Qtablewidget lazy load remaining memory, no card!

Preface

Use tables to load data , A small amount of data shows no abnormality , When the data is too large , In particular, some interfaces may be added to the table to refresh in real time, such as the progress bar , The final effect is very poor , Load card , Occupy memory .
therefore , The following summary and sharing is a lazy loading strategy .

Loading policy description

There are two main points ：

1、 For situations that require real-time update loading , Every time you load data , Don't tune clearContents()、removeRow(int row) Wait for a way to empty new, But to reuse what was already done last time new Out of Item, Change its content to the latest

2、 Only load within the visible range of the interface Item, The specific amount of data only needs to be reflected by the value of the scroll bar , Every time you change the scroll bar , Then follow the above 1 To refresh Item The content of

Go straight to the code

The code structure

mytablewidget.h

#ifndef MYTABLEWIDGET_H
#define MYTABLEWIDGET_H

#include <QTableWidget>
#include <QResizeEvent>
#include <QWheelEvent>
#include <QScrollBar>
#include <QProgressBar>
#include <QHBoxLayout>
#include <QHeaderView>
#include <QMenu>
#include <QContextMenuEvent>
class TableWidget: public QTableWidget
{
    
public:
    TableWidget(QWidget *parent = nullptr):QTableWidget(parent){
    }
    ~TableWidget(){
    }
protected:
    void wheelEvent(QWheelEvent *event) override {
    }// Shield the mouse pulley event 
};

class MyTableWidget: public QWidget
{
    
public:
    MyTableWidget(QWidget *parent = nullptr);
    ~MyTableWidget();
    virtual void InitTable();
    virtual void LoadTableWidget();

    void UpdateView();
    void SetMenu(QMenu* menu);

    void SetItemText(int row, int colunm, QString str);
    void SetItemProgress(int row, int colunm, double value, double total);
protected:
    void wheelEvent(QWheelEvent *event) override;
    void resizeEvent(QResizeEvent *event) override;
    void contextMenuEvent(QContextMenuEvent *event) override;
private:
    TableWidget* m_table;
    QScrollBar *m_scrollBar;
    int m_itemHeight;
    int m_currentRow;
    int m_dataCnt;
public:
    //data
    std::map<QString, double> m_mapData;//name boxOffice
    QMenu* m_menu = nullptr;
};
#endif // MYTABLEWIDGET_H

mytablewidget.cpp

#include "mytablewidget.h"

MyTableWidget::MyTableWidget(QWidget *parent):QWidget(parent)
{
    
    m_table = new TableWidget(this);
    // Click the header to sort 
// connect(m_table->horizontalHeader(),&QHeaderView::sectionClicked,this,[=](int colunm){
    
// m_table->sortItems(colunm,Qt::AscendingOrder);
// });
    m_table->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);// Turn off scroll bar 
    QHBoxLayout* hbox =new QHBoxLayout(this);
    hbox->setMargin(0);
    hbox->setSpacing(0);
    hbox->addWidget(m_table);
    m_itemHeight = 20;
    m_dataCnt = 0;
    m_scrollBar = new QScrollBar(Qt::Vertical);
    connect(m_scrollBar,&QScrollBar::valueChanged,this,[=](int value){
    
       // qDebug()<<"value:"<<value;
        LoadTableWidget();
    });
    hbox->addWidget(m_scrollBar);

