I Created buttons dynamically for data from the database
QPushButton *btnComment = new QPushButton("Comment");
btnComment->setProperty("id",qry.value(0).toString());
Is the button that i created dynamically
I set a connect
connect(btnComment, &QPushButton::clicked, this, &Planner::commentButton);
and created a function on slots
public slots:
void commentButton();
How can I get the id value so I can execute a SQL query after the button click
I tested the function
void Planner::commentButton()
{
QMessageBox inpass;
inpass.setText("Comment");
inpass.exec();
return;
}
It works but after clicking OK the application closes
I get something like this in the console
QMainWindowLayout::addItem: Please use the public QMainWindow API instead
Any possible approach ?
Update
I was able to solve the lambda issue by declaring the passing variable as a global variable
connect(btnComment, &QPushButton::clicked, this, [this]{ commentButton(taskID); });
As mentioned in the comment you can connect to a lambda rather than directly to a non-static member.
Change the signature/definition of Planner::commentButton to...
void Planner::commentButton (QPushButton *button)
{
/*
* Use button accordingly.
*/
}
Then simply change your connect call to...
connect(btnComment, &QPushButton::clicked, this,
[this, btnComment]
{
commentButton(btnComment);
});
Now a pointer to the QPushButton that triggered the call will be passed to Planner::commentButton.
Related
I have created a little UI with a simple toolbar. I am initing the toolbar within the initToolbarfunction. This function is within a Class inheriting from QMainWindow.
void Main_Frame::initToolBar() {
rectangle.setText(rectangle_text);
circle.setText(circle_text);
triangle.setText(triangle_text);
triangle.setObjectName(triangle_id);
circle.setObjectName(circle_id);
rectangle.setObjectName(rectangle_id);
toolBar.addAction(&triangle);
toolBar.addAction(&circle);
toolBar.addAction(&rectangle);
connect(
&toolBar, &QToolBar::actionTriggered, this, [=]() {
process_toolbar_ac_evt(*sender());
});
}
I want any tool bar events to be processed through process_toolbar_ac_ect(QObject obj). Within that method, I want to decide what action (within the toolbar) has been triggered.I want to do this by the objectname. Therefore I have given any action an object name. But when I call sender().objectName() I get an empty QString.
My suggestion is, that sender returns a pointer to on of my actions that I put to the toolbar. If this is the case, why I get an empty QString on the sender()?
void Main_Frame::process_toolbar_ac_evt(QObject &evt) {
if (evt.objectName() == circle_id) {
// If circle action has clicked, to this ...
}
}
As you are connecting to one of QToolBar's signals the sender() will be your tool bar object.
Simply use the QAction argument that is passed in the QToolBar::actionTriggered signal. That's what it is for.
NB: Avoid QObject::sender() wherever possible. It virtually breaks the desired decoupling achieved by signals and slots.
How to link a variable to a push button so it is enabled as true for first time when the push button is pressed, and made false when it is pressed for the second time, and so on?
I want to use it because in my program a certain loop should be executed when the push button is pressed so that the variable is enabled as true.
Can someone help me?
In order to achieve that, you need to connect the clicked() signal (inherent to a QPushButton) to a slot of yours. Then, in this slot, you just need to change a boolean of your object each time you enter this slot. This is the code you need.
In your .h file :
private:
bool bForButton;
QPushButton* m_button;
public slots :
void onClicked();
In your .cpp :
MyClass::MyClass()
{
bForButton = false;
m_button = new QPushButton(this);
connect(m_button , SIGNAL(clicked()), this, SLOT(onClicked()));
}
void MyClass::onClicked()
{
bForButton = !bForButton;
}
This way, you notice that we change the boolean to its opposite, so it will change each time you click the button, as required.
You can display a button that keeps the state (checked or not) so each time you click on it its state change and the user can see the current state.
You can achieve that by setting your button checkable setCheckable(true) and test in your loop the value of isChecked(). The button will keep the checked state and update on click automatically so you don't need any extra code.
The QPushButton has such variable, i.e. the checked property.
