My problem is the following:
I have QPushbutton* that calls this
void Reflex::buttonClicked(){
QObject* senderObject = sender();
QPushButton* senderButton = qobject_cast<QPushButton*>(senderObject);
if (senderButton->text() == " "){
.
.
.
QTimer::singleShot(1000, senderButton, SLOT(repair()));
}
And when the singleshot proc i want to make some changes on the senderButton but i cant figure out how should i do it.
Possibilities:
1) (This option is more OO, and much more sane to maintain)
Subclass QButton to have a signal that looks something like this:
void delayedClick(QPushButton *);
Now, override void QPushButton::mousePressEvent ( QMouseEvent * e ) [virtual protected] and have it start a timer to emit the delayedCLick signal on timeout.
Finally, connect this to whatever cares about the button, and you're done.
2) (Using what you've got)
Using what you've shown us so far, you could just save the clicked button as a member variable (in Reflex) and reference it in react to perform your tasks.
Note from the QT docs:
Warning: This function [sender()] violates the object-oriented principle of modularity. However, getting access to the sender might be useful when many signals are connected to a single slot.
IE: AVOID if possible. It is pretty easy to do the subclassing.
Related
I have some labels and layouts nested inside a QWidget to build a part of a sidebar. Each QWidget is its own section and one component currently looks like this:
To my understanding, you can only set hyperlinks with QLabel, but I'm trying to get the whole area between the white lines clickable. This is including the icon and the whitespace. Is there any way to achieve this?
This got marked as a duplicate to the opposite of what I was asking, so I'd like to reiterate that I'm trying to implement a hyperlink without QLabel.
You can easily have a widget open a link on click:
class Link : public QWidget {
Q_OBJECT
public:
Link(QUrl url, QWidget p = nullptr) : QWidget(p), _url(url) {}
QUrl _url;
void mouseReleaseEvent(QMouseEvent *) { QDesktopServices::openUrl(_url); }
}
You can avoid any extra signals and connections, and have each link widget store its own link internally, the url can be set on construction and changed at any time. Not using signals and slots makes it easier to change the link too, without having to disconnect previous connections.
IMO going for a signals and slots solution is only justified when you want different arbitrary behavior. In this case you always want the same - to open a particular link, so you might as well hardcode that and go for an easier and more computationally efficient solution.
I would just manually catch the SIGNAL for clicked() and use desktop services to open the url in code.
bool QDesktopServices::openUrl ( const QUrl & url ) [static]
Opens the given url in the appropriate Web browser for the user's desktop environment, and returns true if successful; otherwise returns false.
http://doc.qt.io/qt-4.8/signalsandslots.html
Using this type of syntax, or in the designer, you can also connect a signal to a slot.
connect(widgetThatRepresentsURL, SIGNAL(clicked()),
handlerThatWillOpenTheURL, SLOT(clicked_on_url()));
For widgets that don't have a signal set up for clicked (or whatever event you are interested in), you can subclass the widget in question and reimplement...
void QWidget::mousePressEvent ( QMouseEvent * event ) [virtual protected]
Specifically for creating a signal, there is emit. I've used this in the past like the following
void Cell::focusInEvent(QFocusEvent *e)
{
emit focus(this, true);
QLineEdit::focusInEvent(e);
}
with the following in the header
signals:
void focus(Cell *, bool);
My program has 2 classes. One of them is MainWindow and another is Calc.
In main window I use automatic generated function on_PushButton_clicked. This function should send two values: double & char to function in Calc.
first:
void MainWindow::on_OneButton_clicked(){
QObject::connect(ui->ZeroButton , SIGNAL(clicked()), this, SLOT(...)) );
ui->TextEdit->insertPlainText("1");
}
second :
void Calc::Add(double val, char oper){
//compute something
}
It's my first app with Qt and I do not know how can I connect them. I've searched similar question on this forum, but can't found.
Sorry if i'm wrong.
First of all, you have to well understand what signal/slot mecanism is, and what you are doing.
