How to access QStandardItemModel in a thread (QThread)?

Did not fit in the comment, leave as an answer:

It’s better not to work with threads.

There is at least QThreadPool , as well as Qt Concurrent - I really don’t understand it, a quote from the documentation - The QtConcurrent namespace provides high-level APIs that make it possible to write multi-threaded programs without using low-level threading primitives such as mutexes, read-write locks, wait conditions, or semaphores.

Inheriting from QThread is not recommended - Proper use of QThread . In short, QThread is first of all needed to start QEventLoop in another thread and be able to send signals to this stream and receive them from there. Read more - read the article on the link to Habré.

Original articles:

youre-doing-it-wrong QThread

how to realy use qthreads

* UPD. *

Read the source.

Do you get that several threads will be created in the loop, and each of them will access the same static item ( item_one )?

No sync?

* UPD 2. Example. *

I made an assumption about what you need and made an example.

The example loads from a folder all the jpg/png format pictures into a table with two columns - the name of the picture and preview. The code for getting the preview was copied from your run method in the stream

The ImageLoader class is a successor of QObject (to send a signal) and QRunnable (so that it can be added to QThreadPool).

I’m not sure what’s right, because the moveToThread QThreadPool probably doesn’t call the method, since a normal QRunnable interface expects the input, but still it’s better than inheriting from QThread .

 #ifndef IMAGELOADER_H #define IMAGELOADER_H #include <QObject> #include <QRunnable> #include <QFileInfo> #include <QImage> class ImageLoader: public QObject, public QRunnable { Q_OBJECT public: explicit ImageLoader(const QFileInfo& img, QObject* parent = nullptr); virtual ~ImageLoader(){ m_img = nullptr; //не удаляем - удалить обязан тот кто будет обрабатывать сигнал imgReady } virtual void run() override; signals: void imgReady(const QFileInfo& file, QImage* img); private: QFileInfo m_imgFile; QImage* m_img; }; #endif // IMAGELOADER_H #include "imageloader.h" #include <QImageReader> #include <QDebug> ImageLoader::ImageLoader(const QFileInfo &img, QObject *parent): QObject(parent), m_imgFile{img}, m_img{nullptr} { setAutoDelete(true); } void ImageLoader::run() { if (!m_imgFile.exists()){ qDebug() << __FUNCTION__ << "file" << m_imgFile.absoluteFilePath() << "do not exists"; return; } int icoWidth = 200; int icoHeight = 200; QImageReader imageReader(m_imgFile.absoluteFilePath()); QSize size; int image_width; int image_height; if (imageReader.supportsOption(QImageIOHandler::Size)) { size = imageReader.size(); image_width = size.width(); image_height = size.height(); }else{ qCritical() << "QImageReader don support option QImageIOHandler::Size"; return; } double ratio = (double)image_width / (double)image_height; if (ratio >= 1) { image_width = icoWidth; image_height = image_width / ratio; } else { image_height = icoHeight; image_width = image_height * ratio; } imageReader.setScaledSize(QSize(image_width, image_height)); m_img = new QImage(); if (imageReader.read(m_img)){ emit imgReady(m_imgFile, m_img); }else{ qWarning() << "can't read image" << m_imgFile.fileName() << imageReader.errorString(); delete m_img; } } 

MainWindow

 #ifndef MAINWINDOW_H #define MAINWINDOW_H #include <QMainWindow> #include <QDir> #include <QStandardItemModel> #include <QMutex> #include <QFileInfo> namespace Ui { class MainWindow; } class MainWindow : public QMainWindow { Q_OBJECT public: explicit MainWindow(QWidget *parent = 0); ~MainWindow(); private slots: void on_m_selectDirBtn_clicked(); void onImgReady(const QFileInfo& file, QImage* img); private: Ui::MainWindow *ui; QDir m_imgDir; QStandardItemModel* m_imgModel; }; #endif // MAINWINDOW_H 

