C++ QGraphicsItem仅通过X轴移动对象
我无法仅通过x轴移动对象。我知道您需要使用函数C++ QGraphicsItem仅通过X轴移动对象,c++,qt,C++,Qt,我无法仅通过x轴移动对象。我知道您需要使用函数QVariant-itemChange(GraphicsItemChange-change,const-QVariant&value)来更改某些内容。我发现了这样的东西: QVariant CircleItem::itemChange(GraphicsItemChange change, const QVariant &value) { if (change == ItemPositionChange) ret
QVariant-itemChange(GraphicsItemChange-change,const-QVariant&value)
来更改某些内容。我发现了这样的东西:
QVariant CircleItem::itemChange(GraphicsItemChange change, const QVariant &value)
{
if (change == ItemPositionChange)
return QPointF(pos().x(), value.toPointF().y());
return QGraphicsItem::itemChange( change, value );
}
CircleItem::CircleItem() // where is parent parameter?
{
RectItem = new RoundRectItem();
MousePressed = false;
setFlag(ItemIsMovable | ItemSendsGeometryChanges);
}
但它不起作用。我是Qt新手,所以我不知道如何更改它。下面是我的GraphicsSitem的代码:
#include "circleitem.h"
CircleItem::CircleItem()
{
RectItem = new RoundRectItem();
MousePressed = false;
setFlag( ItemIsMovable );
}
void CircleItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
if( MousePressed )
{
painter->setBrush( QBrush( QColor( 0, 0, 255 ) ) );
painter->setPen( QPen( QColor( 0, 0, 255 ) ) );
}
else
{
painter->setBrush( QBrush( QColor( 255, 255, 255 ) ) );
painter->setPen( QPen( QColor( 255, 255, 255 ) ) );
}
painter->drawEllipse( boundingRect().center(), boundingRect().height() / 4 - 7, boundingRect().height() / 4 - 7 );
}
QRectF CircleItem::boundingRect() const
{
return RectItem->boundingRect();
}
void CircleItem::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
MousePressed = true;
update( QRectF().x(), boundingRect().y(), boundingRect().width(), boundingRect().height() );
QGraphicsItem::mousePressEvent( event );
}
void CircleItem::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
{
MousePressed = false;
update( QRectF().x(), boundingRect().y(), boundingRect().width(), boundingRect().height() );
QGraphicsItem::mouseReleaseEvent( event );
}
QVariant CircleItem::itemChange(GraphicsItemChange change, const QVariant &value)
{
if (change == ItemPositionChange)
return QPointF(pos().x(), value.toPointF().y());
return QGraphicsItem::itemChange( change, value );
}
感谢您的回答。请阅读的文档。它说:
项目的位置发生变化。如果
ItemSendsGeometryChanges标志已启用,并且当项目的本地
相对于其父级的位置变化(即,由于调用
setPos()或moveBy()。value参数是新位置(即a
QPointF)。您可以调用pos()来获取原始位置。不要打电话
itemChange()中的setPos()或moveBy()与此通知相同
交付;相反,您可以从返回新的调整位置
itemChange()。发出此通知后,QGraphicsItem会立即发送
如果位置更改,则ItemPositionHasChanged通知
在我们的代码中,我看不到您设置了itemssendsgeometrychanges
标志,因此请更正如下构造函数:
QVariant CircleItem::itemChange(GraphicsItemChange change, const QVariant &value)
{
if (change == ItemPositionChange)
return QPointF(pos().x(), value.toPointF().y());
return QGraphicsItem::itemChange( change, value );
}
CircleItem::CircleItem() // where is parent parameter?
{
RectItem = new RoundRectItem();
MousePressed = false;
setFlag(ItemIsMovable | ItemSendsGeometryChanges);
}
谢谢回答,它起作用了(只是我太头晕了)等一些问题在一段时间内回答:)