Signal/slot mecanism is a Qt concept to link a function (signal) to another function (slot). To "make a link" between a signal and a slot, you have to connect them using QObject::connect(...).
When you use automatic generated function on_PushButton_Clicked() with Qt designer, you, in fact, "make a link" between the signal clicked() emitted when the pushButton is clicked, with a slot on_PushButton_Clicked(). However, the connection between this signal and this slot doesn't appear in your code so it may be confusing and that's why I'm pointing it out.
When you write this:
void MainWindow::on_OneButton_clicked(){
QObject::connect(ui->ZeroButton , SIGNAL(clicked()), this, SLOT(...)) );
ui->TextEdit->insertPlainText("1");
}
You create a connection with zeroButton when clicked and a slot, each time you clic on your button. As a connection is valid till an object is destructed, if you clic again on your pushButton, you'll have a second connection between zeroButton when clicked and your slot.
A better way to create connection is to use connect(...) function when you create your object (mainWindow in your case).
To make it simple for your calculator, you can create 9 buttons for digits, 4 buttons for operators, and 1 button to compute everything.
In your mainwindow constructor, you could have something like:
connect(ui->pushButton1, SIGNAL(clicked()), this, SLOT(onPushButton1Clicked()));
.... // Every other signal for each button
connect(ui->pushButtonEqual, SIGNAL(clicked(), this, SLOT(onPushButtonEqualClicked());
And in your body
void MainWindow::onPushButton1Clicked()
{
// concatenate current value + 1
ui->textEdit->insertPlainText(ui->textEdit->toPlainText() + "1");
}
void MainWindow::onPushButtonEqualClicked()
{
// check textedit content (need a digit + operator + digit)
...
// compute result
...
// write result in TextEdit
...
}
I hope it will help a little bit ;)
I've found a few similar questions on this but these appear to refer to cases where a message box is used in the slot handler. In my case I am a bit stuck as I am getting the editFinished signal twice even when my slot handler is doing nothing.
For a test, I have an array of QLineEdit which use a signalMapper to connect the editingFinished() signals to a single slot. The signalMapper passes the array index so I can see where the signal came from.
eg:
testenter::testenter(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::testenter)
{
// setup the UI according to the .h file
ui->setupUi(this);
signalMapper = new QSignalMapper(this);
// init the labels and edit boxes
for (int i = 0; i < 10; i++)
{
pm_label[i] = new QLabel(ui->scrollArea);
QString text = QString("Number %1").arg(i);
pm_label[i]->setText(text);
pm_label[i]->setGeometry(10,20+i*30, 50, 20);
pm_label[i]->show();
pm_editBox[i] = new QLineEdit(ui->scrollArea);
pm_editBox[i]->setGeometry(80,20+i*30, 50, 20);
pm_editBox[i]->show();
signalMapper->setMapping(pm_editBox[i], int(i));
connect(pm_editBox[i], SIGNAL(editingFinished()), signalMapper, SLOT(map()));
}
connect(signalMapper, SIGNAL(mapped(int)), this, SLOT(data_entry(int)));
}
void testenter::data_entry(int entry)
{
//dummy
}
When run in the debugger, if I enter data into one box then either hit return or select another box with the mouse (ie change focus) , then it calls data_entry twice, the first time with index of the box that is losing focus and the 2nd time with the box which gets the focus.
So my question: Am I missing something? Is this expected behaviour or a bug?
If a bug, anyone know a way round it as I wanted to use this signal to do custom validation on data when it is entered (by either return, tab or mouse click to change focus).
First off, no this isn't expected behavior, i.e. selecting a QLineEdit should not cause it's editingFinished signal to be emitted.
There are a couple of possible things that may cause this problem:
You've accidentally connected a signal twice to a slot
The slot map() is causing the newly selected box to lose focus
In the same vain, if you're debugging and using a break point to detect when the slots are getting called you may be causing the QLineEdit to lose focus when the active application changes from your QWidget to your debugger, again causing the signal to be sent again.
