QSettings 详解

前言

在开发应用程序时࿰c;保存用户偏好设置、配置参数或其他小型持久化数据是一个常见需求。例如࿰c;记住窗口大小、用户登录状态或程序的语言选项。Qt 提供了 <code>QSettingscode> 类࿰c;可以方便地存储和读取这些配置信息。

<code>QSettingscode> 是一个跨平台的解决方案࿰c;支持多种存储方式࿰c;如注册表（Windows）或文件（INI 文件或类似格式）࿰c;并且可以处理分层结构的键值对。通过 <code>QSettingscode>࿰c;开发者无需关心平台差异即可轻松实现配置管理。

什么是 QSettings？

<code>QSettingscode> 是 Qt 的一个类࿰c;专门用于存储和读取持久化的键值对数据。其主要特点包括：

1. 跨平台支持：在 Windows 上默认使用注册表存储࿰c;在 Unix 系统上使用文本文件。
2. 层次化结构：支持分层的键值对存储࿰c;类似 JSON 树结构。
3. 方便快捷：提供简单的接口࿰c;无需手动解析或管理配置文件格式。

典型应用场景包括：

• 保存用户偏好（如主题、语言、窗口位置等）。
• 存储小型的应用程序配置。

QSettings 的构造函数和常用成员函数

构造函数

1. 默认构造函数

• 函数原型：

  <code class="prism language-cpp">class="token function">QSettingsclass="token punctuation">(QObject class="token operator">*parent class="token operator">= class="token keyword">nullptrclass="token punctuation">)class="token punctuation">;
  code>

• 作用：
  使用默认位置和格式创建一个 <code>QSettingscode> 对象。

• 示例代码：

  <code class="prism language-cpp">QSettings settingsclass="token punctuation">;
  code>

2. 指定组织和应用名称

• 函数原型：

  <code class="prism language-cpp">class="token function">QSettingsclass="token punctuation">(class="token keyword">const QString class="token operator">&organizationclass="token punctuation">, class="token keyword">const QString class="token operator">&applicationclass="token punctuation">, QObject class="token operator">*parent class="token operator">= class="token keyword">nullptrclass="token punctuation">)class="token punctuation">;
  code>

• 作用：
  指定组织名称和应用名称࿰c;用于确定配置文件的存储路径和命名规则。

• 参数：

  • <code>organizationcode>：组织名称࿰c;通常是公司名称。
  • <code>applicationcode>：应用名称。

• 示例代码：

  <code class="prism language-cpp">QSettings class="token function">settingsclass="token punctuation">(class="token string">"MyCompany"class="token punctuation">, class="token string">"MyApp"class="token punctuation">)class="token punctuation">;
  code>

3. 使用自定义文件

• 函数原型：

  <code class="prism language-cpp">class="token function">QSettingsclass="token punctuation">(class="token keyword">const QString class="token operator">&fileNameclass="token punctuation">, Format formatclass="token punctuation">, QObject class="token operator">*parent class="token operator">= class="token keyword">nullptrclass="token punctuation">)class="token punctuation">;
  code>

• 作用：
  使用指定文件和格式存储配置。

• 参数：

  • <code>fileNamecode>：配置文件路径。
  • <code>formatcode>：文件格式࿰c;可以是 <code>QSettings::IniFormatcode> 或 <code>QSettings::NativeFormatcode>。

• 示例代码：

  <code class="prism language-cpp">QSettings class="token function">settingsclass="token punctuation">(class="token string">"/path/to/config.ini"class="token punctuation">, QSettingsclass="token operator">::IniFormatclass="token punctuation">)class="token punctuation">;
  code>

常用成员函数

1. 写入设置

<code>setValuecode>

• 函数原型：

  <code class="prism language-cpp">class="token keyword">void class="token function">setValueclass="token punctuation">(class="token keyword">const QString class="token operator">&keyclass="token punctuation">, class="token keyword">const QVariant class="token operator">&valueclass="token punctuation">)class="token punctuation">;
  code>

• 作用：
  向配置文件写入一个键值对。

• 参数：

  • <code>keycode>：键名࿰c;支持分层结构（如 <code>"Window/Size"code>）。
  • <code>valuecode>：值࿰c;可以是基本类型或复杂类型（如 <code>QVariantcode> 支持的类型）。

• 示例代码：

  <code class="prism language-cpp">QSettings class="token function">settingsclass="token punctuation">(class="token string">"MyCompany"class="token punctuation">, class="token string">"MyApp"class="token punctuation">)class="token punctuation">;
  settingsclass="token punctuation">.class="token function">setValueclass="token punctuation">(class="token string">"Window/Size"class="token punctuation">, class="token function">QSizeclass="token punctuation">(class="token number">800class="token punctuation">, class="token number">600class="token punctuation">)class="token punctuation">)class="token punctuation">;
  settingsclass="token punctuation">.class="token function">setValueclass="token punctuation">(class="token string">"User/Name"class="token punctuation">, class="token string">"JohnDoe"class="token punctuation">)class="token punctuation">;
  code>

