1、事件传递顺序规则
在Qt中，事件传递的顺序事件首先传递到目标对象的事件过滤器，然后传递到事件处理函数，最后传递到父对象的事件过滤器和事件处理函数。
为了更好地理解这一过程，下面将通过一个示例来展示事件在父窗口和子窗口之间的传递顺序。
2、示例：父子窗口的事件传递
2.1 项目结构
myproject/
├── main.cpp
├── parentwidget.h
├── parentwidget.cpp
├── childwidget.h
└── childwidget.cpp
2.2 main.cpp
#include <QApplication>
#include "parentwidget.h"int main(int argc, char *argv[]) {QApplication app(argc, argv);ParentWidget parentWidget;parentWidget.setGeometry(100, 100, 400, 400);parentWidget.setStyleSheet("background-color: lightblue;");parentWidget.show();return app.exec();
}
2.3 parentwidget.h
#ifndef PARENTWIDGET_H
#define PARENTWIDGET_H#include <QWidget>
#include "childwidget.h"class ParentWidget : public QWidget {Q_OBJECT
public:ParentWidget();protected:bool eventFilter(QObject *obj, QEvent *event) override;void mousePressEvent(QMouseEvent *event) override;private:ChildWidget *childWidget;
};#endif // PARENTWIDGET_H
2.4 parentwidget.cpp
#include "parentwidget.h"
#include <QDebug>
#include <QEvent>ParentWidget::ParentWidget() {childWidget = new ChildWidget(this);childWidget->setGeometry(50, 50, 200, 200);childWidget->setStyleSheet("background-color: yellow;");// Only install event filter on itself, not on the child widgetthis->installEventFilter(this);
}bool ParentWidget::eventFilter(QObject *obj, QEvent *event) {if (event->type() == QEvent::MouseButtonPress) {if (obj == this) {qDebug() << "Mouse button press event filtered in ParentWidget";}}return QWidget::eventFilter(obj, event);
}void ParentWidget::mousePressEvent(QMouseEvent *event) {qDebug() << "Mouse press event in ParentWidget";QWidget::mousePressEvent(event);
}
2.5 childwidget.h
#ifndef CHILDWIDGET_H
#define CHILDWIDGET_H#include <QWidget>class ChildWidget : public QWidget {Q_OBJECT
public:ChildWidget(QWidget *parent = nullptr);protected:bool eventFilter(QObject *obj, QEvent *event) override;void mousePressEvent(QMouseEvent *event) override;
};#endif // CHILDWIDGET_H
2.6 childwidget.cpp
#include "childwidget.h"
#include <QDebug>
#include <QEvent>ChildWidget::ChildWidget(QWidget *parent) : QWidget(parent) {// Install event filter on itselfthis->installEventFilter(this);
}bool ChildWidget::eventFilter(QObject *obj, QEvent *event) {if (event->type() == QEvent::MouseButtonPress) {if (obj == this) {qDebug() << "Mouse button press event filtered in ChildWidget";}}return QWidget::eventFilter(obj, event);
}void ChildWidget::mousePressEvent(QMouseEvent *event) {qDebug() << "Mouse press event in ChildWidget";QWidget::mousePressEvent(event);
}
3、示例解释和运行结果
3.1 点击 ChildWidget 时
ChildWidget的事件过滤器首先捕捉到事件并打印Mouse button press event filtered in ChildWidget。- 然后，
ChildWidget的mousePressEvent捕捉到事件并打印Mouse press event in ChildWidget。 - 最后，如果事件未被完全处理，传递到父窗口
ParentWidget的事件过滤器，并打印Mouse button press event filtered in ParentWidget from ChildWidget。 - 然后，
ParentWidget的mousePressEvent捕捉到事件并打印Mouse press event in ParentWidget。
3.2 点击 ParentWidget 时
ParentWidget的事件过滤器首先捕捉到事件并打印Mouse button press event filtered in ParentWidget。- 然后，
ParentWidget的mousePressEvent捕捉到事件并打印Mouse press event in ParentWidget。
