First Commit

Projects/01_UnitConverter/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.16)
+project(UnitConverter VERSION 1.0 LANGUAGES CXX)
+set(CMAKE_AUTOMOC ON)
+set(CMAKE_AUTOUIC ON)
+set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)
+find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Widgets)
+find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS Widgets)
+if(QT_VERSION_MAJOR EQUAL 5 AND Qt5Core_VERSION VERSION_LESS 5.14.2)
+    message(FATAL_ERROR "Qt 5.14.2 or newer is required.")
+endif()
+if(QT_VERSION_MAJOR EQUAL 6)
+    set(CMAKE_CXX_STANDARD 17)
+endif()
+if(MSVC)
+    add_compile_options(/utf-8)
+else()
+    add_compile_options(-Wall -Wextra -Wpedantic)
+endif()
+add_executable(UnitConverter WIN32 main.cpp appearance.h mainwindow.cpp mainwindow.h conversion.cpp conversion.h mainwindow.ui)
+target_link_libraries(UnitConverter PRIVATE Qt${QT_VERSION_MAJOR}::Widgets)
+option(BUILD_TEACHING_TESTS "Build teaching project tests" OFF)
+if(BUILD_TEACHING_TESTS)
+    enable_testing()
+    find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS Test)
+    add_executable(test_UnitConverter tests/test_UnitConverter.cpp mainwindow.cpp mainwindow.h
+                   conversion.cpp conversion.h mainwindow.ui)
+    target_include_directories(test_UnitConverter PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+    target_link_libraries(test_UnitConverter PRIVATE Qt${QT_VERSION_MAJOR}::Widgets Qt${QT_VERSION_MAJOR}::Test)
+    add_test(NAME UnitConverter COMMAND test_UnitConverter -platform offscreen)
+endif()
+

Projects/01_UnitConverter/README.md

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+# 项目一：单位换算器
+
+适合第2—3章讲解信号槽、组件访问和函数分工，第4章可继续练习下拉框与字符串处理。
+
+## 运行后试什么
+
+初始输入为 25，源单位为摄氏度，目标单位为华氏度。点击“换算”，应显示 77 °F，并在下方显示公式。也可以在输入框内按 Enter。
+
+切换到长度后，默认将米换成厘米。输入 1，结果应为 100 cm。“交换单位”只交换源单位与目标单位，输入值保持不变。修改输入或单位会清空旧结果，防止把上次的答案当成当前答案。
+
+支持摄氏度、华氏度、开尔文，以及毫米、厘米、米、千米、英寸和英尺。结果最多显示 12 位有效数字。
+
+## 课堂任务
+
+第一步只保留温度输入、换算按钮和结果框。让学生完成摄氏度到华氏度的换算，并解释输入框返回的是字符串，计算需要数值。
+
+第二步加入返回值检查。分别输入空字符串、abc 和 25.5，观察程序怎样决定是否继续计算。当前工程用完整字符串的格式检查配合 toDouble，支持小数和科学计数法，不接受千位分隔符。
+
+第三步加入源单位和目标单位。先统一到摄氏度，再计算目标温度。让学生画出华氏度到开尔文的两步过程，避免只背诵一个总公式。
+
+第四步加入长度换算。单位比例写在数组中，先解释数组下标与下拉框顺序的对应关系，再讨论增加一个单位时需要修改哪些位置。
+
+## 一次换算怎样完成
+
+1. convertButton 发出 clicked 信号，调用 convertValue。
+2. 主窗口读取 inputEdit 的文本和两个下拉框的索引。
+3. Conversion::convert 检查输入，计算结果，返回 Result。
+4. 主窗口根据 Result::ok 显示结果或错误原因。
+5. 计算成功后允许复制；输入变化后立即禁用复制并清除旧结果。
+
+Conversion::convert 不直接操作输入框或标签，因此可以使用不同界面调用，也可以单独测试。
+
+## 需要解释的条件
+
+- 温度不能低于绝对零度。摄氏度下限为 −273.15，华氏度下限为 −459.67，开尔文下限为 0。
+- 边界比较保留极小的浮点误差余量，防止换算时的舍入把绝对零度判为非法值。
+- 本工具中的长度表示非负长度，不表示带方向的坐标位移。
+- 输入可以合法，但结果仍可能溢出。输入检查和结果检查分别负责两个阶段。
+- 显示的有效数字有限，程序不承诺任意精度计算。
+
+## 学生练习
+
+1. 增加“码”，已知 1 yd = 0.9144 m。检查它与米、英尺之间的换算。
+2. 增加“使用本次结果继续换算”按钮，说明它与“交换单位”的区别。
+3. 为结果增加可选择的显示精度，并解释显示精度为什么不等于计算精度。
+
+## 验收用例
+
+| 操作 | 预期 |
+|---|---|
+| 0 °C → °F | 32 |
+| 212 °F → °C | 100 |
+| −459.67 °F → K | 0 |
+| −274 °C → K | 显示低于绝对零度的提示 |
+| 1 in → cm | 2.54 |
+| 1 ft → m | 0.3048 |
+| 输入 12abc、nan 或 1,000 | 拒绝计算 |
+| 算出结果后修改输入 | 旧结果清空，复制按钮不可用 |
+

