Subclass of QTextEdit makes the program to crash
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Hi,
I'm having problem with a subclass of QTextEdit. First of all I had to subclass QTextEdit because I need the 'editingFinish' signal that is not supported by QTextEdit. But now I don't understand why this new class is causing the crash. I'll try to make you understand better with the code.
qcustomtextedit.h
class QCustomTextEdit : public QTextEdit { Q_OBJECT public: QCustomTextEdit( QWidget *parent = 0):QTextEdit(parent) { } signals: void editingFinished(QString); protected: void focusOutEvent(QFocusEvent *e) { QTextEdit::focusOutEvent(e); emit editingFinished(this->toPlainText()); } };
archivio.h
#include "qcustomtextedit.h" namespace Ui { class Archivio; } class Archivio : public QMainWindow { Q_OBJECT public: explicit Archivio(QWidget *parent = 0); ~Archivio(); public slots: void on_PushButton_clicked(); void textedit_editingFinished(QString); private: Ui::Archivio *ui; QCustomTextEdit *textedit; };
archivio.cpp
Archivio::Archivio(QWidget *parent) : QMainWindow(parent), ui(new Ui::Archivio) { ui->setupUi(this); setAttribute(Qt::WA_DeleteOnClose); ArchivioAperto = true; textedit = new QCustomTextEdit; textedit->setStyleSheet("*{background-color:white; color:black;}"); QVBoxLayout *layout = new QVBoxLayout(ui->frame_3); layout->addWidget(textedit); layout->setSpacing(0); layout->setMargin(0); layout->setContentsMargins(0,0,0,0); ui->frame_3->setLayout(layout); connect(textedit, SIGNAL(editingFinished(QString)), this, SLOT(textedit_editingFinished(QString))); } void Archivio::on_PushButton_clicked() { qDebug() << "HERE4"; QFile note("C:/Progetti/QT_Project"+ "/Note.txt"); if(note.open(QIODevice::ReadOnly)) { qDebug() << "HERE5"; QByteArray baNote = note.readAll(); qDebug() << "HERE8"; textedit->setText(QString(baNote));//the program crashes here note.close(); qDebug() << "HERE6"; } else { } } void Archivio::textedit_editingFinished(QString message) { qDebug() << message; QFile o_filenote("C:/Progetti/QT_Project"+ "/Note.txt"); o_filenote.remove(); QFile n_filenote("C:/Progetti/QT_Project" + "/Note.txt"); if(n_filenote.open(QIODevice::WriteOnly)) { n_filenote.write(message.toLatin1()); n_filenote.close(); } }
I cannot understand how the textedit object can be 0x0 after I have created the Archivio class.
Have I made some mistake while creating the subclass?The interesting thing is that when I launch the debugger everything works fine, I have problems only if I don't launch the program from it.
Thanks in advance!
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Hi,
From the looks of it, you didn't show all your code. Do you have somewhere another assignment to that variable ?
On an unrelated note, there's no need for the call to
clear
since you are callingsetText
which replaces the content of the text edit. -
Hi,
From the looks of it, you didn't show all your code. Do you have somewhere another assignment to that variable ?
On an unrelated note, there's no need for the call to
clear
since you are callingsetText
which replaces the content of the text edit.@SGaist I have updated the code with all the instance of 'textedit', I'm sorry to make you lose time but I can't show all the code. Anyway these are ALL the instances of 'textedit' so it should be enough, am I wrong?
@SGaist said in Subclass of QTextEdit makes the program to crash:
On an unrelated note, there's no need for the call to
clear
since you are callingsetText
which replaces the content of the text edit.Yes, you are right, I tried it just because maybe the problem was not the textedit object but the
textedit->setText()
function. I just tried it without theclear
but it crashes the same way.Maybe is something in the subclass? I can't even try to understand better the problem launching the Debugger engine because with it everything works.
Can it be a problem of optimizations?
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Hi,
I'm having problem with a subclass of QTextEdit. First of all I had to subclass QTextEdit because I need the 'editingFinish' signal that is not supported by QTextEdit. But now I don't understand why this new class is causing the crash. I'll try to make you understand better with the code.