MainWindow.cpp

 #include "mainwindow.h" #include "ui_mainwindow.h" #include <QFileDialog> #include <QDebug> #include <QThreadPool> #include <QMutexLocker> #include "imageloader.h" MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow), m_imgDir{"", "*.jpg; *.png", QDir::Name | QDir::IgnoreCase, QDir::Files}, m_imgModel{} { ui->setupUi(this); m_imgModel = new QStandardItemModel(0, 2, this); ui->m_imageTableView->setModel(m_imgModel); } MainWindow::~MainWindow() { delete ui; } void MainWindow::on_m_selectDirBtn_clicked() { QString dir = QFileDialog::getExistingDirectory(this); qDebug() << dir; if (dir.isEmpty()){ qWarning() << "Пользователь отменил выбор директории"; }else{ m_imgDir.setPath(dir); qDebug() << m_imgDir.entryList(); m_imgModel->clear(); for (const auto& img: m_imgDir.entryList()){ ImageLoader* imgLoader = new ImageLoader(QFileInfo(m_imgDir.filePath(img))); connect(imgLoader, SIGNAL(imgReady(QFileInfo,QImage*)), this, SLOT(onImgReady(QFileInfo,QImage*)), Qt::QueuedConnection); QThreadPool::globalInstance()->start(imgLoader); } } } void MainWindow::onImgReady(const QFileInfo &file, QImage *img) { if (img){ QStandardItem* imgItem = new QStandardItem(); imgItem->setData(QVariant(QPixmap::fromImage(*img)), Qt::DecorationRole); m_imgModel->appendRow({new QStandardItem(file.fileName()), imgItem}); ui->m_imageTableView->resizeRowToContents(m_imgModel->rowCount()-1); ui->m_imageTableView->resizeColumnsToContents(); qInfo() << "img loaded" << "threads count:" << QThreadPool::globalInstance()->activeThreadCount(); } if (img){ delete img; } } 

There is one button on the form to select the directory and the TableView to display the model:

mainwindow.ui

 <?xml version="1.0" encoding="UTF-8"?> <ui version="4.0"> <class>MainWindow</class> <widget class="QMainWindow" name="MainWindow"> <property name="geometry"> <rect> <x>0</x> <y>0</y> <width>489</width> <height>256</height> </rect> </property> <property name="maximumSize"> <size> <width>640</width> <height>480</height> </size> </property> <property name="windowTitle"> <string>Потоки</string> </property> <widget class="QWidget" name="centralWidget"> <layout class="QVBoxLayout" name="verticalLayout_2"> <item> <widget class="QTableView" name="m_imageTableView"/> </item> <item> <widget class="QPushButton" name="m_selectDirBtn"> <property name="text"> <string>Выбрать директорию</string> </property> </widget> </item> </layout> </widget> <widget class="QMenuBar" name="menuBar"> <property name="geometry"> <rect> <x>0</x> <y>0</y> <width>489</width> <height>21</height> </rect> </property> </widget> <widget class="QToolBar" name="mainToolBar"> <attribute name="toolBarArea"> <enum>TopToolBarArea</enum> </attribute> <attribute name="toolBarBreak"> <bool>false</bool> </attribute> </widget> <widget class="QStatusBar" name="statusBar"/> </widget> <layoutdefault spacing="6" margin="11"/> <resources/> <connections/> </ui> 

How it looks like:

Output to console:

 "C:/Users/User/Pictures" ("2017-07-17_01.13.04.png", "galio.jpg", "galio.under.lol.png", "galio_and_text.png", "galio_w320.png", "lol.jpg", "lol.png", "LoL_Bug.1.png", "LoL_Bug.2.png", "LoL_Bug.3.png", "LoL_Bug.png", "photo_2018-03-08_23-37-28.jpg", "photo_2018-03-08_23-37-45.jpg", "photo_2018-03-08_23-37-51.jpg", "photo_2018-03-08_23-37-54.jpg", "photo_2018-03-08_23-37-57.jpg", "photo_2018-03-08_23-38-00.jpg", "photo_2018-03-08_23-38-02.jpg", "photo_2018-03-08_23-38-05.jpg", "photo_2018-03-08_23-38-08.jpg", "twitch.png", "Безымянный.png", "Снимок.PNG") img loaded threads count: 4 img loaded threads count: 4 img loaded threads count: 4 img loaded threads count: 4 img loaded threads count: 4 img loaded threads count: 4 img loaded threads count: 4 img loaded threads count: 2 img loaded threads count: 2 img loaded threads count: 1 img loaded threads count: 1 img loaded threads count: 1 img loaded threads count: 1 img loaded threads count: 1 img loaded threads count: 1 img loaded threads count: 1 img loaded threads count: 1 img loaded threads count: 1 img loaded threads count: 1 img loaded threads count: 1 img loaded threads count: 1 img loaded threads count: 1 img loaded threads count: 0 