Projects/01_UnitConverter/UnitConverter.pro

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+QT += widgets
+CONFIG += c++14
+greaterThan(QT_MAJOR_VERSION, 5): CONFIG += c++17
+TEMPLATE = app
+TARGET = UnitConverter
+SOURCES += main.cpp mainwindow.cpp conversion.cpp
+HEADERS += mainwindow.h conversion.h
+FORMS += mainwindow.ui
+msvc: QMAKE_CXXFLAGS += /utf-8
+

Projects/01_UnitConverter/appearance.h

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+#pragma once
+#include <QApplication>
+#include <QFont>
+#include <QStyleFactory>
+
+inline void applyAppearance(QApplication &app)
+{
+    app.setStyle(QStyleFactory::create(QStringLiteral("Fusion")));
+    app.setFont(QFont(QStringLiteral("Microsoft YaHei UI"), 11));
+    app.setStyleSheet(QStringLiteral(
+        "QMainWindow { background: #f5f7fb; }"
+        "QLabel { color: #23364c; }"
+        "QLabel#titleLabel { font-size: 27px; font-weight: bold; color: #173b63; }"
+        "QLabel#subtitleLabel, QLabel#helpLabel { color: #52657a; }"
+        "QGroupBox { background: white; border: 1px solid #d6e0eb;"
+        " border-radius: 8px; margin-top: 12px; padding: 18px 12px 12px; }"
+        "QGroupBox::title { subcontrol-origin: margin; left: 12px; padding: 0 6px; }"
+        "QLineEdit, QSpinBox, QComboBox { min-height: 32px; padding: 3px 8px; }"
+        "QLineEdit, QSpinBox, QComboBox, QPlainTextEdit, QListWidget"
+        " { background: white; color: #23364c; }"
+        "QPushButton { min-height: 34px; padding: 4px 14px; }"
+        "QPushButton#convertButton, QPushButton#startButton, QPushButton#drawButton,"
+        " QPushButton#applyButton, QPushButton#groupsButton { background: #255c93;"
+        " color: white; border: 1px solid #255c93; border-radius: 5px; }"
+        "QPushButton:disabled, QPushButton#convertButton:disabled,"
+        " QPushButton#startButton:disabled, QPushButton#drawButton:disabled,"
+        " QPushButton#applyButton:disabled, QPushButton#groupsButton:disabled"
+        " { color: #8995a3; background: #e6ebf1; border-color: #d6e0eb; }"
+        "QLabel#statusLabel { color: #185376; }"
+        "QLineEdit#resultEdit { font-size: 23px; min-height: 45px; color: #175e53; }"
+        "QLabel#timeLabel { font: bold 76px 'Consolas'; color: #173b63; }"
+        "QProgressBar { border: 1px solid #d6e0eb; border-radius: 6px; height: 14px; }"
+        "QProgressBar::chunk { background: #2b8a7d; border-radius: 5px; }"));
+}

