教学示例补 5 个：3 个坑点复现 + QTableWidget + Day5 学员管理器参考实现
- pitfall_stack_widget / pitfall_lambda_capture / pitfall_double_connect： 默认跑正确写法（离屏验证退出码 0），--crash / --dangle 开关课堂现场触发 真实崩溃/悬空访问 - table_widget：QTableWidget 单元格事件最小示例（新安排 Day4「表格事件」） - student_manager：Day5 综合案例参考实现，离屏自测覆盖 JSON round-trip 与 QThread 后台导入闭环 - 均接入 examples/CMakeLists.txt 的 add_teaching_example，手工维护区不影响生成器
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张宗平
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// ============================================================================
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// qt_student_manager —— Day5 综合案例参考实现：学员信息管理器
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// 对应教案：OUTLINE_4DAY.md §3（Day5 综合项目案例讲解）——把 Day1–4 作业线
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// 收束成一个完整小软件：QMainWindow 骨架 + QTableWidget 列表 + 增改对话框 +
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// JSON 落盘读回 + QThread 后台导入不卡界面。
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// 配套文档：docs/teaching/examples/student_manager/README.md
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//
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// 离屏验证（自测模式）：QT_QPA_PLATFORM=offscreen tools/run_qt.sh qt_student_manager
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// 自测流程：添加 2 条记录 → 保存 JSON → 清空 → 读回校验 → 后台导入 3 条 →
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// 总数校验，全部通过退出码 0，任一步失败退出码 1。
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// ============================================================================
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#include <QAction>
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#include <QApplication>
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#include <QDebug>
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#include <QDialog>
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#include <QDialogButtonBox>
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#include <QFile>
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#include <QFormLayout>
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#include <QHeaderView>
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#include <QJsonArray>
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#include <QJsonDocument>
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#include <QJsonObject>
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#include <QJsonParseError>
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#include <QLineEdit>
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#include <QMainWindow>
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#include <QMenuBar>
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#include <QMessageBox>
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#include <QStatusBar>
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#include <QTableWidget>
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#include <QThread>
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#include <QTimer>
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#include <QToolBar>
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// ---------------------------------------------------------------- 数据层 ----
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struct Student {
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QString name;
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double score = 0.0;
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QString tag;
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};
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// 序列化/反序列化是一对互逆操作（Day4）：正确性标准 = 写出去再读回来数据一致。
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static QJsonObject toJson(const Student& s) {
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return QJsonObject{{"name", s.name}, {"score", s.score}, {"tag", s.tag}};
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}
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static Student fromJson(const QJsonObject& obj) {
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// 类型不匹配时 toString()/toDouble() 不报错只给默认值（Day4 坑卡）——
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// 教学示例里字段固定，生产代码应先 contains()+isDouble() 逐字段校验。
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return Student{obj["name"].toString(), obj["score"].toDouble(), obj["tag"].toString()};
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}
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// ---------------------------------------------------------- 添加记录对话框 ----
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class AddStudentDialog : public QDialog {
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Q_OBJECT
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public:
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explicit AddStudentDialog(QWidget* parent = nullptr) : QDialog(parent) {
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setWindowTitle(QStringLiteral("添加学员"));
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m_name = new QLineEdit(this);
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m_score = new QLineEdit(this);
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m_tag = new QLineEdit(this);
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auto* buttons = new QDialogButtonBox(
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QDialogButtonBox::Ok | QDialogButtonBox::Cancel, this);
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connect(buttons, &QDialogButtonBox::accepted, this, &QDialog::accept);
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connect(buttons, &QDialogButtonBox::rejected, this, &QDialog::reject);
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auto* form = new QFormLayout(this);
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form->addRow(QStringLiteral("姓名"), m_name);
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form->addRow(QStringLiteral("成绩"), m_score);
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form->addRow(QStringLiteral("标签"), m_tag);
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form->addRow(buttons);
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}
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Student student() const {
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return Student{m_name->text(), m_score->text().toDouble(), m_tag->text()};
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}
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private:
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QLineEdit* m_name;
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QLineEdit* m_score;
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QLineEdit* m_tag;
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};
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// ------------------------------------------------------ 后台导入 worker ----
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// worker-object 模式（而非继承 QThread）：耗时活儿放进 worker，把 worker
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// moveToThread 到工作线程；worker 与界面之间只通过信号槽通信——跨线程连接
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// 自动变 Queued，槽在接收者所属线程执行，天然不碰 GUI 线程以外的控件。
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class ImportWorker : public QObject {
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Q_OBJECT
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public slots:
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void doImport(int rows) {
