(Qt)I want to know why the if statement won't be excuted - qt

Question

I want to make a simple timer by Qt. When I want to implement pause and resume functionality,it seemed that the if statement in void Widget::on_Pause_clicked()didn't work .
widget.h:
#include <QWidget>
#include <QTimer>
#include <QTime>
#include <QString>
#include <QLCDNumber>
#include <QMouseEvent>
QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACE
class Widget : public QWidget
{
Q_OBJECT
private:
Ui::Widget *ui;
QLCDNumber *lcd;
QTimer *ptime;
QTime *timerecord;
QPoint windowPos;
QPoint mousePos;
QPoint dPos;
bool isStart;
public:
Widget(QWidget *parent = nullptr);
~Widget();
void mousePressEvent(QMouseEvent *event);
void mouseMoveEvent(QMouseEvent *event);
private slots:
void on_Start_clicked();
void updatetime();
void initTime();
void on_Pause_clicked();
void on_Clear_clicked();
public slots:
};
widget.cpp:
#include "widget.h"
#include "ui_widget.h"
Widget::Widget(QWidget *parent)
: QWidget(parent)
, ui(new Ui::Widget)
{
ui->setupUi(this);
ptime = new QTimer;
timerecord = new QTime;
ui->Timer->setDigitCount(11);
initTime();
connect(ptime,SIGNAL(timeout()),this,SLOT(updatetime()));
this->setWindowFlags(Qt::FramelessWindowHint);//remove system border
isStart=false;//determine if the timer is running
ui->Start->setEnabled(true);
ui->Pause->setEnabled(false);
ui->Clear->setEnabled(false);
}
Widget::~Widget()
{
delete ui;
}
void Widget::initTime()
{
timerecord->setHMS(0, 0, 0);
ui->Timer->display(timerecord->toString("mm:ss:zzz "));
}
void Widget::updatetime()
{
*timerecord = timerecord->addMSecs(1);
ui->Timer->display(timerecord->toString("mm:ss:zzz "));
}
void Widget::on_Start_clicked()//when the start button is clicked
{
ptime->start(1);
isStart=true;
ui->Start->setEnabled(false);
ui->Pause->setEnabled(true);
ui->Clear->setEnabled(false);
}
void Widget::on_Pause_clicked()//when the pause button is clicked
{
if(isStart == true)
{
ptime->stop();
ui->Pause->setText("继续");
isStart=false;
ui->Start->setEnabled(false);
ui->Pause->setEnabled(true);
ui->Clear->setEnabled(true);
}
if(isStart == false)
{
ptime->start(1);
ui->Pause->setText("暂停");
isStart=true;
ui->Start->setEnabled(false);
ui->Pause->setEnabled(true);
ui->Clear->setEnabled(false);
}
}
void Widget::on_Clear_clicked()
{
ptime->stop();
initTime();
ui->Start->setEnabled(true);
ui->Pause->setEnabled(false);
ui->Clear->setEnabled(false);
}
void Widget::mousePressEvent(QMouseEvent *event)//make the window movable
{
this->windowPos = this->pos();
this->mousePos = event->globalPos();
this->dPos = mousePos - windowPos;
}
void Widget::mouseMoveEvent(QMouseEvent *event)//make the window movable
{
this->move(event->globalPos() - this->dPos);
}

Answer 1

In your code:
void Widget::on_Pause_clicked()//when the pause button is clicked
{
if(isStart == true)
{
ptime->stop();
ui->Pause->setText("继续");
isStart=false;
ui->Start->setEnabled(false);
ui->Pause->setEnabled(true);
ui->Clear->setEnabled(true);
}
if(isStart == false)
{
ptime->start(1);
ui->Pause->setText("暂停");
isStart=true;
ui->Start->setEnabled(false);
ui->Pause->setEnabled(true);
ui->Clear->setEnabled(false);
}
}
if isStart starts out to be true, then it enters the first if condition block. Within it, isStart becomes false.
However, when it exits that block, it hits the if (isStart == false) block and since isStart is false, therefore it goes into that block and changes isStart to true.
What you should do (bear in mind my qT is rusty):
void Widget::on_Pause_clicked()//when the pause button is clicked
{
if(isStart == true)
{
ptime->stop();
ui->Pause->setText("继续");
isStart=false;
ui->Start->setEnabled(false);
ui->Pause->setEnabled(true);
ui->Clear->setEnabled(true);
} else {
ptime->start(1);
ui->Pause->setText("暂停");
isStart=true;
ui->Start->setEnabled(false);
ui->Pause->setEnabled(true);
ui->Clear->setEnabled(false);
}
}