QScrollArea:由垂直滚动条引起的水平滚动条

我有一个简单的对话框,里面有一个QScrollArea:

// Vertical container for the dialog
QVBoxLayout *cont = new QVBoxLayout;
this->setLayout(cont); //"this" is my derived QDialog class

// ScrollArea for iconFrame
QScrollArea *scroll = new QScrollArea;
cont->insertWidget(0, scroll );

// The frame to be added to the QScrollArea
QFrame *iconFrame = new QFrame;
scroll->setWidget(iconFrame);
scroll->setWidgetResizable(true);

// Grid layout for iconFrame
QGridLayout *grid = new QGridLayout;
iconFrame->setLayout(grid);

// Second child widget for the dialog
QDialogButtonBox *buttonBox = new QDialogButtonBox(QDialogButtonBox::Ok|QDialogButtonBox::Cancel);
cont->insertWidget(1, buttonBox);

int maxcol = int(ceil(sqrt(numberOfButtons)));
if(maxcol > 6) maxcol = 6;
for(int i=0; i<numberOfButtons; i++)
{
    QPushButton *button= new QPushButton("My Button");
    button->setFixedSize(48, 48);

    int row = int(floor(i/maxcol));
    grid->addWidget(button, row, i-row*maxcol);
}

因为最多有6列,所以框架和对话框会垂直增长。

我尝试过sizePolicies和sizeconstraint的不同组合,但似乎没有任何效果。