I have a couple of checkboxes on my form, and I don't want to write separate event handler for each, because they all will implement the same logic. Instead I want to write just one event handler that will know about what checkbox has been clicked.
E.g. in Delphi I can use it this way:
function click_handler(sender):
begin
checked_box := sender.tag;
end;
Here I remember current checked box number in some variable (tag property was manually set in Delphi IDE).
I searched and can't find how I can implement this using Qt, because event handlers don't have sender argument.
I implemented it like this, but it's not convenient:
# assign handlers (n assignments)
checkbox_1.clicked.connect(self.cb_1_click)
...
checkbox_<n>.clicked.connect(self.cb_<n>_click)
# separate handler for each check box (n functions, doing the same stupid work)
def cb_1_click:
self.cb_click(sender=1)
...
def cb_<n>_click:
self.cb_click(sender=n)
# main check box click logic (1 function)
def cb_click(sender):
# do something common for all checkboxes
Thank you.
You may use QObject::sender() in slots to find out who emitted the signal.
Also you might want to check out QSignalMapper which is intended exactly for solving these problems.
Related
I'm using Qt Designer and pyqt code to write an app.
I have a very simple question: in my UI I have 2 checkboxes and what I need is to set the first checkbox as always unchecked when the second checkbox is unchecked.
In other words the first checkbox can be checked only when the second checkbox is checked, but the second checkbox can be checked also if the first one is not checked.
In Qt Designer I have not find an easy way to do that with the Signals/Slots function.
I had a look in the Qt API and I tried to write some code:
class CreateRIVLayerDialog(QDialog, FORM_CLASS):
def __init__(self, iface)
# some more code here...
if self.addCheckDB.isChecked():
self.addCheck.setChecked(False)
but without results.
Does anybody have some hints?
Thanks
The simplest way is with two signal connections, one of which can be done in Qt Designer.
Your design requires that "the first checkbox can be checked only when the second checkbox is checked". This is equivalent to saying the first checkbox should be disabled when the second checkbox is unchecked. Disabling the checkbox makes it clear to the user that the option is unavailable.
So in Qt Designer, you should connect the toggled signal of checkbox2 to the setEnabled slot of checkbox1. (It may also be necessary to set the initial enabled state of checkbox1 in Qt Designer as well).
Then, in your code, you should make a second connection, like this:
self.checkbox2.toggled.connect(
lambda checked: not checked and self.checkbox1.setChecked(False))
This will clear the checked state of checkbox1 whenever checkbox2 is unchecked.
If you wanted to do the whole thing in code, it would look like this:
self.checkbox1.setEnabled(False)
self.checkbox2.toggled.connect(self.checkbox1.setEnabled)
self.checkbox2.toggled.connect(
lambda checked: not checked and self.checkbox1.setChecked(False))
Just use signals. You are correct when saying that you cannot directly do that via the designer since you have to invert the checked property. The easiest and most readable way that comes to my mind is using a common slot plus an internal member variable that holds the checked state for both:
Add self._toggle = INITIAL_VALUE to your class - the INITIAL_VALUE holds a boolean value, which you use to check/uncheck your checkboxes
self._toggle = True
self.check1 = QCheckBox('Check 1', self)
self.check1.setChecked(self._toggle)
self.check2 = QCheckBox('Check 2', self)
self.check2.setChecked(not self._toggle)
Add a slot:
#pyqtSlot()
def toggle(self):
self._toggle = not self._toggle
self.check1.setChecked(self._toggle)
self.check2.setChecked(not self._toggle)
Connect the clicked signal of both checkboxes to this slot.
Warning! Do not use the stateChanged signal here or you will start an infinite recursion. :3
self.check1.clicked.connect(self.toggle)
self.check2.clicked.connect(self.toggle)
What I'm doing here is basically taking over the change of the state of both checkboxes and do it manually using the value of self._toggle for the first checkbox and the inverted value of self._toggle for the second checkbox.
