I just started reading into QT but I don't quite get the SIGNAL SLOT functions.
I have a form with 2 QLineEdit and I want to copy the text from the first QLineEdit to the second one when a button is clicked but I don't know how to set up the connect function properly.
I tried tying textChanged function to itself but the result is that the text will edit everytime I press a letter, since that's the signal.
newForm::newForm() {
widget.setupUi(this);
connect(widget.nameEdit, SIGNAL(textChanged(const QString&)),
this, SLOT(textChanged(const QString&)));
connect(widget.pushMe, SIGNAL(pressed()),
this, SLOT(handleButton()));
}
void newForm::handleButton(){
}
I think I have to do something inside the handleButton function but I don't understand how to read and copy the text from the first line since the text() doesn't work inside handleButton
To copy the text from the first QLineEdit called widget.nameEdit to a second one, widget.nameEdit2, when a button is clicked, you can do it with one SIGNAL/SLOT connection using the QLineEdit setText() in a lambda:
connect(widget.pushMe, &QPushButton::released,this, [=](){
widget.nameEdit2.setText(widget.nameEdit.text());
};
You don't need to use the first QLineEdit textChanged() signal, and the above connection copies the whole text available in first field to second filed all at once when you press the button. One the other hand, if you want second QLineEdit to get updated continuously as text changes in first field, then you could use the textchanged() signal of first field , to setText() of second :
connect(widget.nameEdit, &QLineEdit::textChanged,
widget.nameEdit2, &QLineEdit::setText);
Related
I have a dialpad with numbers 1-9 and 0, and a QLabel above it to show the numbers when clicked(same as a keypad on any phone). All are push buttons. What is the easiest way to get the QLabel to show the numbers as the push buttons are clicked?
For example, if 2 then 0 then 7 is clicked, the label would update in real time with 207. The format of the Qlabel should follow standard phone numbers, 000-000-0000. I understand how to setText for one number at a time, but they keep overriding each other.
Any help is appreciated.
Thank you in advance
What you are looking for is a QSignalMapper. It maps multiple inputs through a single interface and does the sender dispatching for you.
QSignalMapper *mapper(new QSignalMapper(parent));
for (int i=0; i<10; ++i){
QPushButton *button = some_new_button_function();
connect(button, &QPushButton::clicked, mapper, &QSignalMapper::map);
mapper->setMapping(button, i);
}
connect(mapper, QOverload<int>::of(&QSignalMapper::mapped),
[this](int i){/*here your append code*/});
The easiest is to connect the clicked signal of the buttons to a slot (possibly a lambda) that changes the text of the QLabel (using setText()). If you want to append to the current text, then just do setText(label.text() + "new text");.
You have to connect the signals clicked() emitted by each QPushButton to a slot that update the QLabel text.
A brief example
In the parent constructor:
connect(qpb1, &QPushButton::clicked, this, &MyClass::handleQLabel);
And the possible slot implementation:
void MyClass::handleQLabel()
{
QPushButton * qpb = qobject_cast<QPushButton*>(sender()); // Find the sender of the signal
if(qpb != nullptr)
this->myLabel->setText(qpb->text()); // Write anything you want in the QLabel
else
{
// Do what you want.
}
}
This will do the job.
Of course if you don't want use sender() (for multi-threading concerns for example) you can either create one slot by QPushButton and do the same number of connect (heavy and quite a dirty workaround), or create a subclass of QPushButton to add a custom signal to emit with an identifier of the QPushButton and get it with a slot for example.
I hope it can help :)
QLineEdit might better suit your needs in this case if you also want your data representation to follow phone number standard such as "000-000-0000". You can make it read-only, disable interaction flags if you like (but from UI/UX perspective it is better not to, since mostly there is no reason to disallow copying), and also you can set input mask you like. Given your current situation, you can base your needs on the following example:
// Set your format.
ui->lineEdit->setInputMask("000-000-0000");
// Make sure that your text would be in the format you like initially.
ui->lineEdit->setText("999-999-9999");
// Text will be not editable.
ui->lineEdit->setReadOnly(true);
// And here, you can use QSignalMapper as other members have suggested. Or you can just connect multiple buttons somehow. The choice is yours to make.
connect(ui->pushButton, &QPushButton::clicked, ui->lineEdit, [this]
{
// Just keep in mind taht when returning text, some of the mask elements might be here, too.
ui->lineEdit->setText(ui->lineEdit->text().replace("-", "") + "1");
});
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 ;)
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;
}
}
I have QTextEdit with Text init like :
write something here....
Now I'd like that the start signal that triggered only once so when the user enter its mouse cursor into the text area the string will removed and the text area will be ready to write.
I need it to be triggers only once when the widget is up.
I only found the :
connect( textEdit, SIGNAL( cursorPositionChanged( int para, int pos ) ),
<.....>, SLOT( Position ( int para, int pos ) ) );
but I don't know how to trigger it once , or is it the right way for this.
You could disconnect that connection in the Position slot. That way that slot will only be triggered once.
Another option is simply to keep a boolean in the object that receives the signal that indicates whether or not it should do something when the slot is called.
(You'll probably find yourself wanting to "rearm" that slot. Either call connect again, or reset that boolean, depending on what option you chose.)
If your QTextEdit widget is only a single line, you might want to consider using a QLineEdit widget instead. Then you can call setPlaceholderText("write something here.... ") to get the effect you want. Click here for more info.