send messages from central widget to mainwindow (statusBar)??

[fatecasino]

• I have created a mainwindow with a status bar
• then i created a widget
• i set that widget as the central widget
• now, I added several other widgets in that widget.

The question how I can send some text messages from those widgets to the mainwindow status bar?!

[ChrisW67]

Connect to the QStatusBar::showMessage() slot and send away.

[fatecasino]

well, it seems obvious, but I have something missing (probably important block of knowledge) here:
I have successfully constructed a status bar in the mainwindow:

mainwindow.h
 public slots:
     void printInfoToStatusBar (QString);
mainwindow.cpp
void MainWindow::printInfoToStatusBar (QString msg)
{
statusBar()->showMessage(msg);
}

mainwindow.h
 public slots:
     void printInfoToStatusBar (QString);
mainwindow.cpp
void MainWindow::printInfoToStatusBar (QString msg)
{
statusBar()->showMessage(msg);
}

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I have a central widget and in the central widget I have added a widget with a slidebar. I want to see the values of the slidebar in the statusbar. How will i connect them? (i have more messages to send to the mainwindow, but if I get this, I will do the rest similaringly):

connect( myslider, SIGNAL(  valueChangedinQStringType(QString)   ), ???mainwindow??, SLOT(   printInfoToStatusBar (QString )  ) );

connect( myslider, SIGNAL(  valueChangedinQStringType(QString)   ), ???mainwindow??, SLOT(   printInfoToStatusBar (QString )  ) );

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PS: I have seen some examples of people using ui->this,etc,etc, but the way I started building my application had no ui whatsoever and now I cannot change the constructor of the main window (the ui way).

[boudie]

in mainwindow.h
 
private slots:
    void mySliderChanged(int);

in mainwindow.h

private slots:
    void mySliderChanged(int);

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in MainWindow.cpp
 
in constructor MainWindow::MainWindow
    connect(mySlider, SIGNAL(valueChanged(int)), this, SLOT(mySliderChanged(int)));
 
void MainWindow::mySliderChanged(int newValue)
{
    ... send something to your statusbar ...
}

in MainWindow.cpp

in constructor MainWindow::MainWindow
    connect(mySlider, SIGNAL(valueChanged(int)), this, SLOT(mySliderChanged(int)));

void MainWindow::mySliderChanged(int newValue)
{
    ... send something to your statusbar ...
}

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In some cases you can send a value directly from one control to another, but processing a signal the way shown above, gives you freedom to change values or formats before sending it to someplace else.

Make sure that mySlider has tracking == true, if you want immidiate update when moving the slider:

mySlider.setTracking(true);

mySlider.setTracking(true);

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[fatecasino]

@boudie
the point is that mySlider does not belong to "MainWindow" class, but to a widget (central) of the MainWindow.That means that:

constructor MainWindow::MainWindow
    connect(mySlider, SIGNAL(valueChanged(int)), this, SLOT(mySliderChanged(int)));

constructor MainWindow::MainWindow
    connect(mySlider, SIGNAL(valueChanged(int)), this, SLOT(mySliderChanged(int)));

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cannot be used

[boudie]

How and where did you create mySlider?
Please show complete code.

[ChrisW67]

If the slider is part of a Designer built QMainWindow, i.e. the central widget sub-widgets are accessible to the main window, then something like this will work:

connect(ui->mySlider, SIGNAL(valueChanged(int)), this, SLOT(mySliderChanged(int)));

connect(ui->mySlider, SIGNAL(valueChanged(int)), this, SLOT(mySliderChanged(int)));

