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 am new to QT and C++ and i have legacy qt-c++ code here which i cant get to work.
Probably its something about the lifetime of the calling objects but hey, but please tell me what i am missing.
In a QT .ui i have various Frames and Widgets containing Frames and Widgets containing a QVBoxLayout which we shall call "myLayout"
On click in the .ui file i use
myWidget = new mywidget(some params);
myLayout->addWidget(myWidget);
where myWidget is declared as mywidget *myWidget; in the header file
myWidget is a QWidget which internally adds a QVBoxLayout to itself and adds a QGraphicsView. Using the MouseReleaseEvent i emit a signal from the QWidget.
now when i try to connect the signal slot (which i do in cpp file from the ui)
connect(myWidget, SIGNAL(mySignal(QString)), this, SLOT(mySlot(QString)));
the signals never catch the slot. the slot is public, the signal isnt.
What did i do wrong? Can somebody help. Feel free to ask further questions since i dont really know whats important in c++ questions;)
edit:
the signal gets emitted by QGraphicsObjects which themselfs connect to a slot in the QGraphicsView. This Slot is called and debuggable. at the end of the Routine an emit mySignal("..."); is called.
Maybe you forgot to add Q_OBJECT macro in your widget declaration. Qt documentation: http://doc.qt.io/qt-5/qobject.html#Q_OBJECT
I have a QWidget B which is contained inside a QWidget A. QWidget A has a QLabel. I have some data inside QWidget B, which I want to set as the value of the QLabel. How can something like this be done?
First of all, if I understand your topic correctly, you have your own derivations of QWidget for A and B.
The clean solution to your problem is that B emits a signal, like newLabelText(QString text);.
Then, A provides a slot setLabelText(QString text);. You connect the signal to the slot and you are done.
In this solution, only one entity needs to know both A and B to perform the Signal/Slot-Connection, while A and B do not have to know each other, or mangle with each other.
I'm repeatedly using a pair of QComboBox and QListWidget in a project. Their interaction is highly coupled - when an item is selected in the combo box, the list is filtered in some way. I'm copy pasting all the signal and slot connections between these two widgets across multiple dialog box implementation which I don't think is a good idea.
Is it possible to create a custom widget, which will hold these two widgets and will have all signal and slot connection in one place? Something like as follows:
class CustomWidget
{
QComboBox combo;
QListWidget list;
...
};
I want to use this widget as a single widget.
The usual way of doing this is to sub-class QWidget (or QFrame).
class CustomWidget: public QWidget {
Q_OBJECT
CustomWidget(QWidget *parent)
: QWidget(parent) {
combo = new QComboBox(...);
list = new QListWidget(...);
// create the appropriate layout
// add the widgets to it
setLayout(layout);
}
private:
QComboBox *combo;
QListWidget *list;
};
Handle all the interactions between the list and the combo in that custom widget (by connecting the appropriate signals to the appropriate slots, possibly defining your own slots for this).
You then expose your custom widget's behavior/API through dedicated signals and slots, possibly mimicking the ones in the list and/or the combo.
The Address book tutorial walks you through all of that, including creating a custom widget and defining signals and slots for it.
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