I want to execute my slot with parameter when dynamically created QAction clicked, but I can't add my variables when creating QAction in QMenu, and default triggered() slot can't pass it.
To be more clear, I want to archieve something like this:
connect(someAction, SIGNAL( triggered(MyClass*) ), this, SLOT( execute(MyClass*) );
How I can get this? I tried to create custom QAction, but I don't know how to add it to QMenu - there is no function like addAction(QAction).
You can store your parameter in the action itself as a QVariant using QAction::setData() function. For example:
QVariant v = qVariantFromValue((void *) yourClassObjPointer);
action->setData(v);
In the slot you will have to extract the pointer like:
void execute()
{
QAction *act = qobject_cast<QAction *>(sender());
QVariant v = act->data();
YourClass yourPointer = (YourClass *) v.value<void *>();
}
Gather your dynamic QAction's in one QActionGroup using QAction::setActionGroup()
Use QAction::setData() to store the custom data in each QAction.
connect QActionData's signal triggered(QAction*) to some slot.
Related
I have a QAction which when clicked emits a triggered signal which calls the slot method RegroupEtudes::OnNouvelleEtude
connect(ui.actionNouvelle_tude, &QAction::triggered, this, &RegroupEtudes::OnNouvelleEtude);
It is possible for void RegroupEtudes::OnNouvelleEtude() to take a QString parameter if I change its definition. But how can i have QAction::triggered give its text QString parameter to void RegroupEtudes::OnNouvelleEtude() ?
That is, if my QAction is named "etude 1", is there anyway that RegroupEtudes::OnNouvelleEtude(QString) gets called as RegroupEtudes::OnNouvelleEtude("etude 1") ?
Since Qt5, you can use a lambda expression and the new connect synthax to pass an extra parameter to your slot:
QAction *actionNouvelle_tude = new QAction(tr("Nouvelle étude..."), this);
connect(actionNouvelle_tude, &QAction::triggered, this, [openAct, this]() {
this->OnNouvelleEtude(openAct->text());
});
It will call OnNouvelleEtude with the text of your action as parameter
After my post here : Associate signal and slot to a qcheckbox create dynamically I need to associate :
• The signal clicked() when I click on a qCheckBox to my function cliqueCheckBox(QTableWidget *monTab, int ligne, QCheckBox *pCheckBox)
To do so, I have to use QSignalMapper, after two hours of trying to understand how it works, I can't have a good result, here's the code I make, this is obviously wrong :
QSignalMapper *m_sigmapper = new QSignalMapper(this);
QObject::connect(pCheckBox, SIGNAL(mapped(QTableWidget*,int, QCheckBox*)), pCheckBox, SIGNAL(clicked()));
QObject::connect(this, SIGNAL(clicked()), this, SLOT(cliqueCheckBox(QTableWidget *monTab, int ligne, QCheckBox *pCheckBox)));
m_sigmapper->setMapping(pCheckBox, (monTab,ligne, pCheckBox));
QObject::connect(m_sigmapper, SIGNAL(clicked()),this, SLOT(cliqueCheckBox(QTableWidget *monTab, int ligne, QCheckBox *pCheckBox)));
Can you explain to me, how QSignalMapper works ? I don't really understand what to associate with :(
QSignalMapper class collects a set of parameterless signals, and re-emits them with integer, string or widget parameters corresponding to the object that sent the signal. So you can have one like:
QSignalMapper * mapper = new QSignalMapper(this);
QObject::connect(mapper,SIGNAL(mapped(QWidget *)),this,SLOT(mySlot(QWidget *)));
For each of your buttons you can connect the clicked() signal to the map() slot of QSignalMapper and add a mapping using setMapping so that when clicked() is signaled from a button, the signal mapped(QWidget *) is emitted:
QPushButton * but = new QPushButton(this);
QObject::connect(but, SIGNAL(clicked()),mapper,SLOT(map()));
mapper->setMapping(but, but);
This way whenever you click a button, the mapped(QWidget *) signal of the mapper is emitted containing the widget as a parameter.
First I will explain you how QSignalMapper works. Then I will explain you why you don't need it.
How QSignalMapper works:
Create s QSignalMapper. Lets assume that you want to assign an integer value to each checkbox, so every time you click on any checkbox, you will get a signal with the integer value assigned to it.
Connect the mapper signal to your SLOT, that you will implement:
connect(mapper, SIGNAL(mapped(int)), this, SLOT(yourSlot(int)));
Now you can write slot, that will take integer argument. The argument will be different for each checkbox you have.