Projects/01_UnitConverter/conversion.cpp

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+#include "conversion.h"
+#include <QRegularExpression>
+#include <cmath>
+
+namespace Conversion {
+QStringList units(Category category)
+{
+    if (category == Category::Temperature)
+        return {QStringLiteral("摄氏度 °C"), QStringLiteral("华氏度 °F"),
+                QStringLiteral("开尔文 K")};
+    return {QStringLiteral("毫米 mm"), QStringLiteral("厘米 cm"),
+            QStringLiteral("米 m"), QStringLiteral("千米 km"),
+            QStringLiteral("英寸 in"), QStringLiteral("英尺 ft")};
+}
+
+Result convert(const QString &text, Category category, int from, int to)
+{
+    Result result;
+    const QString input = text.trimmed();
+    // 先检查完整输入，避免把“12abc”误当成有效数值。
+    static const QRegularExpression number(
+        QStringLiteral("^[+-]?(?:[0-9]+(?:\\.[0-9]*)?|\\.[0-9]+)(?:[eE][+-]?[0-9]+)?$"));
+    if (!number.match(input).hasMatch()) {
+        result.error = QStringLiteral("请输入完整的数值，例如 25、-10.5 或 1e3；小数点使用英文句点。");
+        return result;
+    }
+    bool ok = false;
+    const double value = input.toDouble(&ok);
+    if (!ok || !std::isfinite(value)) {
+        result.error = QStringLiteral("输入超出了可计算的数值范围，请减小数值。");
+        return result;
+    }
+    const QStringList names = units(category);
+    if (from < 0 || to < 0 || from >= names.size() || to >= names.size()) {
+        result.error = QStringLiteral("请选择有效的单位。");
+        return result;
+    }
+    if (category == Category::Temperature) {
+        // 先统一为摄氏度，再换算为目标单位，避免为每对单位各写一套公式。
+        double celsius = value;
+        QString first;
+        if (from == 1) {
+            celsius = (value - 32.0) / 1.8;
+            first = QStringLiteral("先换成摄氏度：C = (F − 32) ÷ 1.8。");
+        } else if (from == 2) {
+            celsius = value - 273.15;
+            first = QStringLiteral("先换成摄氏度：C = K − 273.15。");
+        } else {
+            first = QStringLiteral("输入已经是摄氏度，可直接作为中间值。");
+        }
+        if (celsius < -273.15 - 1e-9) {
+            result.error = QStringLiteral("温度不能低于绝对零度：−273.15 °C / −459.67 °F / 0 K。");
+            return result;
+        }
+        // 允许边界处的浮点舍入误差，避免把绝对零度误判为非法输入。
+        if (celsius < -273.15)
+            celsius = -273.15;
+        QString second;
+        if (to == 1) {
+            result.value = celsius * 1.8 + 32.0;
+            second = QStringLiteral("再换成华氏度：F = C × 1.8 + 32。");
+        } else if (to == 2) {
+            result.value = celsius + 273.15;
+            second = QStringLiteral("再换成开尔文：K = C + 273.15。");
+        } else {
+            result.value = celsius;
+            second = QStringLiteral("目标是摄氏度，中间值就是结果。");
+        }
+        result.explanation = first + QStringLiteral("\n") + second;
+    } else {
+        if (value < 0.0) {
+            result.error = QStringLiteral("本工具换算的是长度，输入值不能为负数。");
+            return result;
+        }
+        const double metersPerUnit[] = {0.001, 0.01, 1.0, 1000.0, 0.0254, 0.3048};
+        result.value = value * (metersPerUnit[from] / metersPerUnit[to]);
+        result.explanation =
+            QStringLiteral("以米为统一单位：结果 = 输入值 × 源单位的米数 ÷ 目标单位的米数。\n"
+                           "本次计算：%1 × %2 ÷ %3。")
+                .arg(input)
+                .arg(metersPerUnit[from], 0, 'g', 12)
+                .arg(metersPerUnit[to], 0, 'g', 12);
+    }
+    if (!std::isfinite(result.value)) {
+        result.error = QStringLiteral("换算结果超出了可显示的数值范围。");
+        return result;
+    }
+    if (result.value == 0.0)
+        result.value = 0.0; // 避免显示 -0。
+    result.ok = true;
+    return result;
+}
+}
+

Projects/01_UnitConverter/conversion.h

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+#pragma once
+#include <QString>
+#include <QStringList>
+
+namespace Conversion {
+enum class Category { Temperature, Length };
+
+struct Result {
+    bool ok = false;
+    double value = 0.0;
+    QString explanation;
+    QString error;
+};
+
+QStringList units(Category category);
+Result convert(const QString &text, Category category, int from, int to);
+}
+

Projects/01_UnitConverter/main.cpp

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+#include "mainwindow.h"
+#include "appearance.h"
+#include <QApplication>
+#include <QFont>
+#include <QStyleFactory>
+
+int main(int argc, char *argv[])
+{
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
+    QApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+    QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
+#endif
+    QApplication app(argc, argv);
+    applyAppearance(app);
+    MainWindow window;
+    window.show();
+    return app.exec();
+}
+

