I have two simple classes:
class Parent: public QWidget {
Q_OBJECT
public:
Parent(QWidget * parent): QWidget(parent) {}
public:
void slot() const {
qDebug() << "slot:" << state;
}
private:
int state {
42
};
};
class Child: public QWidget {
Q_OBJECT
public:
Child(QWidget * parent): QWidget(parent) {}
~Child() override {
emit signal();
}
signals:
void signal();
};
int main(int argc, char * argv[]) {
QApplication app(argc, argv);
QMainWindow w;
auto * p = new Parent( & w);
auto * c = new Child(p);
QObject::connect(c, & Child::signal, p, & Parent::slot);
QTimer::singleShot(1000, & app, & QApplication::quit);
w.show();
return app.exec();
}
This program crashes because signal from the child destructor calls a slot of already destructed parent. There is no problem with ~QObject(), which clears all its connections before deleteChildren() call, but ~QWidget() calls this function before base QObject destruction.
Related
I have written a project which includes a mainwindow and a replacedlg.ui. I want to use replacedlg.ui in mainwindow.cpp.
I'd like to write things like ui->button in mainwindow.cpp, but I can't.
Who can help me make this work?
The whole project is here.
Don't try to share the ui variable between classes. It is bad design. Instead add methods in your classes which will let you do what you need to do.
In your case where you want to send the text of your line edit from replaceDlg class to your MainWindow class, you should use signals and slots. Here is an example:
#include <QtWidgets>
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = Q_NULLPTR) : QMainWindow(parent)
{
setCentralWidget(&text_edit);
}
public slots:
void addText(const QString &text)
{
text_edit.append(text);
}
private:
QTextEdit text_edit;
};
class Dialog : public QDialog
{
Q_OBJECT
public:
Dialog(QWidget *parent = Q_NULLPTR) : QDialog(parent)
{
setLayout(new QHBoxLayout);
QPushButton *send_button = new QPushButton("Send");
layout()->addWidget(&line_edit);
layout()->addWidget(send_button);
connect(send_button, &QPushButton::clicked, this, &Dialog::sendButtonClicked);
}
signals:
void sendText(const QString &text);
private slots:
void sendButtonClicked()
{
emit sendText(line_edit.text());
accept();
}
private:
QLineEdit line_edit;
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
Dialog d;
QObject::connect(&d, &Dialog::sendText, &w, &MainWindow::addText);
w.show();
d.show();
return a.exec();
}
#include "main.moc"
I have implemented custom QQuickItem which is exposed to QML. Now it becomes more useful item in all platforms but due some reasons in Windows we are not using QML it's pure QT Application.
But I am not able to instantiate custom QQuickItem in Qt, could some one help me out of this?
Here is the code:
customItem.h
#include <QQuickItem>
#include <QQuickWindow>
class CustomItem : public QQuickItem
{
Q_OBJECT
public:
explicit CustomItem(QQuickItem *parent = 0);
signals:
public slots:
void paint();
private slots:
void handleWindowChanged(QQuickWindow * win);
};
customItem.cpp:
#include "customItem.h"
CustomItem::CustomItem(QQuickItem *parent) :
QQuickItem(parent)
{
connect(this, &CustomItem::windowChanged, this, &CustomItem::handleWindowChanged);
}
void CustomItem::paint()
{
QQuickWindow * win = window();
qreal ratio = win->devicePixelRatio();
int w = int(ratio * win->width());
int h = int(ratio * win->height());
glViewport(0, 0, w, h);
glDisable(GL_DEPTH_TEST);
glClearColor(0, 1, 0, 1);
glClear(GL_COLOR_BUFFER_BIT);
}
void CustomItem::handleWindowChanged(QQuickWindow * win)
{
if (win) {
connect(win, &QQuickWindow::beforeRendering, this, &CustomItem::paint, Qt::DirectConnection);
win->setClearBeforeRendering(false);
}
}
main.cpp:
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QQuickView *view = new QQuickView ();
QWidget *container = QWidget::createWindowContainer(view);
CustomItem *customitem = new CustomItem();///how can i set it view
container->show();
return app.exec();
}
Issue:
Not able to instantiate CustomItem
I have a QDialog for beginning of my game.in this class I have a QGraphicsTextItem. I want to it is clickable. When user clicked play game start. I do this but not work.
