I have a QTextEdit widget in a private slot, which I update regularly with setText() and insertPlainText().
I have found that setText()/insertPlainText() does not update the QTextEdit widget immediately. Instead, the QTextWidget is updated when the slot function returns. To test this, I have put a sleep() just after the setText()/insertPlainText().
class MyWindow : public Widget
{
MyWindow()
{
my_button = new QPushButton(this);
my_edit = new QTextEdit(this);
connect(my_button,
&QPushButton::clicked,
this,
&MyWindow::my_callback);
}
private slots:
void my_callback()
{
my_edit->setText("sample text");
// nothing happens; the QTextEdit
// widget does not show "sample text"
sleep(10);
// the QTextEdit widget will show
// "sample text" AFTER the sleep,
// when my_callback returns.
}
private:
QPushButton* my_button;
QTextEdit* my_edit;
}
This is a problem for me because I need to print a message in my QTextEdit widget BEFORE launching a time-consuming process (using QProcess). Currently, this message is not being printed until after QProcess process has returned.
Does anyone know how I can get the QTextEdit widget to show its contents right after setText()/insertPlainText()?
Using Qt5 on Fedora 29.
Never execute a task that consumes a lot of time in the GUI thread. In general, the solution is to execute that task in another thread, but in your case it indicates that you use QProcess, so I assume that you are using one of the methods waitForFinished(), waitForStarted() or waitForReadyRead(), instead you should use the signals:
#include <QtWidgets>
class Widget: public QWidget{
Q_OBJECT
public:
Widget(QWidget *parent=nullptr):
QWidget(parent)
{
button.setText("Press me");
QVBoxLayout *lay = new QVBoxLayout{this};
lay->addWidget(&button);
lay->addWidget(&textedit);
connect(&button, &QPushButton::clicked, this, &Widget::onClicked);
connect(&process, &QProcess::readyReadStandardError, this, &Widget::onReadyReadStandardError);
connect(&process, &QProcess::readyReadStandardOutput, this, &Widget::onReadAllStandardOutput);
}
private Q_SLOTS:
void onClicked(){
textedit.setText("sample text");
process.start("ping 8.8.8.8");
}
void onReadyReadStandardError(){
textedit.append(process.readAllStandardError());
}
void onReadAllStandardOutput(){
textedit.append(process.readAllStandardOutput());
}
private:
QPushButton button;
QTextEdit textedit;
QProcess process;
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Widget w;
w.show();
return a.exec();
}
#include "main.moc"
I wonder if calling
QCoreApplication::processEvents()
right after the ->setText("sample text") would do the trick in your case.
Related
I'm new in Qt and have a question.
I have QLabel and QLineEdit objects, and when QLabel text is clicked on, I want to set this text in QLineEdit.
Also I have read that QLabel has not clicked signal.
Can you explain how can I do this and write code for me ?!
Either style another type of QWidget such as a specific QPushButton to look like a QLabel and use its clicked() signal or inherit QLabel yourself and emit your own clicked() signal.
See this example:
https://wiki.qt.io/Clickable_QLabel
If you choose the latter option you can pass the text in the signal. Then connect the necessary signals/slots up between the QLabel and the QLineEdit like so:
QObject::connect(&label, SIGNAL(clicked(const QString& text)),
&lineEdit, SLOT(setText(const QString& text)));
A simple way to accomplish that, without a need for any subclassing, is a signal source that monitors the events on some object and emits relevant signals:
// main.cpp - this is a single-file example
#include <QtWidgets>
class MouseButtonSignaler : public QObject {
Q_OBJECT
bool eventFilter(QObject * obj, QEvent * ev) Q_DECL_OVERRIDE {
if ((ev->type() == QEvent::MouseButtonPress
|| ev->type() == QEvent::MouseButtonRelease
|| ev->type() == QEvent::MouseButtonDblClick)
&& obj->isWidgetType())
emit mouseButtonEvent(static_cast<QWidget*>(obj),
static_cast<QMouseEvent*>(ev));
return false;
}
public:
Q_SIGNAL void mouseButtonEvent(QWidget *, QMouseEvent *);
MouseButtonSignaler(QObject * parent = 0) : QObject(parent) {}
void installOn(QWidget * widget) {
widget->installEventFilter(this);
}
};
The emit keyword is an empty macro, Qt defines it as follows:
#define emit
It is for use by humans as a documentation aid prefix only, the compiler and moc ignore it. As a documentation aid, it means: the following method call is a signal emission. The signals are simply methods whose implementation is generated for you by moc - that's why we have to #include "main.moc" below to include all the implementations that moc has generated for the object class(es) in this file. There's otherwise nothing special or magical to a signal. In this example, you could look in the build folder for a file called main.moc and see the implementation (definition) of void MouseButtonSignaler::mouseButtonEvent( .. ).
