Qt error: no matching function for call to ‘QDrag::QDrag(QWidget*)‘

原创已于 2025-03-29 17:00:52 修改 · 586 阅读

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于 2022-09-20 17:54:25 首次发布

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本文记录并解决了Qt应用程序中使用QDrag时出现的构造函数不匹配问题，涉及QWidget与QObject之间的转换。

今天遇到这样一个错误，记录一下。

..\QtDropGraphicsItem\graphicscoloritem.cpp: In member function 'virtual void GraphicsColorItem::mousePressEvent(QGraphicsSceneMouseEvent*)':
..\QtDropGraphicsItem\graphicscoloritem.cpp:39:67: warning: unused parameter 'event' [-Wunused-parameter]
 void GraphicsColorItem::mousePressEvent(QGraphicsSceneMouseEvent *event)
                                                                   ^~~~~
..\QtDropGraphicsItem\graphicscoloritem.cpp: In member function 'virtual void GraphicsColorItem::mouseMoveEvent(QGraphicsSceneMouseEvent*)':
..\QtDropGraphicsItem\graphicscoloritem.cpp:46:44: error: no matching function for call to 'QDrag::QDrag(QWidget*)'
     QDrag *drag = new QDrag(event->widget());
                                            ^
In file included from C:\Qt\Qt5.14.2\5.14.2\mingw73_64\include\QtGui/QDrag:1:0,
                 from ..\QtDropGraphicsItem\graphicscoloritem.cpp:5:
C:\Qt\Qt5.14.2\5.14.2\mingw73_64\include\QtGui/qdrag.h:62:14: note: candidate: QDrag::QDrag(QObject*)
     explicit QDrag(QObject *dragSource);
              ^~~~~
C:\Qt\Qt5.14.2\5.14.2\mingw73_64\include\QtGui/qdrag.h:62:14: note:   no known conversion for argument 1 from 'QWidget*' to 'QObject*'
..\QtDropGraphicsItem\graphicscoloritem.cpp: In member function 'virtual void GraphicsColorItem::mouseReleaseEvent(QGraphicsSceneMouseEvent*)':
..\QtDropGraphicsItem\graphicscoloritem.cpp:65:69: warning: unused parameter 'event' [-Wunused-parameter]
 void GraphicsColorItem::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
                                                                     ^~~~~
mingw32-make[1]: *** [Makefile.Release:438: release/graphicscoloritem.o] Error 1
mingw32-make[1]: Leaving directory 'D:/StudyCodeDemo/build-QtDropGraphicsItem-Desktop_Qt_5_14_2_MinGW_64_bit-Release'
mingw32-make: *** [Makefile:45: release] Error 2

error: no matching function for call to 'QDrag::QDrag(QWidget*)'
     QDrag *drag = new QDrag(event->widget());

总体分析，错误是在QDrap构造函数中没有匹配到QDrag(QWidget*)。

解决方法：

#include <QWidget>