class Mydialog_start:public QDialog
{
Q_OBJECT
public:
explicit Mydialog_start(QWidget *parent = 0);
signals:
public slots:
void on_play_clicked();
void on_exit_clicked();
private:
QGraphicsScene* scene;
QGraphicsView* view;
QPixmap image;
QBrush brush;
QGraphicsTextItem* text;
QFont font;
const int x_size;
const int y_size;
};
Mydialog_start::Mydialog_start(QWidget *parent) :
QDialog(parent),x_size(400),y_size(400)
{
scene=new QGraphicsScene(this);
view=new QGraphicsView(this);
view->setScene(scene);
scene->setSceneRect(0,0,x_size,y_size);
image.load(":picture/image/background.jpg");
image=image.scaled(x_size,y_size);
brush.setTexture(image);
scene->setBackgroundBrush(brush);
font.setBold(true);
font.setPointSize(40);
font.setItalic(true);
text=scene->addText("play",font);
text->setDefaultTextColor(QColor("red"));
text->setPos(100,300);
this->setFixedSize(400,400);
connect(text,SIGNAL(linkActivated(QString("play"))),this,SLOT(on_play_clicked()));
}
void Mydialog_start::on_play_clicked()
{
accept();
}
void Mydialog_start::on_exit_clicked()
{
reject();
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
Mydialog_start dialog;
dialog.exec();
if( dialog.exec()==QDialog::Accepted)
{
w.show();
}
else
{
w.close();
}
}
Not quite sure whether you needed your text item to be "editable" - see Mitch's comment...
It seems that you need your item to be "clickable" - then all you need are some flags:
text->setFlags(QGraphicsItem::ItemIsSelectable | QGraphicsItem::ItemIsFocusable);
I try to call slot of my class via newConnection() signal of QTcpServer class. connect() function returns true, but the slot weren't executed.
Here's what i made:
class server : QObject
{
Q_OBJECT
public:
server();
QTcpServer *srv;
void run();
public slots:
void handleClient();
}
Bind the slot:
void server::run()
{
srv = new QTcpServer();
bool status = connect(srv, SIGNAL(newConnection()), this, SLOT(handleClient()));
// status contains true now
srv->listen(QHostAddress::Any, port);
}
Slot's body:
void server::handleClient()
{
/* This code is not being executed */
qDebug() << "zxc";
QMessageBox msg;
msg.setText("zxc");
msg.exec();
}
Why doesn't it work?
I'm not quite sure what you're doing wrong try adding public in the inheritance line (: public QObject).
The following code works for me:
server.hpp
#ifndef _SERVER_HPP_
#define _SERVER_HPP_
#include <QtNetwork>
class Server : public QObject
{
Q_OBJECT
public:
Server();
private slots:
void handleClient();
private:
QTcpServer* mServer;
};
#endif
server.cpp
#include "server.hpp"
Server::Server() : mServer(new QTcpServer())
{
connect(mServer, SIGNAL(newConnection()), this, SLOT(handleClient()));
mServer->listen(QHostAddress::Any, 10000);
}
void Server::handleClient()
{
while (mServer->hasPendingConnections())
{
QTcpSocket* skt = mServer->nextPendingConnection();
skt->write("READY\n");
skt->waitForReadyRead(5000);
qDebug() << skt->readAll();
skt->write("OK\n");
skt->waitForBytesWritten();
skt->close();
skt->deleteLater();
}
}
main.cpp
#include "server.hpp"
int main(int argc, char** argv)
{
QCoreApplication app(argc, argv);
Server srv;
return app.exec();
}
I am trying to make a Collaborative Editor(I have to use Linux networking libraries for all the networking stuff), I have the main widget(custom made class that inherits QWidget) with all the components. In the constructor I create all the Widgets on this main Widget and at the end I try to create a new thread using QFuture(I use QFuture instead of QThread cause it allows me easily to call functions with any type of parameters, like QTextEdit, QTextCursor...) but it gives me this error at compilation:
"QObject: Cannot create children for a parent that is in a different thread.
