I have many line edits on the form created in the Qt creator designer panel. I want to connect them with the signal and the slot:
connect(ui->lineEdit_AmperageMaxCode,SIGNAL(textChanged(QString)),
this,SLOT(slot_ConvertCodesInValues(QString)));
Is there a way to not use the connect() for each object, but do it with a loop or some other way?
You can get all QLineEdit children from your widget using findChildren:
QList<QLineEdit*> lineEdits = this->findChildren<QLineEdit*>();
and then connect their signals using a loop.
If you want to do it only for some QLineEdit instances, you can give them a specific name, and use it as a parameter for findChildren (see the documentation).
Related
I want to understand if the following sequence is possible? If yes, how can we achieve the same?
MainWindow Qt GUI has a QPushButton
While we click on the QPushButton, it must open another Qt GUI Window (a different class, say 'DialogClass')
In the newly opened Qt GUI Window we have a QLineEdit and QPushButton
While we enter data in the QLineEdit and click on the QPushButton (of the DialogClass) the MainWindow class should receive the data entered in QLineEdit
Any help on this item will be appreciated. Thanks in advance!
Qt foresees its signals and slots approach for such purposes.
The QPushButton of your class offers a signal clicked which you connect to a custom (self-written) slot of your dialog. The dialog's slot then should read the contents of the QLineEdit and publish these on the dialogs own (custom) signal, which is connected to a (custom) slot of your main window, which then can process the value originally contained in the line edit.
Details will resemble pretty much the example of Qt's signals and slots documentation, so I won't be more explicit about.
I have a very simple Qt window that contains combo box, and I try to create signal slots for this combo box with Qt Creator. I tried activated, currentIndexChanged, currentTextChanged, nothing works.
What may be the reason?
Other signals (button click, menu item click) on the same window fire normally. Operating system is Windows 7.
When you create slots in Qt Designer, on a Form, like a QMainWindow Form, if you right click and Go to slot..., it uses naming conventions to automagically connect the ui form elements to slots based on their name.
After you create those slots, you go and change the object name to something else.
Like instead of comboBox1, you change it to myComboBox, it will break the automagically connected ui form elements, because the name is different.
http://doc.qt.io/qt-5/designer-using-a-ui-file.html#automatic-connections
Widgets and Dialogs with Auto-Connect
Although it is easy to implement a custom slot in the dialog and
connect it in the constructor, we could instead use QMetaObject's
auto-connection facilities to connect the OK button's clicked() signal
to a slot in our subclass. uic automatically generates code in the
dialog's setupUi() function to do this, so we only need to declare and
implement a slot with a name that follows a standard convention:
void on_<object name>_<signal name>(<signal parameters>);
That is the most likely reason why your combobox started to not connect.
If it wasn't that you can see the output of every explicit connect call when they fail based on naming:
QObject::connect(ui->comboBox, SIGNAL(misspelled_signal()), this, SLOT(non_existent_slot()));
And you will get very useful output in your Application Output tab at runtime to help diagnosis the errors.
Hope that helpls.
As far as the GUI designer, I understand how certain signals affect certain slots and invoke code. Other than that method, I am unsure about how to invoke a slot from a signal.
Take this example:
void QFileDialog::directoryEntered ( const QString & directory ) [signal]
This is a signal. When the directory is entered, I want this to populate a widget QColumnView with the contents of the directory.
How does a non widget signal invoke a slot of a UI widget.
I assume you use connect but the example provided uses two separate objects.
Signals and slots are features of QObject. It works well even for non-GUI code.
Connecting a signal to a slot is always done through the connect function:
connect(myDialog, SIGNAL(directoryEntered(QString)),
this, SLOT(updateColumn(QString)));
here assuming that you have updateColumn() slot in your main object handling the actual UI update of that QColumnView.