While you create checkboxes, for each checkbox you need to do following:
mapper->setMapping(checkBox, integerValueForThisCheckbox);
connect(checkBox, SIGNAL(clicked()), mapper, SLOT(map()));
From now on, every time you click on a checkbox, it will emit clicked() signal to the QSignalMapper, which will then map it to the assigned integer value and will emit mapped() signal. You connected to that mapped() signal, so yourSlot(int) will be called with the proper integer value.
Instead of integers, you can assign QString, QWidget* or QObject* (see Qt documentation).
This is how QSignalMapper work.
You don't need it:
The QTableWidget *monTab is the single object, it doesn't change. Keep it as a class member field and use it from your slot function.
The QCheckBox *pCheckBox - you can get it by casting sender() to QCheckBox*.
Like this:
void supervision::yourSlot()
{
QCheckBox* pCheckBox = qobject_cast<QCheckBox*>(sender());
if (!pCheckBox) // this is just a safety check
return;
}
The sender() function is from QObject, which you do inherit from, so you have access to it.
The int linge (it's a line number, right?) - when you create checkboxes, you can store pointers to that checkboxes in QList class field and use it from your slot function find out which line is it, like this:
In class declaration:
private:
QList<QCheckBox*> checkboxes;
When creating checkboxes:
QCheckBox* cb = new QCheckBox();
checkboxes << cb;
In your slot function:
void supervision::yourSlot()
{
QCheckBox* pCheckBox = qobject_cast<QCheckBox*>(sender());
if (!pCheckBox) // this is just a safety check
return;
int linge = checkboxes.indexOf(pCheckBox);
}
If you want, you can skip that QList and use QSignalMapper and assign lines to checkboxes using mapper. That's just a matter of what you prefer.
I have created instance of QAction inside QGraphicsView child class and connected it to my slot in the same class.
QAction *action = new QAction(tr("New"), this);
action->setObjectName("addStopAction");
action->setShortcut(QKeySequence(Qt::ControlModifier | Qt::Key_N));
connect(action, SIGNAL(triggered()), this, SLOT(addNew()));
addAction(action);
Slot is a function creating new instance of QGraphicsItem on scene assigned to QGraphicsView.
void MyGraphicsView::addNew() {
// Insert new item at cursor position
}
I also add this action to a QMenu which serves as my class context menu.
QMenu *contextMenu = new QMenu(this);
contextMenu->addAction(action);
Everything works fine. When I press Command/Ctrl + N new item is created at cursor position. But when I right-click and select action from context menu I want new item to be created at menu positon.
I can, of course, do some little hack to flag if SLOT was called after contextMenuEvent or something like that, but what I would like to know is:
Is there any way to find out what made QAction emit its triggered() signal inside connected SLOT? That way I could handle when I should place new item at cursor position and when at context menu position inside SLOT implementation.
Of course, you can find out what signal emit inside connected SLOT.
Just use QObject::sender(). In you case:
void MyGraphicsView::addNew() {
QAction* pAction = qobject_cast<QAction*>(sender());
Q_ASSERT(pAction);
// do something with pAction
}
I think you can use custom data that a QAction object can contain.
You can set it when you create a context menu:
void showContextMenu(const QPoint &pos)
{
...
action->setData(pos);
...
}
And in the addNew() function you check if data exists and reset it in the end:
void addNew()
{
QPoint pos;
QPoint posFromAction = action->data()->toPoint();
if (posFromAction.isNull())
{
pos = QCursor::pos(); ///< pos will be current cursor's position
}
else
{
pos = posFromAction; ///< pos will be menu's position
}
doYourStuffAt(pos)
action->setData(QPoint()); ///< reset action's data
}
i managed something similar by connecting the menu to a function like connect (menu, SIGNAL( triggered(QAction*) ), this, SLOT( menuAction_triggered(QAction*) ));
when you execute you context menu, the QMenu::exec(QPoint) will return you the pointer to the action, so you may not need a extra function/slot for it.
you can check for the name of the action with its text QAction::text() or if you have stored your pointers somewhere by comparing the address.
soo long zai
You can reference self.sender() in the function that is called when by customContextMenuRequested signal.
self.tree1.customContextMenuRequested.connect(self.menu1pop) # rightclick menu signal
...
def menu1pop(self, pos):
widget = self.sender()
item = widget.itemAt(pos)
if item is None: return # only show contextmenu if on an item
self.setProperty("mywidget", widget) # pass current widget
self.menu1.popup(QCursor.pos()) # show menu at right click cursor position
self.sender() will return your widget object and then you can set the widget object inside a property.
Then when your action function is called you can recall the widget object by reading the property.
widget = self.property("mywidget")
It's a bit of a hack, but a simple and reliable way to know which widget your action was called from.
You MIGHT be able to use QObject::sender() in the slot that receives the call. Not tried this for actions though. It's probably a bit uglier than your proposed 'hack' (where you could actually implement that quite nicely with a scoped class).