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for (int i = 1; i <= rows; ++i) {
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QThread::msleep(20); // 模拟耗时 IO；放主线程就是界面冻结（Day4 埋点）
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emit rowReady(QStringLiteral("导入学员%1").arg(i), 60.0 + i, QStringLiteral("导入"));
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}
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emit finished();
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}
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signals:
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void rowReady(const QString& name, double score, const QString& tag);
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void finished();
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};
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// -------------------------------------------------------------- 主窗口 ----
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class MainWindow : public QMainWindow {
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Q_OBJECT
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public:
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explicit MainWindow(QWidget* parent = nullptr) : QMainWindow(parent) {
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setWindowTitle(QStringLiteral("学员信息管理器"));
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// QMainWindow 不是大号 QWidget：中心部件必须显式安放（Day3 坑卡）
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m_table = new QTableWidget(0, 3, this);
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m_table->setHorizontalHeaderLabels(
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{QStringLiteral("姓名"), QStringLiteral("成绩"), QStringLiteral("标签")});
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m_table->horizontalHeader()->setSectionResizeMode(QHeaderView::Stretch);
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setCentralWidget(m_table);
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auto* actAdd = new QAction(QStringLiteral("添加记录"), this);
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auto* actSave = new QAction(QStringLiteral("保存"), this);
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auto* actLoad = new QAction(QStringLiteral("读取"), this);
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m_actImport = new QAction(QStringLiteral("后台导入"), this);
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auto* actAbout = new QAction(QStringLiteral("关于"), this);
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QMenu* fileMenu = menuBar()->addMenu(QStringLiteral("文件(&F)"));
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fileMenu->addAction(actSave);
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fileMenu->addAction(actLoad);
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QMenu* recordMenu = menuBar()->addMenu(QStringLiteral("记录(&R)"));
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recordMenu->addAction(actAdd);
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recordMenu->addAction(m_actImport);
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menuBar()->addMenu(QStringLiteral("帮助(&H)"))->addAction(actAbout);
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QToolBar* bar = addToolBar(QStringLiteral("main"));
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bar->addAction(actAdd);
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bar->addAction(actSave);
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bar->addAction(actLoad);
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bar->addAction(m_actImport);
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// QAction 显示出来 ≠ 生效：忘 connect 就是「菜单点了没反应」（Day3 坑卡）
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connect(actAdd, &QAction::triggered, this, &MainWindow::onAdd);
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connect(actSave, &QAction::triggered, this, [this] { saveTo(m_dataPath); });
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connect(actLoad, &QAction::triggered, this, [this] { loadFrom(m_dataPath); });
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connect(m_actImport, &QAction::triggered, this, &MainWindow::onImport);
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connect(actAbout, &QAction::triggered, this, [this] {
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QMessageBox::about(this, QStringLiteral("关于"),
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QStringLiteral("Day5 综合案例参考实现：Day1–4 全部知识点的收束。"));
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});
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// 相对路径随工作目录漂移（Day4 坑卡）——一律基于 applicationDirPath 拼路径
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m_dataPath = QCoreApplication::applicationDirPath() + "/students.json";
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statusBar()->showMessage(QStringLiteral("数据文件：") + m_dataPath);
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}
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int rowCount() const { return m_table->rowCount(); }
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void clearAll() { m_table->setRowCount(0); }
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void addRow(const Student& s) {
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const int row = m_table->rowCount();
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m_table->insertRow(row);
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m_table->setItem(row, 0, new QTableWidgetItem(s.name));
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m_table->setItem(row, 1, new QTableWidgetItem(QString::number(s.score)));
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m_table->setItem(row, 2, new QTableWidgetItem(s.tag));
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}
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bool saveTo(const QString& path) {
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QJsonArray arr;
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for (int row = 0; row < m_table->rowCount(); ++row) {
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arr.append(toJson(Student{m_table->item(row, 0)->text(),
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m_table->item(row, 1)->text().toDouble(),
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m_table->item(row, 2)->text()}));
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}
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QFile file(path);
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if (!file.open(QIODevice::WriteOnly)) { // open() 必须检查（Day4 坑卡）
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statusBar()->showMessage(QStringLiteral("保存失败：打不开 ") + path);
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return false;
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}
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file.write(QJsonDocument(arr).toJson(QJsonDocument::Indented));
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statusBar()->showMessage(QStringLiteral("已保存 %1 条记录").arg(arr.size()));
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return true;
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}
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bool loadFrom(const QString& path) {
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QFile file(path);
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if (!file.open(QIODevice::ReadOnly)) {
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statusBar()->showMessage(QStringLiteral("读取失败：打不开 ") + path);
