My QT learning path -- how qdatetimeedit is empty

Study Qt It's been a few months , Gradually fell in love Qt, To record Qt Problems encountered in development ：

QDatetimeEdit Is a commonly used date editing control , But the official control cannot be displayed as null . There is a new requirement in the recent test. We hope that the date editing control defaults to null , This is a little strange for a newcomer , But considering that I'm still in internship, I don't think much of it , Can only bear in silence . Although it doesn't sound difficult , But it still took a lot of time to realize , Hope to help students with similar needs .

QDateTimeEdit The default display of

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The following is a .h Content of header file

#ifndef BLANKDATETIMEEDIT_H
#define BLANKDATETIMEEDIT_H
#include <QDateTimeEdit>
#include <QLineEdit>
#include <QDebug>


class BlankDateTimeEdit : public QDateTimeEdit
{
     Q_OBJECT
public:
    explicit BlankDateTimeEdit(QWidget *parent = 0);

public:
    void SetNull(bool NullSwitch);// Setting is allowed to be empty 

protected:
    virtual QValidator::State validate(QString &input, int &pos) const override;
    virtual QString textFromDateTime(const QDateTime &dt) const override;
    void focusInEvent(QFocusEvent *e)override;// Rewrite the get focus function , Make it display time normally when it gets focus 
    void mousePressEvent(QMouseEvent *e)override;// Override mouse down function 

private:
    bool m_NullSwitch;// Is it allowed to be empty 



};

#endif // BLANKDATETIMEEDIT_H

The following is a .cpp Specific implementation of file function

#include "blankdatetimeedit.h"

BlankDateTimeEdit::BlankDateTimeEdit(QWidget *parent) :
    QDateTimeEdit(parent),m_NullSwitch(true)
{
    this->setParent(parent);
    lineEdit()->clear();
}

void BlankDateTimeEdit::SetNull(bool NullSwitch)
{
    m_NullSwitch=NullSwitch;
    if(m_NullSwitch)
    {
        lineEdit()->clear();
    }
    else
    {
        this->setDateTime(QDateTime::currentDateTime());
    }
}
//QDateTime Call this virtual function to determine whether the input is valid ,pos The parameter represents the position in the string 
QValidator::State BlankDateTimeEdit::validate(QString &input, int &pos) const
{
    qDebug()<<"validate"<<input<<" "<<pos;
    if(m_NullSwitch)
    {
        input="";
        return QValidator::Intermediate;
    }
    return QDateTimeEdit::validate(input,pos);
}

QString BlankDateTimeEdit::textFromDateTime(const QDateTime &dt) const
{
    return QDateTimeEdit::textFromDateTime(dt);
}
// It is used to get focus and pop-up keyboard in embedded , And display normally 
// Note that there is only one control on the page , This control will get the focus when the page is initially displayed , Normal display 
void BlankDateTimeEdit::focusInEvent(QFocusEvent *e)
{
    if(0 == this->text().length())
    {
//        SetNull(false);
        return;
    }
    QDateTimeEdit::focusInEvent(e);
}

void BlankDateTimeEdit::mousePressEvent(QMouseEvent *e)
{
    if(0 == this->text().length())
    {
        SetNull(false);
        return;
    }
    QDateTimeEdit::mousePressEvent(e);
}