First of all my apologies for big looking question but indeed it's not. I’m reading Foundation of qt development book and while reading fourth chapter author tells the basics of MDI window by showing this example :
MdiWindow::MdiWindow( QWidget *parent ) : QMainWindow( parent ) {
setWindowTitle( tr( "MDI" ) );
QWorkspace* workspace = new QWorkspace;
setCentralWidget( workspace );
connect( workspace, SIGNAL(windowActivated(QWidget *)), this, SLOT(enableActions()));
QSignalMapper* mapper = new QSignalMapper( this );
//my problem is in this line
connect( mapper, SIGNAL(mapped(QWidget*)), workspace, SLOT(setActiveWindow(QWidget*)) );
createActions();
createMenus();
createToolbars();
statusBar()->showMessage( tr("Done") );
enableActions();
}
His this para of explanation completely eluded me (is it me or others having problem understanding it too?) :
Next, a signal mapping object called QSignalMapper is created and
connected. A signal mapper is used to tie the source of the signal to
an argument of another signal. In this example, the action of the menu
item corresponding to each window in the Window menu is tied to the
actual document window. The actions are in turn connected to mapper.
When the triggered signal is emitted by the action, the sending action
has been associated with the QWidget* of the corresponding document
window. This pointer is used as the argument in the mapped(QWidget*)
signal emitted by the signal mapping object.
My question : I still don’t get what is signal mapper class, how it’s used and what's functionality it's doing in the example above?. Can anyone please explain the above para using easy terms? also It’d be awesome if you could please teach me about mapper class’s basics with simple example? possibly in layman’s term?
P.S : A confusion is when we have MDI window, do menu changes (though actions are disabled/enabled) e.g suppose for one particular document we have menu “File/close” and for other document we have “File/remaper” ?
The QSignalMapper is used to re-emit signals with optional parameters. In other words (from the documentation):
This class collects a set of parameterless signals, and re-emits them
with integer, string or widget parameters corresponding to the object
that sent the signal.
A good example (also from the doc - take a look at it) is set as follows:
Suppose we want to create a custom widget that contains a
group of buttons (like a tool palette). One approach is to connect
each button's clicked() signal to its own custom slot; but in this
example we want to connect all the buttons to a single slot and
parameterize the slot by the button that was clicked.
So imagine you have a number of buttons encapsulated in a class, say ButtonWidget, with a custom signal void clicked(const QString &text). Here is the definition:
class ButtonWidget : public QWidget {
Q_OBJECT
public:
ButtonWidget(QStringList texts, QWidget *parent = 0);
signals:
void clicked(const QString &text);
private:
QSignalMapper *signalMapper;
};
The constructor could then be defined like the following:
ButtonWidget::ButtonWidget(QStringList texts, QWidget *parent)
: QWidget(parent)
{
signalMapper = new QSignalMapper(this);
QGridLayout *gridLayout = new QGridLayout;
for (int i = 0; i < texts.size(); ++i) {
QPushButton *button = new QPushButton(texts[i]);
connect(button, SIGNAL(clicked()), signalMapper, SLOT(map()));
signalMapper->setMapping(button, texts[i]);
gridLayout->addWidget(button, i / 3, i % 3);
}
connect(signalMapper, SIGNAL(mapped(const QString &)),
this, SIGNAL(clicked(const QString &)));
setLayout(gridLayout);
}
So what happens here? We construct a grid layout and our buttons of type QPushButton. The clicked() signal of each of these is connected to the signal mapper.
One of the forces using QSignalMapper is that you can pass arguments to the re-emitted signals. In our example each of the buttons should emit a different text (due to the definition of our signal), so we set this using the setMapping() method.
Now all that's left to do is map the signal mapper to the signal of our class:
connect(signalMapper, SIGNAL(mapped(const QString &)),
this, SIGNAL(clicked(const QString &)));
Assume we have a testing class called TestClass then ButtonWidget can be used thusly:
TestClass::TestClass() {
widget = new ButtonWidget(QStringList() << "Foo" << "Bar");
connect(widget, SIGNAL(clicked(const QString &)),
this, SLOT(onButtonClicked(const QString &)));
}
void TestClass::onButtonClicked(const QString &btnText) {
if (btnText == "Foo") {
// Do stuff.
}
else {
// Or something else.
}
}
By using the signal mapper this way you don't have to declare and manage all the buttons and their clicked signals, just one signal pr. ButtonWidget.
The buttom line is that the signal mapper is great for bundling multiple signals and you can even set parameters when it re-emits them. I hope that gave some intuition about the usage of QSignalMapper.
