mouseOver Label

[eLancaster]

I'm trying to write a program in which there is a QWidget with a QLabel inside of it. When the mouse moves over the QLabel, the text changes and when the moves away from QLabel it changes back to the original.
I've been reading the documentation and have become boggled about how to do this. Could someone tell me which class I ought to be using and give an example of its use.

Thanks

[Lykurg]

See QWidget::enterEvent() and QWidget::leaveEvent().

[eLancaster]

This is the code I wrote. I got errors in Widget.cpp file - what do i do about those?

widget.h

#ifndef WIDGET_H
#define WIDGET_H
 
#include <QLabel>
#include <QWidget>
 
namespace Ui {
    class Widget;
}
 
class Widget : public QWidget
{
    Q_OBJECT
 
public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();
 
private:
    Ui::Widget *ui;
};
 
class Label : public QLabel
{
    Q_OBJECT
 
public:
    Label(QWidget *parent=NULL);
    ~Label();
 
public slots:
    void mouseOverLabel();
    void mouseNotOverLabel();
 
protected:
    virtual void enterEvent(QEvent *);
    virtual void leaveEvent(QEvent *);
 
signals:
    void enter(QString);
    void leave(QString);
 
};
 
#endif // WIDGET_H

#ifndef WIDGET_H
#define WIDGET_H

#include <QLabel>
#include <QWidget>

namespace Ui {
    class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();

private:
    Ui::Widget *ui;
};

class Label : public QLabel
{
    Q_OBJECT

public:
    Label(QWidget *parent=NULL);
    ~Label();

public slots:
    void mouseOverLabel();
    void mouseNotOverLabel();

protected:
    virtual void enterEvent(QEvent *);
    virtual void leaveEvent(QEvent *);

signals:
    void enter(QString);
    void leave(QString);

};

#endif // WIDGET_H

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widget.cpp

#include "widget.h"
#include "ui_widget.h"
 
Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    setFixedSize(145,45);
 
    Label *label = new Label;
    label->setGeometry(10,10,100,30);
    label->setText("Where is the Mouse?");
 
    connect(label,SIGNAL(enter(QString)),label,SLOT(mouseOverLabel()));
    connect(label,SIGNAL(leave(QString)),label,SLOT(mouseNotOverLabel()));
}
 
void Label::mouseOverLabel()
{
    label->setText("The Mouse is Over Me :-) ");

#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    setFixedSize(145,45);

    Label *label = new Label;
    label->setGeometry(10,10,100,30);
    label->setText("Where is the Mouse?");

    connect(label,SIGNAL(enter(QString)),label,SLOT(mouseOverLabel()));
    connect(label,SIGNAL(leave(QString)),label,SLOT(mouseNotOverLabel()));
}

void Label::mouseOverLabel()
{
    label->setText("The Mouse is Over Me :-) ");

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ERROR: Label was not declared in this scope

}
 
void Label::mouseNotOverLabel()
{
    label->setText("Where is the Mouse?");

}

void Label::mouseNotOverLabel()
{
    label->setText("Where is the Mouse?");

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ERROR: Label was not declared in this scope

}
 
void Label::enterEvent(QEvent *e)[B][COLOR="red"]ERROR:unused paramter e[/COLOR][/B]
{
    emit enter( text() );
}
 
void Label::leaveEvent(QEvent *e)
{
    emit leave( text() );
}
 
Widget::~Widget()
{
    delete ui;
}

}

void Label::enterEvent(QEvent *e)[B][COLOR="red"]ERROR:unused paramter e[/COLOR][/B]
{
    emit enter( text() );
}

void Label::leaveEvent(QEvent *e)
{
    emit leave( text() );
}

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

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[aamer4yu]

ERROR: Label was not declared in this scope

There must be more to the error...
are u getting warnings or errors ?

[tbscope]

You have no object called "label" in your Label class.
I guess this is a copy and paste error.

Did you mean to use this?

setText("Where is the Mouse?");

setText("Where is the Mouse?");

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(remove the label-> part)

[eLancaster]

OK I fixed the issues above, and the program not give any errors, but whenever I build the program, it terminates unexpectedly giving an exit status of 0. Why is that happening? The code is below:

LabelChange.h

#ifndef LABELCHANGE_H
#define LABELCHANGE_H
 
#include <QWidget>
#include <QLabel>
 
namespace Ui {
    class LabelChange;
}
 
class LabelChange : public QWidget
{
    Q_OBJECT
 
public:
    explicit LabelChange(QWidget *parent = 0);
    ~LabelChange();
 
public slots:
    void mouseOverLabel();
    void mouseNotOverLabel();
 
protected:
    virtual void enterEvent(QEvent *);
    virtual void leaveEvent(QEvent *);
 
signals:
    void enter(QString);
    void leave(QString);
private:
    Ui::LabelChange *ui;
    QLabel *label;
};
 
#endif // LABELCHANGE_H

#ifndef LABELCHANGE_H
#define LABELCHANGE_H

#include <QWidget>
#include <QLabel>

namespace Ui {
    class LabelChange;
}

class LabelChange : public QWidget
{
    Q_OBJECT

public:
    explicit LabelChange(QWidget *parent = 0);
    ~LabelChange();

public slots:
    void mouseOverLabel();
    void mouseNotOverLabel();

protected:
    virtual void enterEvent(QEvent *);
    virtual void leaveEvent(QEvent *);

signals:
    void enter(QString);
    void leave(QString);
private:
    Ui::LabelChange *ui;
    QLabel *label;
};

#endif // LABELCHANGE_H

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LabelChange.cpp

#include "labelchange.h"
#include "ui_labelchange.h"
 
