C++ QWidget keyPressEvent 覆盖

QWidget keyPressEvent override

提问by Erik Aigner

I'm trying for half an eternity now overriding QWidgets keyPressEvent function in QT but it just won't work. I've to say i am new to CPP, but I know ObjC and standard C.

我现在正在尝试覆盖 QT 中的 QWidgets keyPressEvent 函数，但它不起作用。我不得不说我是 CPP 的新手，但我知道 ObjC 和标准 C。

My problem looks like this:

我的问题是这样的：

class QSGameBoard : public QWidget {
Q_OBJECT

public:
  QSGameBoard(QWidget *p, int w, int h, QGraphicsScene *s);

signals:
  void keyCaught(QKeyEvent *e);

protected:
  virtual void  keyPressEvent(QKeyEvent *event);
};

QSGameBoard is my QWidget subclass and i need to override the keyPressEvent and fire a SIGNAL on each event to notify some registered objects.

QSGameBoard 是我的 QWidget 子类，我需要覆盖 keyPressEvent 并在每个事件上触发 SIGNAL 以通知一些已注册的对象。

My overridden keyPressEvent in QSGameBoard.cpp looks like this:

我在 QSGameBoard.cpp 中重写的 keyPressEvent 如下所示：

void QSGameBoard::keyPressEvent(QKeyEvent *event) {
  printf("\nkey event in board: %i", event->key());
  //emit keyCaught(event);
}

When i change QSGameBoard:: to QWidget:: it receives the events, but i cant emit the signal because the compiler complains about the scope. And if i write it like this the function doesn't get called at all.

当我将 QSGameBoard:: 更改为 QWidget:: 时，它会接收事件，但我无法发出信号，因为编译器会抱怨范围。如果我这样写，该函数根本不会被调用。

What's the problem here?

这里有什么问题？

采纳答案by Gayan

EDIT: As pointed out by other users, the method I outlined originally is not the proper way to resolve this. Answer by Vasco Rinaldo

编辑：正如其他用户所指出的，我最初概述的方法不是解决这个问题的正确方法。瓦斯科·里纳尔多的回答

Use Set the FocusPolicy to Qt::ClickFocus to get the keybordfocus by mouse klick. setFocusPolicy(Qt::ClickFocus);

使用 Set the FocusPolicy to Qt::ClickFocus 以通过鼠标点击获取 keybordfocus。setFocusPolicy(Qt::ClickFocus);

The previous (albeit imperfect) solution I gave is given below:

我给出的先前（尽管不完美）的解决方案如下：

Looks like your widget is not getting "focus". Override your mouse press event:

看起来您的小部件没有获得“焦点”。覆盖您的鼠标按下事件：

void QSGameBoard::mousePressEvent ( QMouseEvent * event ){
    printf("\nMouse in board");
    setFocus();
}

Here's the source code for a working example:

这是一个工作示例的源代码：

QSGameBoard.h

QSGameBoard.h

#ifndef _QSGAMEBOARD_H
#define _QSGAMEBOARD_H

#include <QWidget>
#include <QGraphicsScene>

class QSGameBoard : public QWidget {
Q_OBJECT

public:
  QSGameBoard(QWidget *p, int w, int h, QGraphicsScene *s);

signals:
  void keyCaught(QKeyEvent *e);

protected:
  virtual void  keyPressEvent(QKeyEvent *event);
  void  mousePressEvent ( QMouseEvent * event );
};


#endif  /* _QSGAMEBOARD_H */

QSGameBoard.cpp

QSGameBoard.cpp

#include <QKeyEvent>
#include <QLabel>
#include <QtGui/qgridlayout.h>
#include <QGridLayout>

#include "QSGameBoard.h"


QSGameBoard::QSGameBoard(QWidget* p, int w, int h, QGraphicsScene* s) :
    QWidget(p){

    QLabel* o = new QLabel(tr("Test Test Test"));
    QGridLayout* g  = new QGridLayout(this);
    g->addWidget(o);
}

void QSGameBoard::keyPressEvent(QKeyEvent* event){
    printf("\nkey event in board: %i", event->key());
}

void QSGameBoard::mousePressEvent ( QMouseEvent * event ){
    printf("\nMouse in board");
    setFocus();
}

main.cpp

主程序

#include <QtGui/QApplication>
#include <QtGui/qmainwindow.h>

#include "QSGameBoard.h"

int main(int argc, char *argv[]) {
    // initialize resources, if needed
    // Q_INIT_RESOURCE(resfile);

    QApplication app(argc, argv);

    QMainWindow oM;
    QGraphicsScene o;
    QSGameBoard a(&oM, 1, 2, &o);
    oM.setCentralWidget(&a);
    a.show();
    oM.show();

    // create and show your widgets here

    return app.exec();
}

回答by squid

You don't have to reimplement mousePressEventyourself just to call setFocus. Qt planed it already.

您不必为了调用setFocus 而自己重新实现mousePressEvent。Qt 已经计划好了。

Set the FocusPolicyto Qt::ClickFocusto get the keybordfocus by mouse klick.

设置FocusPolicy以Qt::ClickFocus获得通过鼠标克利克的keybordfocus。

setFocusPolicy(Qt::ClickFocus);

setFocusPolicy(Qt::ClickFocus);

As said in the manual:

正如手册中所说：

This property holds the way the widget accepts keyboard focus.

The policy is Qt::TabFocus if the widget accepts keyboard focus by tabbing, Qt::ClickFocus if the widget accepts focus by clicking, Qt::StrongFocus if it accepts both, and Qt::NoFocus (the default) if it does not accept focus at all.

You must enable keyboard focus for a widget if it processes keyboard events. This is normally done from the widget's constructor. For instance, the QLineEdit constructor calls setFocusPolicy(Qt::StrongFocus).

If the widget has a focus proxy, then the focus policy will be propagated to it.

此属性保存小部件接受键盘焦点的方式。

策略是 Qt::TabFocus 如果小部件通过 Tab 键接受键盘焦点，Qt::ClickFocus 如果小部件通过点击接受焦点，Qt::StrongFocus 如果它同时接受，Qt::NoFocus（默认）如果它不接受完全接受焦点。

如果小部件处理键盘事件，则必须为小部件启用键盘焦点。这通常是通过小部件的构造函数完成的。例如，QLineEdit 构造函数调用 setFocusPolicy(Qt::StrongFocus)。

如果小部件具有焦点代理，则焦点策略将传播到它。

回答by Vasco Rinaldo

Set the FocusPolicy to Qt::ClickFocus to get the keybordfocus by mouse klick. setFocusPolicy(Qt::ClickFocus);

将 FocusPolicy 设置为 Qt::ClickFocus 以通过鼠标点击获取 keybordfocus。setFocusPolicy(Qt::ClickFocus);