学习记录-Qt中使用Q指针和D指针

本文主要是介绍学习记录-Qt中使用Q指针和D指针，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

 

总结网上看到的文章，使用D指针的好处如下：

1.保证代码的二进制兼容性；

2.隐藏实现细节；

3.提高编译速度；

Qt关于D指针和Q指针的定义：

d_ptr指针指向私有实现类，使用如下宏定义辅助函数和声明友元类

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

 q_ptr指针指向父类，使用如下宏定义辅助函数和声明友元类

#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;  

 使用D指针和Q指针的宏定义

#define Q_D(Class) Class##Private * const d = d_func()  
#define Q_Q(Class) Class * const q = q_func()  

 

/*Some classes do not permit copies to be made of an object. Theseclasses contains a private copy constructor and assignmentoperator to disable copying (the compiler gives an error message).
*/
#define Q_DISABLE_COPY(Class) \Class(const Class &) Q_DECL_EQ_DELETE;\Class &operator=(const Class &) Q_DECL_EQ_DELETE;

定义一个类如下：

class TestClassPrivate;
class TestClass
{
public:TestClass();~TestClass();private:TestClassPrivate * const d_ptr;Q_DECLARE_PRIVATE(TestClass);
};

 

定义一个私有类如下：

class TestClass;
class TestClassPrivate
{
public:TestClassPrivate(TestClass *q);private:TestClass * const q_ptr;Q_DECLARE_PUBLIC(TestClass);int m_val1;
};

一个实例：

testclass.h

#ifndef TESTCLASS_H
#define TESTCLASS_H#include <QObject>class TestClassPrivate;
class TestClass
{
public:explicit TestClass(QObject *parent);~TestClass();void doFunc();private:void showMsg(QString str);private:TestClassPrivate * const d_ptr;Q_DECLARE_PRIVATE(TestClass);Q_DISABLE_COPY(TestClass);
};#endif // TESTCLASS_H

testclass.cpp

#include "testclass.h"
#include <QtDebug>class TestClassPrivate
{
public:TestClassPrivate(TestClass *q) :q_ptr(q){}void testFunc(){Q_Q(TestClass);q->showMsg("hello!");}private:TestClass * const q_ptr;Q_DECLARE_PUBLIC(TestClass);
};TestClass::TestClass(QObject *parent):d_ptr(new TestClassPrivate(this))
{}TestClass::~TestClass()
{Q_D(TestClass);delete d;
}void TestClass::doFunc()
{Q_D(TestClass);d->testFunc();
}void TestClass::showMsg(QString str)
{qDebug() << str;
}

以上是使用Qt自带宏实现。

 存在问题：

1.d_ptr需要手动释放，有可能粗心忘记了；

2.d_ptr和q_pt的声明看起来不够简洁；

问题改进：

1.使用QScopedPointer，不用关注D指针的释放；

2.使用宏改进使用；

#define DQ_DECLARE_PRIVATE(Class) \Q_DECLARE_PRIVATE(Class) \QScopedPointer<Class##Private> d_ptr;#define DQ_DECLARE_PUBLIC(Class) \Q_DECLARE_PUBLIC(Class) \Class* q_ptr;#define DQ_SAFE_DELETE(p) do { if(p) { delete (p); (p) = 0; } } while(0)

使用实例：

dqglobal.h

#ifndef DQGLOBAL_H
#define DQGLOBAL_H#include <QtGlobal>
#include <QScopedPointer>#define DQ_DECLARE_PRIVATE(Class) \Q_DECLARE_PRIVATE(Class) \QScopedPointer<Class##Private> d_ptr;#define DQ_DECLARE_PUBLIC(Class) \Q_DECLARE_PUBLIC(Class) \Class* q_ptr;#define DQ_SAFE_DELETE(p) do { if(p) { delete (p); (p) = 0; } } while(0)#endif // DQGLOBAL_H

testclass.h

#ifndef TESTCLASS_H
#define TESTCLASS_H#include <QObject>
#include "dqglobal.h"class TestClassPrivate;
class TestClass
{DQ_DECLARE_PRIVATE(TestClass)
public:explicit TestClass(QObject *parent);~TestClass();void doFunc();private:void showMsg(QString str);//private:
//    TestClassPrivate * const d_ptr;
//    Q_DECLARE_PRIVATE(TestClass);
//    Q_DISABLE_COPY(TestClass);
};#endif // TESTCLASS_H

testclass.cpp

#include "testclass.h"
#include <QtDebug>class TestClassPrivate
{DQ_DECLARE_PUBLIC(TestClass)
public:TestClassPrivate(TestClass *q) :q_ptr(q){}void testFunc(){Q_Q(TestClass);q->showMsg("hello!");}//private:
//    TestClass * const q_ptr;
//    Q_DECLARE_PUBLIC(TestClass);
};TestClass::TestClass(QObject *parent):d_ptr(new TestClassPrivate(this))
{}TestClass::~TestClass()
{
//    Q_D(TestClass);
//   delete d;
}void TestClass::doFunc()
{Q_D(TestClass);d->testFunc();
}void TestClass::showMsg(QString str)
{qDebug() << str;
}

 

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