QThread within the same class

marlenet15

I have a QPushButton and two QLabel's. When the pushbutton is clicked, each QLabel will display over 1000 frames every 500 milliseconds or so making it appear as a video. However, each QLabel will display different frames from different directorie's locations but both QLabels need to display their frames/video at the same time. After some research, I believe I need two threads in order to run them at the same time. I have written the important sections of the code below.
I am not sure how to use Threads here. Will each tread call the same timer or is it two separate ones? I know for sure that both threads need to call the updateLabel but I am not sure how to make this work and where to put the threads.

#include "setup.h"
#include "ui_setup.h"
#include <QFile>
#include <QTextStream>
#include <QDir>
#include <QTimer>
#include <QThread>
#include <QDebug>

setup::setup(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::setup)
{
    ui->setupUi(this);
    timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(updateLabel())); //not sure how this will work
    directory1 = QString("directory1_name");
    directory2= QString("directory2_name");
}

void setup::updateLabel(QString directory)
{
  // if fileList is empty
   //  timer->stop

else {
    //save images into vector
}
ui->label1->setPixmap(images[x]);
ui->label1->update();
}

void setup::onClickPlay()
{
    QDir myDir(directory1);
    filelist = myDir.entryList(QStringList("*.png")); //saves all images
    timer->start(500);
}

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

jsulm

In the code you provided I cannot see any threads.
In general there is no need for threads in this case: just use a timer and update the labels on each timer event.

A note: in Qt you should NEVER modify UI from another threads! This is not supported.

marlenet15

@jsulm I didn't add any threads since I wasn't sure how or where to add them. But how do I updated both QLabels at the same time id threads are not necessary?

kshegunov

@marlenet15
Strictly speaking you can't unless you call QWidget::repaint() on each of the widgets manually from the same function/slot. Otherwise Qt will schedule the paint events as it sees fit, which is absolutely fine for most of the cases. Also you can't call QWidget functions from a separate thread (as @jsulm noted), it must be from the main thread. So @jsulm is absolutely correct that you don't actually need any threads and stand to gain nothing from them.

Kind regards.

marlenet15

I guess you are right. I will work on this without the Threads. Thank you for your help!