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return false;
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}
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QJsonParseError err; // 不检查 ParseError = 坏文件静默变空表（Day4 坑卡）
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const QJsonDocument doc = QJsonDocument::fromJson(file.readAll(), &err);
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if (err.error != QJsonParseError::NoError || !doc.isArray()) {
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statusBar()->showMessage(QStringLiteral("JSON 解析失败：") + err.errorString());
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return false;
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}
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clearAll();
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const QJsonArray arr = doc.array();
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for (const QJsonValue& v : arr) addRow(fromJson(v.toObject()));
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statusBar()->showMessage(QStringLiteral("已读取 %1 条记录").arg(arr.size()));
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return true;
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}
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void startImport(int rows) {
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m_actImport->setEnabled(false); // 防重复启动（也防重复 connect，Day2 坑卡）
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auto* thread = new QThread(this);
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auto* worker = new ImportWorker; // 不能给 parent：有 parent 的对象禁止 moveToThread
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worker->moveToThread(thread); // 必须在 start() 之前（Day5 讲授点）
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connect(thread, &QThread::started, worker, [worker, rows] { worker->doImport(rows); });
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// 跨线程信号 → 主线程槽：自动 Queued，addRow 在 GUI 线程安全执行
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connect(worker, &ImportWorker::rowReady, this,
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[this](const QString& name, double score, const QString& tag) {
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addRow(Student{name, score, tag});
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});
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connect(worker, &ImportWorker::finished, this, [this] {
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m_actImport->setEnabled(true);
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statusBar()->showMessage(QStringLiteral("后台导入完成"));
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emit importFinished();
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});
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connect(worker, &ImportWorker::finished, thread, &QThread::quit);
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connect(thread, &QThread::finished, worker, &QObject::deleteLater);
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connect(thread, &QThread::finished, thread, &QObject::deleteLater);
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thread->start();
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}
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signals:
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void importFinished();
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private slots:
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void onAdd() {
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AddStudentDialog dlg(this); // 模态：exec() 阻塞等结果（Day3）
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if (dlg.exec() == QDialog::Accepted) addRow(dlg.student());
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}
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void onImport() { startImport(10); }
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private:
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QTableWidget* m_table = nullptr;
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QAction* m_actImport = nullptr;
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QString m_dataPath;
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};
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// ------------------------------------------------------------ 自测入口 ----
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// 离屏自测：走一遍「添加→保存→清空→读回→后台导入」完整闭环并校验。
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static void runSelfTest(MainWindow* win) {
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const QString path = QCoreApplication::applicationDirPath() + "/students_selftest.json";
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win->addRow({QStringLiteral("张三"), 91.5, QStringLiteral("组长")});
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win->addRow({QStringLiteral("李四"), 88.0, QStringLiteral("美工")});
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if (!win->saveTo(path)) { QCoreApplication::exit(1); return; }
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win->clearAll();
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if (!win->loadFrom(path) || win->rowCount() != 2) {
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qCritical() << "自测失败：JSON 读回记录数 =" << win->rowCount() << "预期 2";
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QCoreApplication::exit(1);
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return;
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}
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qInfo() << "自测 1/2 通过：JSON 写入→清空→读回，2 条记录完整";
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QObject::connect(win, &MainWindow::importFinished, win, [win, path] {
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QFile::remove(path);
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if (win->rowCount() != 5) {
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qCritical() << "自测失败：导入后总数 =" << win->rowCount() << "预期 5";
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QCoreApplication::exit(1);
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return;
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}
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qInfo() << "自测 2/2 通过：后台线程导入 3 条，总计 5 条，界面未阻塞";
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QCoreApplication::exit(0);
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});
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win->startImport(3);
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}
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int main(int argc, char* argv[]) {
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QApplication app(argc, argv);
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MainWindow win;
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win.resize(560, 360);
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win.show();
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if (qgetenv("QT_QPA_PLATFORM") == "offscreen") {
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QTimer::singleShot(0, &win, [&win] { runSelfTest(&win); });
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}
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return app.exec();
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}
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#include "qt_student_manager.moc"
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