这是我第一次尝试使用Qt的Drag& Drop功能。我是初学者,虽然我过去做过其他2个Qt课程,但本周我做了第一个子课程。
我需要一个可移动的Drag& Drop QGraphicsTextItem来显示连接到相应QGraphicScene的QGraphicsView。所以我可以检索该项目的新位置。
我查看了动画机器人示例和此链接:http://www.qtcentre.org/threads/50028-Drag-and-Drop-QGraphicsTextItem
上面链接的代码,看起来很好。所以我重新实现了它,但在构建时,编译器显示了所有类型的错误,我不知道如何克服。我不知道从哪里开始,也不知道哪一段代码不正确......
出现错误的示例:
error: no matching function for call to 'GraphicsTextItem::setCursor(Qt::CursorShape)'
setCursor(Qt::OpenHandCursor);
^
error: invalid use of incomplete type 'class QGraphicsSceneDragDropEvent'
if(event->mimeData()->hasText())
^
error: forward declaration of 'class QGraphicsSceneDragDropEvent'
class QGraphicsSceneDragDropEvent;
^
我会留下代码:
部首:
#ifndef GRAPHICSTEXTITEM_H
#define GRAPHICSTEXTITEM_H
#include <QGraphicsTextItem>
class GraphicsTextItem : public QGraphicsTextItem
{
Q_OBJECT
public:
GraphicsTextItem(QGraphicsItem *parent = 0);
protected:
void dragEnterEvent(QGraphicsSceneDragDropEvent *event);
void dragLeaveEvent(QGraphicsSceneDragDropEvent *event);
void dropEvent(QGraphicsSceneDragDropEvent *event);
void mousePressEvent(QGraphicsSceneMouseEvent *);
void mouseReleaseEvent(QGraphicsSceneMouseEvent *);
void mouseMoveEvent(QGraphicsSceneMouseEvent *event);
private:
bool dragOver;
};
//! [0]
#endif // GRAPHICSTEXTITEM_H
和实施:
#include <graphicstextitem.h>
#include <QDrag>
//#include <QGraphicsScene>
GraphicsTextItem::GraphicsTextItem(QGraphicsItem *parent)
:QGraphicsTextItem(parent)
{
//setFlag(QGraphicsItem::ItemIsSelectable);
setFlag(QGraphicsItem::ItemIsMovable);
setTextInteractionFlags(Qt::TextEditorInteraction);
setAcceptedMouseButtons(Qt::LeftButton);
setAcceptDrops(true);
setCursor(Qt::OpenHandCursor);
}
void GraphicsTextItem::dragEnterEvent(QGraphicsSceneDragDropEvent *event)
{
if(event->mimeData()->hasText())
{
event->setAccepted(true);
update();
dragOver = true;
}
else
event->setAccepted(false);
}
void GraphicsTextItem::dragLeaveEvent(QGraphicsSceneDragDropEvent *event)
{
Q_UNUSED(event);
dragOver = false;
update();
}
void GraphicsTextItem::dropEvent(QGraphicsSceneDragDropEvent *event)
{
event->setAccepted(true);
//qDebug() << "I dropped it";
dragOver = false;
update();
}
void GraphicsTextItem::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
Q_UNUSED(event);
setCursor(Qt::ClosedHandCursor);
}
void GraphicsTextItem::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
if (QLineF(event->screenPos(), event->buttonDownScreenPos(Qt::LeftButton)).length()
< QApplication::startDragDistance())
return;
QDrag *drag = new QDrag(event->widget());
QMimeData *mime = new QMimeData;
mime->setText(this->toPlainText());
drag->setMimeData(mime);
drag->exec();
setCursor(Qt::OpenHandCursor);
}
void GraphicsTextItem::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
{
Q_UNUSED(event);
setCursor(Qt::OpenHandCursor);
}
答案 0 :(得分:1)
错误消息告诉您代码中的某处有前向声明,但根据您目前所显示的代码,这是不正确的。
无论哪种方式,对于访问堆对象的成员,您需要的不仅仅是前向声明。你错过了这个包括:
#include <QGraphicsSceneDragDropEvent>