Qt ItemDelegate with a tool button: can't click - qt

Question

I use a custom widget for an item delegate.
This widget is composed of a combobox and a tool button, see below for the source.
Now when I use this widget in an item delegate, pressing on the tool button has no effect if the combobox has not the focus.
For a demo, see this video: http://youtu.be/o5AgjC4cCqY
Any idea how to handle this?
Thanks a lot!
Source of the widget:
QgsFieldExpressionWidget::QgsFieldExpressionWidget( QWidget *parent )
: QWidget( parent )
{
QHBoxLayout* layout = new QHBoxLayout( this );
layout->setContentsMargins( 0, 0, 0, 0 );
mCombo = new QComboBox( this );
mCombo->setEditable( true );
mCombo->setSizePolicy( QSizePolicy::MinimumExpanding, QSizePolicy::Minimum );
mButton = new QToolButton( this );
mButton->setSizePolicy( QSizePolicy::Minimum, QSizePolicy::Minimum );
mButton->setIcon( QgsApplication::getThemeIcon( "/mIconExpressionEditorOpen.svg" ) );
layout->addWidget( mCombo );
layout->addWidget( mButton );
}
Source of the delegate:
QgsComposerColumnSourceDelegate::QgsComposerColumnSourceDelegate( QgsVectorLayer* vlayer, QObject* parent ) : QItemDelegate( parent ),
mVectorLayer( vlayer )
{
}
QWidget* QgsComposerColumnSourceDelegate::createEditor( QWidget* parent, const QStyleOptionViewItem& option, const QModelIndex& index ) const
{
Q_UNUSED( option );
Q_UNUSED( index );
QgsFieldExpressionWidget *fieldExpression = new QgsFieldExpressionWidget( parent );
fieldExpression->setLayer( mVectorLayer );
connect( fieldExpression, SIGNAL( fieldChanged( QString ) ), this, SLOT( commitAndCloseEditor() ) );
return fieldExpression;
}
void QgsComposerColumnSourceDelegate::setEditorData( QWidget* editor, const QModelIndex& index ) const
{
QString field = index.model()->data( index, Qt::EditRole ).toString();
//set the value for the field combobox
QgsFieldExpressionWidget *fieldExpression = static_cast<QgsFieldExpressionWidget*>( editor );
fieldExpression->setField( field );
}
void QgsComposerColumnSourceDelegate::setModelData( QWidget* editor, QAbstractItemModel* model, const QModelIndex& index ) const
{
QgsFieldExpressionWidget *fieldExpression = static_cast<QgsFieldExpressionWidget*>( editor );
QString field = fieldExpression->currentField();
model->setData( index, field, Qt::EditRole );
}
void QgsComposerColumnSourceDelegate::updateEditorGeometry( QWidget* editor, const QStyleOptionViewItem& option, const QModelIndex& index ) const
{
Q_UNUSED( index );
editor->setGeometry( option.rect );
}

Answer 1

Add the following line to your QgsFieldExpressionWidget constructor anywhere after the QComboBox is created:
setFocusProxy(mCombo);