I am using a QTableWidget to display and edit a data matrix. For validation purpose, I used the QLineEdit as items in this table. As following,
pTable=new QTableWidget(N,N,this);
pItem=new QLineEdit();
pItem->setText(tr("%1").arg(pInfra->adjacencyM(i,j)));
rx=new QRegExp("0|1");
validatorRegexp=new QRegExpValidator(*rx,0);
pItem->setValidator(validatorRegexp);
pTable->setCellWidget(i,j,pItem);
Since I want to know if data in certain cell has been changed, so I tried cellChanged(int, int) signal, and connect it with my own slot cellEdited(int,int), like this
connect(pTable,SIGNAL(cellChanged(int,int)),this, SLOT(cellEdited(int,int)));
But, when I edit QLineEdit in the cell, I can not catch this signal. When will this signal be fired? Or can I do this using another signal or in some other way?
Thanks!
The problem is that the cellChanged() signal is emittet only if the table model is issued the setData() method, which normally comes from the QLineEdit of the delegate. Since You have your own mechanism by setting the cell widget the setData() method of the model will never be called. Which means you'll have to connect to the textChanged() or the textEdited() signal of the QLineEdit object you put in the cells.
Another valid option is the approach mentioned by beduin in the comment.
Also possible: You could subclass the used delegate and make it create QLineEdit objects with your validator. Which would be the cleanest approach since you don't interfere with the model/view architecture and can rely on the signals the table object is sending.
Best regards
D
Not aware about causes of this problem. Considering another ways. You can catch QLineEdit signal textChanged and use QSignalMapper to bind signal, fired by each QLineEdit to particular cell number. Maybe itsn't the best qway to do that, but you can use it in case this problem won't be solved.
Whenever I use the signal/slot editor dialog box, I have to choose from the existing list of slots. So the question is how do I create a custom named slot?
right click on the main window and select "change signals and slots" and add a new slot.
It will appear in your signal slot editor.
This does seem to be possible in the version of Qt Designer 4.5.2, but it can't be done from the Signal/Slot Editor dock-widget in the main window.
This is what worked for me
Switch to Edit Signals/Slots mode (F4)
Drag and drop from the widget which is to emit the signal, to the widget which is to receive the signal.
A Configure Connection dialog appears, showing the signals for the emitting widget, and the slots for the receiving widget. Click Edit... below the slots column on the right.
A Signals/Slots of ReceivingWidget dialog appears. In here its is possible to click the plus icon beneath slots to add a new slot of any name.
You can then go back and connect to your new slot in the Configure Connection dialog, or indeed in the Signal/Slot Editor dockwidget back in the main window.
Caveat: I'm using PyQt, and I've only tried to use slots added in this way from Python, not from C++, so your mileage may vary...
Unfortunately this is not possible in Qt4.
In Qt3 you could create custom slots which where then implemented in the ui.h file. However, Qt4 does not use this file so custom slots are not supported.
There is some discussion of this issue over on QtForum
I am able to do it by:
In MainWindow.h, add the line:
public slots:
void example();
in the MainWindow class.
In MainWindow.cpp
void MainWindow::example() {
<code>
}
This doesn't seem to be possible in a simple way.
The designer only allows you to promote existing widgets to your own custom widgets. yet it doesn't allow you to connect the signals and slots of the class of promoted widgets.
The way this is possible is creating a plugin for the designer as is described here and in the pages that follow it.
The normal course of action is to promote a widget to your own class and then to connect it manually in your own code. this process is described here
It is not possible to do it, because it means you would add a slot to an existing Qt class like QPushButton which is not really the way to go.
You should create your own QWidget eventually by subclassing an existing one. Then integrating it into Qt Designer as a plugin as suggested. Having your own class allows you to add/modifiy the signals/slots available as you want.
Don't forget about the slot auto-connection features. There are a few drawbacks, like having to rename your function if you rename your widget, but we use those a lot at my company.
You can use the magic slot format of
void on_objectName_signal() {
// slot code here, where objectname is the Qt Designer object name
// and the signal is the emission
}
The connection to this method is established by the method connectSlotsByName and whenever the signal is emitted, this slot is invoked.
Maybe it'll help.
By default you have to choose from the existing list of slots. But you can add slot by right-clicking at you object in the list at right side of designer and choose "slot/signals" and add your custom slot/signal. After that, you can choose it in signal/slot editor.
click the widget by right button
promote the widget into a class you defined
click the widget by right button again
you will see that signal and slot is editable