(Parent is QTextDocument(0x1b064b0), parent's thread is QThread(0x1985750), current thread is QThread(0x1ae7610)".
How to solve the error?
Here is my code:
mainwindow.h:
...//includes
using namespace QtConcurrent;
...
namespace Ui {
class Widget;
class TextEdit;
}
class TextEdit;
class Widget;
class Widget : public QWidget {
Q_OBJECT
public:
Widget(QWidget *parent = 0);
~Widget();
...
QFuture<void> thread;
}
class TextEdit : public QTextEdit {
Q_OBJECT
...
}
static void receiveKeyPress(TextEdit *textedit, QTextCursor *secondUserCursor) {
unsigned long long int Number = NULL;
QMessageBox::information(textedit->parentWidget(), "UI Component", "This makes the thread to throw the error");
while(1) if(connected == 1) {
read(recvFileDescriptor, &Number, sizeof(unsigned long long int));
if( Number != NULL)
if( Number == Qt::Key_Home )
secondUserCursor->movePosition(QTextCursor::StartOfLine);
...
else {
QTextCharFormat backgroundFormat = textedit->textCursor().charFormat();
backgroundFormat.setBackground(QColor("lightGreen"));
//If I don't use QMessageBox up there, it breaks here on the next command
secondUserCursor->setCharFormat(backgroundFormat);
secondUserCursor->setPosition(textedit->textCursor().position());
secondUserCursor->insertText(QString::number(Number));
} //else
}//while
}//the function
And mainwindow.cpp:
#include "mainwindow.h"
Widget::Widget(QWidget *parent) {
...
thread = run(receiveKeyPress, this->edit1, this->edit1->secondUserCursor); //run is from QtConcurrent namespace
}
main.cpp:
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Widget window;
...
window.show();
return a.exec();
}
I've read here on stackoverflow how others use QObject(which I never used and I don't get the idea of it) and QThread(the only combination) but I already tried to use QThread and I wasn't able to pass QTextEdit and QTextCursor to it.
Thanks in advance
Edit:
mainwindow.h
class TextEdit : public QTextEdit {
Q_OBJECT
...
public slots:
void receiveKeyPress(qulonglong);
...
};
mainwindow.cpp
void TextEdit::receiveKeyPress(qulonglong Number) {
if( Number == Qt::Key_Home )
...
}
recv-thread.h - created based on this link http://developer.qt.nokia.com/doc/qt-4.8/thread-basics.html#example-3-clock
#include <QThread>
#include "mainwindow.h" //To get TextEdit in here
class RecvThread : public QThread {
Q_OBJECT
signals:
void transferDataToSlot(qulonglong Data);
protected:
void run();
};
recv-thread.cpp
#include "recv-thread.h"
void RecvThread::run() {
unsigned long long int Number = NULL;
while(1) if(connected == 1) {
read(recvFileDescriptor, &Number, sizeof(unsigned long long int));
if( Number != NULL) {
emit transferDataToSlot(Number);
}
}
}
main.cpp
...
#include "recv-thread.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Widget window;
RecvThread recvThread;
...
QObject::connect(&recvThread, SIGNAL(transferDataToSlot(qulonglong)), window.edit1, SLOT(receiveKeyPress(qulonglong)), Qt::QueuedConnection); //line 38
recvThread.start();
//Displaying the window
window.show();
a.exec();
recvThread.quit();
recvThread.wait();
return 0;
}
Am I doing it right?