• Qt Signal Slot Thread
• Qt Connect Signal Slot
• Qt Signal Slot Cross Threads
• Qt Signal Slot Cross Threaded

I have a mainWindow class that calls a function mainWIndow::ShowDialogBox() when double clicked on the QTabBar. The dialog box shows up, but it isn't connecting the buttons. I have the connect calls in ShowDialogBox. It gives me a red underline on connect saying

This is my code

I'm using a Qt cross-thread (QueuedConnection) signal and slot to communicate between my service thread and the main thread. The problem I am having is that although the service thread emits the signal (well it executes the instruction) the slot in the main thread doesn't get called. I've removed all of the TCP server code to simplify things. Cross-thread signal slot, how to send char. c,multithreading,qt,signals-slots I've created a simple Qt GUI App and I've created a simple thread in it using worker and worker thread (see below codes, it is a simple code which will be used in a large program). In this program when I push the push button, the thread is created. Cross Thread Signals/slots Default connection between objects of different thread affinity is Qt::QueuedConnection Sender's signal is serialized into an event Event is posted to the receiver's event queue Event is deserialized and the slot is executed Communication between threads is easy!

I have added the signals and slot in mainWindow.h as

I have spend hours on this but no luck. I am new to Qt.

Line:

should be:

Because the third parameter has to be a memory address(pointer).

Qt: Connect inside constructor - Will slot be invoked before object is initialized?

c++,qt,event-handling,signals-slots

You don't have to worry about such scenarios in most cases, because events are delivered in the same thread. There's no 'hidden multithreading' going on you have to care about. If you don't explicitly call a function in the constructor of A that causes events to be processed, you're safe...

Dynamic mapping of all QT signals of one object to one slot

c++,qt,signals-slots

have a look at const char * QMetaMethod::signature() const then you should be able to use it like QObject::connect(object, method->signature(), this, SLOT(signalFired())); you might need to add '2' before the method->signature() call because SIGNAL(a) makro is defined SIGNAL(a) '2'#a as mentioned Is it possible to see definition of Q_SIGNALS, Q_SLOT,...

How to declare New-Signal-Slot syntax in Qt 5 as a parameter to function

c++,qt,qt5,signals-slots

You should create template: template<typename Func> void waitForSignal(const typename QtPrivate::FunctionPointer<Func>::Object *sender, Func signal) { QEventLoop loop; connect(sender, signal, &loop, &QEventLoop::quit); loop.exec(); } Usage: waitForSignal(button, &QPushButton::clicked); ...

Attempting to read stdout from spawned QProcess

qt,signals-slots,qprocess

Issue is in statement QObject::connect(console_backend, SIGNAL(console_backend ->readyReadStandardOutput()), this, SLOT(this->receiveConsoleBackendOutput())); It should be QObject::connect(console_backend, SIGNAL(readyReadStandardOutput()), this, SLOT(receiveConsoleBackendOutput())); ...

How to close Pyqt5 program from QML?

qt,python-3.x,qml,signals-slots,pyqt5

There are a few syntax errors in the python script, but ignoring those, the code can be made to work like this: def main(argv): app = DestinyManager(sys.argv) engine = QtQml.QQmlEngine(app) engine.quit.connect(app.quit) ... Which is to say, you simply need to connect the qml quit signal to an appropriate slot in...

Qt:signal slot pass by const reference

c++,qt,pass-by-reference,signals-slots,pass-by-value

When you pass an argument by reference, a copy would be sent in a queued connection. Indeed the arguments are always copied when you have a queued connection. So here there would be no trouble regarding the life time of images since it will be copied instead of passed by...

Signals and Slots in Qt4

c++,qt,qt4,signals-slots,qt4.7

Basically you need to connect your signal and slot connect(ui->button1, SIGNAL(clicked()), this, SLOT(yourSlot())); and in this link there is good example about signals and slot: signals and slots in qt....

Overriding/Reimplementing Slots in PySide

python,qt,override,pyside,signals-slots

You cannot override QLineEdit.copy or QLineEdit.paste in such a way that they will be called internally by Qt. In general, you can only usefully override or reimplement Qt functions that are defined as being virtual. The Qt Docs will always specify whether this is the case, and for QLineEdit, there...

How often are objects copied when passing across PyQt signal/slot connections?

python,pyqt,signals-slots,pyqt5

As suggested by @ekhumoro, I did try, and surprisingly I get a different result to what the test conducted in C++ reveals. Basically, my test shows that: objects are not copied at all, even when passed across thread boundaries using QueuedConnection Consider the following test code: class Object2(QObject): def __init__(self):...

