How to override keyPressEvent of QTextEdit? - c++

I override keyPressEven() of widget QTextEdit:
void myTextEdit::keyPressEvent(QKeyEvent *e)
{
if(e->key()==Qt::Key_0)
{
qDebug() << "Ok";
}
}
Button 0 works - show "Ok", but does not write in field of QTextEdit. Why? Thanks advance.

You need to call the base class implementation if you want to keep the default behaviour:
void myTextEdit::keyPressEvent(QKeyEvent *e)
{
if(e->key()==Qt::Key_0)
{
qDebug() << "Ok";
}
QTextEdit::keyPressEvent(e);
}
See the docs for keyPressEvent.

In case someone using PySide2 is having trouble overriding QTextEdit's built-in keybindings, I post my solution here. Hopefully this is also useful for C++.
Scenario:
We are using a QTextEdit in an application and want to distribute a series of keybindings, but the text editor has already several hardcoded bindings. We want the editor to ignore them and hand them over to its parent, so they can be eventually handled by our code.
Problem:
While the docs say that whenever an event is ignored (e.g. by returning True in the installed eventFilter method) it automatically gets passed on to the parent, the truth is that when doing that for predefined keybindings QTextEdit did not hand them over: the event got ignored AND absorbed. So any textedit built-in keybindings filtered this way will be effectively globally disabled.
Direct event passing via sendEvent inside the editor's eventFilter had an interesting effect:
When calling sendEvent and returning super().sendEvent, the keybinding got executed by the editor AND the event passed to the receiver.
When calling sendEvent and returning True, the keybinding didn't get executed, and the event didn't get passed to the receiver.
When calling sendEvent and returning False, the keybinding didn't get executed, and the event passed to the receiver twice.
Furthermore:
Using event.ignore() didn't have any effect: the editor executed the built-in anyway.
Trying to discriminate via event.spontaneous() caused a segfault due to a missing pointer. Probably something got GCed but didn't try to debug that.
Trying to replace the event with a "dummy event" and call super also didn't work. Magically, the text editor kept executing the built-ins.
Maybe I missed something. Anyway, below I detail the approach that worked for me.
Solution:
The plan is to completely block the event, but broadcast it via signals, and then connect to them wherever we want. In your text editor instance, define the signal e.g. as follows:
eventCatched = QtCore.Signal(QtCore.QEvent)
Then, e.g. the following event filter will prevent execution of a few keybindings, and emit them once via eventCatched:
def eventFilter(self, obj, evt):
"""
Remember to install via self.installEventFilter(self)
"""
catch_control_keys = {QtCore.Qt.Key_Left, QtCore.Qt.Key_Right}
catch = False
# documentation for keys and modifiers:
# https://doc.qt.io/qtforpython-5/PySide2/QtCore/Qt.html
if evt.type() == QtCore.QEvent.KeyPress:
modifiers = evt.modifiers()
ctrl = bool(modifiers & QtCore.Qt.ControlModifier)
shift = bool(modifiers & QtCore.Qt.ShiftModifier)
alt = bool(modifiers & QtCore.Qt.AltModifier)
key = evt.key()
# catch all undo/redo builtins
if ((ctrl and shift and key == QtCore.Qt.Key_Z) or
evt.matches(QtGui.QKeySequence.Undo) or
evt.matches(QtGui.QKeySequence.Redo)):
catch = True
# catch specified control-keys
if ctrl and not shift and not alt:
if key in catch_control_keys:
catch = True
#
if catch:
# block event but send it as signal
self.eventCatched.emit(evt)
return True
else:
return super().eventFilter(obj, evt)
Then, we are free to connect the signal wherever we want to, we just need a method that handles events. In my case, I just wanted to pass them to the main window, which can be done with the following one-liner in the constructor:
text_editor.eventCatched.connect(lambda evt: QtCore.QCoreApplication.sendEvent(self, evt))
This way, whenever we catch an event in the text editor, it will be ignored and won't be propagated the standard way. Instead, a signal will be emitted, and we can subscribe to that signal to e.g. restart the propagation tree at a different point, as shown here via sendEvent.
Hope this helps!
Cheers,
Andres

