QGraphicsView是QT支持的一套图元显示框架。最近在开发过程中发现一个问题，在QGraphicsView父类（QWidget）中重载mousePressEvent和 mouseMoveEvent事件，只能获取到mousePress事件，mouseMove事件不论如何都获取不到，测试代码如下，为了方便测试将布局的Margin设置成了20。发现在Margin区域所有鼠标事件是OK的，但是在QGraphicsView区域类，重载的两个事件只能获取到mousePress事件。
#include <QMouseEvent>
#include <QGraphicsView>
#include <QtWidgets>
GraphicsView::GraphicsView(QWidget *parent) : QWidget(parent)
{
this->setMouseTracking(true);
QGraphicsView* view = new QGraphicsView(this);
view->setBackgroundBrush(QBrush(Qt::gray));
view->setScene(new QGraphicsScene(view));
QVBoxLayout* layout = new QVBoxLayout(this);
layout->setMargin(20);
layout->addWidget(view);
}
void GraphicsView::mousePressEvent(QMouseEvent *event)
{
QWidget::mousePressEvent(event);
qDebug() << "MouseButtonPress";
}
void GraphicsView::mouseMoveEvent(QMouseEvent *event)
{
QWidget::mouseMoveEvent(event);
qDebug() <<" MouseMove ";
}
遇到这个问题，于是猜想是否是QGraphicsView截断了鼠标事件，于是给QGraphicsView这个类安装了一个事件过滤器，用来截取鼠标事件，代码如下，发现效果与上述一致，并没有我们想象中的效果。
#include <QDebug>
#include <QMouseEvent>
#include <QGraphicsView>
#include <QtWidgets>
GraphicsView::GraphicsView(QWidget *parent) : QWidget(parent)
{
this->setMouseTracking(true);
QGraphicsView* view = new QGraphicsView(this);
view->setBackgroundBrush(QBrush(Qt::gray));
view->setScene(new QGraphicsScene(view));
FilterObj* obj = new FilterObj(this);
view->installEventFilter(obj);
QVBoxLayout* layout = new QVBoxLayout(this);
layout->setMargin(20);
layout->addWidget(view);
}
bool FilterObj::eventFilter(QObject *obj, QEvent *event)
{
if(event->type() == QEvent::MouseButtonPress){
qDebug() << "MouseButtonPress";
}else if(event->type() == QEvent::MouseMove){
qDebug() <<" MouseMove ";
}else if(event->type() == QEvent::MouseButtonRelease){
qDebug() << "MouseButtonRelease";
}
return QObject::eventFilter(obj, event);
}
后查阅到https://zhuanlan.zhihu.com/p/31310711豁然开朗，原来鼠标事件是被QGraphicsView里面的viewport截取了，于是换最后一种实现方式问题解决，在viewport上安装一个事件过滤器，通过事件过滤来截取鼠标事件，实现鼠标事件的透传。
#include <QMouseEvent>
#include <QGraphicsView>
#include <QtWidgets>
GraphicsView::GraphicsView(QWidget *parent) : QWidget(parent)
{
this->setMouseTracking(true);
QGraphicsView* view = new QGraphicsView(this);
view->setBackgroundBrush(QBrush(Qt::gray));
view->setScene(new QGraphicsScene(view));
FilterObj* obj = new FilterObj(this);
view->setMouseTracking(true); //mouse move event occurred even if mouse is not pressed
view->viewport()->installEventFilter(obj);
QVBoxLayout* layout = new QVBoxLayout(this);
layout->setMargin(20);
layout->addWidget(view);
}
bool FilterObj::eventFilter(QObject *obj, QEvent *event)
{
if(event->type() == QEvent::MouseButtonPress){
qDebug() << "MouseButtonPress";
}else if(event->type() == QEvent::MouseMove){
qDebug() <<" MouseMove ";
}else if(event->type() == QEvent::MouseButtonRelease){
qDebug() << "MouseButtonRelease";
}
return QObject::eventFilter(obj, event);
}
from:https://blog.csdn.net/theoryll/article/details/110918779