As you can see, up to 4 threads were involved.

I almost forgot - I had to register QFileInfo in main.cpp in order to send it in the signal as a parameter:

 #include "mainwindow.h" #include <QApplication> #include <QFileInfo> int main(int argc, char *argv[]) { QApplication a(argc, argv); MainWindow w; qRegisterMetaType<QFileInfo>("QFileInfo"); w.show(); return a.exec(); } 

Perhaps not the correct code, but working and fast:

threadsminiature.h

 #ifndef THREADSMINIATURE_H #define THREADSMINIATURE_H #include <QObject> #include <QThread> #include <QImageReader> #include <QVector> class ThreadsMiniature : public QThread { Q_OBJECT public: explicit ThreadsMiniature(QObject *parent=0, QString Path="", int rowTableDisk = 0); void run(); QString _Path; int _rowTableDisk; //QList<QImage> MiniatureList; signals: //QImage drowMiniature(QImage image) {return image;} void drowMiniature(QImage); private: QString name; // Имя потока }; #endif // THREADSMINIATURE_H 

More than two values ​​in the MainWindow :: Miniature function can be passed using

 QImage image = imageReader.read(); image.setText("row", QString("%1").arg(_rowTableDisk)); 

Since QVector <QImage> does not have a SetObjectName method:

threadsminiature.cpp

 #include "threadsminiature.h" #include <QtCore> ThreadsMiniature::ThreadsMiniature(QObject *parent, QString Path, int rowTableDisk) : QThread(parent), _Path(Path), _rowTableDisk(rowTableDisk) { } void ThreadsMiniature::run() { int icoWidth = 200; int icoHeight = 200; QImageReader imageReader(_Path); QSize size; int image_width; int image_height; if (imageReader.supportsOption(QImageIOHandler::Size)) { size = imageReader.size(); image_width = size.width(); image_height = size.height(); } double ratio = (double)image_width / (double)image_height; if (ratio >= 1) { image_width = icoWidth; image_height = image_width / ratio; } else { image_height = icoHeight; image_width = image_height * ratio; } imageReader.setScaledSize(QSize(image_width, image_height)); QImage image = imageReader.read(); image.setText("row", QString("%1").arg(_rowTableDisk)); emit drowMiniature(image); } 

To bypass the call to the model (QStandardItemModel), in the stream, you can bring the call to this model to the separated function MainWindow :: Miniature.

mainwindow.cpp

 ..... //item_one = new QStandardItem("<a href=\""+imagePathListCopy.at(i)+"\">"+QFileInfo(imagePathListCopy.at(i)).fileName()+"</a>"); item_one = new QStandardItem(imagePathListCopy.at(i)); model->setItem(rowTableDisk, 1, item_one); ThreadsMiniature *threadB = new ThreadsMiniature(this,imagePathListCopy.at(i),rowTableDisk); connect(threadB, SIGNAL(drowMiniature(QImage)),this,SLOT(Miniature(QImage))); threadB->start(); item_one = new QStandardItem(DeviceFolder); model->setItem(rowTableDisk, 3, item_one); .... void MainWindow::Miniature (QImage image) { QString rowString = image.text("row"); qDebug()<<rowString; int rowTable = rowString.toInt(); item_one = new QStandardItem(); item_one->setData(QVariant(QPixmap::fromImage(image)), Qt::DecorationRole);//DecorationRole model->setItem(rowTable, 2, item_one); //rowMiniature++; }