I copied qt designers' SheetDelegate class with some modification to show sheets like what's in designers' widgetbox. But the compiler says "StencilView.cpp:21: undefined reference to `SheetDelegate::SheetDelegate(QObject*)' ".

Modified SheetDelegate.h
Qt Code: 
  1. #ifndef SHEET_DELEGATE_H
  2. #define SHEET_DELEGATE_H
  3.  
  4. #include <QStyledItemDelegate>
  5.  
  6. class SheetDelegate: public QStyledItemDelegate
  7. {
  8.     Q_OBJECT
  9. public:
  10.     SheetDelegate(QObject *parent = 0);
  11.  
  12.     virtual void paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const;
  13.     virtual QSize sizeHint(const QStyleOptionViewItem &opt, const QModelIndex &index) const;
  14. };
  15.  
  16. #endif // SHEET_DELEGATE_H
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Modified SheetDelegate.cpp
Qt Code: 
  1. #include <QtGui/QStyle>
  2. #include <QtGui/QPainter>
  3.  
  4.  
  5. SheetDelegate::SheetDelegate(QObject *parent)
  6.     : QStyledItemDelegate(parent)
  7. {
  8. }
  9.  
  10. void SheetDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
  11. {
  12.     if (index.model()->parent(index).isValid()) {
  13.         // this is a top-level item.
  14.         QStyleOptionButton buttonOption;
  15.  
  16.         buttonOption.state = option.state;
  17. #ifdef Q_WS_MAC
  18.         buttonOption.state |= QStyle::State_Raised;
  19. #endif
  20.         buttonOption.state &= ~QStyle::State_HasFocus;
  21.  
  22.         buttonOption.rect = option.rect;
  23.         buttonOption.palette = option.palette;
  24.         buttonOption.features = QStyleOptionButton::None;
  25.         QStyle::drawControl(QStyle::CE_PushButton, &buttonOption, painter, parent);
  26.  
  27.         QStyleOption branchOption;
  28.         static const int i = 9; // ### hardcoded in qcommonstyle.cpp
  29.         QRect r = option.rect;
  30.         branchOption.rect = QRect(r.left() + i/2, r.top() + (r.height() - i)/2, i, i);
  31.         branchOption.palette = option.palette;
  32.         branchOption.state = QStyle::State_Children;
  33.  
  34.         if (parent->isExpanded(index))
  35.             branchOption.state |= QStyle::State_Open;
  36.  
  37.         QStyle::drawPrimitive(QStyle::PE_IndicatorBranch, &branchOption, painter, parent);
  38.  
  39.         // draw text
  40.         QRect textrect = QRect(r.left() + i*2, r.top(), r.width() - ((5*i)/2), r.height());
  41.         QString text = elidedText(option.fontMetrics, textrect.width(), Qt::ElideMiddle, 
  42.             index.model()->data(index, Qt::DisplayRole).toString());
  43.         QStyle::drawItemText(painter, textrect, Qt::AlignCenter,
  44.             option.palette, parent->isEnabled(), text);
  45.  
  46.     } else {
  47.         QStyledItemDelegate::paint(painter, option, index);
  48.     }
  49. }
  50.  
  51. QSize SheetDelegate::sizeHint(const QStyleOptionViewItem &opt, const QModelIndex &index) const
  52. {
  53.     QStyleOptionViewItem option = opt;
  54.     QSize sz = QStyledItemDelegate::sizeHint(opt, index) + QSize(2, 2);
  55.     return sz;
  56. }
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The StencilView class is defined as a QWidget class where shows the result.

StencilView.h
Qt Code: 
  1. #ifndef STENCILVIEW_H
  2. #define STENCILVIEW_H
  3.  
  4. #include "SheetDelegate.h"
  5.  
  6. #include <QWidget>
  7.  
  8. class StencilSelector;
  9. class QFileSystemModel;
  11. class QTreeView;
  12. class QLineEdit;
  14. class SheetDelegate;
  15. class StencilView : public QWidget
  16. {
  17.     Q_OBJECT
  18.  
  19. public:
  20.     StencilView(StencilSelector *parent);
  21.  
  22. private slots:
  23.     void reapplyFilter();
  24.  
  25. private:
  26.     QTreeView *treeView;
  27.     SheetDelegate *delegate;
  28.     QFileSystemModel *sourceModel;
  29.     QSortFilterProxyModel *proxyModel;
  30.     QLineEdit *filterLineEdit;
  31.     QPushButton *moreButton;
  32. };
  33.  
  34. #endif
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StencilView.cpp
Qt Code: 
  1. #include <QtGui>
  2.  
  3. #include "StencilView.h"
  4. #include "StencilSelector.h"
  5.  
  6. StencilView::StencilView(StencilSelector *parent): QWidget(parent)
  7. {
  8.     sourceModel = new QFileSystemModel;
  9.     sourceModel->setReadOnly(true);
  10.     sourceModel->setFilter(QDir::AllEntries);
  11.     //sourceModel->setNameFilters(QStringList::QStringList("*.odg"));
  12.     sourceModel->setNameFilterDisables(false);
  13.     sourceModel->setRootPath("/home/yue/stencils_test");
  14.     //QModelIndex index = sourceModel->rootPath();
  15.  
  16.     proxyModel = new QSortFilterProxyModel;
  17.     proxyModel->setSourceModel(sourceModel);
  18.     proxyModel->setFilterKeyColumn(-1);
  19.     proxyModel->setDynamicSortFilter(true);
  20.  
  21.     delegate = new SheetDelegate(this);
  22.     treeView = new QTreeView;
  23.     treeView->setModel(proxyModel);
  24.     treeView->setItemDelegate(delegate);
  25.     /*treeView->header()->setStretchLastSection(true);
  26.     treeView->header()->setSortIndicator(0, Qt::AscendingOrder);
  27.     treeView->header()->setSortIndicatorShown(true);
  28.     treeView->header()->setClickable(true);
  29.     */
  30.  
  31.     //treeView->setRootIndex(proxyModel->mapFromSource(index));
  32.  
  33.     filterLineEdit = new QLineEdit;
  34.  
  35.     connect(filterLineEdit, SIGNAL(textChanged(const QString &)),
  36.             this, SLOT(reapplyFilter()));
  37.  
  38.     moreButton = new QPushButton("...");
  39.     QVBoxLayout *mainLayout = new QVBoxLayout;
  40.     QHBoxLayout *interLayout = new QHBoxLayout;
  41.  
  42.     interLayout->addWidget(moreButton);
  43.     interLayout->addWidget(filterLineEdit);
  44.     mainLayout->addLayout(interLayout);
  45.     mainLayout->addWidget(treeView);
  46.     setLayout(mainLayout);
  47.     //filterLineEdit->setText(tr("<Filter>"));
  48.     //setWindowTitle(tr("Stencil View"));
  49. }
  50.  
  51. void StencilView::reapplyFilter()
  52. {
  53.     QRegExp regExp(filterLineEdit->text(), Qt::CaseInsensitive, QRegExp::RegExp);
  54.     proxyModel->setFilterRegExp(regExp);
  55. }
  56.  
  57. #include <StencilView.moc>
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Could anyone point out what's wrong there?