I am loading a web page from a file, then i replace some of the html in it:
self.template_web_page = QtWebKit.QWebPage()
self.template_web_page.mainFrame().load(QtCore.QUrl('template.html'))
def load(ok):
main_window.web_view.loadFinished.disconnect(load)
self.table_element = self.template_web_page.mainFrame().findFirstElement("#table")
self.table_element.setInnerXml(table_html)
main_window.web_view.loadFinished.connect(load)
Is there a way to connect to a signal just for one shot?
As already noted, there doesn't appear to be a better (more concise) way than this.
http://comments.gmane.org/gmane.comp.lib.qt.general/6883 suggests that such a solution is fine, although I have had issues with such a solution myself. I found that if I disconnected the slot at the start of the slot (as is done in the code in the question) and then tried to perform some GUI interactions (setting statusbar text was a problem, but not highlighting a row in a list view), I got an exception due to a NULL pointer dereference. This was with PyQt 4.6.2 for Python 2.6 for Windows. When I moved the disconnect() call to the end of the slot, the problem went away.
Apologies in advance if this is not relevant and it's just a stupid mistake I've made.
Related
I updated my QML application from Qt 5.12 to Qt 5.15.
My application loads its qml sources using the following code:
auto* engine = new QQmlApplicationEngine(this);
...
engine->load(QUrl("qrc:/main.qml"));
When engine->load is called, I now get the following warning, which was not there with Qt 5.12:
Qt Quick Layouts: Detected recursive rearrange. Aborting after two
iterations.
How can I find the source of this warning so I can fix my code?
Edit:
After two downvotes, I would like to clarify the intent of my question.
I have a very large application which is loading a big tree of qml files, with main.qml being the main Window. The warning that I posted comes from the Application output pane, without any hint to a source file location that caused the warning.
I am looking for a way to find the source file location that caused this kind of warning. I believe it is reasonable to ask how to achieve that, and I believe that this is a generic problem that will come up for many people who update their qml code to Qt 5.15. It's in the nature of such a issue that a self-contained example (like asked for in the comments) cannot be provided.
It's a totally reasonable ask - the warning is ambiguous so you'd have to post the entire codebase to get a minimum viable. Afaik there is no reasonable way to locate the offending bits programmatically but look for Layout components (RowLayout, ColumnLayout, GridLayout) nested inside the same kind of Layout component; these are the usual offenders. For instance:
ColumnLayout {
ColumnLayout {
id: childColumnLayout
// this is generally the cause of your grief
// changing the the child ColumnLayout to a Column usually fixes it for me
}
}
I have implemented a simple sync routine using the as3commons-async framework (which I thought to be stable as a rock)
I have a CompositeCommand containing a high number of other commands, which can also be composite commands.
Now some strange thing happens:
When executed slowly (over the web) everything works as expected.
Now I leave out the part doing the heavy load causing the commands to run at "machine" speed.
After a couple of dozens, sometimes more than a hundred "progress" events fired, AIR player crashes with this error message:
undefined
at org.as3commons.async.operation.impl::AbstractProgressOperation/dispatchProgressEvent()[C:\projects\as3-commons\as3-commons-async\src\main\actionscript\org\as3commons\async\operation\impl\AbstractProgressOperation.as:135]
at org.as3commons.async.command.impl::CompositeCommand/onCommandResult()[C:\projects\as3-commons\as3-commons-async\src\main\actionscript\org\as3commons\async\command\impl\CompositeCommand.as:287]
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at org.as3commons.async.operation.impl::AbstractOperation/dispatchCompleteEvent()[C:\projects\as3-commons\as3-commons-async\src\main\actionscript\org\as3commons\async\operation\impl\AbstractOperation.as:152]
looking at the AbstractProgressOperation code in the async lib at the given line, there's nothing really done there:
/**
* Convenience method for dispatching a <code>OperationEvent.PROGRESS</code> event.
* #return true if the event was dispatched; false if not
*/
protected function dispatchProgressEvent():void {
dispatchEvent(OperationEvent.createProgressEvent(this));
}
I can rule out my code as the culprit as well, as all parts of it are working seperately and are tested in many other aspects. Plus I don't really do anything either right now other than calling execute() on the command and fire an complete event.
For debugging I added some heavy trace() calls, which assumingly causes a slight delay, and voilà, it now crashes some lines further down in the code, still with "undefined" pointing a line in the code which is very unsuspicious. (once it was a call to invalidateDisplayList() in a component used for several years now without ever having made any problems)
Did anybody else encounter problems before when a large set of events is fired in very short time? What else can cause this strange "undefined" ?