You can then install such a signaler on any number of widgets, such as a QLabel:
int main(int argc, char ** argv) {
QApplication app(argc, argv);
MouseButtonSignaler signaler;
QWidget w;
QVBoxLayout layout(&w);
QLabel label("text");
QLineEdit edit;
layout.addWidget(&label);
layout.addWidget(&edit);
signaler.installOn(&label);
QObject::connect(&signaler, &MouseButtonSignaler::mouseButtonEvent,
[&label, &edit](QWidget*, QMouseEvent * event) {
if (event->type() == QEvent::MouseButtonPress)
edit.setText(label.text());
});
w.show();
return app.exec();
}
#include "main.moc"
You need to create one Custom Label class, which will inherit QLabel. Then you can use MouseButtonRelease event to check clicking of Label and emit your custom signal and catch in one SLOT.
Your .h file will be as below:
class YourLabelClass : public QLabel{
signals:
void myLabelClicked(); // Signal to emit
public slots:
void slotLabelClicked(); // Slot which will consume signal
protected:
bool event(QEvent *myEvent); // This method will give all kind of events on Label Widget
};
In your .cpp file, your constructor will connect signal & slot as below :
YourLabelClass :: YourLabelClass(QWidget* parent) : QLabel(parent) {
connect(this, SIGNAL(myLabelClicked()), this, SLOT(slotLabelClicked()));
}
Remaining event method and SLOT method will be implemented as below:
bool YourLabelClass :: event(QEvent *myEvent)
{
switch(myEvent->type())
{
case(QEvent :: MouseButtonRelease): // Identify Mouse press Event
{
qDebug() << "Got Mouse Event";
emit myLabelClicked();
break;
}
}
return QWidget::event(myEvent);
}
void YourLabelClass :: slotLabelClicked() // Implementation of Slot which will consume signal
{
qDebug() << "Clicked Label";
}
For Changing a Text on QLineEdit, you need to create a Custom Class and share object pointer with custom QLabel Class. Please check test code at this link
In the above example the header needs Q_OBJECT:
class YourLabelClass : public QLabel{
Q_OBJECT
signals:
My application is designed in that way that different plugins can set the central widget of the main windows to show the desired content.
This works so far.
But if I set a QQuickView-WindowContainer as central widget, the app does not quit when I close the main window.
If I set a "normal" widget like QPushButton as central widget the appliation quits just fine. Why is that?
This is the code of a minimal example which shows this behaviour (MainWindow is a class created from the QtCreator wizard):
class AppCore : public QObject
{
Q_OBJECT
public:
explicit AppCore(QObject *parent = 0);
signals:
public slots:
void showMainWindow();
private:
MainWindow *m_mainWindow;
};
AppCore::AppCore(QObject *parent) :
QObject(parent)
{
}
void AppCore::showMainWindow()
{
QQuickView *view;
QWidget *container;
view = new QQuickView();
container = QWidget::createWindowContainer(view);
view->setSource(QUrl("qrc:/main.qml"));
m_mainWindow = new MainWindow();
//m_mainWindow->setCentralWidget(new QPushButton("Button"));
m_mainWindow->setCentralWidget(container);
m_mainWindow->show();
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
AppCore appCore;
appCore.showMainWindow();;
return a.exec();
}
This looks like a bug. I see a dead lock in debugger: v8::internal::RuntimeProfiler::WaitForSomeIsolateToEnterJS and QQmlDataLoader::shutdownThread wait for each other. I can't find a good workaround for this issue.
