I have two forms one is trainee_view.ui
and other is enter_new_trainee.ui
so for that i have trainee_view.cpp,trainee_view.h to see the list of Trainee in DB
and enter_new_trainee.cpp,enter_new_trainee.h to enter new trainee details
now in trainee_view.ui i have a push button "ADD Trainee"
so if i click this button it will go to "enter_new_trainee.ui"
void trainee_view::on_pushButton_2_clicked()
{
newtrainee=new enter_new_trainee(this);
newtrainee->setWindowFlags(Qt::Window);
newtrainee->show();
// connect(newtrainee, SIGNAL(destroyed()), this, SLOT(refresh_form()));
}
so by using connect() i am trying to refresh the trainee_view after entering the new trainee details. so how can i emmit the signal from
2nd form to 1st form such that i call refresh_form() method in 1st form .
I tried to use destroyed() signal on newtrainee but could not refresh my trainee_view form.
To be MOre simple . i just want to get an object is destroyed or not so if destroyed i can call refresh() method to load back the changes done on widget
for that i opted connect() method so how should i call that. becoz if i call
connect(newtrainee, SIGNAL(destroyed()), this, SLOT(refresh_form()));
there is no effect i.e nothing is loading into the view.
am newbie to qt so pls try to help me.
Thank YOu.
I'm not sure if I correctly understand your app, but I think you misunderstand the concept of Signals and Slots. Look here for some examples. In some simplification you can look at signal and slots this way: connect() command is a place which will not do anything - it just stay and keep listening for a signal. So you should place it in trainee_view.cpp. That's the first part and I see you did it correct, or almost correct. But you need also something that will send the signal, and this is exactly what emit() command do - it should be placed in enter_new_trainee.cpp just after description of generation new entry. For example, let assume user input new entry in LineEdit in UI:
[...]
QString newEntry = ui->LineEdit->text(); //Save entry to variable
emit(newEntry); //Emit it to signal slot
[...]
Related
I'm having some trouble, I'm fairly new to Qt and C++ and was testing the waters so to say. Ill try to describe my problem as follows. I have a LineEdit QLineEdit and this edit has a connection which looks like this:
connect(my_lineedit, SIGNAL (textEdited(QString)),this, SLOT (handleEdits()));
The handleEdits() method gets called and does the following:
Disconnect the previous Signal from my_lineedit
Create a new QLineEdit which gets a new signal and calls handleAddedEdits()
Adds the newely created Edit to my layout.
The stated above works fine Im just telling you this so you get the picture.
Now in the new method which I called handleAddedEdits() I want kinda the same procedure to happen again.
Disconnect the Signal which calls handleAddedEdits() from the Edit which invoked this method in the first place.
Create a fresh QLineEdit
Add this to my layout.
The problem is: in the first case my_lineedit is declared in my class so I can freely refer to it and and remove the signal as I wish. In the second case I have a QLineEdit which was created dynamically in the handleEdits() method and is the "Sender". My Question is, how can I refer to the "Sender Object" ro remove the Signal from the dynamically created edit?
You need to use QObject::sender() method in your receiver's slot:
For cases where you may require information on the sender of the
signal, Qt provides the QObject::sender() function, which returns a
pointer to the object that sent the signal.
handleAddedEdits()
{
QObject* obj = sender();
disconnect( obj, SIGNAL(textEdited(QString)), 0, 0 );
//...
}
My QLabel is not updating from slot. I run sender class in separate thread using QObject::moveToThread:
QThread* serviceThread = new QThread;
service = new ExportService();
connect(service,SIGNAL(stateChanged(Service::ServiceState)),
this,SLOT(statusChanged(Service::ServiceState)));
service->moveToThread(serviceThread);
serviceThread->start();
Service object send states by emiting signal with ServiceState enum value, this signal is captured by QDialog slot:
void Dialog::statusChanged(Service::ServiceState s)
{
switch (s) {
case Service::IDLE:
qDebug() << "Idle";
ui->label->setText("Service send response succesfully.");
break;
case Service::REQUESTING:
qDebug() << "Requesting";
ui->label->setText("Requesting response from service...");
break;
case Service::ERROR:
qDebug() << "Error";
ui->label->setText("Error. Cannot get response from service.");
break;
default:
break;
}
}
After operation on the object which emits a signal twice, the first time with value of Service::REQUESTING and second time with value of Service::IDLE my QLabel change text only to "Service send response succesfully.". In the console I can see that qDebug() << "Requesting"; works so the state changed successfully.
After comment out ui->label->setText("Service send response succesfully."); label has changed to requesting state but after the whole operation was done ie i see "Requesting" in console then "Idle" and after that QLabel has changed.
What should I do if I want to see QLabel changing in realtime?
