How to work with QEvent?

Question

How to work with QEvent ??

I tried to transfer information (QString) from the main stream to the next thread through a class inherited from QEvent.

He began to do the example in the book of Max Schlee (Qt5.3), But there I did not even understand the design

public: enum {ProgressType = User + 1}; ProgressEvent() : QEvent((Type)ProgressType) { }

And when I created the same for myself, she gathered, but did not pass the string,; _; sad

mainwindow.h

 #ifndef MAINWINDOW_H #define MAINWINDOW_H #include <QMainWindow> #include <QCheckBox> #include <QHBoxLayout> #include <QDebug> #include <QThread> #include <QEvent> #include <QCoreApplication> #include <iostream> #include <vector> namespace Ui { class MainWindow; } class MainWindow : public QMainWindow { Q_OBJECT int glob_i ; int glob_flow; int vector_schet; // датчик счёта public: explicit MainWindow(QWidget *parent = 0); ~MainWindow(); public slots: void start_sending(bool); // принажатии на чекбокс то выполниться этот слот (отправка сообщений) private slots: void on_pushButton_clicked(); private: Ui::MainWindow *ui; QThread *thread = new QThread(); QVector<QThread*> vector_thread; QList<QCheckBox*> test_checkbox; // вот вектор QCheckBox *checkBox = new QCheckBox(); // Создаём виджет, который будет содержать в себе чекбокс QWidget *checkBoxWidget = new QWidget(); // создаём слой с привязкой к виджету QHBoxLayout *layoutCheckBox = new QHBoxLayout(checkBoxWidget); }; class NewsThread: public QThread { Q_OBJECT public slots: void run_NEW(); // код выполняемый в потоке signals: void otprawka (int); }; class StrokaEvent: public QEvent{ public: enum {qwert = User + 1}; StrokaEvent() : QEvent((Type)qwert) { } QString stroka; QString NewStroka(); void setStroka(QString); };

mainwindow.cpp

 #include "mainwindow.h" #include "ui_mainwindow.h" MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow) { glob_i=0; glob_flow =0; vector_schet =0; ui->setupUi(this); } MainWindow::~MainWindow() { delete ui; } void MainWindow::on_pushButton_clicked() { glob_i++; //-- добавляем чек бокс в таблицу checkBoxWidget = new QWidget(); // создаём новый qwidget() checkBox = new QCheckBox(); // объявляем и инициализируем чекбокс layoutCheckBox = new QHBoxLayout(checkBoxWidget); // создаём слой с привязкой к виджету test_checkbox.append(checkBox); int i =0; connect(checkBox, SIGNAL(toggled(bool)),this, SLOT(start_sending(bool))); // соединение всех чекетов с "действием" start_sending checkBox->setText(QString::number(glob_i)); layoutCheckBox->addWidget(checkBox); // Устанавливаем чекбокс в слой layoutCheckBox->setAlignment(Qt::AlignCenter); // Отцентровываем чекбокс layoutCheckBox->setContentsMargins(0,0,0,0); // Устанавливаем нулевые отступы ui->tW_test->insertRow(ui->tW_test->rowCount());//вводим колич строк (возвращ колич строк) ui->tW_test->setCellWidget(ui->tW_test->rowCount()-1, 1, checkBoxWidget); // добавляем элемент в таблицу (строка, столбец, добавляемый элемент) } void MainWindow::start_sending(bool Value) { // когда нажата отрабатывает, отжата то не отрабатывает if (Value == true) { NewsThread *two_cl = new NewsThread(); // инициализируем второй класс for (int i =0;i < test_checkbox.length();i++ ) { if(test_checkbox[i]->isChecked() ==Value) { glob_flow++; QString strok = "dimasik :3"; StrokaEvent *S_E = new StrokaEvent; S_E->setStroka(strok); connect(test_checkbox[i], SIGNAL(stateChanged(int)), two_cl , SLOT(run_NEW()));// от кого, "реакция", кому, "выполнение" thread = new QThread(); vector_thread.append(thread); vector_schet++; qDebug() << "vector_schet : " << vector_schet ; two_cl->moveToThread(vector_thread[vector_schet-1]); // отправляем в поток vector_thread[vector_schet-1]->start(); // цикл обработки сообщения в потоке (второй поток) } } } else { qDebug() << "chekbocks:" << " False"; glob_flow--; qDebug() << "vector_schet : " << vector_schet ; vector_thread[vector_schet-1]->exit(); } } void NewsThread::run_NEW() { StrokaEvent *S_E = new StrokaEvent; qDebug() << "run_NEW()"; for(;;){ // вечный цикл for (int i=0; i<500; i++){ qDebug()<< "Число :" << i <<"номер \"потока\" :" << S_E->NewStroka(); usleep(100000); } } } QString StrokaEvent::NewStroka() { return stroka; } void StrokaEvent::setStroka(QString str) { stroka = str; }

