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



  • 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
    

    }@



  • @
    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.



  • Thank you,I understand.


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