    InitTable();
    LoadTableWidget();
}

MyTableWidget::~MyTableWidget()
{
    

}

void MyTableWidget::InitTable()
{
    
    QStringList headList;
    headList<<" Serial number "<<" The title of the film "<<" box office ( Ten thousand yuan )"<<" Box office share ";
    m_table->setColumnCount(headList.length());
    m_table->setHorizontalHeaderLabels(headList);
    m_table->verticalHeader()->setVisible(false);// Hide line numbers 
    m_table->verticalHeader()->setDefaultSectionSize(m_itemHeight);// Default line height 
    m_table->horizontalHeader()->setSectionResizeMode(QHeaderView::Stretch);// Automatically divide the width of each column 
    //m_table->horizontalHeader()->setMinimumSectionSize(100);// Default column width 
    m_table->horizontalHeader()->setDefaultAlignment(Qt::AlignCenter);// Center the header 
    m_table->setSelectionBehavior(QAbstractItemView::SelectRows);// Select by behavior unit 
    m_table->setEditTriggers(QAbstractItemView::NoEditTriggers);// No editing 
    m_table->horizontalHeader()->setStyleSheet("QHeaderView::section{background-color:rgb(216,226,236);"
                                                     "border:0.5px solid rgb(254,254,254);}");

}

void MyTableWidget::SetItemText(int row, int colunm, QString str)
{
    
    QTableWidgetItem* item = m_table->item(row, colunm);
    if(nullptr == item)
    {
    
        item = new QTableWidgetItem;
        m_table->setItem(row, colunm, item);
    }
    item->setText(str);
}

void MyTableWidget::SetItemProgress(int row, int colunm, double value, double total)
{
    
    QWidget *widget = m_table->cellWidget(row, colunm);
    QProgressBar* bar = static_cast<QProgressBar*>(widget);
    if(nullptr == bar)
    {
    
        bar = new QProgressBar;
        bar->setObjectName("progress");
        m_table->setCellWidget(row, colunm, bar);// After setting, it will automatically show
        bar->hide();// First hide  After loading, it will automatically show
    }
    double percent =(double) value/total;
    bar->setAlignment(Qt::AlignCenter);
    bar->setRange(0,100);
    bar->setValue(percent*100);
    bar->setFormat(QString("%1%").arg(QString::number(percent*100,'f',1)));
}

void MyTableWidget::LoadTableWidget()
{
    
    int oldRow = m_table->rowCount() - 1;
    if(m_currentRow < oldRow)// If item If you have it, don't delete it and create it again , Before item Just change the content , Interface size changes , The displayed line changes , Delete more ,
    for (int i=oldRow - 1; i>oldRow - m_currentRow - 1; i--)
    {
    
        m_table->removeRow(i);
    }
     m_table->setRowCount(m_currentRow+1);
     int total = 1000;
     std::map<QString, double>::iterator itor = m_mapData.begin();
     int beginRow = m_scrollBar->value();// Scroll bar value , Table row 
     for (int i=0; i<beginRow; i++){
     itor++;}// The corresponding display from the value of the scroll bar 
     for (int i =0 ; i<m_currentRow; i++,itor++)
     {
    
         if(itor == m_mapData.end())
         {
    
             m_table->removeRow(i);
             break;
         }
         SetItemText(i, 0, QString::number(beginRow++));
         SetItemText(i, 1, itor->first);
         SetItemText(i, 2, QString::number(itor->second,'f',2));
         SetItemProgress(i, 3, itor->second, total);
     }
}

void MyTableWidget::UpdateView()
{
    
    LoadTableWidget();
}

void MyTableWidget::SetMenu(QMenu *menu)
{
    
    m_menu = menu;
}

void MyTableWidget::resizeEvent(QResizeEvent *event)
{
    
    m_currentRow = height()/m_itemHeight;
    m_dataCnt = m_mapData.size();
    if(m_dataCnt - m_currentRow > 0)
    {
    
        m_scrollBar->setRange(0,m_dataCnt - m_currentRow + 2);
        m_scrollBar->show();
    }
    else
    {
    
        m_scrollBar->setRange(0,0);
        m_scrollBar->hide();
    }

    LoadTableWidget();
}

void MyTableWidget::contextMenuEvent(QContextMenuEvent *event)
{
    
    QTableWidgetItem* item = m_table->itemAt(event->pos());
    if(item && m_menu)
        m_menu->exec(event->globalPos());
}

void MyTableWidget::wheelEvent(QWheelEvent *event)
{
    
    int value = m_scrollBar->value();
    if(event->delta() > 0)
    {
    
        value -= m_currentRow;
        if(value < m_scrollBar->minimum())
            value = m_scrollBar->minimum();
        m_scrollBar->setValue(value);
    }
    else
    {
    
        value += m_currentRow;
        if(value > m_scrollBar->maximum())
            value = m_scrollBar->maximum();
        m_scrollBar->setValue(value);
    }
}

