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Thread: How to execute a qDialog without passing a parent

  1. #1
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    Default How to execute a qDialog without passing a parent

    Good morning,
    I have to show a qDialog from a class inherited from QObject so I can not pass a parent.
    How can do in this case?

    Regards,

    Franco
    Franco Amato

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    Default Re: How to execute a qDialog without passing a parent

    Pass null as the parent.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


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    Default Re: How to execute a qDialog without passing a parent

    Hi Wysota,
    thank you. Yes I tried to pass null but I got a crash.
    I paste come source code here.

    The header file of dialog:
    Qt Code:
    1. #ifndef PREFERENCESDIALOG_H
    2. #define PREFERENCESDIALOG_H
    3.  
    4. #include "ui_PreferencesDialog.h"
    5.  
    6. class PreferencesDialog : public QDialog, private Ui::PreferencesDialog
    7. {
    8. Q_OBJECT
    9.  
    10. public:
    11. int exec();
    12.  
    13. public:
    14. explicit PreferencesDialog(QWidget* parent = 0);
    15.  
    16. private slots:
    17. void restoreState();
    18. void saveState();
    19. };
    20.  
    21. #endif // PREFERENCESDIALOG_H
    To copy to clipboard, switch view to plain text mode 

    The ctor of the dialog
    Qt Code:
    1. PreferencesDialog::PreferencesDialog(QWidget* parent) : QDialog(parent)
    2. {
    3. setupUi(this);
    4.  
    5. setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
    6.  
    7. QPushButton* resetButton = buttonBox->button(QDialogButtonBox::Reset);
    8. connect(resetButton, SIGNAL(clicked()), SLOT(restoreState()));
    9.  
    10. databasePortEdit->setValidator(new QIntValidator(1024, 65536, this));
    11.  
    12. QSize sizeHint = this->sizeHint();
    13. sizeHint.setWidth(350);
    14. setMinimumSize(sizeHint);
    15. setMaximumSize(sizeHint);
    16. }
    To copy to clipboard, switch view to plain text mode 

    Here I construct the dialog:
    Qt Code:
    1. EyeIdServer::EyeIdServer(QObject* parent) : QObject(parent)
    2. {
    3. ...code..
    4. // Initialize dialogs
    5.  
    6. m_preferencesDialog = new PreferencesDialog(0);
    7. ...more code..
    8. }
    To copy to clipboard, switch view to plain text mode 

    and from this routine I execute it
    Qt Code:
    1. void EyeIdServer::showPreferencesDialog()
    2. {
    3. m_preferencesDialog->exec();
    4. }
    To copy to clipboard, switch view to plain text mode 

    Do you have any idea on why I get the crash?
    I think is because I use the "this" pointer inside the dialog

    Regards
    Last edited by franco.amato; 29th September 2014 at 01:23.
    Franco Amato

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    Default Re: How to execute a qDialog without passing a parent

    It is not because you use "this", that is perfectly fine. Do you by any chance use threads in your application?
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


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    Default Re: How to execute a qDialog without passing a parent

    Quote Originally Posted by franco.amato View Post
    Hi Wysota,
    thank you. Yes I tried to pass null but I got a crash.
    Unrelated. The parent argument of QDialog even defaults to 0.

    Quote Originally Posted by franco.amato View Post
    Do you have any idea on why I get the crash?
    No, but the backtrace would have given at least some hints.

    Quote Originally Posted by franco.amato View Post
    I think is because I use the "this" pointer inside the dialog
    No, this is always valid within a class' instance.

    Btw, what's your reason for overwriting exec()?

    Cheers,
    _

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    Default Re: How to execute a qDialog without passing a parent

    What error are you getting on crash ?
    Also whats the code in restoreState() ? You are running m_preferencesDialog->exec(); and performing something in restoreState..
    May be thats causing crash...

    You could also simply check the value of m_preferencesDialog->exec() and perform necessary action.

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    Default Re: How to execute a qDialog without passing a parent

    Thank you very much to all

    This is the restoreState code

    Qt Code:
    1. void PreferencesDialog::restoreState()
    2. {
    3. // Restore database settings
    4.  
    5. databaseHostEdit->setText(preferences->databaseHost());
    6. databasePortEdit->setText(QString::number(preferences->databasePort()));
    7. databaseUsernameEdit->setText(preferences->databaseUsername());
    8. databasePasswordEdit->setText(preferences->databasePassword());
    9. databaseNameEdit->setText(preferences->databaseName());
    10. }
    To copy to clipboard, switch view to plain text mode 

    Best
    Franco Amato

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    Default Re: How to execute a qDialog without passing a parent

    What are buttonBox, databasePortEdit etc. and where are these pointers declared and initialised?

    Edit: Ignore that... I just noticed you are inheriting the UI object.

    However, your code will crash if the button box does not contain a standard ResetButton.
    Last edited by ChrisW67; 30th September 2014 at 21:28. Reason: updated contents

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