Thanks as always.
I didn't work on this library but you can delay the event firing by using the magical setTimeout as following:
protected function dispatchProgressEvent():void {
setTimeout(function():void
{
dispatchEvent(OperationEvent.createProgressEvent(this));
}, 0);
}
This will delay the execution of the dispatchEvent until all current operations processed.
I have worked on the as3commons-async library. I don't have a definitive answer for you, I'm afraid, just my suspicion that this error isn't necessarily related to as3-async.
You describe similar weird happenings in other areas of the code base (even in Flex itself), so this kind of smells like either a Flex bug or maybe even a bug in the AIR runtime.
The only thing I can advice here is to create a test application that fires events in a similar fashion and speed (so, without using as3-async) to see whether you can re-create the errors.
If it does turn out to be a runtime issue, at least you'll have a solid testcase to send to Adobe.
I apologize for not being able to help you out concretely.
cheers,
Roland
In writing a Qt4 app, I clumsily wrote:
QObject::connect(spinbox, SIGNAL(vlaueChanged(int)), ....
and it compiled, and it ran, but of course the spinbox didn't have any effect.
Such misspellings should be caught. I always assumed that valueChanged() was declared in some header file, but apparently not. Any arbitrary garbage can be given to SIGNAL() or SLOT(), and it'll compile. My toy program is small. For a huge app with dynamically created controls connected on the fly, an error like this could be very hard to track down.
Is there some way to do error checking for this kind of typo? Is it possible for the compiler (gcc) to do this, or is some other tool appropriate?
This has been changed for Qt5. You can read about it here.
SIGNAL and SLOT macros turn their arguments into strings, and they are not checked in compile time (because... they are string actually). In case of wrong signal/slot name Qt writes warning (qWarn) in runtime. They say, in Qt5 something changed there.
In my experience, sometimes you really can do such a mistake (though rarely, autocompletion helps a lot), but it can be easily tracked down and fixed.
Going through the phantomJS code i ran into this in the webpage.cpp file (line 315)
connect(m_networkAccessManager, SIGNAL(resourceRequested(QVariant)),
SIGNAL(resourceRequested(QVariant)));
And i don't quite understand how this works, i'm aware that you can connect signals to signals in Qt.
On the Qt documentation i found out that you can also connect signals directly to a method (http://doc.qt.io/qt-5/qobject.html#connect-2) , seeing that it's a 3 parameters call i thought that this would be the desired function on the webpage.cpp code, but connecting a signal to the same signal...i got completely lost there, any help?
PD: not very experienced in Qt i should say, sorry if it's a dumb question
Three parameters QObject::connect()
connect(m_networkAccessManager, SIGNAL(resourceRequested(QVariant)),
SIGNAL(resourceRequested(QVariant)));
is an equivalent of
connect(m_networkAccessManager, SIGNAL(resourceRequested(QVariant)),
this, SIGNAL(resourceRequested(QVariant)));
Thus, QNetworkAccessManager::resourceRequested(QVariant) is connected to WebPage::resourceRequested(QVariant) and cause the latter to be emitted every time when the former is emitted.
More details in Qt documentation
In my project I have noticed 20-40% CPU time when my app is idle.
In debugger when I pause I always land on a flex.utils.Timer/tick.
This timer has 30ms delay between "ticks"
I didn't create that Timer... so this is problably a component I have added
Unfortunately it will be difficult to remove all compenents until if find the "one" ..
Yes I should have notice the CPU usage sooner !
and yes I will do that if I don't find another solution
I am of course using some components without having their sources...
My questions :
* How can I find the guilty component ?
* I tried to find it using Kap Inspector without success ...any tips for Kap inspector ?
* Is there another great tool to track object creation ?
Thanks for your help
When you set your breakpoint, in the Flex Debugger perspective, find the Variables tab/view. From there, with your breakpoint set, you should be able to see all of the variables currently in local scope (local to the timer-tick event handler, that is). The event variable will contain information about the timer itself -- e.g., in event.target -- and the this variable will tell you where the timer handler is defined.
From there, you might be able to walk back up the stack trace, using the Debug tab/view (with your breakpoint still set), to get a sense of where the Timer object might've been instantiated. If that doesn't work, you can download a trial of Flex Builder Professional here:
http://www.adobe.com/cfusion/entitlement/index.cfm?e=flexbuilder3
... and give the built-in profiler a try. Hope that helps point you in a helpful direction!
No idea about Flex, but for your CPU problems, check this out:
http://www.gskinner.com/blog/archives/2009/05/idle_cpu_usage.html