Your example code
The explanation (your "para") states that all the actions are each individually mapped to a specific QWidget*. When triggering an action its respective QWidget* will be passed to the slot QWorkspace::setActiveWindow(QWidget*) of workspace, which in turn activates the widget.
Also note that the mapping from action to widget has to happen somewhere in your code. I assume it is done in createActions() or enableActions() perhaps.
A QSignalMapper allows you to add some information to a signal, when you need it. This object internally have a map like QMap<QObject*,QVariant>. Then you connect an object to it, and when the slot is called, it re-emit the signal with the associated value.
Workflow:
mySignalMapper:
[ obj1 -> 42 ]
[ obj2 -> "obiwan" ]
[ obj3 -> myWidget ]
connect(obj1,mySignal,mySignalMapper,SLOT(map())); // idem for obj2 and obj3
(obj2 emits "mySignal")
-> (mySignalMapper::map slot is called)
-> (sender() == obj2, associated data = "obiwan")
-> (mySignalMapper emits mapped("obiwan"))
I was going to add a more detailed example, but Morten Kristensen was faster than me ;)
I'm making a little chat messenger program, which needs a list of chat channels the user has joined. To represent this list graphically, I have made a list of QPushButtons, which all represent a different channel. These buttons are made with the following method, and that's where my problem kicks in:
void Messenger::addToActivePanels(std::string& channel)
{
activePanelsContents = this->findChild<QWidget *>(QString("activePanelsContents"));
pushButton = new QPushButton(activePanelsContents);
pushButton->setObjectName("pushButton");
pushButton->setGeometry(QRect(0, 0, 60, 60));
pushButton->setText("");
pushButton->setToolTip(QString(channel.c_str()));
pushButton->setCheckable(true);
pushButton->setChecked(false);
connect(pushButton, SIGNAL(clicked()), this, SLOT(switchTab(channel)));
}
(activePanelContents is a QWidget that holds the list.)
The point is that each button should call the switchTab(string& tabname) method when clicked, including the specific channel's name as variable. This implementation doesn't work though, and I haven't been able to find out how to properly do this.
For strings and integers, you can use QSignalMapper. In your Messenger class, you would add a QSignalMapper mapper object, and your function would look like:
void Messenger::addToActivePanels(std::string& channel)
{
activePanelsContents = this->findChild<QWidget *>(QString("activePanelsContents"));
pushButton = new QPushButton(activePanelsContents);
// ...
connect(pushButton, SIGNAL(clicked()), &mapper, SLOT(map()));
mapper.setMapping(pushButton, QString(channel.c_str()));
}
and after you have added all channels to your active panels, you call
connect(&mapper, SIGNAL(mapped(const QString &)), this, SLOT(switchTab(const QString &)));
Use QSignalMapper to pass variables;
QSignalMapper* signalMapper = new QSignalMapper (this) ;
QPushButton *button = new QPushButton();
signalMapper -> setMapping (button, <data>) ;
connect (signalMapper, SIGNAL(mapped(QString)), this,
SLOT(buttonClicked(QString))) ;
in slot i.e
void class::buttonClicked(QString data){
//use data
// to get sender
QSignalMapper *temp = (QSignalMapper *)this->sender();
QPushButton *btn = (QPushButton *)temp->mapping(data);
// use btn
}
Hope my ans may help you
Don't use the sender method unless you absolutely have to. It ties the function directly to being used only as a slot (can't be called directly). Retain the behavior of having the function accept a string and simply make a mechanism by which you can call it.
One method, among others you might find, is to leverage use of QSignalMapper. It will map objects to values and regenerate signals of the appropriate signature.
I would do it with "relay" objects:
Create TabSwitchRelay which is a sub-class of QObject with this constructor:
TabSwitchRelay::TabSwitchRelay(QObject *parent, Messanger * m, const QString & c)
: QObject(parent), m_messanger(m), m_channel(c)
{
}
It also has a slot clicked():
void TabSwitchRelay::clicked()
{
m_messager->switchTab(m_channel);
}
Now replace the line in your code that does connect with this:
TabSwitchRelay * tabRelay = new TabSwitchRelay(pushButton, this, channel);
connect(pushButton, SIGNAL(clicked()), tabRelay, SLOT(clicked()));
It's not tested but you get teh basic idea.
You could try having your switchTab slot take no argument and use QObject::sender to get the object that sent the signal.
Messenger::switchTab()
{
QObject* sender = this->sender();
QPushButton* button = qobject_cast<QPushButton*>(sender);
if(button)
{
// Do stuff...
}
}
if you're using Qt5, you can do it through lambda:
connect( sender, &Sender::valueChanged, [=](){ myMethod(5); } );
void myMethod(int value)
{
// do stuff
}