How can I resize QMessageBox? - c++

Question

I have a QMessageBox which I'd like it to be bigger. It's a simple QMessageBox with two standard buttons, Ok and Cancel. The problem is that it is very small for my application's purposes. Code shows like this:
QMessageBox msg;
msg.setText("Whatever");
msg.setStandardButtons(QMessageBox::Ok | QMessageBox::Cancel);
msg.setSizePolicy(QSizePolicy::Expanding,QSizePolicy::Expanding);
int ret = msg.exec();
switch (ret) {
case QMessageBox::Ok:
ui->textEdit->clear();
break;
case QMessageBox::Cancel:
break;}
I tried several ways to increase the size:
msg.setSizePolicy(QSizePolicy::Expanding,QSizePolicy::Expanding);
msg.setSizePolicy(QSizePolicy::Maximum,QSizePolicy::Maximum);
msg.setFixedHeight(600);
msg.setFixedWidth(600);
I even cleared and rebuilt, and it compiles everything but nothing take effect...
Do you have any idea on how to set QMessageBox size "by hand"? Thanks.

Answer 1

You can edit the css of the label:
msg.setStyleSheet("QLabel{min-width: 700px;}");
You can similarly edit the css of the buttons to add a margin or make them bigger.
For example:
msg.setStyleSheet("QLabel{min-width:500 px; font-size: 24px;} QPushButton{ width:250px; font-size: 18px; }");
There is also a trick mentioned:
QSpacerItem* horizontalSpacer = new QSpacerItem(800, 0, QSizePolicy::Minimum, QSizePolicy::Expanding);
QGridLayout* layout = (QGridLayout*)msg.layout();
layout->addItem(horizontalSpacer, layout->rowCount(), 0, 1, layout->columnCount());
But this doesn't seem to work for everyone.

Answer 2

coyotte508's answer caused my layout to be horribly off center and at different widths it was cut off. In searching around further I found this thread which explains a better solution.
In essence the layout of a messagebox is a grid, so you can add a SpacerItem to it to control the width. Here's the c++ code sample from that link:
QMessageBox msgBox;
QSpacerItem* horizontalSpacer = new QSpacerItem(500, 0, QSizePolicy::Minimum, QSizePolicy::Expanding);
msgBox.setText( "SomText" );
QGridLayout* layout = (QGridLayout*)msgBox.layout();
layout->addItem(horizontalSpacer, layout->rowCount(), 0, 1, layout->columnCount());
msgBox.exec();

Answer 3

You can subclass QMessageBox and reimplement resize event handler as following:
void MyMessageBox::resizeEvent(QResizeEvent *Event)
{
QMessageBox::resizeEvent(Event);
this->setFixedWidth(myFixedWidth);
this->setFixedHeight(myFixedHeight);
}

Answer 4

I wanted my QMessageBox width to adapt in proportion to the length of the text content with a certain amount of buffer to avoid line wrap. After surveying numerous forums and threads including this one, I came up with:
int x_offset = (2.0 * MainWindow::geometry().x());
int y_offset = (0.5 * MainWindow::geometry().y());
msgBox.setText(vers_msg.data());
QSpacerItem* horizontalSpacer = new QSpacerItem
(8 * vers_msg.size(), 0,
QSizePolicy::Minimum, QSizePolicy::Expanding);
QGridLayout* layout = (QGridLayout*)msgBox.layout();
layout->addItem(horizontalSpacer, layout->rowCount(),
0, 1, layout->columnCount());
msgBox.setGeometry(
MainWindow::geometry().x() + x_offset,
MainWindow::geometry().y() + y_offset,
msgBox.geometry().width(),
msgBox.geometry().height());
Adjust the hard numbers in x_offset, y_offset and horizontalSpacer to suit your situation. I was hoping it would be easier than this but at least this works.

Answer 5

Inspired by the "inspect the Qt source code and adapt" approach, this worked for me with Qt 5.12:
if (auto grid = dynamic_cast<QGridLayout*>(msgBox.layout())) {
if (auto text = grid->itemAtPosition(0, grid->columnCount() - 1); text && text->widget()) {
text->widget()->setFixedWidth(500);
}
}
Keep in mind, of course, that this will break if ever they change the way they do layouts of QMessageBox.