Projects/01_UnitConverter/mainwindow.cpp

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+#include "mainwindow.h"
+#include "ui_mainwindow.h"
+#include "conversion.h"
+#include <QClipboard>
+#include <QApplication>
+
+MainWindow::MainWindow(QWidget *parent)
+    : QMainWindow(parent), ui(new Ui::MainWindow)
+{
+    ui->setupUi(this);
+    ui->categoryCombo->addItems({tr("温度"), tr("长度")});
+    connect(ui->categoryCombo, static_cast<void (QComboBox::*)(int)>(&QComboBox::currentIndexChanged),
+            this, &MainWindow::changeCategory);
+    connect(ui->convertButton, &QPushButton::clicked, this, &MainWindow::convertValue);
+    connect(ui->inputEdit, &QLineEdit::returnPressed, this, &MainWindow::convertValue);
+    connect(ui->inputEdit, &QLineEdit::textChanged, this, &MainWindow::clearResult);
+    connect(ui->fromCombo, static_cast<void (QComboBox::*)(int)>(&QComboBox::currentIndexChanged),
+            this, &MainWindow::clearResult);
+    connect(ui->toCombo, static_cast<void (QComboBox::*)(int)>(&QComboBox::currentIndexChanged),
+            this, &MainWindow::clearResult);
+    connect(ui->swapButton, &QPushButton::clicked, this, [this] {
+        const int previousFrom = ui->fromCombo->currentIndex();
+        ui->fromCombo->setCurrentIndex(ui->toCombo->currentIndex());
+        ui->toCombo->setCurrentIndex(previousFrom);
+        ui->inputEdit->setFocus();
+    });
+    connect(ui->clearButton, &QPushButton::clicked, this, [this] {
+        ui->inputEdit->clear();
+        clearResult();
+        ui->inputEdit->setFocus();
+    });
+    connect(ui->copyButton, &QPushButton::clicked, this, [this] {
+        QApplication::clipboard()->setText(ui->resultEdit->text());
+        ui->statusLabel->setText(tr("结果已复制。"));
+    });
+    changeCategory();
+    ui->inputEdit->setText(QStringLiteral("25"));
+}
+
+MainWindow::~MainWindow() { delete ui; }
+
+void MainWindow::changeCategory()
+{
+    const auto category = ui->categoryCombo->currentIndex() == 0
+        ? Conversion::Category::Temperature : Conversion::Category::Length;
+    const QStringList names = Conversion::units(category);
+    ui->fromCombo->clear();
+    ui->toCombo->clear();
+    ui->fromCombo->addItems(names);
+    ui->toCombo->addItems(names);
+    ui->fromCombo->setCurrentIndex(category == Conversion::Category::Length ? 2 : 0);
+    ui->toCombo->setCurrentIndex(1);
+    clearResult();
+}
+
+void MainWindow::clearResult()
+{
+    ui->resultEdit->clear();
+    ui->formulaLabel->setText(tr("选择单位并输入数值，点击“换算”查看计算过程。"));
+    ui->statusLabel->clear();
+    ui->copyButton->setEnabled(false);
+}
+
+void MainWindow::convertValue()
+{
+    const auto category = ui->categoryCombo->currentIndex() == 0
+        ? Conversion::Category::Temperature : Conversion::Category::Length;
+    const auto result = Conversion::convert(ui->inputEdit->text(), category,
+                                            ui->fromCombo->currentIndex(),
+                                            ui->toCombo->currentIndex());
+    if (!result.ok) {
+        clearResult();
+        ui->statusLabel->setText(result.error);
+        ui->inputEdit->setFocus();
+        return;
+    }
+    ui->resultEdit->setText(QStringLiteral("%1 %2")
+        .arg(result.value, 0, 'g', 12).arg(ui->toCombo->currentText()));
+    ui->formulaLabel->setText(result.explanation);
+    ui->statusLabel->setText(tr("换算完成。结果最多显示 12 位有效数字。"));
+    ui->copyButton->setEnabled(true);
+}
+

Projects/01_UnitConverter/mainwindow.h

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+#pragma once
+#include <QMainWindow>
+namespace Ui { class MainWindow; }
+
+class MainWindow : public QMainWindow {
+    Q_OBJECT
+public:
+    explicit MainWindow(QWidget *parent = nullptr);
+    ~MainWindow() override;
+private:
+    Ui::MainWindow *ui;
+    void changeCategory();
+    void clearResult();
+    void convertValue();
+};
+