Related

call wxHyperlinkEvent without clicking on link

I am using wxHyperLink. OnHyperlinkClicked(wxHyperlinkEvent&) is called when user clicks on the link. OnHyperlinkClicked() helps to switch between 2 screens. I want to call this function explicitly - without user interaction.
I am using the following code for that:
BEGIN_EVENT_TABLE(UserRegistrationFrame, wxFrame)
EVT_HYPERLINK(wxID_ANY, UserRegistrationFrame::OnAuthCodeOptionLinkClicked)
END_EVENT_TABLE()
void MyClass::MyFunction()
{
wxHyperlinkEvent event;
OnAuthCodeOptionLinkClicked(event);
}
void MyClass::OnAuthCodeOptionLinkClicked(wxHyperlinkEvent& event)
{
// code to switch
}
Is this the correct way to achieve my goal? Or do I have to use something different?
The code is not correct, because with EVENT_TABLE you are setting a handler that doesn't exist.
When the user clicks on the control the event is fired, and the static table will call UserRegistrationFrame::OnAuthCodeOptionLinkClicked, not MyClass::OnAuthCodeOptionLinkClicked
I'd better forget EVENT_TABLES and go with Dynamic Event Handling. Using Bind() gives you more features.
Now, you want to call the event-handler function directly, not coming from a user action. Then you need to create an event just to pass it to the handler. That's what you do in MyClass::MyFunction(), right?
Don't mix jobs. If both your direct-call and the event-handler use a common feature, put it in a different function and call it directly or from the event-handler.
But the question is Why do you use a wxHyperlinkCtrl for a task like screen switching? Do you want also the default browser to be launched?

HOw to reload the present UI details once is switch from different UI in QT C++

I have two forms one is trainee_view.ui
and other is enter_new_trainee.ui
so for that i have trainee_view.cpp,trainee_view.h to see the list of Trainee in DB
and enter_new_trainee.cpp,enter_new_trainee.h to enter new trainee details
now in trainee_view.ui i have a push button "ADD Trainee"
so if i click this button it will go to "enter_new_trainee.ui"
void trainee_view::on_pushButton_2_clicked()
{
newtrainee=new enter_new_trainee(this);
newtrainee->setWindowFlags(Qt::Window);
newtrainee->show();
// connect(newtrainee, SIGNAL(destroyed()), this, SLOT(refresh_form()));
}
so by using connect() i am trying to refresh the trainee_view after entering the new trainee details. so how can i emmit the signal from
2nd form to 1st form such that i call refresh_form() method in 1st form .
I tried to use destroyed() signal on newtrainee but could not refresh my trainee_view form.
To be MOre simple . i just want to get an object is destroyed or not so if destroyed i can call refresh() method to load back the changes done on widget
for that i opted connect() method so how should i call that. becoz if i call
connect(newtrainee, SIGNAL(destroyed()), this, SLOT(refresh_form()));
there is no effect i.e nothing is loading into the view.
am newbie to qt so pls try to help me.
Thank YOu.
I'm not sure if I correctly understand your app, but I think you misunderstand the concept of Signals and Slots. Look here for some examples. In some simplification you can look at signal and slots this way: connect() command is a place which will not do anything - it just stay and keep listening for a signal. So you should place it in trainee_view.cpp. That's the first part and I see you did it correct, or almost correct. But you need also something that will send the signal, and this is exactly what emit() command do - it should be placed in enter_new_trainee.cpp just after description of generation new entry. For example, let assume user input new entry in LineEdit in UI:
[...]
QString newEntry = ui->LineEdit->text(); //Save entry to variable
emit(newEntry); //Emit it to signal slot
[...]

Qt find out if QSpinBox was changed by user

Let's suppose I have a QSpinBox, how I can find out if the value was changed manually from user or from a other function?
EDIT: I want to do some actions only when user change values but if your program does it (setValue) I don't want do this actions.
Possible solution:
ui->spinBox->blockSignals(true);
ui->spinBox->setValue(50);
ui->spinBox->blockSignals(false);
In this case, signal will not be emitted, so all what you can catch by valueChanged() signal is only user's action.
For example:
void MainWindow::on_spinBox_valueChanged(int arg1)
{
qDebug() << "called";
}
When user change value by mouse or type by keybord, you see "called", but when you setValue with blocking signals, you don't see "called".
Another approach is to provide some bool variable and set it to true before the setValue and check this variable in slot. If it is false(user action) - do some action, if not - don't do(change bool to false). Advantages: you don't block signal. Disadvantages: maybe hard readable code, if slot calls many times, you will many time do this unnecessary checking.

What signal should I capture to grab the text of Gtk::Entry before it is changed?

I am writing an application using gtkmm 3 (running Ubuntu 12.04 LTS) and working right now with the Gtk::Entry control.
I cannot find the correct signal to capture so that I can grab the Gtk::Entry buffer text before it is changed, and persist it to maintain a record of changes. I know that in some other tool-kits, there is a hook provided that facilitates such. (I believe using a "shadow buffer".)
What signal do I have to grab to do this? What is the slot's signature for this signal? Is this functionality supported at all?
Since you are changing the behaviour, it's better to inherit from Gtk::Entry:
class ValidatedEntry : public Gtk::Entry {
Glib::ustring last_valid;
virtual void on_changed()
{
Glib::ustring text = get_text();
if (... validation here ...)
set_text(last_valid); // WARNING: will call this on_changed() again
else
last_valid = text;
Gtk::Entry::on_changed(); // propagate down
}
};
BUT
This goes against usability, that's why it's not a built-in behaviour. Users won't like the text reverting back just because they miss-typed something; they might hit backspace before they realize the entry threw the wrong character away.
You should at least wait until the user presses the Enter key (i.e. signal_activate or override on_activate()), or do something less drastic, like showing a warning icon.
You could give a try to GObject's "notify" signal. It is used in conjunction with the property to spy. Connecting to "notify::text" will call your callback for each modification of the "text" property, but the first change may be the setter that will set the initial value, that you could then store. Worth a try.
Otherwise, you could try to store it on the first triggering of the "insert-text" or "delete-text" signals. Please give use some feedback if that seems to work.
I also agree with DanielKO: on an usability point of view, modifying user input is just annoying and bad practice. Better to tell her which field is wrong, put the focus there, and/or have a button to reset to defaults, but not enforce any change on user input.

