QML TableView refresh in realtime only updates UI every 1 second - qt

Question

I have a task of showing big amount of data in realtime (as close to that as possible) with UI update every 10 to 100ms (best to worst values), I've managed to create a test model generating random numbers and populating the table view with new set of random values with a Timer. I tried to set different time intervals from 1 to 100 ms, and I can see the timer fires and the new set of data is created, but the UI updates strictly in 1 second every time despite the timer interval value.
Can you guide me on how to handle UI updates in less than 1 second.
I tried different amount of data from tables of 50x1000 to just 50x50. Every time I get UI update rate of 1 second.
It is based on the "Game Of Life" Qt example, so some of the elements are just not used and are obsolete, but as soon as they are "disabled" I think they don't make any influence on the rest of the code and the problem itself.
You can see that in nextStep() method I invoke timestamp logging to console and I can see in the output that the method is invoked according to the timer, but the UI only updates visually every second.
main.qml
ApplicationWindow {
id: root
visible: true
width: 760
height: 810
minimumWidth: 475
minimumHeight: 300
color: "#09102B"
title: qsTr("Conway’s Game of Life")
//! [tableview]
TableView {
id: tableView
anchors.fill: parent
rowSpacing: 1
columnSpacing: 1
ScrollBar.horizontal: ScrollBar {}
ScrollBar.vertical: ScrollBar {}
delegate: Rectangle {
id: cell
implicitWidth: 45
implicitHeight: 15
color: model.value > 100 ? "#f3f3f4" : "#b5b7bf"
Label {
width: parent.width
height: parent.height
text: model.value
}
}
//! [tableview]
//! [model]
model: GameOfLifeModel {
id: gameOfLifeModel
}
//! [model]
//! [scroll]
contentX: 0;
contentY: 0;
//! [scroll]
}
footer: Rectangle {
signal nextStep
id: footer
height: 50
color: "#F3F3F4"
RowLayout {
anchors.centerIn: parent
//! [next]
Button {
text: qsTr("Next")
onClicked: gameOfLifeModel.nextStep()
}
//! [next]
Item {
width: 50
}
Button {
text: timer.running ? "❙❙" : "▶️"
onClicked: timer.running = !timer.running
}
}
FpsItem {
id: fpsItem
anchors.left: parent
color: "black"
}
Timer {
id: timer
interval: 10
running: true
repeat: true
onTriggered: gameOfLifeModel.nextStep()
}
}
}
gameoflifemodel.cpp
GameOfLifeModel::GameOfLifeModel(QObject *parent)
: QAbstractTableModel(parent) {}
//! [modelsize]
int GameOfLifeModel::rowCount(const QModelIndex &parent) const
{
if (parent.isValid())
return 0;
return height;
}
int GameOfLifeModel::columnCount(const QModelIndex &parent) const
{
if (parent.isValid())
return 0;
return width;
}
//! [modelsize]
//! [read]
QVariant GameOfLifeModel::data(const QModelIndex &index, int role) const
{
if (!index.isValid() || role != CellRole)
return QVariant();
return m_state[index.column()][index.row()];
}
//! [read]
//! [write / not used]
bool GameOfLifeModel::setData(const QModelIndex &index, const QVariant &value, int role) {
if (role != CellRole || data(index, role) == value)
return false;
m_state[index.column()][index.row()] = value.toBool();
emit dataChanged(index, index, {role});
return true;
}
//! [write]
Qt::ItemFlags GameOfLifeModel::flags(const QModelIndex &index) const
{
if (!index.isValid())
return Qt::NoItemFlags;
return Qt::ItemIsEditable;
}
//! [update]
void GameOfLifeModel::nextStep()
{
srand(time(NULL));
qDebug() << QTime::currentTime().toString("yyyy/MM/dd hh:mm:ss,zzz");
for (int i = 0; i < width; i++) {
for (int j = 0; j < height; j++) {
m_state[j][i] = (rand() % 1000) + 1;
}
}
emit dataChanged(index(0, 0), index(height - 1, width - 1), {CellRole});
}
//! [update]
gameoflifemodel.h
//! [modelclass]
class GameOfLifeModel : public QAbstractTableModel
{
Q_OBJECT
Q_ENUMS(Roles)
public:
enum Roles {
CellRole
};
QHash<int, QByteArray> roleNames() const override {
return {
{ CellRole, "value" }
};
}
explicit GameOfLifeModel(QObject *parent = nullptr);
int rowCount(const QModelIndex &parent = QModelIndex()) const override;
int columnCount(const QModelIndex &parent = QModelIndex()) const override;
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
bool setData(const QModelIndex &index, const QVariant &value,
int role = Qt::EditRole) override;
Qt::ItemFlags flags(const QModelIndex &index) const override;
Q_INVOKABLE void nextStep();
private:
static constexpr int width = 50;
static constexpr int height = 50;
static constexpr int size = width * height;
template <class T, size_t ROW, size_t COL>
using NativeMatrix = T[ROW][COL];
NativeMatrix<int, height, width> m_state;
};
//! [modelclass]

Answer 1

Okay, the problem is solved. The issue appeared to be in the random number generation process, not in the table view.
In the code I used
srand(time(NULL))
The time(NULL) returns seconds and not milliseconds, thus I was getting the same numbers and they were updated only after 1 second and visually it was similar to updating the UI only every second. In order to solve this I switched to using this to generate random numbers and everything worked well:
struct timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
/* using nano-seconds instead of seconds */
srand((time_t)ts.tv_nsec);