Projects/01_UnitConverter/mainwindow.ui

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+<?xml version="1.0" encoding="UTF-8"?>
+<ui version="4.0">
+ <class>MainWindow</class>
+ <widget class="QMainWindow" name="MainWindow">
+  <property name="windowTitle">
+   <string>单位换算器</string>
+  </property>
+  <property name="geometry">
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>840</width>
+    <height>650</height>
+   </rect>
+  </property>
+  <widget class="QWidget" name="centralwidget">
+   <layout class="QVBoxLayout" name="rootLayout">
+    <property name="spacing">
+     <number>12</number>
+    </property>
+    <property name="leftMargin">
+     <number>24</number>
+    </property>
+    <property name="topMargin">
+     <number>24</number>
+    </property>
+    <property name="rightMargin">
+     <number>24</number>
+    </property>
+    <property name="bottomMargin">
+     <number>24</number>
+    </property>
+    <item>
+     <widget class="QLabel" name="titleLabel">
+      <property name="text">
+       <string>单位换算器</string>
+      </property>
+      <property name="textFormat">
+       <enum>Qt::PlainText</enum>
+      </property>
+     </widget>
+    </item>
+    <item>
+     <widget class="QLabel" name="subtitleLabel">
+      <property name="text">
+       <string>输入一个数值，查看换算结果和计算过程。</string>
+      </property>
+      <property name="textFormat">
+       <enum>Qt::PlainText</enum>
+      </property>
+      <property name="wordWrap">
+       <bool>true</bool>
+      </property>
+     </widget>
+    </item>
+    <item>
+     <widget class="QGroupBox" name="inputGroup">
+      <property name="title">
+       <string>输入与单位</string>
+      </property>
+     <layout class="QGridLayout" name="inputLayout" columnstretch="1,1">
+       <property name="spacing">
+        <number>12</number>
+       </property>
+       <item row="0" column="0">
+        <widget class="QLabel" name="categoryLabel">
+         <property name="text">
+          <string>换算类型</string>
+         </property>
+         <property name="textFormat">
+          <enum>Qt::PlainText</enum>
+         </property>
+        </widget>
+       </item>
+       <item row="0" column="1">
+        <widget class="QLabel" name="inputLabel">
+         <property name="text">
+          <string>输入数值</string>
+         </property>
+         <property name="textFormat">
+          <enum>Qt::PlainText</enum>
+         </property>
+        </widget>
+       </item>
+       <item row="1" column="0">
+        <widget class="QComboBox" name="categoryCombo" />
+       </item>
+       <item row="1" column="1">
+        <widget class="QLineEdit" name="inputEdit">
+         <property name="placeholderText">
+          <string>例如 25、-10.5 或 1e3</string>
+         </property>
+         <property name="maxLength">
+          <number>100</number>
+         </property>
+        </widget>
+       </item>
+       <item row="2" column="0">
+        <widget class="QLabel" name="fromLabel">
+         <property name="text">
+          <string>源单位</string>
+         </property>
+         <property name="textFormat">
+          <enum>Qt::PlainText</enum>
+         </property>
+        </widget>
+       </item>
+       <item row="2" column="1">
+        <widget class="QLabel" name="toLabel">
+         <property name="text">
+          <string>目标单位</string>
+         </property>
+         <property name="textFormat">
+          <enum>Qt::PlainText</enum>
+         </property>