You can connect the loop you need run to the toggled signal:
auto button = new QPushButton(this);
button->setCheckable(true);
...
connect(button, &QAbstractButton::toggled,
this, &ThisClass::executeLoop);
...
void ThisClass::executeLoop(bool checked) {
if (!checked) return;
.... your function body
}
http://doc.qt.io/qt-5/qabstractbutton.html#checked-prop
This is more in the mindset of Qt: don't loop/spin/lock/..., just react to events triggered by the framework (i.e. connect signals to slots).
I want to send two integers, string and fret, to a SLOT that will process the location of the button that was pressed. The SIGNAL and SLOT argument have to match so I am thinking I need to reimplement the QPushButton::clicked event method. Problem is I am new to Qt and could use some direction.
connect(&fretBoardButton[string][fret], SIGNAL(clicked()), this, SLOT (testSlot()));
If you use the C++11 connection syntax you can use a lambda with calls testSlot with your string and fret arguments:
connect(&fretBoard[string][fret], &QPushButton::clicked, [this, string, fret]() {
testSlot(string, fret);
});
This code creates a lambda using the [captures, ...](arguments, ...) { code } syntax. When you make the connection it captures the string and fret variable values, and will then pass them on to testSlot when the button is clicked.
There are Two approaches you could use to add the string and fret information. one is to use the sender() function to get the button which emitted the signal. you can the access fret and string if they are members of your button class so in the SLOT you would have.
MyPushButton *button = (MyPushButton *)sender();
button.getFret();
button.getString();
However since you are already subClassing QPushButton you could use a private SLOT to catch the buttonClicked signal and re-emit a signal with the right values.
In the constructor
connect(this, SIGNAL(clicked()), this, SLOT(reemitClicked()));
and then the reemit SLOT
void MyPushButton::reemitClicked()
{
emit clicked(m_fret, m_string);
}
be sure to add the appropriate private slot and public signal to you class
https://doc.qt.io/archives/qq/qq10-signalmapper.html see this artical for a good discussion on various ways to add an argument to signal.
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 ;)
Let's say I have 2 windows in my application, and two classes responsible for them:
class MainWindow: public QMainWindow and class SomeDialog: public QWidget.
In my Main Window I have a button. When it is clicked, I need to display the second window. I do it this way:
SomeDialog * dlg = new SomeDialog();
dlg.show();
Now, the user does something in the window, and closes it. At this point I want to get some data from that window, and then, I suppose, I will have to delete dlg. But how do I catch the event of that window being closed?
Or is there another way not to have a memory leak? Maybe It would be better to create an instance of each window on startup, and then just Show()/Hide() them?
How do I manage such a case?
It is advised to use show() / exec() and hide() instead of dynamically creating the dialog every time you want to show it. Also use QDialog instead of QWidget.
In the constructor of your main window create it and hide it
MainWindow::MainWindow()
{
// myDialog is class member. No need to delete it in the destructor
// since Qt will handle its deletion when its parent (MainWindow)
// gets destroyed.
myDialog = new SomeDialog(this);
myDialog->hide();
// connect the accepted signal with a slot that will update values in main window
// when the user presses the Ok button of the dialog
connect (myDialog, SIGNAL(accepted()), this, SLOT(myDialogAccepted()));
// remaining constructor code
}
In the slot connected to the buttons's clicked() event simply show it, and if necessary pass some data to the dialog
void myClickedSlot()
{
myDialog->setData(data);
myDialog->show();
}
void myDialogAccepted()
{
// Get values from the dialog when it closes
}
Subclass from QWidget and reimplement
virtual void QWidget::closeEvent ( QCloseEvent * event )
http://doc.qt.io/qt-4.8/qwidget.html#closeEvent
Also it looks like the widget you want to show is a dialog. So consider using QDialog or it's subclasses. QDialog has useful signals you can connect to:
void accepted ()
void finished ( int result )
void rejected ()
I think you are looking for the Qt::WA_DeleteOnClose window flag: http://doc.qt.io/archives/qt-4.7/qt.html#WidgetAttribute-enum
QDialog *dialog = new QDialog(parent);
dialog->setAttribute(Qt::WA_DeleteOnClose)
// set content, do whatever...
dialog->open();
// safely forget about it, it will be destroyed either when parent is gone or when the user closes it.