I create a new QWidget object and I want to know when the close button is pressed.
I have tried the following code:
pWindow = new QWidget();
connect(pWindow , SIGNAL(triggered()), this, SLOT(processCloseButtonWindowsClicked()));
but it give an error:
no signal triggered of pWindow
How to achieve this?
Cause
QWidget does not have a triggered signal.
Solution
I would suggest you to:
Subclass QWidget and reimplement QWidget::closeEvent
Check QEvent::spontaneous to differentiate between a click of the close button and the call to QWidget::close
According to your app's logic either call QWidget::closeEvent(event); to close the widget, or QEvent::ignore to leave it open
Example
I have prepared an example for you of how to implement the proposed solution:
#include <QMainWindow>
#include <QCloseEvent>
#include <QPushButton>
class FooWidget : public QWidget
{
Q_OBJECT
public:
explicit FooWidget(QWidget *parent = nullptr) :
QWidget(parent) {
auto *button = new QPushButton(tr("Close"), this);
connect(button, &QPushButton::clicked, this, &FooWidget::close);
resize(300, 200);
setWindowTitle("Foo");
}
protected:
void closeEvent(QCloseEvent *event) override {
if (event->spontaneous()) {
qDebug("The close button was clicked");
// do event->ignore();
// or QWidget::closeEvent(event);
} else {
QWidget::closeEvent(event);
}
}
};
class MainWindow : public QMainWindow
{
Q_OBJECT
FooWidget *pWindow;
public:
explicit MainWindow(QWidget *parent = nullptr) :
QMainWindow(parent),
pWindow(new FooWidget()) {
pWindow->show();
}
};
void QWidget::closeEvent(QCloseEvent *event) will be the possible way I would go with.
You can read the documentation here.
Before, check if Qt has a class for what you want to do. Maybe you want to use QDialog instead of QWidget for what you want to achieve.
The following code: suppose you want to delete the widget when the X is clicked and you just want to know when to do something.
Try connecting the signal from the base class QObject of your widget when it is Destroyed:
-Your Widget
-attribute setted to destroy your widget after X(closebotton is clicked) or the close() handler is triggered
-connect the destroyed() signal to whatever slot you want to do something before it is destroyed
pWindow = new QWidget();
pWindow->setAttribute(Qt::WA_DeleteOnClose,true);
connect(pWindow , SIGNAL(destroyed()), this,SLOT(processCloseButtonWindowsClicked()));
for more info:
https://doc.qt.io/qt-5/qwidget.html#close
https://doc.qt.io/qt-5/qobject.html#destroyed
Related
I'm trying to understand how to use signals to when one QCheckBox be checked it uncheck all other checkboxes present in the same QGroupBox
class GroupBox : public QGroupBox
{
public:
GroupBox(QWidget *parent = nullptr) : QGroupBox(parent)
{
}
public slots:
void uncheck();
};
class CheckBox : public QCheckBox
{
public:
CheckBox(QWidget *parent = nullptr) : QCheckBox(parent)
{
connect(this, SIGNAL(checked()), this, SLOT(checked()));
}
public slots:
void checked()
{
qDebug() << "checked";
}
};
When I click on one of the checkboxes it didn't go to the function checked().
QCheckBox inherits from QAbstractButton
You should use clicked or stateChanged signal instead of checked.
e.q.
connect(this, SIGNAL(stateChanged(int)), this, SLOT(checked(int)));
Btw; if using a modern Qt version, you should ditch the SIGNAL and SLOTS macros and instead use the new connect() syntax that's checked at compile time.
Refer: New Signal Slot Syntax
e.p.
connect(this, &QCheckBox::clicked, this, &CheckBox::checked);
C++ Qt newbe here. I work with a QDial object that is intended to be controlled with a mouse wheel, it works fine as such, emitting valueChanged() signals when necessary.
I would like to put a semi-transparent QToolButton on top of it, allowing users to click on the button (and set QDial value to a pre-defined number) while maintaining the ability to use the mouse wheel to control QDial as usual.
I experimented a bit with the TransparentForMouseEvents attribute:
ui->toolButton_Example->setAttribute(Qt::WA_TransparentForMouseEvents);
The problem is - the above code switches off all events, including the ability to emit the clicked() signal.