2. 读取设置

<code>valuecode>

• 函数原型：

  <code class="prism language-cpp">QVariant class="token function">valueclass="token punctuation">(class="token keyword">const QString class="token operator">&keyclass="token punctuation">, class="token keyword">const QVariant class="token operator">&defaultValue class="token operator">= class="token function">QVariantclass="token punctuation">(class="token punctuation">)class="token punctuation">) class="token keyword">constclass="token punctuation">;
  code>

• 作用：
  根据键名读取配置值࿰c;如果键不存在则返回默认值。

• 参数：

  • <code>keycode>：要读取的键名。
  • <code>defaultValuecode>：如果键不存在时返回的值࿰c;默认为空。

• 返回值：
  返回一个 <code>QVariantcode>࿰c;包含配置值。

• 示例代码：

  <code class="prism language-cpp">QVariant size class="token operator">= settingsclass="token punctuation">.class="token function">valueclass="token punctuation">(class="token string">"Window/Size"class="token punctuation">, class="token function">QSizeclass="token punctuation">(class="token number">640class="token punctuation">, class="token number">480class="token punctuation">)class="token punctuation">)class="token punctuation">;
  class="token function">qDebugclass="token punctuation">(class="token punctuation">) class="token operator"><< class="token string">"Window size:" class="token operator"><< sizeclass="token punctuation">.class="token function">toSizeclass="token punctuation">(class="token punctuation">)class="token punctuation">;
  code>

3. 检查键是否存在

contains_139"><code>containscode>

• 函数原型：

  <code class="prism language-cpp">class="token keyword">bool class="token function">containsclass="token punctuation">(class="token keyword">const QString class="token operator">&keyclass="token punctuation">) class="token keyword">constclass="token punctuation">;
  code>

• 作用：
  检查指定键是否存在。

• 返回值：
  如果键存在࿰c;返回 <code>truecode>；否则返回 <code>falsecode>。

• 示例代码：

  <code class="prism language-cpp">class="token keyword">if class="token punctuation">(settingsclass="token punctuation">.class="token function">containsclass="token punctuation">(class="token string">"User/Name"class="token punctuation">)class="token punctuation">) class="token punctuation">{class="token function">qDebugclass="token punctuation">(class="token punctuation">) class="token operator"><< class="token string">"Username exists!"class="token punctuation">;
  class="token punctuation">}
  code>

4. 删除设置

<code>removecode>

• 函数原型：

  <code class="prism language-cpp">class="token keyword">void class="token function">removeclass="token punctuation">(class="token keyword">const QString class="token operator">&keyclass="token punctuation">)class="token punctuation">;
  code>

• 作用：
  删除指定键及其所有子键。

• 示例代码：

  <code class="prism language-cpp">settingsclass="token punctuation">.class="token function">removeclass="token punctuation">(class="token string">"User/Name"class="token punctuation">)class="token punctuation">;
  class="token function">qDebugclass="token punctuation">(class="token punctuation">) class="token operator"><< class="token string">"Username removed!"class="token punctuation">;
  code>

5. 获取所有键

<code>allKeyscode>

• 函数原型：

  <code class="prism language-cpp">QStringList class="token function">allKeysclass="token punctuation">(class="token punctuation">) class="token keyword">constclass="token punctuation">;
  code>

• 作用：
  返回配置中所有的键名。

• 示例代码：

  <code class="prism language-cpp">QStringList keys class="token operator">= settingsclass="token punctuation">.class="token function">allKeysclass="token punctuation">(class="token punctuation">)class="token punctuation">;
  class="token keyword">for class="token punctuation">(class="token keyword">const QString class="token operator">&key class="token operator">: keysclass="token punctuation">) class="token punctuation">{class="token function">qDebugclass="token punctuation">(class="token punctuation">) class="token operator"><< keyclass="token punctuation">;
  class="token punctuation">}
  code>

6. 同步数据

c_202"><code>synccode>

• 函数原型：

  <code class="prism language-cpp">class="token keyword">void class="token function">syncclass="token punctuation">(class="token punctuation">)class="token punctuation">;
  code>

• 作用：
  将内存中的更改强制写入存储介质。

• 示例代码：

  <code class="prism language-cpp">settingsclass="token punctuation">.class="token function">setValueclass="token punctuation">(class="token string">"New/Key"class="token punctuation">, class="token number">123class="token punctuation">)class="token punctuation">;
  settingsclass="token punctuation">.class="token function">syncclass="token punctuation">(class="token punctuation">)class="token punctuation">;  class="token comment">// 确保数据立即写入
  code>

