CODEWITHSUNDEEP
c++qt
choosyg
choosyg

Reputation: 794

QDialog not positioned correctly

I have a problem with QDialog which is not displayed centered on the parent window. The following snippet explains it:

void MyWidget::showDialog() {
    QObject* p = parent();
    while (p!=0) {
        qDebug() << p;
        p = p->parent();
    }
    qDebug() << QApplication::activeWindow();

    MyClassDerivedFromQDialog dlg( this );
    if ( dlg.exec() != dlg.Accepted ) {
        return;
    }
    ... do something
}

The output on qDebug is the following

QSplitter(0x2d89930, name = "splitter") 
MyWidget(0x2d89670, name = "widget") 
MainWindow(0x27ef20, name = "application")
MainWindow(0x27ef20, name = "application")

Executing my example opens the dialog somewhere on the screen. Passing QApplication::activeWindow() as a parent to the dialogs constructor results in a dialog centered on the main window. So why is that and how to track down the problem?

Upvotes: 1

Views: 993

Answers (3)

Raphy
Raphy

Reputation: 21

I found that this behavior is related to the timing of the dialog creation. If you create a QDialog (or a derived class) before the dialog parent is shown (e.g., in the parent constructor), the dialog is displayed at a non-predictable location (or at least, not where you'd expect it to show). However, if the dialog is created after the parent is displayed, then you get the expected behavior. For example, if you have a button invoking your dialog. Both the button and the dialog are children of the same widget, so the dialog parent is the same as the button parent. In this case, it is advised to delay the dialog creation until the button is clicked, not before that. This way, you ensure the dialog is created only after the parent is shown.

Upvotes: 2

choosyg
choosyg

Reputation: 794

The Dialog class is instantiated via

MyClassDerivedFromQDialog::MyClassDerivedFromQDialog(QWidget *parent) 
: QDialog(parent), 
  ui(new Ui::MyClassDerivedFromQDialog) 
{ 
    ui->setupUi(this); 

    //remove the ? button in titlebar 
    Qt::WindowFlags flags = windowFlags(); 
    Qt::WindowFlags helpFlag = Qt::WindowContextHelpButtonHint; 
    flags = flags & (~helpFlag); 
    setWindowFlags(flags); 
}

And i always use it as in the showDialog function in the initial post. sometimes it works... And no, i do not have two MyWigets which are parents of each other.

Upvotes: 0

Silicomancer
Silicomancer

Reputation: 9156

I am not sure if understand your problem.

QDialogs are always centered on the widget you pass as parent. This is by design. So if you pass "activeWindow()" as parent it is centered on the active window. If you pass "this" as a parent the dialog is centered above MyWidget.

In which way does your dialog not respect these rules?

Upvotes: 0

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