Can't emit signal in QML custom Item

qt,qml,signals-slots

Functions (which signals are) are first class objects in JS, so it is not an error to refer to them without parentheses. But you need them in order to execute the function (i.e. emit the signal). So just change this line: onClicked: baseButton.clicked() ...

PyQt: ListWidget.insertItem not shown

python,pyqt,signals-slots,qt-designer,qlistwidget

There is only one button in your dialog, and so it will become the auto-default. This means that whenever you press enter in the dialog, the button will receive a press event, even if it doesn't currently have the keyboard focus. So the item does get added to the list-widget...

How to get value of QtComboBox?

python,qt,pyqt,qt-designer

Where you say 'city' you should say 'self.city' so that city is attached to the object. Then later you can get its text as 'self.city.currentText()'.

Iterating all items inside QListView using python

python,pyqt4,qt-designer

Use the model to iterate over the items: model = self.listView.model() for index in range(model.rowCount()): item = model.item(index) if item.isCheckable() and item.checkState() QtCore.Qt.Unchecked: item.setCheckState(QtCore.Qt.Checked) ...

Cannot connect (null)::selectionChanged to QTableView

c++,qt,qt-creator,signals-slots,qtableview

The signal slot connection has failed since table->selectionModel() has returned null. If you set the model for your table before making signal slot connection, table->selectionModel() will return a valid model, making the signal slot connection successful....

How can I anchor widgets in Qt Creator?

python,qt,layout,qt-designer

You need to add a layout to the top widget. You need to right-click the most outside widget (Dialog), select 'Lay out' and select appropriate layout (grid layout will do fine). This will ensure that direct children of the Dialog will react to its size changes. To prevent stretching ListWidget...

Syntax sugar for signal slot

c++,c++11,signals-slots

Is it possible in modern C++ to implement such functionality in, for example, C# way? [...] No, that's not possible in C++. The syntax for taking the address of a member function requires qualifying the function name with the class name (i.e. &MyClassName::myMethodName). If you don't want to specify...

Qt - Connect slot with argument using lambda

python,qt,lambda,pyqt,signals-slots

The issue is python's scoping rules & closures. You need to capture the group: def connections(self): for group in self.widgets: self.widgets[group].clicked.connect(lambda g=group: self.openMenu(g)) def openMenu(self,group): print group ...

QTableView / QTableWidget: Stretch Last Column using Qt Designer

pyqt,pyqt4,qt-designer,pyqt5

In the Qt Designer, Select the QTableWidget / QTableView and navigate to the Property Editor. Here, scroll down to the 'Header section' and enable horizontalHeaderStretchLastSection. ...

Qt Designer: Unable to get scroll area to work properly

qt,scroll,qt-designer

Apply a layout to the Window QWidget (which layout, is irrelevant) and place the scroll area inside. (answering the last phase of my question so I don't have to delete it, after gradually figuring out how to make it work)...

How to manage QSplitter in Qt Designer

c++,qt,qt-creator,qt-designer,qsplitter

You can simply create splitter containing items in Qt Designer : First place your widgets on your dialog or widget in designer (They should not be in a layout) Select the widgets that you want to be in a splitter (By holding CTL and clicking on them) Right click on...

Qt/C++ how to wait a slot when signal emitted

c++,multithreading,qt5,signals-slots

My first thought is that having either thread block until an operation in the other thread completes is a poor design -- it partially defeats the purpose of having multiple threads, which is to allow multiple operations to run in parallel. It's also liable to result in deadlocks if you're...

Pyside: Multiple QProcess output to TextEdit

python,pyside,signals-slots,qprocess

Connect the signal using a lambda so that the relevant process is passed to the slot: p.readyReadStandardOutput.connect( lambda process=p: self.write_process_output(process)) def write_process_output(self, process): self.viewer.text_edit.append(process.readAllStandardOutput()) ...

Qt app receives HUP signal unexpectedly when forked to background

qt,signals,fork,daemon,signals-slots

When daemonizing (forking), the parent process issues a HUP signal upon exit. For some reason on Red Hat this signal doesn't hit child process until much later. On Ubuntu the signal hits the child quickly (or perhaps Ubuntu holds the signal for the child). Solution is to confirm parent process...

Drag n Drop Button and Drop-down menu PyQt/Qt designer

qt,python-2.7,pyqt,pyqt4,qt-designer

In order to add code to a UI generated with QtDesigner, you must generate a .py file using pyuic: pyuic myform.ui -o ui_myform.py This ui_myform.py file, contains generated code that you should not edit, so later you can change your .ui file with QtDesigner, re-run pyuic, and get ui_myform.py updated...

