qt-declare-private

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1. 模型

Example类

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class Example {
    Q_OBJECT
    Q_DECLARE_PRIVATE(Example)
public:
    Example();
    ~Example();

    ExamplePrivate  *d_ptr;
};

ExamplePrivate类

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class ExamplePrivate {
    Q_DECLARE_PUBLIC(Example)
public:
    ExamplePrivate(Example *example);

private:
    Example     *q_ptr;
};

2. Q_DECLARE_PRIVATE 宏的展开

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// 定义
#define Q_DECLARE_PRIVATE(Class) \
    inline Class##Private* d_func() \
    { Q_CAST_IGNORE_ALIGN(return reinterpret_cast<Class##Private *>(qGetPtrHelper(d_ptr));) } \
    inline const Class##Private* d_func() const \
    { Q_CAST_IGNORE_ALIGN(return reinterpret_cast<const Class##Private *>(qGetPtrHelper(d_ptr));) } \
    friend class Class##Private;

// 展开
inline ExamplePrivate* d_func() {
    return reinterpret_cast<ExamplePrivate *>(d_ptr);
}
friend class ExamplePrivate;

3. Q_DECLARE_PUBLIC 宏的展开

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// 定义
#define Q_DECLARE_PUBLIC(Class)                                    \
    inline Class* q_func() { return static_cast<Class *>(q_ptr); } \
    inline const Class* q_func() const { return static_cast<const Class *>(q_ptr); } \
    friend class Class;

// 展开
Example* q_func() {
    return static_cast<Example *>(q_ptr);
}
friend class Example;

4. Q_D

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// 定义
#define Q_D(Class) Class##Private * const d = d_func()

// 展开
Example * const d = d_func();

5. Q_Q

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// 定义
#define Q_Q(Class) Class * const q = q_func()

// 展开
Example * const q = q_func();

6. 总结

Q_DECLARE_PRIVATE一般用于主类的XXXPrivate成员声明，而且声明为friend类型，可以让这个XXXPrivate类型成员方便的访问主类所有成员；Q_DECLARE_PUBLIC用于XXXPrivate类里面对主类的声明，也将主类声明为friend类型；在主类里面可以用Q_D访问XXXPrivate类型的指针，在XXXPrivate类里面可以用Q_Q访问主类指针