LabelChange::LabelChange(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::LabelChange)
{
    ui->setupUi(this);
    setFixedSize(145,45);
 
    label->setGeometry(10,10,100,30);
    label->setText("Where is the Mouse?");
 
    connect(label,SIGNAL(enter(QString)),label,SLOT(mouseOverLabel()));
    connect(label,SIGNAL(leave(QString)),label,SLOT(mouseNotOverLabel()));
}
 
void LabelChange::mouseOverLabel()
{
    label->setText("The Mouse is Over Me :-) ");
}
 
void LabelChange::mouseNotOverLabel()
{
   label->setText("Where is the Mouse?");
}
 
void LabelChange::enterEvent(QEvent *e)WARNING: UNUSED PARAMETER 'e'
{
    emit enter( label->text());
}
 
void LabelChange::leaveEvent(QEvent *e)WARNING: UNUSED PARAMETER 'e'
{
    emit leave(labeltext() );
}
 
LabelChange::~LabelChange()
{
    delete ui;
}

#include "labelchange.h"
#include "ui_labelchange.h"

LabelChange::LabelChange(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::LabelChange)
{
    ui->setupUi(this);
    setFixedSize(145,45);

    label->setGeometry(10,10,100,30);
    label->setText("Where is the Mouse?");

    connect(label,SIGNAL(enter(QString)),label,SLOT(mouseOverLabel()));
    connect(label,SIGNAL(leave(QString)),label,SLOT(mouseNotOverLabel()));
}

void LabelChange::mouseOverLabel()
{
    label->setText("The Mouse is Over Me :-) ");
}

void LabelChange::mouseNotOverLabel()
{
   label->setText("Where is the Mouse?");
}

void LabelChange::enterEvent(QEvent *e)WARNING: UNUSED PARAMETER 'e'
{
    emit enter( label->text());
}

void LabelChange::leaveEvent(QEvent *e)WARNING: UNUSED PARAMETER 'e'
{
    emit leave(labeltext() );
}

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

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---

Added after 7 minutes:

ERROR MESSAGE
The inferior stopped because it received a signal from the Operating System.

Signal name :
SIGSEGV
Signal meaning :
Segmentation fault

How can I remedy this?

[Lykurg]

Please make yourself familiar with basic debugging methods. But to answer you question: Where did you initialize the member called label?

[eLancaster]

Is there a link to find out about debugging methods, i'd appreciate it.
I initialize it in LabelChange.h. It's a private member.

[Lykurg]

I initialize it in LabelChange.h. It's a private member.

Initialisation != Declaring. Hint: Null pointer.

As for learning how to debug, best use google for "gdb" or http://sourceware.org/gdb/current/onlinedocs/gdb/

[eLancaster]

OH! I see it.
and yeah it works too.
Thanks alot! and ill look over debugging.

[eLancaster]

I tried to improve the program by making it so that the cursor has to be precisely over the label to change the text. For, this i made a seperate label class and made an object of it in the widget class. I get an error of undefined reference in widget.cpp, and from what i've read, its because I need to make a destructor for the Label class - but how can I do that without making label a public member.

widget.h

#ifndef WIDGET_H
#define WIDGET_H
 
#include <QWidget>
#include <QLabel>
 
namespace Ui {
    class Widget;
}
 
 
class Label : public QLabel
{
    Q_OBJECT
 
public:
    Label(QWidget *parent);
    ~Label();
 
protected:
    virtual void enterEvent(QEvent *);
    virtual void leaveEvent(QEvent *);
 
signals:
    void enter(QString);
    void leave(QString);
};
 
class Widget : public QWidget
{
    Q_OBJECT
 
public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();
 
public slots:
    void mouseOverLabel();
    void mouseNotOverLabel();
 
private:
    Ui::Widget *ui;
    Label *label;
};
 
#endif // WIDGET_H

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QLabel>

namespace Ui {
    class Widget;
}


class Label : public QLabel
{
    Q_OBJECT

public:
    Label(QWidget *parent);
    ~Label();

protected:
    virtual void enterEvent(QEvent *);
    virtual void leaveEvent(QEvent *);

signals:
    void enter(QString);
    void leave(QString);
};

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();

public slots:
    void mouseOverLabel();
    void mouseNotOverLabel();

private:
    Ui::Widget *ui;
    Label *label;
};

#endif // WIDGET_H

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widget.cpp

#include "widget.h"
#include "ui_widget.h"
 
Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    label = new Label(this);//Undefined Reference Label::Label(QWidget*)
    label->setText("Where is the Mouse?");//Undefined Reference Label::Label(QWidget*)
    connect(label,SIGNAL(enter(QString)),this,SLOT(mouseOverLabel()));
    connect(label,SIGNAL(leave(QString)),this,SLOT(mouseNotOverLabel()));
}
 
void Widget::mouseOverLabel()
//code
 
void Widget::mouseNotOverLabel()
//
 
void Label::enterEvent(QEvent *)
//code
 
void Label::leaveEvent(QEvent *)
//code
 
Widget::~Widget()
//code

#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    label = new Label(this);//Undefined Reference Label::Label(QWidget*)
    label->setText("Where is the Mouse?");//Undefined Reference Label::Label(QWidget*)
    connect(label,SIGNAL(enter(QString)),this,SLOT(mouseOverLabel()));
    connect(label,SIGNAL(leave(QString)),this,SLOT(mouseNotOverLabel()));
}

void Widget::mouseOverLabel()
//code

void Widget::mouseNotOverLabel()
//

void Label::enterEvent(QEvent *)
//code

void Label::leaveEvent(QEvent *)
//code

Widget::~Widget()
//code

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