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include "mytablewidget.h"

QT_BEGIN_NAMESPACE
namespace Ui {
     class Widget; }
QT_END_NAMESPACE

class Widget : public QWidget
{
    
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();

    QString GetStr();

private:
    Ui::Widget *ui;
    MyTableWidget* m_myTable;
};
#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include "ui_widget.h"
#include <QHBoxLayout>
#include <QTimer>
#include <QHeaderView>
#include <QProgressBar>
#include <QScrollBar>
#include <QActionGroup>
#include <QMessageBox>
#include <QDebug>
Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    
    ui->setupUi(this);
    this->setWindowTitle("TableWidget load - Dynamic loading - Load only the display area ");// Put it in  ui->setupUi(this);  After that, it won't work 
    qsrand(time(nullptr));

    m_myTable=new MyTableWidget(this);
    QHBoxLayout* hbox =new QHBoxLayout(this);
    hbox->setMargin(0);
    hbox->setSpacing(0);
    hbox->addWidget(m_myTable);

    int dataCnt = 134217;
    for (int i=0; i<dataCnt;i++) {
    
        double value = rand()%1000000+1000;
        m_myTable->m_mapData[GetStr()] = value/100;
    }
    QMenu* menu = new QMenu(this);
    connect(menu,&QMenu::triggered,this,[=](QAction* action){
    
        QString str = action->text();
        if("test_1" == action->text())
        {
    

            QMessageBox::information(nullptr,"Info","you choice test_1");
        }
        else if("test2" == action->text())
        {
    

            QMessageBox::information(nullptr,"Info","you choice test2");
        }
        else if("test1" == action->text())
        {
    
           QMessageBox::information(nullptr,"Info","you choice test1");
        }
    });
    QMenu* menu_1 = new QMenu("test",this);
    m_myTable->SetMenu(menu);
    QAction *action_Desc = new QAction("test1");
    QAction *action_Asce = new QAction("test2");
    action_Desc->setCheckable(true);
    action_Asce->setCheckable(true);
    action_Asce->setChecked(true);
    QActionGroup *group = new QActionGroup(this);
    group->addAction(action_Asce);
    group->addAction(action_Desc);
    menu_1->addAction(action_Desc);
    menu_1->addAction(action_Asce);
    menu->addMenu(menu_1);
    menu->addAction("test_1");

    QTimer* m_timer = new QTimer(this);
    connect(m_timer,&QTimer::timeout,this,[=]()mutable{
    

        std::map<QString, double>::iterator itor = m_myTable->m_mapData.begin();
        for (; itor!=m_myTable->m_mapData.end();itor++) {
    
            double value = rand()%1000000+1000;
            itor->second = value/100;
        }
        m_myTable->UpdateView();
    });
    m_timer->start(1000);
}

Widget::~Widget()
{
    
    delete ui;
}

QString Widget::GetStr()
{
    
   int length = rand()%15+5;
   const char ch[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
   int size = sizeof(ch);
   char* str = new char[length + 1];
   int num = 0;
   int i;
   for (i = 0; i < length; ++i)
   {
    
       num = rand() % (size - 1);
       str[i] = ch[num];
   }
    str[i] = '\0';
   QString res(str);
   //return res;
   return "《"+res+"》";
}

summary

If you are interested, you can compare , I share and normally load millions of levels of data into the table at a time , These two ways , Look at the program memory , And loading speed , Logic processing is still very fast , draw UI It's really slow , Occupy memory . Theoretically , The maximum size of data loaded by this strategy I share , It is mainly related to the data storage method and capacity , After all, the visual range of the loading interface Item It's still faster ., But for example, you use containers map There is still an upper limit to storage .