Qt User customizable hotkeys

I'm trying to design a Qt GUI application with user customize-able hotkeys. The main issue I'm running into is how to synchronize the hotkeys across the application since a particular hotkey (for example, copy) may be used by multiple widgets/components.
My current strategy is to use a reference class which holds a list of QKeySequence objects for each different hotkey. Each widget would have to have a way to reference this master list and have custom implementations of low-level the keyPressEvent which would compare inputted keys vs. the hotkeys. I don't particularly like this strategy, though, as it requires significant re-implimentation in each widget and feels like I'm trying to re-invent the wheel.
I also tried using QAction objects which can hold QKeySequence shortcuts internally, then use these to trigger higher-level events which I can handle using slots & signals. However, the main issue I have here is how to manage which slots signals get routed to.
For example, say I have 2 open widgets which can both receive a copy action signal. I can connect a slot for both of these to the same signal and take advantage of the single update point for shortcuts, but then things get messy since only the active widget should act on the copy signal, not both widgets. I can re-implement the focusOutEvent and focusInEvent handlers to connect/disconnect slots manually, but this also seems to run into the same issue above where I'm trying to re-invent the wheel and doing more work than is necessary.
Is there an easier way around this problem?
I don't think there is a particularly easy/non-tedious solution to this problem, but when I needed to add user-customizable hotkeys to my application, here is how I did it:
1) Start with your application that has hard-coded key shortcuts, e.g. code like this:
QMenu * editMenu = new QMenu;
QAction * copyItem = menu->addAction(tr("Copy"), this, SLOT(CopyData()));
copyItem->setShortcut(tr("Ctrl+C"));
2) Create a GetKeySequence() function that looks something like this:
static QHash<QString, QKeySequence> _usersKeyPreferences;
static bool _usersKeyPreferencesLoaded = false;
QKeySequence GetKeySequence(const QString & keySequence, const QString & contextStr)
{
if (_usersKeyPreferencesLoaded == false)
{
// Oops, time to load in the user's saved custom-key settings from a file somewhere
_usersKeyPreferences = LoadUsersKeyPreferencesFromFile();
_usersKeyPreferencesLoaded = true; // so we'll only try to load the file once
}
if (_usersKeyPreferences.contains(contextStr))
{
return _usersKeyPreferences[contextStr];
}
else
{
// No user preference specified? Okay, fall back to using the
// hard-coded default key sequence instead.
return QKeySequence(qApp->translate(contextStr, keySequence));
}
}
3) Now the tedious part: grovel over all of your code, and anywhere you've specified a key-sequence explicitly (like in the third line of the code shown for step 1), wrap it with a call to GetKeySequence(), like this:
copyItem->setShortcut(GetKeySequence(tr("Ctrl+C"), tr("Edit_Menu|Copy")));
4) At this point, your program's key-sequences will be customizable; just make sure that the key-settings-file is present on disk before GUI-creation code runs. Here's an excerpt from my program's key-mappings file (which I store as a simple ASCII text file):
Edit_Menu|Copy = Ctrl+C
Edit_Menu|Cut = Ctrl+X
Edit_Menu|Paste = Ctrl+V
[... and so on for all other menu items, etc...]
... of course one downside to this approach is that once the GUI is created, the key-bindings can't be modified "on the fly" (at least, not without a lot of additional coding). My program gets around this simply by closing and then re-creating all windows after the user clicks "Save and Apply" in the Edit Key Bindings dialog.
5) An optional further step (which is some extra work up front but saves time in the long run) is to write a program (or script) that greps all the .cpp files in your program's codebase looking for calls GetKeySequence() in the code. When it finds a GetKeySequence() call, it parses out the two arguments to the call and prints them as a line in a key-bindings file with the default settings. This is useful because you can make this script part of your autobuild, and thereafter you'll never have to remember to manually update the default key-settings-file whenever you add a new menu item (or other key-sequence specifier) to your program.
This worked well for me, anyway. The advantage is that you don't have to refactor your existing program at all; you can just go through it inserting GetKeySequence() as necessary while leaving the larger logic/structure of the program intact.