that
it is indeed a slot.  Why is that important?  

Well, here is how I would allow my child to set my status... without
them ever knowing that I am a QMainWIndow, a QDialog or a console going
to stdout..

MainWIndow::MainWindow(.....)
{
    fChildWindow = new childWIndow();
    connect( fChildWindow, SIGNAL( sigStatusMessage( const QString &,
int ) ), this, SIGNAL( sigStatusMessage( const QString &, int ) ) )
    connect( this, SIGNAL( sigStatusMessage( const QString &, int ) ),
statusBar(), SLOT( showMessage( const QString &, int ) ) )
}


Now.. any one of my children can update my status bar...  and if I
change to a QDialog or change how I "show the message" they don't care..
Maybe I add a logging report of every message.. So I add the following

    connect( this, SIGNAL( sigStatusMessage( const QString &, int ) ),
fLogger, SIGNAL( sigStatusMessage( const QString &, int ) ) )

Now inside my logger, I connect to that signal and do something...


Now.. say my MainWindow was 1 of MANY QMainWindows in the application...
and my custom QApplication had a better way of showing messages...
    connect( this, SIGNAL( sigStatusMessage( const QString &, int ) ),
qApp, SIGNAL( sigStatusMessage( const QString &, int ) ) )

BAM...  And my code in my child window never has to change...

Scott

> -----Original Message-----
> From: qt-interest-bounces at trolltech.com [mailto:qt-interest-
> bounces at trolltech.com] On Behalf Of Denton Vis
> Sent: Thursday, March 26, 2009 5:40 PM
> To: qt-interest at trolltech.com
> Subject: Re: [Qt-interest] statusBar()
> 
> Hi Alex,
> I may be wrong but I do not think the problem is with calling methods
of a
> class in C++. It may seem obvious later, but when new to Qt, it may
not be
> as obvious how to get to the top widget sometimes.
> 
> I understand that it has more to do with having a main window and
several
> subclasses (widgets) and then getting access to the main window in
order to
> update the status during an operation.
> 
> Sujan:
> It is generally a good idea when creating child widgets of your
MainWindow,
> to pass the MainWindow as the parent object. That way, it becomes easy
to
> make a call on the parent and update the status. You could create a
method
> 
> void ChildWidget::updateStatus(const QString & message) {
> QObject * parent = mainWindow.parent();
> QMainWindow * mainWindow = qobject_cast<QMainWindow*>(parent);
> if (mainWindow) // if cast was successful
>     mainWindow->statusBar()->showMessage(message, 2000);
> return;
> }
> 
> and then make a call to this method each time you wish to update the
status
> on the status Bar.
> 
> If you update your status bar message a lot, it may help to create a
> QStatusBar* widget in your child widget and run
> the code once to get a pointer to the status bar: like so.
> QStatusBar* mStatusBar = mainWindow->statusBar();
> 
> then each time you update the status bar, it is only necessary to call
> mStatusBar->showMessage(...)
> 
> Hope this helps you out.
> 
> "Malyushytsky, Alex" <alex at wai.com> wrote in message
> news:F8145CF983B4DB42855E9BB7F5BE8FCC113ED004 at camail2.wai.com...
> > There is no way to help you, until you read and understand basics of
C++.
> > Don't take it as offence, this is just a reason why you can't be
helped
> > here and you don't get any answer on your second time asked
question.
> >
> > Giving you a solution just encourages you to keep flouding this
mailing
> > list with basic C++ question. That makes nothing good even to you.
> > Hope you finally will follow people advice. Start with definition of
the
> > class and object.
> >
> > Once you get it, you will find your first way to do what you want.
> >
> > Regads,
> >     Alex
> >
> >
> > ________________________________________
> > From: qt-interest-bounces at trolltech.com
> > [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Sujan
Dasmahapatra
> > Sent: Thursday, March 26, 2009 2:55 AM
> > To: qt-interest at trolltech.com
> > Subject: [Qt-interest] statusBar()
> >
> > Dear Friends
> > In my prpoject I have many classes and the  main class is
"MainWindow"
> > which is derived  from QMainWindow. So I am able to show message in
my
> > 'MainWindow' class......How could I show message on the statusBar
from any
> > other class. When I am trying to do that its not happening.Plss tell
me
> > some idea to show message from other class than MainWindow..
> >
> > Kind regards,
> > LM Glasfiber R&D (India) Pvt. Ltd.
> >
> > Sujan Dasmahapatra
> > Project Engineer - CFD
> >
> > Telephone: +91 80 66470248
> > Mobile:
> > E-mail: sdh at lmglasfiber.com
> >
> >
> >
> >
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