+        </widget>
+       </item>
+       <item row="3" column="0">
+        <widget class="QComboBox" name="fromCombo" />
+       </item>
+       <item row="3" column="1">
+        <widget class="QComboBox" name="toCombo" />
+       </item>
+      </layout>
+     </widget>
+    </item>
+    <item>
+     <layout class="QHBoxLayout" name="actionLayout">
+      <property name="spacing">
+       <number>12</number>
+      </property>
+      <item>
+       <widget class="QPushButton" name="convertButton">
+        <property name="text">
+         <string>换算</string>
+        </property>
+        <property name="default">
+         <bool>true</bool>
+        </property>
+       </widget>
+      </item>
+      <item>
+       <widget class="QPushButton" name="swapButton">
+        <property name="text">
+         <string>交换单位</string>
+        </property>
+       </widget>
+      </item>
+      <item>
+       <widget class="QPushButton" name="clearButton">
+        <property name="text">
+         <string>清空输入</string>
+        </property>
+       </widget>
+      </item>
+     </layout>
+    </item>
+    <item>
+     <widget class="QGroupBox" name="resultGroup">
+      <property name="title">
+       <string>换算结果</string>
+      </property>
+      <layout class="QVBoxLayout" name="resultLayout">
+       <property name="spacing">
+        <number>12</number>
+       </property>
+       <item>
+        <widget class="QLineEdit" name="resultEdit">
+         <property name="readOnly">
+          <bool>true</bool>
+         </property>
+         <property name="placeholderText">
+          <string>结果将在这里显示</string>
+         </property>
+        </widget>
+       </item>
+       <item>
+        <widget class="QLabel" name="formulaLabel">
+         <property name="text">
+          <string />
+         </property>
+         <property name="textFormat">
+          <enum>Qt::PlainText</enum>
+         </property>
+         <property name="wordWrap">
+          <bool>true</bool>
+         </property>
+         <property name="minimumSize">
+          <size>
+           <width>0</width>
+           <height>70</height>
+          </size>
+         </property>
+        </widget>
+       </item>
+       <item>
+        <widget class="QPushButton" name="copyButton">
+         <property name="text">
+          <string>复制结果</string>
+         </property>
+         <property name="enabled">
+          <bool>false</bool>
+         </property>
+        </widget>
+       </item>
+      </layout>
+     </widget>
+    </item>
+    <item>
+     <widget class="QLabel" name="statusLabel">
+      <property name="text">
+       <string />
+      </property>
+      <property name="textFormat">
+       <enum>Qt::PlainText</enum>
+      </property>
+      <property name="wordWrap">
+       <bool>true</bool>
+      </property>
+      <property name="minimumSize">
+       <size>
+        <width>0</width>
+        <height>55</height>
+       </size>
+      </property>
+     </widget>
+    </item>
+    <item>
+     <widget class="QLabel" name="helpLabel">
+      <property name="text">
+       <string>长度须为非负数，温度须不低于绝对零度。修改输入或单位后，需要重新换算。</string>
+      </property>
+      <property name="textFormat">
+       <enum>Qt::PlainText</enum>
+      </property>
+      <property name="wordWrap">
+       <bool>true</bool>
+      </property>
+     </widget>
+    </item>
+   </layout>
+  </widget>
+ </widget>
+ <resources />
+ <connections />
+</ui>