First, try adding update() after setText(), chances are setText() doesn't automatically schedule a repaint() for the QLabel, if it works then problem solved.
However, for update() function:
http://doc.qt.io/qt-4.8/qwidget.html#update
void QWidget::update()
This function does not cause an immediate repaint; instead it
schedules a paint event for processing when Qt returns to the main
event loop. This permits Qt to optimize for more speed and less
flicker than a call to repaint() does.
> Calling update() several times normally results in just one
paintEvent() call.
which basically says, if you call them too frequently and some of them will be optimized away.
If this is not the desired behaviour, try adding a forced repaint() after setText(), or using a timer to schedule periodical forced repaints.
http://doc.qt.io/qt-4.8/qwidget.html#repaint
UPDATE
As is mentioned in the comment, forcing repaint() isn't good solution.
This answer is intended to provide an analysis of the cause of the code's behaviour and the "forced repaint()" suggestion is more of a way to verify this analysis than a solution to the problem.
However, without further information on the purpose of the program, it's very difficult to provide further suggestions.
The status change from requesting to idle happens quickly. The text "Requesting response from service..." is not on the label long enough for the eye to see it.
The fact that "Requesting ..." is in the debug output is proof of this, but if you want more proof there are other things you could do:
use a counter that counts each time the statusChanged() function is called and display this either in the same label as the status text (in addition to the status text) or a different label.
add a high accuracy timer output to the debug outputs - see how close together the status changes are.
use a couple of check boxes, one for idle status and one for requesting status. Change their state when the appropriate status is received. That is whne the first Idle is received set the check box to checked. When the next idle is received toggle it to unchecked.
I would just accept that the debug outputs are telling the truth and move on.
I override keyPressEven() of widget QTextEdit:
void myTextEdit::keyPressEvent(QKeyEvent *e)
{
if(e->key()==Qt::Key_0)
{
qDebug() << "Ok";
}
}
Button 0 works - show "Ok", but does not write in field of QTextEdit. Why? Thanks advance.
You need to call the base class implementation if you want to keep the default behaviour:
void myTextEdit::keyPressEvent(QKeyEvent *e)
{
if(e->key()==Qt::Key_0)
{
qDebug() << "Ok";
}
QTextEdit::keyPressEvent(e);
}
See the docs for keyPressEvent.
In case someone using PySide2 is having trouble overriding QTextEdit's built-in keybindings, I post my solution here. Hopefully this is also useful for C++.
Scenario:
We are using a QTextEdit in an application and want to distribute a series of keybindings, but the text editor has already several hardcoded bindings. We want the editor to ignore them and hand them over to its parent, so they can be eventually handled by our code.
Problem:
While the docs say that whenever an event is ignored (e.g. by returning True in the installed eventFilter method) it automatically gets passed on to the parent, the truth is that when doing that for predefined keybindings QTextEdit did not hand them over: the event got ignored AND absorbed. So any textedit built-in keybindings filtered this way will be effectively globally disabled.
Direct event passing via sendEvent inside the editor's eventFilter had an interesting effect:
When calling sendEvent and returning super().sendEvent, the keybinding got executed by the editor AND the event passed to the receiver.
When calling sendEvent and returning True, the keybinding didn't get executed, and the event didn't get passed to the receiver.
When calling sendEvent and returning False, the keybinding didn't get executed, and the event passed to the receiver twice.
Furthermore:
Using event.ignore() didn't have any effect: the editor executed the built-in anyway.
Trying to discriminate via event.spontaneous() caused a segfault due to a missing pointer. Probably something got GCed but didn't try to debug that.
Trying to replace the event with a "dummy event" and call super also didn't work. Magically, the text editor kept executing the built-ins.
Maybe I missed something. Anyway, below I detail the approach that worked for me.