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If you have a completely separate widget (OtherWidget) that you set as the central widget then its sub-widgets are not usually accessible from outside. In this case you should expose a signal in class OtherWidget that simply repeats the slider's valueChanged(int) signal to the outside world. Then you connect that externally visible signal as above. Something like:

class OtherWidget: public QWidget {
  Q_OBJECT
public:
  OtherWidget() {
    mySlider = new QSlider(this);
...
    connect(mySlider, SIGNAL(valueChanged(int)), this, SIGNAL(sliderChanged(int)));
  }
signals:
  void  sliderChanged(int value);
private:
  QSlider *mySlider;
};

class OtherWidget: public QWidget {
  Q_OBJECT
public:
  OtherWidget() {
    mySlider = new QSlider(this);
...
    connect(mySlider, SIGNAL(valueChanged(int)), this, SIGNAL(sliderChanged(int)));
  }
signals:
  void  sliderChanged(int value);
private:
  QSlider *mySlider;
};

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[fatecasino]

thanks ChrisW67 ,
I am close to understand, but I am still a bit confused. After further reading, here's what I have got:

mainwindow.h

public slots:
     void printInfoToStatusBar (QString);

public slots:
     void printInfoToStatusBar (QString);

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mainwindow.cpp

void MainWindow::printInfoToStatusBar (QString msg)
{
statusBar()->showMessage(msg);
}

void MainWindow::printInfoToStatusBar (QString msg)
{
statusBar()->showMessage(msg);
}

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then indeed OtherWidget is the central widget of the main window
OtherWidget.h

class OtherWidget : public QWidget
{
public:
    OtherWidget(QWidget *parent = 0);
signals:
  void  sliderChanged(int value);
private:
    .....
........other widgets....
    QSlider mySlider;
};

class OtherWidget : public QWidget
{
public:
    OtherWidget(QWidget *parent = 0);
signals:
  void  sliderChanged(int value);
private:
    .....
........other widgets....
    QSlider mySlider;
};

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OtherWidget.cpp

OtherWidget::OtherWidget(QWidget *parent)
    : QWidget(parent)
{
mySlider = new QSlider(this);
connect(mySlider, SIGNAL(valueChanged(int)), this, SIGNAL(sliderChanged(int)));//connecting two SIGNALS, right?
}
 
void OtherWidget::sliderChanged(int)
{
//is this the place that I should reflect the slider signal to the mainwindow?how?
}

OtherWidget::OtherWidget(QWidget *parent)
    : QWidget(parent)
{
mySlider = new QSlider(this);
connect(mySlider, SIGNAL(valueChanged(int)), this, SIGNAL(sliderChanged(int)));//connecting two SIGNALS, right?
}

void OtherWidget::sliderChanged(int)
{
//is this the place that I should reflect the slider signal to the mainwindow?how?
}

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PS: I haven't used Designer, just Creator.

[ChrisW67]

Yes, connecting two SIGNALS together. When the source signal is emitted the destination signal will be emitted. It is in the docs.

As you have it now, you need to find the correct spot to:

connect(
  otherWidget, SIGNAL(sliderChanged(int)),     
  mainWindow, SLOT(printInfoToStatusBar(QString))   // the function templates do not match: you'll need to sort this out
);

connect(
  otherWidget, SIGNAL(sliderChanged(int)),     
  mainWindow, SLOT(printInfoToStatusBar(QString))   // the function templates do not match: you'll need to sort this out
);

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Probably immediately after creating an instance of OtherWidget.

You could redefine the signal out of OtherWidget:

public slots:
  void sliderChanged(int value);
signals:
  void statusMessage(QString msg);
...
connect(mySlider, SIGNAL(valueChanged(int)), this, SLOT(sliderChanged(int)));
...
void OtherWidget::sliderChanged(int value)
{
  emit statusMessage( QString("Some status message including the %1").arg(value) );
}

public slots:
  void sliderChanged(int value);
signals:
  void statusMessage(QString msg);
...
connect(mySlider, SIGNAL(valueChanged(int)), this, SLOT(sliderChanged(int)));
...
void OtherWidget::sliderChanged(int value)
{
  emit statusMessage( QString("Some status message including the %1").arg(value) );
}

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or redefine the slot in the main window class to accept an int.