Projects/01_UnitConverter/tests/test_UnitConverter.cpp

@@ -0,0 +1,90 @@
+#include <QtTest>
+#include <QComboBox>
+#include <QLineEdit>
+#include <QLabel>
+#include <QPushButton>
+#include "conversion.h"
+#include "mainwindow.h"
+#include <QApplication>
+#include <QDir>
+#include "appearance.h"
+
+static void savePreview(QWidget &window, const QString &fileName)
+{
+    const QString folder = QString::fromLocal8Bit(qgetenv("QT_TEACHING_SCREENSHOTS"));
+    if (folder.isEmpty()) return;
+    QDir().mkpath(folder);
+    window.show();
+    QApplication::processEvents();
+    QVERIFY(window.grab().save(QDir(folder).filePath(fileName)));
+}
+
+class ConverterTest : public QObject {
+    Q_OBJECT
+private slots:
+    void initTestCase() { applyAppearance(*qApp); }
+    void knownValues_data()
+    {
+        QTest::addColumn<int>("category");
+        QTest::addColumn<QString>("input");
+        QTest::addColumn<int>("from");
+        QTest::addColumn<int>("to");
+        QTest::addColumn<double>("expected");
+        QTest::newRow("freezing") << 0 << QStringLiteral("0") << 0 << 1 << 32.0;
+        QTest::newRow("boiling") << 0 << QStringLiteral("212") << 1 << 0 << 100.0;
+        QTest::newRow("minus40") << 0 << QStringLiteral("-40") << 0 << 1 << -40.0;
+        QTest::newRow("kelvin") << 0 << QStringLiteral("273.15") << 2 << 0 << 0.0;
+        QTest::newRow("absolute-zero-C") << 0 << QStringLiteral("-273.15") << 0 << 2 << 0.0;
+        QTest::newRow("absolute-zero-F") << 0 << QStringLiteral("-459.67") << 1 << 2 << 0.0;
+        QTest::newRow("meter-cm") << 1 << QStringLiteral("1") << 2 << 1 << 100.0;
+        QTest::newRow("inch-cm") << 1 << QStringLiteral("1") << 4 << 1 << 2.54;
+        QTest::newRow("foot-meter") << 1 << QStringLiteral("1") << 5 << 2 << 0.3048;
+        QTest::newRow("km-mm") << 1 << QStringLiteral("1") << 3 << 0 << 1000000.0;
+        QTest::newRow("scientific") << 1 << QStringLiteral(" 1e3 ") << 0 << 2 << 1.0;
+        QTest::newRow("same-unit") << 1 << QStringLiteral("12.25") << 2 << 2 << 12.25;
+    }
+    void knownValues()
+    {
+        QFETCH(int, category); QFETCH(QString, input);
+        QFETCH(int, from); QFETCH(int, to); QFETCH(double, expected);
+        auto result = Conversion::convert(input, static_cast<Conversion::Category>(category), from, to);
+        QVERIFY2(result.ok, qPrintable(result.error));
+        QVERIFY(qAbs(result.value - expected) <= 1e-9 * qMax(1.0, qAbs(expected)));
+    }
+    void rejectsInvalid()
+    {
+        for (const QString &text : {QString(), QStringLiteral("12abc"), QStringLiteral("nan"),
+             QStringLiteral("inf"), QStringLiteral("1,000"), QStringLiteral("1e309")})
+            QVERIFY(!Conversion::convert(text, Conversion::Category::Length, 2, 1).ok);
+        QVERIFY(!Conversion::convert(QStringLiteral("-1"), Conversion::Category::Length, 2, 1).ok);
+        QVERIFY(!Conversion::convert(QStringLiteral("-274"), Conversion::Category::Temperature, 0, 2).ok);
+        QVERIFY(!Conversion::convert(QStringLiteral("-0.1"), Conversion::Category::Temperature, 2, 0).ok);
+        QVERIFY(!Conversion::convert(QStringLiteral("1e308"), Conversion::Category::Length, 3, 0).ok);
+    }
+    void uiWorkflow()
+    {
+        MainWindow w; w.show();
+        auto *input = w.findChild<QLineEdit *>(QStringLiteral("inputEdit"));
+        auto *result = w.findChild<QLineEdit *>(QStringLiteral("resultEdit"));
+        auto *convert = w.findChild<QPushButton *>(QStringLiteral("convertButton"));
+        input->setText(QStringLiteral("25"));
+        QTest::mouseClick(convert, Qt::LeftButton);
+        QVERIFY(result->text().startsWith(QStringLiteral("77 ")));
+        savePreview(w, QStringLiteral("01_converter.png"));
+        input->setText(QStringLiteral("bad"));
+        QVERIFY(result->text().isEmpty());
+        QTest::mouseClick(convert, Qt::LeftButton);
+        QVERIFY(!w.findChild<QLabel *>(QStringLiteral("statusLabel"))->text().isEmpty());
+        QVERIFY(!w.findChild<QPushButton *>(QStringLiteral("copyButton"))->isEnabled());
+        w.findChild<QComboBox *>(QStringLiteral("categoryCombo"))->setCurrentIndex(1);
+        input->setText(QStringLiteral("1"));
+        QTest::mouseClick(convert, Qt::LeftButton);
+        QVERIFY(result->text().startsWith(QStringLiteral("100 ")));
+        QTest::mouseClick(w.findChild<QPushButton *>(QStringLiteral("swapButton")), Qt::LeftButton);
+        QTest::mouseClick(convert, Qt::LeftButton);
+        QVERIFY(result->text().startsWith(QStringLiteral("0.01 ")));
+    }
+};
+QTEST_MAIN(ConverterTest)
+#include "test_UnitConverter.moc"
+

Projects/01_UnitConverter/tests/test_UnitConverter.pro

@@ -0,0 +1,11 @@
+QT += widgets testlib
+CONFIG += c++14 console testcase
+greaterThan(QT_MAJOR_VERSION, 5): CONFIG += c++17
+TEMPLATE = app
+TARGET = test_UnitConverter
+INCLUDEPATH += ..
+SOURCES += test_UnitConverter.cpp ../mainwindow.cpp ../conversion.cpp
+HEADERS += ../mainwindow.h ../conversion.h
+FORMS += ../mainwindow.ui
+msvc: QMAKE_CXXFLAGS += /utf-8
+