If you want less inverting inside the slot the following also works though it is less readable omho:
#pyqtSlot()
def toggle(self):
self.check2.setChecked(self._toggle) # Old value of our check1 becomes the value of check2
self._toggle = not self._toggle # Invert
self.check1.setChecked(self._toggle) # New value is assigned to check1
Note: You can also use isChecked() inside the slot and do all of the above without the extra variable however I find this more readable and with much less function calls (every isChecked() and setChecked() is a function call)
I know I am late to this party but there is a way to accomplish this easier and I think how the original person wanted. Here you go. If you have a checkbox_1 and you check/uncheck it, it connects to the following function.
def Change_the_Checkbox_Function(self):
if self.checkbox_1.isChecked():
if self.checkbox_2.isChecked():
pass
else:
self.checkbox_2.setChecked(True)
else:
self.checkbox_2.setChecked(False)
If you want checkbox_1 to check or uncheck many other checkboxes (like a select all), then instead of checkbox_1 directly calling the above function, you have another function that calls other functions to check/uncheck the boxes, as follows:
def Select_ALL_checkboxes(self):
self.Change_the_Checkbox_1_Function()
self.Change_the_Checkbox_2_Function()
self.Change_the_Checkbox_3_Function()
....etc
To me, this follows the most logical way without getting too technical. It works well and is fast. May not be the most efficient or prettiest, but I found this to be the best way to check/uncheck many checkboxes at once.
I may have worked myself into a corner but this sounded to me like a good idea at the time.
I have been developing an interface that permits a user to modify settings of a robotic device, i.e. speed, directions, force, etc. with a very large series of options in the form of ComboBoxes. The problem is that there are about a thousand of these things, in sub categories. e.g. Speed category x1, x2, x3, Y1, y2, etc. So rather than create a thousand comboboxes in QT, I thought the good idea was to create one set of 50 (ish) and then provide a few button to switch between categories. So when the user selects speed QT, populates the comboboxes with the appropriate options, sets the style sheets and text for the labels etc. So it appears as though a dedicated page exists. Then if the user selects Direction, QT Writes the current index of each box to a dedicated array and then repopulates the boxes, labels etc with the appropriate content. I then do this over and over for the various needs of the system.
All of that seems to work fine. However I am now in a bind where the options provided to navigate to each page have grown. For instance I have forward / backward buttons (like you woudl expect in a set-up wizard), as well as action menus at the top to jump to a page. So now the code is becoming very repetitious. If you select the next button, I write the current values to array, then repopulate. If you jump to the page from anywhere, I look to see where I am, write it to array, and populate the boxes. Thus if I need to change anything I have to make the change in numerous places in the code.
I know that this is not optimal. What I woudl like to do is run a continuous loop as I woudl normally do with Micros in C. So the program can look at a variable in each pass and if it is then it does. I am not however skilled enough to figure this loop out in QT. So my new thought was...
Is it possible to trigger an action or slot with a variable. For example, if the user presses the Next button it triggers a slot for a button that does not exist, so that QT will execute a particular line of Code? Then I can have 1 dedicated section focused on reading and writing boxes, with a bunch of actions that will take me there.
You can make a signal that is triggered with an emit call in your code, so you'd hook up the next button signal of clicked to a slot that does some work and moves on, or directly calls another signal that you've created that triggers a slot elsewhere, or do some work in a lambda triggered by the button press.
I would first load all the ComboBoxes options in a QStringList array (or maybe an array of QList<QLatin1String> lists - for memory saving and code efficiency).
Then I would keep an array of a 1000 integers for current ComboBox indexes.
When the user changes a value in some ComboBox, the currentIndexChanged signal will trigger the corresponding slot (a single slot for all the ComboBoxes would be enough - sender()->objectName() to get the name of the ComboBox which had sent the signal):
void WindowWidget::on_ComboBox_currentIndexChanged(int index)
{
name = sender()->objectName();
/* here change the corresponding integer in the current
indexes array */
}
On Next/Back button push repopulate the ComboBoxes. Also, provide some 'Save' button for saving the ComboBoxes indexes (or trigger the Save slot on some action, i.e. on window close either even on a timer signal).
