How to set Font for widgets in the parent from a child widget

[ramsailesh]

Dear all,

I've a mainwindow M with some widgets L and a Custom-dropdown D which contains list of Fonts.
I need to set font for all the widgets in M if dropdown D is changed.
I tried to set the font which resulted in Segmentation fault.

void UpdateFont()
{
    QObject *obj = this->parent();
    QObjectList objlistChildren = obj->children();
    int iCount = objlistChildren.count();
 
    for(int iIndex = 0; iIndex < iCount; iIndex++)
    {
        QObject *temp = objlistChildren[iIndex];
        ( (QWidget*)objlistChildren[iIndex] )->setFont(font);
    }
}

void UpdateFont()
{
    QObject *obj = this->parent();
    QObjectList objlistChildren = obj->children();
    int iCount = objlistChildren.count();

    for(int iIndex = 0; iIndex < iCount; iIndex++)
    {
        QObject *temp = objlistChildren[iIndex];
        ( (QWidget*)objlistChildren[iIndex] )->setFont(font);
    }
}

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How can i access the parent widgets and set its font from the child control.

Thanks in advance for your suggestions.

[Lykurg]

Not tested, but shouldn't do QApplication::setFont() the trick?

EDIT: No, only changes the default font... sorry.

EDIT EDIT: Umpf... Yes it works!

[Santosh Reddy]

1. Emit a signal from the child widget (L) to indicate that font has changed, eg. emit fontChanged(font);
2. Connect this signal to the Mainwindow's (M) slot where you set the font, eg. M->setFont(font);

[ramsailesh]

Thanks Lykurg and SantoshReddy.

[ChrisW67]

Your segmentation faults come from assuming pointers are valid and point to things of certain types:

void Class::UpdateFont()
{
    QObject *obj = this->parent();  // this can be NULL
    QObjectList objlistChildren = obj->children();  // which will crash here
    int iCount = objlistChildren.count();
 
    for(int iIndex = 0; iIndex < iCount; iIndex++)
    {
        QObject *temp = objlistChildren[iIndex];
        ( (QWidget*)objlistChildren[iIndex] )->setFont(font); // what do you suppose happens if the child is not a QWidget?
    }
}

void Class::UpdateFont()
{
    QObject *obj = this->parent();  // this can be NULL
    QObjectList objlistChildren = obj->children();  // which will crash here
    int iCount = objlistChildren.count();

    for(int iIndex = 0; iIndex < iCount; iIndex++)
    {
        QObject *temp = objlistChildren[iIndex];
        ( (QWidget*)objlistChildren[iIndex] )->setFont(font); // what do you suppose happens if the child is not a QWidget?
    }
}

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You should get out of the habit of using C-style casts preferring C++-style casts of the correct type. Casts in general are last-resort mechanisms and worthy of avoidance. In this circumstance you could use qobject_cast and check the cast was successful.