qcustomtextedit.h
class QCustomTextEdit : public QTextEdit { Q_OBJECT public: QCustomTextEdit( QWidget *parent = 0):QTextEdit(parent) { } signals: void editingFinished(QString); protected: void focusOutEvent(QFocusEvent *e) { QTextEdit::focusOutEvent(e); emit editingFinished(this->toPlainText()); } };
archivio.h
#include "qcustomtextedit.h" namespace Ui { class Archivio; } class Archivio : public QMainWindow { Q_OBJECT public: explicit Archivio(QWidget *parent = 0); ~Archivio(); public slots: void on_PushButton_clicked(); void textedit_editingFinished(QString); private: Ui::Archivio *ui; QCustomTextEdit *textedit; };
archivio.cpp
Archivio::Archivio(QWidget *parent) : QMainWindow(parent), ui(new Ui::Archivio) { ui->setupUi(this); setAttribute(Qt::WA_DeleteOnClose); ArchivioAperto = true; textedit = new QCustomTextEdit; textedit->setStyleSheet("*{background-color:white; color:black;}"); QVBoxLayout *layout = new QVBoxLayout(ui->frame_3); layout->addWidget(textedit); layout->setSpacing(0); layout->setMargin(0); layout->setContentsMargins(0,0,0,0); ui->frame_3->setLayout(layout); connect(textedit, SIGNAL(editingFinished(QString)), this, SLOT(textedit_editingFinished(QString))); } void Archivio::on_PushButton_clicked() { qDebug() << "HERE4"; QFile note("C:/Progetti/QT_Project"+ "/Note.txt"); if(note.open(QIODevice::ReadOnly)) { qDebug() << "HERE5"; QByteArray baNote = note.readAll(); qDebug() << "HERE8"; textedit->setText(QString(baNote));//the program crashes here note.close(); qDebug() << "HERE6"; } else { } } void Archivio::textedit_editingFinished(QString message) { qDebug() << message; QFile o_filenote("C:/Progetti/QT_Project"+ "/Note.txt"); o_filenote.remove(); QFile n_filenote("C:/Progetti/QT_Project" + "/Note.txt"); if(n_filenote.open(QIODevice::WriteOnly)) { n_filenote.write(message.toLatin1()); n_filenote.close(); } }
I cannot understand how the textedit object can be 0x0 after I have created the Archivio class.
Have I made some mistake while creating the subclass?The interesting thing is that when I launch the debugger everything works fine, I have problems only if I don't launch the program from it.
Thanks in advance!
@davidesalvetti Hi,
I don't think the code you show which can cause a crash.
I have few remarks from your code:
Don't set a parent to a QWidget or a QLayout when you put them in another layouts.textedit = new QCustomTextEdit; QVBoxLayout *layout = new QVBoxLayout; ... layout->addWidget(textedit); //layout becomes the parent of textedit ui->frame_3->setLayout(layout); //frame_3 becomes the parent of layout
- You need to call QWidget::focusOutEvent() in focusOutEvent(), otherwise your textedit will never lose focus
void focusOutEvent(QFocusEvent *e) { QWidget::focusOutEvent(e); emit editingFinished(this->toPlainText()); }
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@davidesalvetti Hi,
I don't think the code you show which can cause a crash.
I have few remarks from your code:
Don't set a parent to a QWidget or a QLayout when you put them in another layouts.textedit = new QCustomTextEdit; QVBoxLayout *layout = new QVBoxLayout; ... layout->addWidget(textedit); //layout becomes the parent of textedit ui->frame_3->setLayout(layout); //frame_3 becomes the parent of layout
- You need to call QWidget::focusOutEvent() in focusOutEvent(), otherwise your textedit will never lose focus
void focusOutEvent(QFocusEvent *e) { QWidget::focusOutEvent(e); emit editingFinished(this->toPlainText()); }
@Gojir4 Thank you for your answer! I modify my code with your advice, but the problem is still there...
What should it be if not the 'textedit'? I mean, if I comment the line of 'textedit->setText()' everything works fine.
The lastqDebug
message is "HERE8".
Have you got any other idea?
I don't know why with the debugger engine evrything works, this is a strange thing, don't you think? -
@Gojir4 Thank you for your answer! I modify my code with your advice, but the problem is still there...
What should it be if not the 'textedit'? I mean, if I comment the line of 'textedit->setText()' everything works fine.
The lastqDebug
message is "HERE8".
Have you got any other idea?
I don't know why with the debugger engine evrything works, this is a strange thing, don't you think?@davidesalvetti said in Subclass of QTextEdit makes the program to crash:
textedit->setText()
Set a break point at this line and start debugging. If it stops at that line check the values of the variables, then execute the line and check what exactly is the crash (SIGSEGV, ...?). You can post the stacktrace after crash here.
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@Gojir4 Thank you for your answer! I modify my code with your advice, but the problem is still there...
What should it be if not the 'textedit'? I mean, if I comment the line of 'textedit->setText()' everything works fine.
The lastqDebug
message is "HERE8".
Have you got any other idea?