完整示例代码

以下示例展示了如何使用 <code>QSettingscode> 保存和读取用户配置：

<code class="prism language-cpp">class="token macro property">class="token directive-hash">#class="token directive keyword">include class="token string"><QCoreApplication>
class="token macro property">class="token directive-hash">#class="token directive keyword">include class="token string"><QSettings>
class="token macro property">class="token directive-hash">#class="token directive keyword">include class="token string"><QDebug>
class="token macro property">class="token directive-hash">#class="token directive keyword">include class="token string"><QSize>class="token keyword">int class="token function">mainclass="token punctuation">(class="token keyword">int argcclass="token punctuation">, class="token keyword">char class="token operator">*argvclass="token punctuation">[class="token punctuation">]class="token punctuation">) class="token punctuation">{QCoreApplication class="token function">appclass="token punctuation">(argcclass="token punctuation">, argvclass="token punctuation">)class="token punctuation">;class="token comment">// 创建 QSettings 对象QSettings class="token function">settingsclass="token punctuation">(class="token string">"MyCompany"class="token punctuation">, class="token string">"MyApp"class="token punctuation">)class="token punctuation">;class="token comment">// 写入设置settingsclass="token punctuation">.class="token function">setValueclass="token punctuation">(class="token string">"Window/Size"class="token punctuation">, class="token function">QSizeclass="token punctuation">(class="token number">800class="token punctuation">, class="token number">600class="token punctuation">)class="token punctuation">)class="token punctuation">;settingsclass="token punctuation">.class="token function">setValueclass="token punctuation">(class="token string">"User/Name"class="token punctuation">, class="token string">"JohnDoe"class="token punctuation">)class="token punctuation">;class="token comment">// 读取设置QSize windowSize class="token operator">= settingsclass="token punctuation">.class="token function">valueclass="token punctuation">(class="token string">"Window/Size"class="token punctuation">, class="token function">QSizeclass="token punctuation">(class="token number">640class="token punctuation">, class="token number">480class="token punctuation">)class="token punctuation">)class="token punctuation">.class="token function">toSizeclass="token punctuation">(class="token punctuation">)class="token punctuation">;QString userName class="token operator">= settingsclass="token punctuation">.class="token function">valueclass="token punctuation">(class="token string">"User/Name"class="token punctuation">, class="token string">"Unknown"class="token punctuation">)class="token punctuation">.class="token function">toStringclass="token punctuation">(class="token punctuation">)class="token punctuation">;class="token function">qDebugclass="token punctuation">(class="token punctuation">) class="token operator"><< class="token string">"Window size:" class="token operator"><< windowSizeclass="token punctuation">;class="token function">qDebugclass="token punctuation">(class="token punctuation">) class="token operator"><< class="token string">"User name:" class="token operator"><< userNameclass="token punctuation">;class="token comment">// 检查键是否存在class="token keyword">if class="token punctuation">(settingsclass="token punctuation">.class="token function">containsclass="token punctuation">(class="token string">"User/Name"class="token punctuation">)class="token punctuation">) class="token punctuation">{class="token function">qDebugclass="token punctuation">(class="token punctuation">) class="token operator"><< class="token string">"Username exists!"class="token punctuation">;class="token punctuation">}class="token comment">// 删除键settingsclass="token punctuation">.class="token function">removeclass="token punctuation">(class="token string">"User/Name"class="token punctuation">)class="token punctuation">;class="token comment">// 列出所有键QStringList keys class="token operator">= settingsclass="token punctuation">.class="token function">allKeysclass="token punctuation">(class="token punctuation">)class="token punctuation">;class="token keyword">for class="token punctuation">(class="token keyword">const QString class="token operator">&key class="token operator">: keysclass="token punctuation">) class="token punctuation">{class="token function">qDebugclass="token punctuation">(class="token punctuation">) class="token operator"><< keyclass="token punctuation">;class="token punctuation">}class="token keyword">return class="token number">0class="token punctuation">;
class="token punctuation">}
code>

总结

<code>QSettingscode> 是一个强大、灵活且简单易用的配置管理工具࿰c;它为应用程序的配置持久化提供了跨平台的解决方案。无论是保存窗口大小、用户偏好࿰c;还是管理复杂的键值对结构࿰c;<code>QSettingscode> 都能很好地满足需求。

通过合理地组织和使用 <code>QSettingscode> 的键值结构࿰c;可以大大简化配置的存取逻辑࿰c;从而提升程序的易维护性和用户体验。