Getting rid of QtTabWidget margins

qt,qt-designer

Sounds like you might want documentMode: ...

PyQt5: one signal comes instead of two as per documentation

python,pyqt,python-3.3,signals-slots,pyqt5

You only connected to one of the two signal overloads. Since you also didn't specify which overload you wanted, a default will be selected - which in this case will be valueChanged(int). To explicitly select both overloads, you would need to do: self.spb.valueChanged[int].connect(self.onValueChanged) self.spb.valueChanged[str].connect(self.onValueChanged) ... def onValueChanged(self, x): print('QSpinBox: value...

C++ Signal QML Slot on registered type

c++,qml,signals-slots,qt5.4

I hadn't realized that I had connected to the wrong instance of MsgController in my code. One instance was created by the C++ code, but I really wanted to call the slot on the instance created by the Qml Engine. Once I connected to the correct instance, the code above...

Disconnecting signals fails

c++,qt,signals-slots

I've checked how QObject::disconnect is implemented and I don't see how this is supposed to work if you only specify receiver. QMetaObjectPrivate::disconnect will return immediately with false when sender is not specified. This means that second part of QObject::disconnect will no set res to true. The only other place you...

QT Designer how to assign 2 hotkeys to a QPushButton (python3)

python-3.x,keyboard-shortcuts,qt-designer,pyqt5,qpushbutton

There are several ways to do this. Probably the simplest is to use QShortcut: QShortcut(Qt.Key_Enter, self.Begin, self.handleBegin) QShortcut(Qt.Key_Return, self.Begin, self.handleBegin) To get the button animation behaviour, try this instead: QShortcut(Qt.Key_Enter, self.Begin, self.Begin.animateClick) QShortcut(Qt.Key_Return, self.Begin, self.Begin.animateClick) ...

QtDesigner for Raspberry Pi

qt4,raspberry-pi,qt-creator,qt-designer

To run qt-creator on Rpi itself. You can install it by 'sudo apt-get install qt-creator' It will install qt-creator and qt4-base modules on rpi. After installing, you can run 'qt-creator' on terminal to get started with design. You will be using drag and drop for UI design and c++ as...

How to connect signal to boost::asio::io_service when posting work on different thread?

c++,multithreading,boost,boost-asio,signals-slots

In light of new information, the problem is with your boost::bind. You are trying to call a member function without an object to call it on: you are trying to call ProcessData but you haven't told the bind on which object you wish to call it on. You need to...

PyQt5 - Signals&Slots - How to enable a button through content change of lineEdit?

button,signals-slots,pyqt5,qlineedit

Looks like you want the textChanged signal, since that sends the current text: self.lineEdit_SelectedDirectory.textChanged.connect( lambda text: self.pushButton_CreateFileList.setEnabled(bool(text))) ...

C++: Thread Safety in a Signal/Slot Library

c++,multithreading,thread-safety,signals-slots

I suspect there is no clearly good answer, but clarity will come from documenting the guarantees you wish to make about concurrent access to an Emitter object. One level of guarantee, which to me is what is implied by a promise of thread safety, is that: Concurrent operations on the...

Qt: How to remove the default main toolbar from the mainwindow?

c++,qt,qt-creator,qt-designer,qtgui

You need to remove the main toolbar from either QtDesigner as can be seen below or from the code manually: Then, you will need to rerun qmake for the changes to take effect as the ui_mainwindow.h header file needs to be regenerated from the updated mainwindow.ui description file. ...

PyQt QTreeview not displaying first column of QAbstractItemModel when built with Qt Designer

python,qt,pyqt,qt-designer

Change: self.treeView.setRootIsDecorated(False) To: self.treeView.setRootIsDecorated(True) ...

How to implement Recent Files action with Qt designer？

c++,qt,qt-designer

When I tried to implement the Recent Files I come up with a solution like this: I create the menù items on startup and set them non visible: separatorAct = ui.menu_File->addSeparator(); for (int i = 0; i < MAXRECENTFILE; ++i) { RecentProjects[i] = new QAction(this); RecentProjects[i]->setVisible(false); connect(RecentProjects[i], SIGNAL(triggered()), this, SLOT(OpenRecentFile()));...

connecting signals and slots with different relations

c++,qt,connect,signals-slots

You need to create new slot for that purpose. But in C++ 11 and Qt 5 style you can use labmdas! It is very comfortable for such short functions. In your case: connect(ui->horizontalSlider, &QSlider::sliderMoved, this, [this](int x) { this->ui->progressBar->setValue(x / 2); }); ...