If you're having problems because of a doubly connected slot, which doesn't seem to be the case because you're specifically getting a signal from two different QLineEdits, you can make sure that this isn't happening by specifying the connection type, the connect method actually has an additional optional argument at the end which allows you to change the type from a DefaultConnection to a UniqueConnection.
That being said, data validation is something that Qt has an established mechanism for, and I suggest that you use it if possible, look into extending the QValidator abstract base class Ref Doc. You then tell each of your QLineEdit's to use the same validator.
I have run into the same issue. It really does emit the signal twice, which is a known bug: https://bugreports.qt.io/browse/QTBUG-40 which however has not been addressed for a very long time.
Finally I found that the best solution in my case is to change the signal from editingFinished to returnPressed. As a side effect this behaves much more predictably from the user perspective. See also here: http://www.qtforum.org/article/33631/qlineedit-the-signal-editingfinished-is-emitted-twice.html?s=35f85b5f8ea45c828c73b2619f5750ba9c686190#post109943
The OP "found a few similar questions on this but these appear to refer to cases where a message box is used in the slot handler." Well, that is my situation also, and here is where I ended up. So, at the risk of going off topic...
In my situation, when my slot receives the editingFinished signal sent from the QLineEdit, I launch a modal QMessageBox to ask the user something. The appearance of that message box is what triggers the QLineEdit to send the second, undesirable editingFinished signal.
A post in the bug report (https://bugreports.qt.io/browse/QTBUG-40) mentioned by #V.K. offers a workaround which helped me. The following is my implementation of the workaround. I let Qt magic mojo automatically connect the QLineEdit signal to my MainWindow slot.
void MainWindow::on_textbox_editingFinished( void )
{
QLineEdit * pTextbox = qobject_cast<QLineEdit *>( QObject::sender() );
if ( !pTextbox->isModified() )
{
// Ignore undesirable signals.
return;
}
pTextbox->setModified( false );
// Do something with the text.
doSomething( pTextbox->text() );
}
void MainWindow::doSomething( QString const & text )
{
QMessageBox box( this );
box.setStandardButtons( QMessageBox::Yes | QMessageBox::No );
box.setText( "Are you sure you want to change that text value?" );
if ( box.exec() == QMessageBox::Yes )
{
// Store the text.
m_text = text;
}
}
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 have some dynamically added QWidgets and I want to carry out some task when they are changed.
I think I can't use connect() because I also need the name of the QWidget that triggered the change.
How can I also see which QWidget was changed and still catch the value change event with a common handler?
The quick-and-dirty way is to use connect() as usual, and then in your slot method, call sender() to find out which object sent the signal. For example:
// slot method that you've connected all of your widgets' stateChanged(int) signals to
void MyClass :: someWidgetsStateChanged(int newState)
{
const QObject * s = sender();
if (dynamic_cast<const QCheckBox *>(s) == _myFirstCheckbox) printf("First checkbox is now %s\n", newState?"Checked":"unchecked");
else if (dynamic_cast<const QCheckBox *>(s) == _mySecondCheckbox) printf("Second checkbox is now %s\n", newState?"Checked":"unchecked");
[... and so on...]
}
Note that the reason this is considered "dirty" is that it breaks encapsulation. In particular, the someWidgetsStateChanged() method above now behaves differently depending on which object generated the signal, and so if e.g. at some point in the future you connected a QPushButton::clicked() (or whatever) to that same slot, you'd probably have to update the someWidgetsStateChanged() implementation to handle it appropriately. Still, this works and doesn't require a lot of effort to implement.
Use this to catch events before they are passed to QObject subclass instances:
http://qt-project.org/doc/qt-4.8/qobject.html#installEventFilter
After some additional thinking I arrived at saying why not to extend these controllers?
So that I could hook them to the parent object using parent() or using a custom constructor.
It requires potentially though that I define them as friend classes...