Slot never called
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The only difference is the main function that i'm not using.
And that's the problem.
Since you put the downloader in some method it goes out of scope and is destroyed, ie.void someFunction() { Downloader d; //d is created here d.doDownload(); } //d is destroyed hereThe difference is that in the example downloader is created in the
main()and right afterdoDownload()is called the appplication enters an event loop:return a.exec();, which blocks until the download is finished, so the downloader does not exit the scope.To fix this either put Downloader instance in a scope that is wide enough or create it on the heap and delete after the download is finished.
Great explanation!
But if I want use within this function?
Create it on the heap is the solution?
How can I do this?Thanks.
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How can you create an instance on the heap? Just as with any other c++ class: with the
newkeyword.Downloader* d = new Downloader(); d->doDownload();but that is leaking memory, so you need to make sure the downloader is deleted when it finishes. You could, for example, emit a signal when it's done:
class Downloader : public QObject { ... signals: void finished() const; ...Emit it in the
replyFinished():void Downloader::replyFinished (QNetworkReply *reply) { ... reply->deleteLater(); emit finished(); }and then you can use it like this:
void someFunction() { Downloader* d = new Downloader(); d->doDownload(); connect(d, &Downloader::finished, d, &Downloader::deleteLater); } -
How can you create an instance on the heap? Just as with any other c++ class: with the
newkeyword.Downloader* d = new Downloader(); d->doDownload();but that is leaking memory, so you need to make sure the downloader is deleted when it finishes. You could, for example, emit a signal when it's done:
class Downloader : public QObject { ... signals: void finished() const; ...Emit it in the
replyFinished():void Downloader::replyFinished (QNetworkReply *reply) { ... reply->deleteLater(); emit finished(); }and then you can use it like this:
void someFunction() { Downloader* d = new Downloader(); d->doDownload(); connect(d, &Downloader::finished, d, &Downloader::deleteLater); }@Chris-Kawa
Yes! Now it is being called!Now i'm getting a compile error:
C2248: 'Downloader::finished' : cannot access protected member declared in class 'Downloader'
signals:
void finished() const; -
Hi,
please post the full source code. -
@Helson said:
C2248: 'Downloader::finished' : cannot access protected member declared in class 'Downloader'
Looks like you misplaced something.
finished()should be a public method (a signal). Posting your code is a good idea as @Wieland suggested. -
Here is the code:
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Hi
note:
its Qt4 -
@Helson said:
C2248: 'Downloader::finished' : cannot access protected member declared in class 'Downloader'
Looks like you misplaced something.
finished()should be a public method (a signal). Posting your code is a good idea as @Wieland suggested.Looks like you misplaced something. finished() should be a public method (a signal).
Chris, in Qt4 signals used to be protected, so it might be simply that he's using a bit older version than we assumed. ;)
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awww, ok. Good catch guys.
@Helson so just replace
connect(d, &Downloader::finished, d, &Downloader::deleteLater);with
connect(d, SIGNAL(finished()), d, SLOT(deleteLater()));and think about upgrading to Qt5. Especially since you're following tutorials there's no point in learning obsolete stuff.
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@Chris-Kawa said:
connect(d, SIGNAL(finished()), d, SLOT(deleteLater()));we did. still said it was protected ?!
so we moved to ctor in Download class -
so we moved to ctor in Download class
Don't do that. It makes your class dependent on being created on the heap, which you can't guarantee. If someone creates it on the stack you will crash on double delete.
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so we moved to ctor in Download class
Don't do that. It makes your class dependent on being created on the heap, which you can't guarantee. If someone creates it on the stack you will crash on double delete.
@Chris-Kawa
Ah yes I see. Luckily we did not do it, ;)
we moved to dodownload member function and
used old syntax.Im not used to Qt4 so the whole protected signals were
confusing. -
@Chris-Kawa
Ah yes I see. Luckily we did not do it, ;)
we moved to dodownload member function and
used old syntax.Im not used to Qt4 so the whole protected signals were
confusing.Im not used to Qt4 so the whole protected signals were
confusing.If you think about it, semantically it's more correct that signals are
protected. A signal is raised from the object itself to notify others and in principle shouldn't be available for others to emit it! My suspicion is that they're nowpublicbecause of the new way of connecting, which by my opinion is not such an improvement over the old one.PS.
Is it me, or the forum is going nuts? I have the distinct feeling that I see Helson's posts as mrjj's? -
hi, I talked with him in chat also, so I did post here.
Forums crash every 2 minutes for me though.@mrjj
Yes, but who are you? Are you indeed mrjj, or there's some bug in the forum and you're in fact Helson? :)Read and abide by the Qt Code of Conduct
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@mrjj
Yes, but who are you? Are you indeed mrjj, or there's some bug in the forum and you're in fact Helson? :)@kshegunov
Heh. Im mrjj
(i hope) -
@kshegunov
Heh. Im mrjj
(i hope)@mrjj
Ok, because I would have expected this:Ah yes I see. Luckily we did not do it, ;)
we moved to dodownload member function and
used old syntax.to be written by Helson. So it's my mistake, sorry for the misunderstanding. :)
Read and abide by the Qt Code of Conduct
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@mrjj
Ok, because I would have expected this:Ah yes I see. Luckily we did not do it, ;)
we moved to dodownload member function and
used old syntax.to be written by Helson. So it's my mistake, sorry for the misunderstanding. :)
@kshegunov
well You should have the credits as you solved it :)
and sorry for writing a bit unclear :) -
@kshegunov
well You should have the credits as you solved it :)
and sorry for writing a bit unclear :)
