QT中私有公有化（Q_DECLARE_PUBLIC Q_DECLARE_PRIVATE）原理小DEMO

结果：

b.ljtcnt() 8889

b.ljtcnt() 1457

代码如下：

DrawToolButton.h：
#ifndef DrawToolButton_H
#define DrawToolButton_H

#include <QToolButton>

class DrawToolButtonPrivate;
class DrawToolButton
{
public:
    DrawToolButton(QWidget *parent=0);
    ~DrawToolButton();//析构函数必须把定义放到CPP中 否则编译通不过
    Q_PROPERTY(int txcnt READ txcnt WRITE settxcnt)
    int txcnt() const;
    void settxcnt(int i);
private:
    QScopedPointer<DrawToolButtonPrivate> d_ptr;

    Q_DISABLE_COPY(DrawToolButton)
    Q_DECLARE_PRIVATE(DrawToolButton)
};

#endif

DrawToolButton.cpp：
#include "DrawToolButton.h"
#include <qobject.h>

class DrawToolButtonPrivate
{
    Q_DECLARE_PUBLIC(DrawToolButton)
    inline DrawToolButtonPrivate()
        : q_ptr(0)
    {}
public:
    int prljltcnt;
    void init();
private:
    DrawToolButton *q_ptr;
};

void DrawToolButtonPrivate::init()
{
    Q_Q(DrawToolButton);
    prljltcnt = 8889;
}

DrawToolButton::DrawToolButton(QWidget * parent)
: d_ptr(new DrawToolButtonPrivate)
{
    d_ptr->q_ptr = this;

    Q_D(DrawToolButton);
    d->init();
}

DrawToolButton::~DrawToolButton()
{
<pre style="margin-top: 0px; margin-bottom: 0px;"><span style=" color:#808bed;">delete</span><span style=" color:#646482;"> </span><span style=" font-weight:600;">d_ptr</span><span style=" color:#cfbfad;">;</span>

    d_ptr = NULL;

}int DrawToolButton::txcnt() const{ Q_D(const DrawToolButton); return d->prljltcnt;}void DrawToolButton::settxcnt(int i){ Q_D(DrawToolButton); if (d->prljltcnt == i) return; d->prljltcnt = i;}调用：DrawToolButton b; qDebug()<<"b.ljtcnt()"<<b.txcnt(); b.settxcnt(1457); qDebug()<<"b.ljtcnt()"<<b.txcnt();

另外一种方案：

DrawToolButton.h:
#ifndef DrawToolButton_H
#define DrawToolButton_H

#include <QToolButton>

class DrawToolButtonPrivate;
class DrawToolButton : public QToolButton
{
    Q_OBJECT
public:
    DrawToolButton(QWidget *parent=0);
    ~DrawToolButton();//析构函数必须把定义放到CPP中 否则编译通不过
    Q_PROPERTY(int txcnt READ txcnt WRITE settxcnt)
    int txcnt() const;
    void settxcnt(int i);
private:
    QScopedPointer<DrawToolButtonPrivate> d_ptr;

    Q_DISABLE_COPY(DrawToolButton)
    Q_DECLARE_PRIVATE(DrawToolButton)
};

#endif
DrawToolButton.cpp:
#include "DrawToolButton.h"
#include <qobject.h>

class DrawToolButtonPrivate
{
    Q_DECLARE_PUBLIC(DrawToolButton)
    inline DrawToolButtonPrivate()
        : q_ptr(0)
    {}
public:
    int prljltcnt;
    void init();

    void aboutToDestroy() {}
private:
    DrawToolButton *q_ptr;
};

void DrawToolButtonPrivate::init()
{
    Q_Q(DrawToolButton);
    prljltcnt = 8889;
}

DrawToolButton::DrawToolButton(QWidget * parent)
   : d_ptr(new DrawToolButtonPrivate)
{
    d_ptr->q_ptr = this;

    Q_D(DrawToolButton);
    d->init();
}

DrawToolButton::~DrawToolButton()
{

}

int DrawToolButton::txcnt() const
{
    Q_D(const DrawToolButton);
    return d->prljltcnt;
}

void DrawToolButton::settxcnt(int i)
{
    Q_D(DrawToolButton);
    if (d->prljltcnt == i)
        return;

    d->prljltcnt = i;
}