PyQt4 signals and slots - QToolButton

python,qt,pyqt4,signals-slots

I'm not sure why you're doing the following, but that's the issue: def showSettings(self): dialog = QtGui.QDialog() dialog.ui = SettingsDialog() dialog.ui.setupUi(dialog) dialog.exec_() SettingsDialog itself is a proper QDialog. You don't need to instantiate another QDialog. Right now, you're creating an empty QDialog and then populate it with the same ui...

Qt Signal Slot Thread

QTabWidget Content Not Expanding

c++,xml,user-interface,qt5,qt-designer

To set the layout on a tab, you first need to select its parent tab-widget. You can do this either by selecting it by name in the Object Inspector (i.e. by clicking on xMarketTabWidget in your example), or by simply clicking on an appropriate tab in its tab-bar. The parent...

qt slots and signalls autoconnecting

qt,qt5,signals-slots,qt5.2

I fixed it by accident while writing this question... My model was missing a name. When I added kontrahentModel->setObjectName('kontrahentModel'); All worked like a charm... BUT - 'there is no rose without a thorn'. When assigning a parent for the model, an old problem returns - described here: QSqlQueryModel with a...

How to dock horizontally Qt widgets?

c++,qt,qt-creator,qt-designer

In Qt, widget geometry can be automatically managed by layouts. A widget by itself won't fill the parent. You need to set a layout on the parent widget, and add the widget to the parent. There are numerous tutorials on that. The particular layout that would apply to your situation...

PyQt: slot is called many times

python,pyqt,signals-slots

The reason why the output is being printed three times, is because of the way you named the signal handlers. The connect slots by name feature will automatically connect signal handlers that are named using the following format: on_[object name]_[signal name] Since the clicked signal has two overloads, and you...

Cross-thread signal slot, how to send char *

c++,multithreading,qt,signals-slots

The problem you have is completely unrelated to Qt, signals or multiple threads. The char* you're creating isn't null-terminated, so you cannot use it with functions (or operators) that expect char*s to be C strings - they rely on the null terminator. What you're seeing on your console is the...

How to execute a function in Qt when a variable changes its value in the QML?

Qt Connect Signal Slot

c++,qt,signals,signals-slots

Using your example regarding ints, it would be done like this: class foo : public QObject { Q_OBJECT Q_PROPERTY( int value READ getValue WRITE setValue NOTIFY valueChanged ) public: explicit foo( QObject* parent = nullptr ) : QObject{ parent }, i_{ 0 } {} virtual ~foo() {} int getValue() const...

PyQt: Wrapping Dialog from QDesigner and Connect pushbutton

Qt Signal Slot Cross Threads

python,pyqt,signals-slots,qpushbutton,pyuic

The problem in the original code is in this section: if True: qApp = QtGui.QApplication(sys.argv) Dialog = QtGui.QDialog() u = Testdialog() u.setupUi(Dialog) Dialog.exec_() sys.exit(qApp.exec_()) What you want instead is something like this: if __name__ '__main__': app = QtGui.QApplication(sys.argv) u = Testdialog() u.show() sys.exit(app.exec_()) The reason why the original code...

How to resolve 2 sequential calls on Qt slot and perform action only once

c++,qt,lambda,signals-slots,qt-signals

You can apply next pattern to your code: class MyClass : public QObject { private slots: void updateRequest(); private: QTimer *_timer; CodeEditor *_editor; }; MyClass::MyClass() { // Init members // ... _timer->setSingleShot( true ); _timer->setInterval( 0 ); connect( _editor, &CodeEditor:: cursorPositionChanged, _timer, &QTimer::start); connect( _editor, &CodeEditor:: selectionChanged, _timer, &QTimer::start); connect(...

Event loops and signal-slot processing when using multithreading in Qt

c++,multithreading,qt,event-loop,signals-slots

All results you got are perfectly correct. I'll try to explain how this works. An event loop is an internal loop in Qt code that processes system and user events. Event loop of main thread is started when you call a.exec(). Event loop of another thread is started by default...

qt 'emit' signal not working properly

c++,qt,signals-slots,emit

Remove the multiple instances of dosecalibration, or make sure to connect each one of those, if you really need multiple instances.

Calling a C++ function from Qt (slot does not work)

c++,qt,signals-slots

Qt Signal Slot Cross Threaded

Just register a Qt slot within your header file. class Log { ... Q_SLOTS: void sendMessage (); } and implement the slot in the implementation, e.g. by: Log::sendMessage() { send_message(); } Do not forget to change connect statement to just the sendMessage() function rather than your send_message function....