[Solved] questions about an example of "C++ GUI Programming with Qt 4 (2nd Edition)"

? Offline

There is an example in chapter 2 of the book
finddialog.h
@#ifndef FINDDIALOG_H
#define FINDDIALOG_H

#include <QDialog>

class QCheckBox;
class QLabel;
class QLineEdit;
class QPushButton;

class FindDialog : public QDialog
{
Q_OBJECT

public:
FindDialog(QWidget *parent = 0);

signals:
void findNext(const QString &str, Qt::CaseSensitivity cs);
void findPrevious(const QString &str, Qt::CaseSensitivity cs);

private slots:
void findClicked();
void enableFindButton(const QString &text);

private:
QLabel *label;
QLineEdit *lineEdit;
QCheckBox *caseCheckBox;
QCheckBox *backwardCheckBox;
QPushButton *findButton;
QPushButton *closeButton;
};

#endif@
part of finddialog.cpp
@#include <QtGui>

#include "finddialog.h"

FindDialog::FindDialog(QWidget *parent)//Why is parent never used?
: QDialog(parent)
{
label = new QLabel(tr("Find &what:"));
lineEdit = new QLineEdit;
label->setBuddy(lineEdit);

caseCheckBox = new QCheckBox(tr("Match &case"));
backwardCheckBox = new QCheckBox(tr("Search &backward"));

findButton = new QPushButton(tr("&Find"));
findButton->setDefault(true);
findButton->setEnabled(false);

closeButton = new QPushButton(tr("Close"));

connect(lineEdit, SIGNAL(textChanged(const QString &)),
        this, SLOT(enableFindButton(const QString &)));
connect(findButton, SIGNAL(clicked()),
        this, SLOT(findClicked()));
connect(closeButton, SIGNAL(clicked()),
        this, SLOT(close()));

QHBoxLayout *topLeftLayout = new QHBoxLayout;
topLeftLayout->addWidget(label);
topLeftLayout->addWidget(lineEdit);

QVBoxLayout *leftLayout = new QVBoxLayout;
leftLayout->addLayout(topLeftLayout);
leftLayout->addWidget(caseCheckBox);
leftLayout->addWidget(backwardCheckBox);

QVBoxLayout *rightLayout = new QVBoxLayout;
rightLayout->addWidget(findButton);
rightLayout->addWidget(closeButton);
rightLayout->addStretch();

QHBoxLayout *mainLayout = new QHBoxLayout;
mainLayout->addLayout(leftLayout);
mainLayout->addLayout(rightLayout);
setLayout(mainLayout);//question:Why isn't it in the way of "object. setLayout(mainLayout); "? And which is object?

setWindowTitle(tr("Find"));//same question
setFixedHeight(sizeHint().height());//same question

}@

gmaro

@
setLayout(mainLayout);//question:Why isn't it in the way of "object. setLayout(mainLayout); "? And which is object?

setWindowTitle(tr("Find"));//same question
setFixedHeight(sizeHint().height());//same question

@
You're applying layout/title/height to object itself in constructor. This is the same as:
@
this->setLayout(mainLayout);
this->setWindowTitle(tr("Find"));
this->setFixedHeight(sizeHint().height());
@
You should read some C++ book of C++ FAQ about "this".

@
FindDialog::FindDialog(QWidget *parent)//Why is parent never used?
@
Technically it is used in init list
@
: QDialog(parent)
@
There is not alway necessary to use parent pointer, as you can see in .h file it is 0 by default. Book that you're reading explains QObject parentship pretty well.

? Offline

Thank you,I understand.