I don't know why with the debugger engine evrything works, this is a strange thing, don't you think?@Gojir4 said in Subclass of QTextEdit makes the program to crash:
QWidget::focusOutEvent(e);
I was wrong here, you have to call
QTextEdit::focusOutEvent(e);
, sorry@davidesalvetti Actually I have tested your QCustomTextEdit class and I don't have any crash with it, so, as @SGaist suggested, I think it's coming from somewhere else in your code too.
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@davidesalvetti said in Subclass of QTextEdit makes the program to crash:
textedit->setText()
Set a break point at this line and start debugging. If it stops at that line check the values of the variables, then execute the line and check what exactly is the crash (SIGSEGV, ...?). You can post the stacktrace after crash here.
@jsulm It would be the right solution if the crash would still remain also after starting the debugging.
When I use the debugging everything works fine, no crash. That's why I think it's some kind of optimization that is causing the problem. -
I think it's some kind of optimization that is causing the problem.
Don't blame the compiler, we all do and it's never its fault
ui->frame_3->setLayout(layout);
is useless. remove it- before
QVBoxLayout *layout = new QVBoxLayout(ui->frame_3);
addQ_ASSERT(!ui->frame_3->layout());
to make sure you don't have a layout already - after
qDebug() << "HERE8";
addif(!textedit) qDebug("textedit is NULL!");
- in the constructor add
connect(textedit,&QObject::destroyed,[](){qDebug("textedit was destroyed!");});
to check if it gets deleted
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I think it's some kind of optimization that is causing the problem.
Don't blame the compiler, we all do and it's never its fault
ui->frame_3->setLayout(layout);
is useless. remove it- before
QVBoxLayout *layout = new QVBoxLayout(ui->frame_3);
addQ_ASSERT(!ui->frame_3->layout());
to make sure you don't have a layout already - after
qDebug() << "HERE8";
addif(!textedit) qDebug("textedit is NULL!");
- in the constructor add
connect(textedit,&QObject::destroyed,[](){qDebug("textedit was destroyed!");});
to check if it gets deleted
@VRonin Thanks for your answer.
I updated my code with your changes, this is the debug output:HERE4 HERE5
and then the crash...I don't understand :/
It crashes every time I call the textedit object. After "HERE5" there is the code lineif(!textedit) qDebug() << "textedit is NULL!"; qDebug() << "HERE8" << textedit;
But these message are not shown in the application output.
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@VRonin Thanks for your answer.
I updated my code with your changes, this is the debug output:HERE4 HERE5
and then the crash...I don't understand :/
It crashes every time I call the textedit object. After "HERE5" there is the code lineif(!textedit) qDebug() << "textedit is NULL!"; qDebug() << "HERE8" << textedit;
But these message are not shown in the application output.
create your Pointer with a nullptr set
private: Ui::Archivio *ui; QCustomTextEdit *textedit = nullptr;
then it's created pointed to 0 and only changes when you
new
it, in case your function is called before the customTextEdit could be created. -
create your Pointer with a nullptr set
private: Ui::Archivio *ui; QCustomTextEdit *textedit = nullptr;
then it's created pointed to 0 and only changes when you
new
it, in case your function is called before the customTextEdit could be created.@J.Hilk Thanks for your answer. I tried but no changes, it's still crashing.
Anyway I don't know if this could be usefull but I've seen that sometimes it works right just for the first time I click the button, then I close the 'Archivio' and then I reopen it and clicking again on the button makes the crash.
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@J.Hilk Thanks for your answer. I tried but no changes, it's still crashing.
Anyway I don't know if this could be usefull but I've seen that sometimes it works right just for the first time I click the button, then I close the 'Archivio' and then I reopen it and clicking again on the button makes the crash.
@davidesalvetti
from the code example I can see that you have a ui-file for your class,why don't you Promote your CustomWidget in the Desginer and let Qt's internal manage the creation and destruction of the object?
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As an experiment you could also just try with a normal
QTextEdit
rather than aQCustomTextEdit
@VRonin I just tried it. Creating the QTextEdit object from the constructor doesn't make change to the behaviour of the program. Is it possible that the problem is in how I create and put into the layout the Object?
If I create the QTexteEdit from the layout it works perfectly.
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@davidesalvetti
from the code example I can see that you have a ui-file for your class,why don't you Promote your CustomWidget in the Desginer and let Qt's internal manage the creation and destruction of the object?
@J.Hilk That made the trick! I din't know about promoting custom widget, but it worked!
So there must be something wrong in the way I've put the object into the layout and into the frame.
If somebody knows what is the problem is welcome so that I can avoid it the next times.Anyway the topic is solved, thank you all.