Is there a way to make a QToolButton transparent selectively for MouseWheelEvents while preserving the ability to respond to MouseClick events? Or would this require rewriting the event filter from scratch?
EDIT: Just to clarify - This question is about making QToolButton transparent to MouseWheel EVENTS while still allowing it to respond to MouseClick EVENTS. It is not about making the button transparent in the graphical sense.
SOLUTION
OK, problem solved the traditional way by subclassing QDial and overriding MousePressEvent and MouseReleaseEvent:
#include <QDial>
#include <QMouseEvent>
class QSuperDial : public QDial {
public:
QSuperDial (QWidget *parent = nullptr) : QDial(parent) {
}
virtual void mousePressEvent (QMouseEvent *event) override {
emit sliderPressed();
}
virtual void mouseMoveEvent (QMouseEvent * event) override {
}
virtual void mouseReleaseEvent (QMouseEvent *event) override {
}
};
Promoting QDial to QSuperDial results in a QDial object that 'behaves' like a button when pressed, emitting sliderPressed signal, while still being responsive to MouseWheelEvent (like a normal QDial).
I think this is the simplest and the most 'Qt-like' solution, but please do correct me if I'm mistaken.
You can use QObject::installEventFilter to have the parent object filter the events before they reach the tool button. Then, override the parent's QObject::eventFilter to handle/ignore the event.
I create an example below:
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QToolButton>
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
bool eventFilter(QObject *watched, QEvent *event) override;
private:
QToolButton tool_button_ignored_;
QToolButton tool_button_handled_;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include <QDebug>
#include <QEvent>
#include <QHBoxLayout>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
tool_button_ignored_.setObjectName("tool_button_ignored_");
tool_button_ignored_.setText("Ignored button");
tool_button_ignored_.installEventFilter(this);
tool_button_handled_.setObjectName("tool_button_handled_");
tool_button_handled_.setText("Handled button");
tool_button_handled_.installEventFilter(this);
QWidget *central_widget = new QWidget{this};
QHBoxLayout *layout = new QHBoxLayout{central_widget};
layout->addWidget(&tool_button_ignored_);
layout->addWidget(&tool_button_handled_);
this->setCentralWidget(central_widget);
}
MainWindow::~MainWindow()
{
}
bool MainWindow::eventFilter(QObject *watched, QEvent *event)
{
if (watched != &tool_button_ignored_ || event->type() != QEvent::Wheel)
{
qDebug() << event->type() << watched->objectName() << "handled";
return QMainWindow::eventFilter(watched, event);
}
else
{
qDebug() << event->type() << watched->objectName() << "ignored";
return true; // stop being handled further
}
}
I connected the clicked(bool) event from QPushButton to a private slot mySlot() of my own Widget. But the slot is never called (I placed a breakpoint in mySlot()). I'm using c++ and Qt5.
I wrote a minimal version of my code:
MyLayout.h
class MyLayout : public QWidget
{
Q_OBJECT
public:
MyLayout(QWidget* parent = NULL);
private:
QPushButton *next;
private slots:
void mySlot();
}
MyLayout.cpp
MyLayout::MyLayout(QWidget* parent) : QWidget(parent)
{
next = new QPushButton("Next Step");
QObject::connect(next, SIGNAL(clicked(bool)), this, SLOT(mySlot()));
}
void MyLayout::mySlot() { /* do something */ }
Any ideas?
You created a parentless button and never showed it. Start by giving it parent (this), so it gets shown together with your widget:
next = new QPushButton("Next Step", this);
Then learn how to use layouts.
I'm trying to write a very basic program. The main window contains a label. Pressing the "Add New" button opens a QDialog with a QLineEdit. Changing the text, press "Add" and I would like the QLabel in the main window to be updated with the text from QLineEdit. I can get the signals through but the label is not updating. I understand that connect only works on instances of classes, not classes themselves. The problem seems to be the one class is not aware of the instance of the main window.
What I've tried to do is once the Add button is pressed, a signal is emitted. Once that signal is emitted, the slot in the mainWindow class receives a string to use in QLabel::setText().
