QTreeWidget slow deletion after click - c++

Question

I have made a QTreeWidget to display a very large and continuous data set. Since the data set is continuous, I delete initial rows when the total number of rows is greater than a specified amount.
The whole system is working correctly and displaying data.
But when I click on the tree view, the whole system slows done drastically. I have debugged. And the problem is in the deletion code, deleting each QTreeWidgetItem costs a lot of time after click ~ 20 ms
I debugged it in Qt source, and the problem seemed to be with QItemSelectionModel::setCurrentIndex
This line -> emit currentChanged(d->currentIndex, previous);
Now I couldn't debug it any further as I couldn't find out which slots are connected to this signal and slowing it down.
I am using Qt 4.7.1
I have pasted the whole code below:
Header file:
#ifndef WINDOW_H
#define WINDOW_H
#include <QWidget>
#include "ui_service.h"
#include <qtimer.h>
typedef std::pair<std::string, std::string> tSEntry;
typedef std::vector<tSEntry> tSFifo;
typedef struct tGUIData
{
std::string strCName;
std::string strFName;
std::string strPName;
std::string strMName;
std::string strMIDHex;
std::string strMIDDec;
std::string strTimeStamp;
std::string strRawDataHex;
std::string strRawDataDec;
tSFifo oSQueue;
} tGUIData;
class Window : public QWidget
{
Q_OBJECT
/// The Tree Widget where the data is shown
QTreeWidget* m_pTreeHead;
Ui::ListView* m_pForm;
int m_nMaxItemAmount;
QTimer m_oDataProducer;
QTimer m_oListClearer;
public:
Window();
~Window();
private slots:
void ProduceData();
void ClearTree();
void Window::AddEntry(tGUIData& tGUIData);
private:
void Window::DeleteItems();
};
#endif
Code file:
#include <QtGui>
#include "window.h"
#include <cstdlib>
#include <ctime>
Window::Window()
{
m_pForm = new Ui::ListView();
m_pForm->setupUi(this);
QHeaderView* pHeader = m_pForm->treeWidget->header();
pHeader->setResizeMode(0, QHeaderView::Interactive);
pHeader->setResizeMode(1, QHeaderView::Interactive);
pHeader->setResizeMode(2, QHeaderView::Interactive);
pHeader->setResizeMode(3, QHeaderView::Interactive);
pHeader->setResizeMode(4, QHeaderView::Stretch);
m_pTreeHead = m_pForm->treeWidget;
m_nMaxItemAmount = 1000;
m_oDataProducer.start(1);
m_oListClearer.start(10);
connect(&m_oDataProducer, SIGNAL(timeout()), this, SLOT(ProduceData()));
connect(&m_oListClearer, SIGNAL(timeout()), this, SLOT(ClearTree()));
}
std::string CreateRandomString(size_t nLength)
{
std::string o_str = "";
o_str.resize(nLength);
char cSymbols[] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
unsigned int nIndexer = 0;
srand(static_cast<long int>(std::time(NULL)) + rand());
while (nIndexer < nLength)
{
o_str[nIndexer++] = cSymbols[rand() % 62];
}
return o_str;
}
void Window::ClearTree()
{
DeleteItems();
}
void Window::ProduceData()
{
for (size_t i = 0; i < 500; i++)
{
tGUIData oGUIData;
oGUIData.strCName = CreateRandomString(10);
oGUIData.strFName = CreateRandomString(10);
oGUIData.strMIDDec = CreateRandomString(10);
oGUIData.strMIDHex = CreateRandomString(10);
oGUIData.strMName = CreateRandomString(10);
tSEntry oSEntry;
oSEntry.first = CreateRandomString(10);
oSEntry.second = CreateRandomString(10);
oGUIData.oSQueue.push_back(oSEntry);
AddEntry(oGUIData);
}
}
Window::~Window()
{
m_oDataProducer.stop();
if (m_pForm)
{
delete m_pForm;
m_pForm = NULL;
}
}
void Window::DeleteItems()
{
while (m_pTreeHead->topLevelItemCount() >= m_nMaxItemAmount)
{
QTreeWidgetItem* pTreeWidget = m_pTreeHead->topLevelItem(0);
if (pTreeWidget)
{
delete pTreeWidget;
pTreeWidget = NULL;
}
}
}
void Window::AddEntry(tGUIData& oGUIData)
{
QTreeWidgetItem* pMessageItem = new QTreeWidgetItem(m_pTreeHead);
pMessageItem->setText(0, oGUIData.strCName.c_str());
pMessageItem->setText(1, oGUIData.strMName.c_str());
pMessageItem->setText(2, oGUIData.strTimeStamp.c_str());
pMessageItem->setText(3, oGUIData.strRawDataDec.c_str());
pMessageItem->setText(4, oGUIData.strPName.c_str());
while (!oGUIData.oSQueue.empty())
{
QTreeWidgetItem* pSubItem = new QTreeWidgetItem(pMessageItem);
tSEntry& sEntry = oGUIData.oSQueue.front();
pSubItem->setText(1, sEntry.first.c_str());
pSubItem->setText(2, sEntry.second.c_str());
oGUIData.oSQueue.erase(oGUIData.oSQueue.begin());
}
}

Answer 1

When you delete items disable update, like this:
QTreeWidget tw;
tw.setUpdatesEnabled(false);
To delete all items use(if items don't contains pointers):
tw.clear()
You don't need to delete items before QTreeWidget destructor.