Alexander Alexander 3,222 one four 15 · Accepted Answer · 2018-06-27T07:56:31

To create a new type of QEvent :: Type it is better to use the static method QEvent :: registerEventType (), so that there are no repetitions.

StrokaEvent needs to be caught in the overridden virtual QObject :: event method.

You create a new instance and wonder why it is empty:

 void NewsThread::run_NEW() { StrokaEvent *S_E = new StrokaEvent; ... S_E->NewStroka() }

I do not know what Schlee wrote there, maybe you misunderstood him? Here is an example of using QEvent to send messages between threads:

stringEvent.h

 #ifndef STRINGEVENT_H #define STRINGEVENT_H #include <QEvent> #include <QString> class StringEvent : public QEvent { public: StringEvent(const QString &_text); static QEvent::Type type(); const QString &getText() const; private: const QString text; static QEvent::Type m_eventType; }; #endif // STRINGEVENT_H

stringEvent.cpp

 #include "stringevent.h" QEvent::Type StringEvent::m_eventType = QEvent::None; StringEvent::StringEvent(const QString &_text): QEvent(StringEvent::type()), text(_text) { } QEvent::Type StringEvent::type() { if (m_eventType == QEvent::None) { int generatedType = QEvent::registerEventType(); m_eventType = static_cast<QEvent::Type>(generatedType); } return m_eventType; } const QString &StringEvent::getText() const { return text; }

threadedclass.h

 #ifndef THREADEDCLASS_H #define THREADEDCLASS_H #include <QThread> #include <QDebug> #include "stringevent.h" class ThreadedClass : public QObject { Q_OBJECT public: ThreadedClass(QObject *_parent = nullptr): QObject(_parent) { } public: virtual bool event(QEvent *event) override { if(event->type() == StringEvent::type()) { StringEvent *strEvent = static_cast<StringEvent*>(event); qDebug() << "Handle string | " << strEvent->getText() << " | from thread < " << QThread::currentThread(); } return QObject::event(event); } }; #endif // THREADEDCLASS_H

MainWindow.h

 #ifndef MAINWINDOW_H #define MAINWINDOW_H #include <QMainWindow> #include "threadedclass.h" namespace Ui { class MainWindow; } class MainWindow : public QMainWindow { Q_OBJECT public: explicit MainWindow(QWidget *parent = nullptr); ~MainWindow(); private slots: void on_pushButton_clicked(); private: Ui::MainWindow *ui; ThreadedClass *m_thread; QThread *m_th1; }; #endif // MAINWINDOW_H

MainWindow.cpp

 #include "mainwindow.h" #include "ui_mainwindow.h" #include "stringevent.h" #include <QDebug> MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow) { ui->setupUi(this); m_thread = new ThreadedClass(); m_th1 = new QThread(); m_th1->start(); m_thread->moveToThread(m_th1); } MainWindow::~MainWindow() { delete ui; } void MainWindow::on_pushButton_clicked() { const QString text = ui->lineEdit->text(); qDebug() << "Try send text string from thread < " << QThread::currentThread(); qApp->postEvent(m_thread, new StringEvent(text)); }

After starting the program, entering text into lineEdit and pressing a button, we get the output:

 Try send text string from thread < QThread(0x36db80) Handle string | "test1" | from thread < QThread(0x370938)

And what is the difference between this method and sending a signal and "catching" it through connect?
stackoverflow.com/questions/3794649/qt-events-and-signal-slots

Cerbo cerbo 5,755 one 15 40 · Answer 2 · 2018-06-27T08:00:23

You have not done the main thing, the transfer of the message. In Qt, this is done in two ways:

synchronously, using the QCoreApplication::sendEvent() function, the message will be processed by the recipient in the body sendEvent() ; in this case, if the recipient is in a different stream, the flow of the sender will be suspended.
Asynchronously, using the QCoreApplication::postEvent() function, the message will only be added to the queue to the recipient, the threads will not pause.

How to work with QEvent?

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