Solution:
The plan is to completely block the event, but broadcast it via signals, and then connect to them wherever we want. In your text editor instance, define the signal e.g. as follows:
eventCatched = QtCore.Signal(QtCore.QEvent)
Then, e.g. the following event filter will prevent execution of a few keybindings, and emit them once via eventCatched:
def eventFilter(self, obj, evt):
"""
Remember to install via self.installEventFilter(self)
"""
catch_control_keys = {QtCore.Qt.Key_Left, QtCore.Qt.Key_Right}
catch = False
# documentation for keys and modifiers:
# https://doc.qt.io/qtforpython-5/PySide2/QtCore/Qt.html
if evt.type() == QtCore.QEvent.KeyPress:
modifiers = evt.modifiers()
ctrl = bool(modifiers & QtCore.Qt.ControlModifier)
shift = bool(modifiers & QtCore.Qt.ShiftModifier)
alt = bool(modifiers & QtCore.Qt.AltModifier)
key = evt.key()
# catch all undo/redo builtins
if ((ctrl and shift and key == QtCore.Qt.Key_Z) or
evt.matches(QtGui.QKeySequence.Undo) or
evt.matches(QtGui.QKeySequence.Redo)):
catch = True
# catch specified control-keys
if ctrl and not shift and not alt:
if key in catch_control_keys:
catch = True
#
if catch:
# block event but send it as signal
self.eventCatched.emit(evt)
return True
else:
return super().eventFilter(obj, evt)
Then, we are free to connect the signal wherever we want to, we just need a method that handles events. In my case, I just wanted to pass them to the main window, which can be done with the following one-liner in the constructor:
text_editor.eventCatched.connect(lambda evt: QtCore.QCoreApplication.sendEvent(self, evt))
This way, whenever we catch an event in the text editor, it will be ignored and won't be propagated the standard way. Instead, a signal will be emitted, and we can subscribe to that signal to e.g. restart the propagation tree at a different point, as shown here via sendEvent.
Hope this helps!
Cheers,
Andres
In my project, I have 40 QPushButtons all put into a QButtonGroup like this:
QButtonGroup* group = new QButtonGroup(this);
group->addButton(ui->slot_0);
group->addButton(ui->slot_1);
//...
group->addButton(ui->slot_38);
group->addButton(ui->slot_39);
Each button is a QPushButton that I made checkable. That way only one button can be checked at a time. All works great, but how can I "make a slot" when one of the buttons becomes checked? I don't want to have 40 different slots, one for each button all to end up doing essentially the same thing. Is there any way I can just use the QButtonGroup I put them in?
As Jamin and Nikos stated: you should create your own slot to handle the signal emitted by QButtonGroup. It could be something like this:
In the header file:
public slots:
void buttonWasClicked(int);
In the *.cpp file:
void MainWindow::buttonWasClicked(int buttonID)
{
cout << "You have clicked button: " << buttonID << endl;
}
And in the code responsible for creation of the MainWindow (i.e. in constructor but not necessairly) there should be this line:
connect(group, SIGNAL(buttonClicked(int)), this, SLOT(buttonWasClicked(int)));
Be aware that since Qt5 the connect syntax has changed. The syntax I used here is from Qt4. It still works but is deprecated now (for more information please refer to New Signal Slot Syntax in Qt 5). Moreover I would suggest going through QButtonGroup class reference as there are other available signals which could suit your needs better than the one I've chosen.
BR
The documentation for QButtonGroup shows a QButtonGroup::buttonClicked() signal - have you already tried that one?
The signal comes in two variants - one that gives the QPushButton as a parameter (as a QAbstractButton), and one that gives the ID of the button in the group.
You can use connect() to setup signal and slot connections in your C++ code.
Sometime during the initialization of your window's class (perhaps in the constructor), call this:
connect(myButtonGroup, SIGNAL(buttonClicked(QAbstractButton*)), this, SLOT(theSlotThatYouWrite(QAbstractButton*));
Where myButtonGroup is probably this->ui->nameOfTheButtonGroup, and theSlotThatYouWrite is a function that you write in your own code, that belongs to your window's class, that returns void and takes a signal QAbstractButton* as a parameter (since that's what this specific signal gives as an argument).
Make sure theSlotThatYouWrite is under the label "private slots:" or "public slots:" in your class's interface.
Here's a screenshot of actual usage of some signals and slots in my own code.
Signals and Slots is something very important to learn, but can be bit of a hill to climb when first trying to understand it!
I am populating a sytem tray icon menu (QMenu) from entries in an xml file which is read when my application starts up.
I am unsure of how to properly set up the SLOT end of the action:
QList<CMenuItem> menuItems = m_layout->getMenuItems();
QListIterator<CMenuItem> iter(menuItems);
while (iter.hasNext())
{
CMenuItem menuItem = iter.next();
QAction *action = new QAction(menuItem.qsTitle, this);
connect(action, SIGNAL(triggered()), this, SLOT(launchMenuItem()));
trayIconMenu->addAction(action);
}
How does my "launchMenuItem()" SLOT know which menu item was triggered? I can't make a SLOT for each menu item as I don't know how many items will exist until run time.
I can think of some ugly ways to do this, but I am looking for the RIGHT way.
What I usually do is to use QAction::setData(const QVariant&) to store whatever action ID I need. Then on slot side I retrieve ID with QAction::data() and behave accordingly.
Note that QVariant obviously accepts much more than basic int (which is what I use to identify actions), you can pass any QVariant-compatible info.
edit : oh! btw, this is somehow ugly because I make use of QObject::sender() to cast triggered action back. Sorry for that, but it works anyway.