I've read countless examples and documentation but the examples seem to be too different from the simple task I'm lost in. Any help is appreciated.
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QtWidgets>
#include <QLabel>
class QLineEdit;
class QPushButton;
class QLabel;
class addDlg : public QDialog{
Q_OBJECT
public:
addDlg(QWidget *parent = 0);
signals:
void textChanged(const QString &text);
private slots:
void sendText(QWidget *parent);
private:
QPushButton *addButton;
QLineEdit *inputText;
};
class mainWindow : public QWidget{
Q_OBJECT
public:
mainWindow();
QLabel *textLabel;
public slots:
void recvText(const QString &text);
private slots:
void addDlgShow();
private:
QPushButton *addWindow;
addDlg *dialog;
};
#endif // MAINWINDOW_H
MainWindow.cpp
addDlg::addDlg(QWidget *parent)
: QDialog(parent){
inputText = new QLineEdit(tr("enter here"));
addButton = new QPushButton(tr("Accept"));
QVBoxLayout *vLayout = new QVBoxLayout;
vLayout->addWidget(inputText);
vLayout->addWidget(addButton);
setLayout(vLayout);
setWindowTitle(tr("Add new text"));
connect(addButton, SIGNAL(clicked()),
this, SLOT(sendText()));
}
void addDlg::sendText(){
QString text = inputText->text();
emit textChanged(text);
// This connect is where I believe the problem lies.
connect(this, SIGNAL(textChanged(QString)),
mainPtr, SLOT(recvText(QString)));
//mainPtr is uninitialized as I can't seem to point it to the manWindow instance
//I can do mainWindow* mainPtr = new mainWindow but that just creates a new instance.
//How do I pass on the first mainWindow main instance "mainPtr" to this class addDlg?
}
mainWindow::mainWindow()
: QWidget(0){
textLabel = new QLabel(tr("Empty"));
addWindow = new QPushButton(tr("Add New"));
dialog = new addDlg();
QVBoxLayout *vLayout = new QVBoxLayout;
vLayout->addWidget(textLabel);
vLayout->addWidget(addWindow);
setLayout(vLayout);
setWindowTitle(tr("Test 4"));
connect(addWindow, SIGNAL(clicked()),
this, SLOT(addDlgShow()));
}
void mainWindow::addDlgShow(){ dialog->show(); }
void mainWindow::recvText(const QString &text){
QString input = text;
textLabel->clear();
textLabel->setText(input);
textLabel->update();
}
One solution is to put your connect code in mainWindow::mainWindow where you have pointers to both the mainwindow and your newly created dialog. The snippet might change to this:
mainWindow::mainWindow() : QWidget(0) {
// ... existing code ..
// add this
connect(dialog, SIGNAL(textChanged(QString)),
this, SLOT(recvText(QString)));
}
I'm trying to make a simple program consisting of a button and a label. When the button is pressed, it should change the label text to whatever is in a QString variable inside the program. Here's my code so far:
This is my widget.h file:
class Widget : public QWidget
{
Q_OBJECT
public:
Widget(QWidget *parent = 0);
~Widget();
private:
Ui::WidgetClass *ui;
QString test;
private slots:
void myclicked();
};
And here's the implementation of the Widget class:
#include "widget.h"
#include "ui_widget.h"
Widget::Widget(QWidget *parent)
: QWidget(parent), ui(new Ui::WidgetClass)
{
ui->setupUi(this);
test = "hello world";
connect(ui->pushButton, SIGNAL(clicked()), ui->label, SLOT(myclicked()));
}
Widget::~Widget()
{
delete ui;
}
void Widget::myclicked(){
ui->label->setText(test);
}
It runs but when the button is clicked, nothing happens. What am I doing wrong?
Edit: after i got it working, the text in the label was larger than the label itself, so the text got clipped. I fixed it by adding ui->label->adjustSize() to the definition of myclicked().
You are connecting the signal to the wrong object. myclicked() is not a slot of QLabel, it is a slot of your Widget class. The connection string should be:
connect(ui->pushButton, SIGNAL(clicked()), this, SLOT(myclicked()));
Take a look at the console output of your program. There should be an error message saying something like:
Error connecting clicked() to
myclicked(): No such slot defined in QLabel