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.
Related
I'm currently trying to use Qt Designer to build a GUI and I would like to customize slots of my menu actions.
E-g: I'd like the user to press a menu action and it'd show a widget if it is hidden or hide it if it is already visible.
Basically, what I want to do is execute some code of mine and not the default actions such as show() or hide().
So I'm wondering if I should create a subclass of QMenuBar, add custom slots to it, then create a plugin to use it inside Qt Designer or if I should create a subclass for QMenu or QAction ? Or maybe it isn't the right way to do that ?
I'm working under Visual Studio and I'm only using Qt Designer, not Qt creator.
I'm new to GUI and Qt programming and I'm a bit lost here.
Thanks in advance :)
You have basically 2 options:
Implement the custom logic in the Mainwindow sublcass.
For this, you simply add the slots required for your handling in the class, and make them available in Qt Designer. You can do this:
either in the Signal/Slot editor and click "Modify" and then click on the + Symbol. By this you make new slots available in QtDesigner;
or when your slot is called on_(senderName)_(signalName), Qt autowiring will automatically connect the signals, and you don't have to do this in code or desinger.
Create a QMenuBar subclass and implement the custom logic there.
Your case tell Qt Designer to select your specific subclass as replacement for the default QMenuBar by right-clicking on it, and select "Promote to...". In the new dialog, you can specify your custom class that will be used as replacement in actual code, but in design time a QMenuBar is used. With this mehtod, you don't have to write a separate plugin to make your class available in Qt Designer.
Note that with the second option, your custom logic will only be called when the actions are triggered through the menu bar, not by shortcuts or tool buttons
Create a slot in your class:
onMenuActionTriggered()
Use the connect() to react on action's signal:
connect(ui.myAction, SIGNAL(triggered()), this, SLOT(onMenuActionTriggered()));
In your slot you can do whatever you want.
Another solution (not my favourite one, but possible) is to use the auto-connect functionality, which means, by declaring a slot 'on_myAction_triggered()' (where myAction is the name of your QAction) you don't need to use the connect() since it is automatically connected by Qt
The menu bar is automatically added to any new form derived from QMainWindow (the default when creating a gui application, but you can create new main windows using file->new file or project... and selecting Qt->Qt Designer Form Class ).
To add options to it you simply click in the area labeled "Type here" and write your option text. When you do so an action will appear in a list in the lower part of Qt Designer. Right click on that action and select "go to slot". It will pop up a dialog with "triggered()" already selected for you. Simply click "Ok" and Qt Creator will take care of all the details and transport you to the body of the slot function.
I have a settings dialog that has some settings that require another dialog to fully configure. My window shows a preview of the data as it's being tweaked by these settings. Upon clicking on the configuration button I launch another modal dialog with some knobs to twist to fine tune the particular setting.
I wish to send the result of the twisting of the knobs on the child dialog back to the parent dialog so that it can show the new preview data as the knobs on the child are being played with. The way I imagine it is I have a "refresh preview" function in the parent that is called after modification of it's data preview member variables. The question is, how do I do this? How can I access getters/setters from the parent dialog as a modal child dialog? If I do access them will the preview change or will it be blocked because of the modality of the child?
Thank you!
In Qt world, it is generally encouraged to exploit the Signal/Slot mechanism. In short, classes can send signals when something changes within that class. And slots can receive such signals provided we notified the receiving classes appropriately.
Let us look at how we can do it for our present case.
In our settings dialog constructor, we include this code (assumption is that you display the "another" dialog when a button is pressed):
Dialog *dialog = new Dialog();
connect(dialog->dial(), &QDial::valueChanged, this, &QSettingsDialog::changeTemp);
Code walkthrough:
Our QDialog has been constructed with a QDial object, dial. We access that member pointer with dialog->dial().
We tie the signal that emits the value changed on the dial to the slot called changeTemp that receives the value changed and sets the display widget on the settings dialog (parent) accordingly.
The changeTemp method might be like so:
void QSettingsDialog::changeTemp(int val)
{
lineEdit->setText(QString::number(val));
}
Notes:
You need to declare the Q_OBJECT macro on all classes that need to implement Signals and slot. In this case, both the settings dialog and the child dialog.
The above signal/slot signature is the new Qt5 signature. If you are on a version below 5.0, the signature is different. Refer to the docs.
I've been watching a Qt tutorial series on YouTube, in which the author shows how to call a function, when a button is pressed. He right-clicked on the button in Qt Creator IDE and chose "Go to slot", from where he chose the signal which would fire the generated function. Since I am used to develop with Netbeans, I simply tried to follow his example using the embedded Qt Designer. Unfortunately, there is no "Go to slot..." entry when I right-click on my button or any widget. I could, of course, create a new slot for my main window and then connect the button's signal to it, but doing it with a single function just seems way more convenient and clean to me. Is there a way to fix is, or if not, at least a way to do with via code entirely, without having to add a new slot to the main window for every single button that servers a different purpose? Thanks for your help.
While I don't know why the QtDesigner in Netbeans doesn't provide this feature, I know what the feature does: It just creates a slot with a special name in your widget class. Note that it does not add a connect statement. It uses the automatic connection feature, which works like this:
For each slot which name matches this pattern:
void on_X_Y(...)
it will be connected to the signal named Y of the object named X. So if you have a QPushButton named button, and you want to handle the signal pressed, simply create a slot with the following signature:
void on_button_pressed()
If you wonder how this slot gets connected to the signal: This happens in the ui_...h file at the end of setupUi():
QMetaObject::connectSlotsByName(WidgetName);
I just started using QtCreator tonight, and it seems it puts all of the interface stuff inside of the ui file. I followed a tutorial to create a resource for my icons, then I added them to a menu bar at the top.
I need to make a connection when one of them is clicked though, and cannot figure out how to make a callback for it.
Am I going to have to completely create them through code or is there some way to add a callback for them (rather than just making them interact with other objects).
Menu bar items are action objects. To do something when they are clicked, you need to catch the triggered() signal from the action. Read more about signals and slots here.
To do this, you need to declare a new slot in your MainWindow class. Qt also supports doing this automatically, without the need to connect anything, but I prefer doing it myself. If you're not interested, just skip this part.
First, we declare a new slot in your window class:
private slots:
void clickMenuButton();
Then, in your constructor, you need to connect the triggered signal to your new slot:
connect(ui.actionObject, SIGNAL(triggered()), this, SLOT(clickMenuButton()));
The first argument is the object that holds the signal we'll listen to (your menu button). The second is the name of the signal. The third is the object that holds the receiving slot (in this case, our window). The fourth is the slot.
And just like that, clickMenuButton() will be called whenever the action is clicked.
As I said before, Qt can also automatically connect signals to slots. The disadvantage here seems to be that you can't change the slot's name, but you don't need to connect it either.
Qt Creator supports creation of slots for widgets: in the case of your menu action, you should go to the form designer, and you should see a list of actions in your form (if you don't, find the Action Editor). Right click the action you want, and push Go to slot.... There, double click triggered().
Qt Creator will then open the new slot in your code editor, and you can do whatever you want to here!
To do that you'll need to add a QAction, add it to the menu, associate an icon with it and then create a callback for it. I'm using the VS Integration so I don't know the details of how to do it in Creator but it should be possible without creating stuff in code.
There should be somewhere an actions editor. from there you add an action, then right-click it or something to add an icon to it, then drag it do the menu and then possibly double click it to create a slot for it. This is how it works in the VS Integration atleast.
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