（3）创建一个查找对话框

首先新建一个工程，Qt Gui Application，然后最后一步注意，Base Dialog选择QDialog，而不是默认的QMainWindow

头文件

#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>

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

class FindDialog : public QDialog
{
    Q_OBJECT

public:
    FindDialog(QWidget *parent = 0);
    ~FindDialog();
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 // DIALOG_H

源文件：

#include "dialog.h"

#include <QCheckBox>
#include <QLabel>
#include <QLineEdit>
#include <QPushButton>
#include <QHBoxLayout>

FindDialog::FindDialog(QWidget *parent)
    : QDialog(parent)
{
    //&字母相当于定义个快捷键，当你按下Alt+F的时候，这个按钮就相当于被点击
    label = new QLabel(tr("Find &what:"));
    lineEdit = new QLineEdit;
    //这个label使用了setBuddy函数，它的意思是，当label获得焦点时，
    //比如按下Alt+W，它的焦点会自动传给它的buddy，也就是lineEdit
    label->setBuddy(lineEdit);

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

    findButton = new QPushButton(tr("&Find"));
    findButton->setEnabled(false);//初始禁用

    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()));

    //左上布局
    QHBoxLayout *topLeftLayout = new QHBoxLayout;
    topLeftLayout->addWidget(label);
    topLeftLayout->addWidget(lineEdit);

    //左边布局
    QVBoxLayout *leftLayout = new QVBoxLayout;
    leftLayout->addLayout(topLeftLayout);
    leftLayout->addWidget(caseCheckBox);
    leftLayout->addWidget(backwardCheckBox);

    //右侧布局
    QVBoxLayout *rightLayout = new QVBoxLayout;
    rightLayout->addWidget(findButton);
    rightLayout->addWidget(closeButton);
    //右侧整体置顶
    rightLayout->addStretch();

    //将左半部分和右半部分整体加入水平布局
    QHBoxLayout *mainLayout = new QHBoxLayout;
    mainLayout->addLayout(leftLayout);
    mainLayout->addLayout(rightLayout);
    setLayout(mainLayout);

    //对话框的标题
    setWindowTitle(tr("Find"));
    setFixedHeight(sizeHint().height());
}

FindDialog::~FindDialog()
{

}

void FindDialog::findClicked()
{
    //首先取出lineEdit的输入值
    QString text = lineEdit->text();
    //然后判断caseCheckBox是不是选中，如果选中就返回Qt::CaseInsensitive，否则返回Qt::CaseSensitive
    Qt::CaseSensitivity cs = caseCheckBox->isChecked() ? Qt::CaseInsensitive : Qt::CaseSensitive;
    //查找方向分支
    if(backwardCheckBox->isChecked()) {
        emit findPrevious(text, cs);
    } else {
        emit findNext(text, cs);
    }
}

void FindDialog::enableFindButton(const QString &text)
{
    //当文本不为空时启用Find按钮
    findButton->setEnabled(!text.isEmpty());
}

解释见注释。

下面是main函数，这部分工程自动生成：

#include "dialog.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    FindDialog w;
    w.show();

    return a.exec();
}