There is a dictionary taken from JSON file, that is represented by QTreeView QStandardItemModel.
A user can reorganize QTreeView(add, delete, drag-n-drop) and rename items.
The goal is: call function that reads changed QTreeView, makes the dictionary and writes it to initial JSON file.
I can do it by pressing a QPushButton after changes occurred or by binding that function to every change e.g. call function when an item is deleted, call function when an item is added, call a function when an item is renamed and so on.
Is there any way to call a function if any of changes occur? Is there such a signal that corresponds to all of the mentioned changes?
The rowsMoved and itemChanged signals do what you think they do. See http://doc.qt.io/qt-4.8/qstandarditemmodel.html
As #vahancho suggests in the comments, you should connect to the layoutChanged signal. All models should emit this immedaitely after making any changes which could affect the view. So this will include sorting and filtering, as well as re-ordering, editing, deleting, etc.
The dataChanged signal is similar, but only really useful if you want to monitor specific items.
I am subclassing QFileDialog to try to get some custom behavior. I would like to connect to signals emitted by components of the dialog, e.g. the textEdited signal when the file name line edit is manually edited. I understand that QFileDialog emits some signals itself, but these do not cover the cases I would like to respond to.
I have two ways about this I can think of, but don't know how to implement. One is to somehow attain a reference to the component to connect to it's signal. The other would be something with event filters, but the event source is the dialog itself, so I don't know how to determine where mouse clicks or key presses occur.
Are either of these methods feasible? Or another way?
Here is one option (your first suggestion):
dialog = QFileDialog()
layout = dialog.layout()
# for i in range(layout.rowCount()):
# for j in range(layout.columnCount()):
# try:
# print i,j
# print layout.itemAtPosition(i,j).widget()
# except:
# pass
line_edit = layout.itemAtPosition(2,1).widget()
line_edit.setText('Hello Stack Overflow')
dialog.exec_()
This gives you access to the QLineEdit in the dialog, which has a bunch of signals you can connect to.
I've also included the code I used to find this widget. I just iterated over the widgets in the layout of the dialog and found the indices of the one I was after. So if you need access to anything else in the dialog, you should be able to find it pretty easily!
Downside to this method: If the layout changes in a future version of Qt, this will break. I suppose you could make the algorithm more robust by looking for widgets that are instances of QLineEdit, but there are always risks with hacky approaches like this!
How can I refresh view after a certain event?
I have a view which contains multiple groups. I want to show or hide some groups.
onCreationComplete() or initialize() method works only at the beginning of the view creation.
Try invalidateDisplayList() on the view
Let me know if that doesn't do the trick and we'll try some other tricks.
I personally don't like the answer that says to call invalidateDisplayList (sorry no offense Nate nothing personal). I feel it's too vague and doesn't explain what this does under the hood and furthermore you shouldn't have to call it directly in cases such as the one explained in the OPs question. You can simply create booleans that are bindable for each of the groups you'd like to show/hide then in the event handler set those booleans to the appropriate value and if they are bound to the visible and include in layout properties of the containers those containers will internally call invalidateDisplayList after calling set visible and consequently commitProperties.
This is basically what happens under the hood as I understand it: The way this works is values aren't committed or used to update the display until the next frame this way it doesn't get bogged down doing unnecessary layout calculations. So you update the bindable property which fires an event which triggers a notification in the listener (in this case a function that sets the property on your control), that in turn passes along the value to the control which sets an internal flag to update the property and calls invalidateProperties. When it hits the next frame redraw it sees that the properties flag is dirty (true) and then calls commitProperties, this computes/sets the appropriate values (possibly also invalidating then "fixing" the size using invalidateSize() and measure()) and calls invalidateDisplayList, then during the same frame it sees that the display list flag is dirty so it calls updateDisplayList, here it uses the values of the properties to draw appropriately.
You should also be able to achieve this using states, which add or remove children from the display list based on an array of "actions" for each state.