使用 Qt 的构造函数出现问题

我正在学习如何使用Qt进行C++GUI编程，但由于一个奇怪的错误，我无法编译项目。

我收到以下错误消息：

error: out-of-line definition of 'FindDialog' does not match any declaration in 'FindDialog'

但我不明白为什么这么说，因为 FindDialog 类的定义和实现完全匹配。这是 .h 和 .cpp 文件的代码。我希望任何人都可以告诉我错误在哪里以及如何解决它。

.h 文件：

#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 // FINDDIALOG_H

.cpp文件：

#include "finddialog.h"
#include <QDialog>
#include <QLabel>
#include <QPushButton>
#include <QLineEdit>
#include <QCheckBox>
#include <QHBoxLayout>
#include <QVBoxLayout>
FindDialog::FindDialog (QDialog *parent) : 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);
    setWindowTitle(tr("Find"));
    setFixedHeight(sizeHint().height());
}
void FindDialog::findClicked ()
{
    QString text = lineEdit->text();
    Qt::CaseSensitivity cs =
            caseCheckBox->isChecked() ? Qt::CaseSensitive : Qt::CaseInsensitive;
    if (backwardCheckBox->isChecked())
        emit findPrevious(text, cs);
    else
        emit findNext(text, cs);
}
void FindDialog::enableFindButton (const QString &text)
{
    findButton->setEnabled(!text.isEmpty());
}