I'm building an application that requires a Qdialog, and a few buttons.
I am attempting to use the Command behavioural design pattern in my implementation. My project so far has 4 classes. (Please excuse the rough UML)
Command
+execute()
zoomInAndOut : Command
+execute()
MenuItem
-QPushButton
-command
+clicked()
Dialog
So within the dialog class, I create a menuItem (which has a QPushButton and Command member variable), and what I need to happen is that when the menuItems button has been clicked, it calls the menuItems "clicked" method (which in turn calls the commands execute method). I know that the "connect" function must be used, however after many, many attempts, I cannot get it to work correctly.
Within Dialog the code roughly looks like this
zoomInAndOut zoomCommand;
menuItem *zoom = new menuItem(new QPushButton("Zoom", this), QRect(QPoint(300, 0), QSize(100, 50)), &zoomCommand);
connect(zoom->getButton(), SIGNAL(clicked()), SLOT(zoom->clicked()));
As mentioned before the connect method is completely wrong, but you can see what I am attempting to achieve. How can I make this work?
Thank you in advance for any help.
Change code
connect(zoom->getButton(), SIGNAL(clicked()), SLOT(zoom->clicked()));
to
connect(zoom->getButton(), SIGNAL(clicked()), zoom, SLOT(clicked()));
Make sure your menuItem class contains the Q_OBJECT macro the line after the opening {. And make sure the clicked() method is in the slots section of the class body.
Related
I am using Qt5.
I have a very simple dialog class that inherits from QDialog.
I have a class that uses this dialog, and also a QFileDialog:
NameDlg m_name_dlg;
QFileDialog m_file_dlg;
This class also has some slots to handle dialog closing:
private slots:
void on_dlgName_accepted();
void on_FileDlgClosed(int result);
In the constructor I do some connecting:
QObject::connect(&m_file_dlg, SIGNAL(finished(int)),
this, SLOT(on_FileDlgClosed(int)));
QObject::connect(&m_name_dlg, SIGNAL(accepted()),
this, SLOT(on_dlgName_accepted()));
The first call to connect is fine, but the second call generates the output:
QMetaObject::connectSlotsByName: No matching signal for on_dlgName_accepted()
Curiously, my slot is correctly called when the name dialog is accepted!
The documentation (and header file) for QDialog says:
Signals
void accepted()
So it isn't a parameter mismatch.
As I said above, the signal is correctly called so my code all works fine, I just would really really like to understand why I get this warning (as an educational exercise) and also get rid of it (for peace of mind).
I cannot post full code, but I do believe there should be enough for anyone to understand the problem.
Things I have tried:
Using finished() instead.
Casting &m_name_dialog to a QDialog *.
Changing the signal to QDialog::accepted().
Thanks in advance.
In some part of your code you are using the method connectSlotsByName, if you have created a design (.ui) this usually calls it since compiling generates a file ui_somefile.h, and this file is used.
According to the docs:
void QMetaObject::connectSlotsByName(QObject *object)
Searches recursively for all child objects of the given object, and
connects matching signals from them to slots of object that follow the
following form:
void on_<object name>_<signal name>(<signal parameters>);
From the above it is observed that this method will try to connect the slots that have that format, and in your case the second slot fulfills it, when trying to connect it looks for the objects and signals but in your case it does not find it since the object does not exist dlgName and generates the warning you see.
This method is created by the .ui file because through the design you can create slots by right clicking on the widget and selecting go to slot, choosing the signal and finally creating the slot.
Note:
If you are going to create your own slot, avoid using the underscores as this could cause you problems because Qt would try to connect it and if the objects do not exist it will send you several warnings.
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.
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