change text of QLabel in another class with button - qt

Question

I have ever post a question at there: change text in another class by button But it justs working when second class is create by first class. Now I have 2 classes, they're created sametime, so how to I connect with together? below is all my code, first class has a button, and second class has a label, I want to when user click on the button in first class, label in second class will be changed. They're put in stackWidget:
// file.h
#include <QWidget>
#include <QtGui>
class widgetA;
class widgetB;
class A : public QWidget
{
Q_OBJECT
public:
explicit A(QWidget *parent = 0);
private:
QComboBox* comboBox;
QStackedWidget* stackWidget;
widgetA *wa;
widgetB *wb;
};
class widgetA : public QWidget
{
Q_OBJECT
public:
widgetA(QWidget *parent = 0);
public slots:
void buttonClicked();
private:
QPushButton* button;
};
class widgetB : public QWidget
{
Q_OBJECT
public slots:
void labelChangeText(const QString);
public:
widgetB(QWidget *parent = 0);
QLabel* label;
};
And this's cpp file:
//file.cpp
#include "a.h"
A::A(QWidget *parent) :
QWidget(parent)
{
comboBox = new QComboBox(this);
comboBox->addItem(tr("Widget A"));
comboBox->addItem(tr("Widget B"));
wa = new widgetA(this);
wb = new widgetB(this);
stackWidget = new QStackedWidget(this);
stackWidget->addWidget(wa);
stackWidget->addWidget(wb);
stackWidget->setCurrentIndex(0);
connect(comboBox, SIGNAL(currentIndexChanged(int)), stackWidget, SLOT(setCurrentIndex(int)));
QVBoxLayout* layout = new QVBoxLayout;
layout->addWidget(comboBox);
layout->addWidget(stackWidget);
setLayout(layout);
}
widgetA::widgetA(QWidget *parent):
QWidget(parent)
{
button = new QPushButton(tr("Click"));
connect(button, SIGNAL(clicked()), this, SLOT(buttonClicked()));
QHBoxLayout* lay = new QHBoxLayout;
lay->addWidget(button);
setLayout(lay);
}
void widgetA::buttonClicked()
{
// what I have to do at there for call the function at widgetB class?
}
widgetB::widgetB(QWidget *parent):
QWidget(parent)
{
label = new QLabel("....");
QHBoxLayout* lay = new QHBoxLayout;
lay->addWidget(label);
setLayout(lay);
}
void widgetB::labelChangeText(const QString text)
{
label->setText(text);
}
P/S: sorry my english

Answer 1

You can either pass a pointer of widgetB object to widgetA, or you can connect a signal from widgetA to a slot in widgetB.
Here's an example of the signal/slot option:
// widgeta.h
signals:
void changeText(QString text);
-
// widgeta.cpp
void widgetA::buttonClicked()
{
emit changeText("button clicked");
}
-
//widgetb.h
public slots:
void labelChangeText(const QString & text);
-
// a.cpp
connect(wa, SIGNAL(changeText(QString)), wb, SLOT(labelChangeText(QString)));

Answer 2

What hinders you to call wb->labelChangeText("some string") in widgetA::buttonClicked()? You have a pointer to widgetB in class A. And labelChangeText is public in class B. Just that it is a slot does not mean that you cannot call it as a normal method.