Qt——自定义二进制兼容（d/q指针）的类实现继承笔记

亦凉 2023-06-28 11:28 6阅读 0赞

### d/q指针的原理 ###

[参考链接][Link 1]  
维基百科上讲得很详细，故不再进行赘述。

### 关于为什么写这篇文章 ###

最近因为自定义输入框，采用了d/p指针来实现二进制兼容。在参考官方例子，也就是上面的参考链接时，始终都无法实现。一直报错**无法调用已删除函数**。最后实在没有办法去查阅Qt源码，参考了QLineEdit本身的实现，发现了是因为没有给Private加默认构造函数构成的。

### 为什么类的数据类要以Private结尾？ ###

这是因为Q\_D宏定义的

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

### 一个具体的例子的描述 ###

1.  定义一个类LineEdit，继承于QLineEdit；
2.  定义一个子类，继承于LineEdit；

### 具体代码实现 ###

*lineedit\_p.h*

#ifndef LINEEDIT_P_H
    #define LINEEDIT_P_H
    
    #include <QObject>
    class LineEdit;
    class LineEditPrivate{
        
    
        Q_DECLARE_PUBLIC(LineEdit)
    public:
    
        LineEditPrivate(){
        }
        ~LineEditPrivate(){
        }
    
        LineEditPrivate(LineEdit *parent):
            q_ptr(parent){
        }
    
        //data
        QString tipText;
        QRegExp regExp;
    
    protected:
        LineEdit * q_ptr;
    };
    
    #endif // LINEEDIT_P_H

*lineedit.h*

#ifndef LINEEDIT_H
    #define LINEEDIT_H
    
    #include <QLineEdit>
    #include <QFocusEvent>
    
    class QRegExp;
    
    class LineEditPrivate;
    
    class LineEdit:public QLineEdit
    {
        
        Q_OBJECT
    public:
        explicit LineEdit(QWidget *parent=nullptr);
        virtual ~LineEdit();
    
        void setRegExp(const QRegExp &regExp);
        void setTipText(const QString &text);
        void clearRegExp();
    signals:
        void verificationResult(bool,QString);
    protected:
        void updateValidator();
        void focusOutEvent(QFocusEvent *pEvent);
    
        LineEdit(LineEditPrivate &d,QWidget *parent=nullptr);
    
        LineEditPrivate * d_ptr;
    private:
        Q_DECLARE_PRIVATE(LineEdit)
        Q_DISABLE_COPY(LineEdit)
    
    };
    
    #endif // LINEEDIT_H

*lineedit.cpp*

#include "lineedit.h"
    
    #include <QRegExp>
    #include <QRegExpValidator>
    
    #include "lineedit_p.h"
    
    LineEdit::LineEdit(QWidget *parent):
        QLineEdit(parent),
        d_ptr(new LineEditPrivate(this))
    {
        
    
    }
    
    LineEdit::~LineEdit()
    {
        
        Q_D(LineEdit);
    
        delete d;
    }
    
    void LineEdit::setRegExp(const QRegExp &regExp)
    {
        
        Q_D(LineEdit);
        d->regExp = regExp;
    }
    
    void LineEdit::setTipText(const QString &text)
    {
        
        Q_D(LineEdit);
        d->tipText = text;
    }
    
    void LineEdit::clearRegExp()
    {
        
        Q_D(LineEdit);
        d->regExp.setPattern("");
    }
    
    void LineEdit::focusOutEvent(QFocusEvent *pEvent)
    {
        
        Q_D(LineEdit);
    
        if(!d->regExp.exactMatch(this->text())){
        
            this->setStyleSheet("QLineEdit{border:1px solid red }");
            emit verificationResult(false,d->tipText);
        }else{
        
            this->setStyleSheet("QLineEdit{border:1px solid gray border-radius:1px}");
            emit verificationResult(true,"");
        }
    
        QLineEdit::focusOutEvent(pEvent);
    }
    
    LineEdit::LineEdit(LineEditPrivate &d, QWidget *parent):
        d_ptr(&d),
        QLineEdit(parent)
    {
        
    
    }

*intedit.h*

#ifndef INTEDIT_H
    #define INTEDIT_H
    
    #include "lineedit.h"
    
    class IntEditPrivate;
    
    class IntEdit:public LineEdit
    {
        
        Q_OBJECT
    public:
        explicit IntEdit(QWidget *parent=nullptr);
        virtual ~IntEdit();
    
    protected:
    
    private:
        Q_DECLARE_PRIVATE(IntEdit)
    };
    
    #endif // INTEDIT_H

*intedit.cpp*

#include "intedit.h"
    
    #include "lineedit_p.h"
    
    class IntEditPrivate:public LineEditPrivate{
        
        Q_DECLARE_PUBLIC(IntEdit)
    public:
        IntEditPrivate(){
        }
        ~IntEditPrivate(){
        }
    
        QString test;
    };
    
    IntEdit::IntEdit(QWidget *parent):
        LineEdit(*new IntEditPrivate,parent)
    {
        
        Q_D(IntEdit);
        d->test = "AAA";
    }
    
    IntEdit::~IntEdit()
    {
        
    
    }

[Link 1]: https://wiki.qt.io/D-Pointer