I found a dirty hack that solved the issue. If container is deleted a bit earlier, all works ok:
void MainWindow::closeEvent(QCloseEvent *e) {
QMainWindow::closeEvent(e);
if (e->isAccepted() && centralWidget()) {
delete centralWidget();
}
}
You probably should send a bug report. Note that m_mainWindow is not needed to reproduce the issue. Using container->show(); gives the same result.
I am a QT beginner and I am writing a GUI app that has two QPushButtons and two QTextEdits. When button 1 is clicked, I want only QTextEdit 1 to show something, when button 2 is clicked, I want only QTextEdit 2 to show something, below is my code, but it doesn't work because it seems that I cannot pass parameters to slot method....
class EventProcessor: public QObject {
Q_OBJECT
public slots:
void PopulateEditTest(QTextEdit *textEdit, QString text)
{
textEdit->setText(text);
}
};
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QWidget *window = new QWidget;
QTextEdit *result1 = new QTextEdit();
QTextEdit *result2 = new QTextEdit();
QPushButton *btFacility1 = new QPushButton("Facility 1");
QPushButton *btFacility2 = new QPushButton("Facility 2");
EventProcessor eventprocessor;
QObject::connect(btFacility1, SIGNAL(clicked()), &eventprocessor, SLOT(PopulateEditTest
(result1, "textEdit1")));
QObject::connect(btFacility2, SIGNAL(clicked()), result, SLOT(PopulateEditTest
(result2, "textEdit2")));
..........
return app.exec();
}
I am wondering if there is a similar way to get this working? Thank you for your answer.
You are correct in that you cannot specify arguments to be passed to a slot when you call QObject::connect. All you are providing are function definitions, not function calls.
The simplest way to accomplish what you're trying to do would be to add a couple of slots to your event processor class:
class EventProcessor: public QObject {
Q_OBJECT
public slots:
void PopulateEditTest(QTextEdit *textEdit, QString text) { ... }
void button1Clicked() {
PopulateEditTest(dynamic_cast<QTextEdit*>(sender()), "textEdit1");
}
void button2Clicked() {
PopulateEditTest(dynamic_cast<QTextEdit*>(sender()), "textEdit1");
}
};
...
QObject::connect(btFacility1, SIGNAL(clicked()), &eventprocessor, SLOT(button1clicked()));
QObject::connect(btFacility2, SIGNAL(clicked()), &eventprocessor, SLOT(button2Clicked()));
There are various reasons why it is generally considered to be "evil" to use the QObject::sender() function in this manner, but it is the simplest way to accomplish what you're trying to do without rewriting all of your code, which would be pointless me of to do without knowing what your long term goals are.
I have a use case when user actions initialise application data at each runtime. To represent that behavior here is my sample code:
SignalSlotChange.h
#ifndef SIGNALSLOTCHANGE_H
#define SIGNALSLOTCHANGE_H
#include <QtGui>
class SignalSlotChange : public QWidget
{
Q_OBJECT
public:
SignalSlotChange(QWidget *parent = 0);
private slots:
void firstCall();
void secondCall();
private:
QPushButton *button;
};
#endif // SIGNALSLOTCHANGE_H
SignalSlotChange.cpp
#include "SignalSlotChange.h"
SignalSlotChange::SignalSlotChange(QWidget *parent) : QWidget(parent)
{
button = new QPushButton("Messgage", this);
QObject::connect(button, SIGNAL(clicked()), this, SLOT(firstCall()));
show();
}
void SignalSlotChange::firstCall()
{
QMessageBox::information(this, "SignalSlotChange", "First call", QMessageBox::Ok, QMessageBox::NoButton);
// Change the signal-slot connection to secondCall()
QObject::disconnect(button, SIGNAL(clicked()), this, SLOT(firstCall()));
QObject::connect(button, SIGNAL(clicked()), this, SLOT(secondCall()));
}
void SignalSlotChange::secondCall()
{
QMessageBox::information(this, "SignalSlotChange", "Second call", QMessageBox::Ok, QMessageBox::NoButton);
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
SignalSlotChange ssc;
return app.exec();
}
When the button is pressed then the initialising slot firstCall() is called. It changed the signal-slot connection to secondCall() for subsequent signals.
