c++ - Set QLineEdit focus in Qt

Question

I am having a qt question. I want the QLineEdit widget to have the focus at application startup. Take the following code for example:

#include <QtGui/QApplication>
#include <QtGui/QHBoxLayout>
#include <QtGui/QPushButton>
#include <QtGui/QLineEdit>
#include <QtGui/QFont>


 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);

     QWidget *window = new QWidget();
     window->setWindowIcon(QIcon("qtest16.ico"));
     window->setWindowTitle("QtTest");

     QHBoxLayout *layout = new QHBoxLayout(window);

     // Add some widgets.
     QLineEdit *line = new QLineEdit();

     QPushButton *hello = new QPushButton(window);
     hello->setText("Select all");
     hello->resize(150, 25);
     hello->setFont(QFont("Droid Sans Mono", 12, QFont::Normal));

     // Add the widgets to the layout.
     layout->addWidget(line);
     layout->addWidget(hello);

     line->setFocus();

     QObject::connect(hello, SIGNAL(clicked()), line, SLOT(selectAll()));
     QObject::connect(line, SIGNAL(returnPressed()), line, SLOT(selectAll()));

     window->show();
     return app.exec();
 }

Why does line->setFocus() sets the focus on the line widget @app startup only if it is placed after laying out the widgets and if used before it's not working?

Answer 1

Another trick that might work is by using the singleshot timer:

QTimer::singleShot(0, line, SLOT(setFocus()));

Effectively, this invokes the setFocus() slot of the QLineEdit instance right after the event system is "free" to do so, i.e. sometime after the widget is completely constructed.