The problem with the way I do it is that it is highly coupled and requires that slot knows exact method and signals to change it.
With QObject::sender() I would know origin of sender but not its signal, and I would know about just one sender which happened to emit that signal.
I can do it with a Boolean first_call but that would be making a check on Boolean value for all subsequent calls, something which I want to avoid and hence this question.
A somewhat different solution could be implemented by using a pointer-to-member approach:
SignalSlotChange.h
#ifndef SIGNALSLOTCHANGE_H
#define SIGNALSLOTCHANGE_H
#include <QtGui>
class SignalSlotChange : public QWidget {
Q_OBJECT
public:
SignalSlotChange(QWidget *parent = 0);
private slots:
void callCall();
private:
void (SignalSlotChange::* delegate) ();
void firstCall();
void secondCall();
QPushButton *button;
};
#endif // SIGNALSLOTCHANGE_H
SignalSlotChange.cpp
#include "SignalSlotChange.h"
SignalSlotChange::SignalSlotChange(QWidget *parent) : QWidget(parent) {
delegate = &SignalSlotChange::firstCall;
button = new QPushButton("Messgage", this);
QObject::connect(button, SIGNAL(clicked()), this, SLOT(callCall()));
show();
}
void SignalSlotChange::callCall() {
(this->*delegate) ();
}
void SignalSlotChange::firstCall() {
QMessageBox::information(this, "SignalSlotChange", "First call", QMessageBox::Ok, QMessageBox::NoButton);
// Change the effective signal-slot connection to secondCall()
delegate = &SignalSlotChange::secondCall;
}
void SignalSlotChange::secondCall() {
QMessageBox::information(this, "SignalSlotChange", "Second call", QMessageBox::Ok, QMessageBox::NoButton);
}
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
SignalSlotChange ssc;
return app.exec();
}
I am not sure if this is better solution from a decoupling perspective, but the advantage is that the mechanism does not need to know anything about the slot which was actually triggered. The complete logic to implement the "method switch" is encapsulated within the SignalSlotChange class. The callCall() slot can be connected to any other compatible signal and the method switch still works, with no further code changes.
I am trying to open a new dialog Window from a existing dialog on a a button click event,but I am not able to do this as i opened the dialog window from MainWindow.
I am trying with:
Dialog1 *New = new Dialog1();
New->show();
Is there a different way of opening dialog window form existing dialog Window???
There must be some other problem, because your code looks good to me. Here's how I'd do it:
#include <QtGui>
class Dialog : public QDialog
{
public:
Dialog()
{
QDialog *subDialog = new QDialog;
subDialog->setWindowTitle("Sub Dialog");
QPushButton *button = new QPushButton("Push to open new dialog", this);
connect(button, SIGNAL(clicked()), subDialog, SLOT(show()));
}
};
class MainWindow : public QMainWindow
{
public:
MainWindow()
{
Dialog *dialog = new Dialog;
dialog->setWindowTitle("Dialog");
dialog->show();
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.setWindowTitle("Main Window");
w.show();
return a.exec();
}
By the way, note how I've connected QPushButton's "clicked" signal to QDialog's "show" slot. Very handy.
I am new to QT and I did have a similar problem. In my case, I was calling the new dialog from a function from the main dialog. I was using dlg->show which does not wait until the result of the new dialog. Hence the program still running. I change dlg->show for dlg->exec and the dialog works now. In your code, the dialog seems to be a local variable, perhaps you have the same problem. Other option could be to use a static pointer instead.
Dialog1 *newDlg = new Dialog1();
this->hide();
int result = newDlg->exec();
this->show();
delete newDlg;
in mainwindow.h file you should declare a pointer to your new dialog
and include the new dialog.h like
#include <myNewDialog.h>
private:
Ui::MainWindow *ui;
MyNewDialog *objMyNewDialog;
and after that you can call your dialog to be shown up in mainwindow.cpp
like
void MainWindow::on_btnClose_clicked()
{
objMyNewDialog= new MyNewDialog(this);
objMyNewDialog->show();
}