Qt 调用更新 (QRegion&) 不触发对 paintEvent(..) 的调用

Question

我在玩Qt教程中的一些代码，我被卡住了，因为我的一个QWidget继承类调用update(QRegion&(，但它不会触发对paintEvent(..(的调用-本质上，我正试图对教程源代码进行简单的重构，以使用Qt教程第12章中的CannonShot类添加多个镜头(请参阅链接：http://doc.trolltech.com/4.3/tutorial-t12.html)

CannonField update((仍然正常工作，并导致调用其paintEvent重新实现。它的唯一CannonShot的update((不调用自己的paintEvent。(我已经确认，它确实会在更新电话之前和之后出现(。以下是一些片段：

class CannonShot : public QWidget
{
   Q_OBJECT
public:
   CannonShot(QWidget *parent = 0);
   int angle() const { return shotAngle; }
   int force() const { return shotForce; }
   void shoot();
private slots:
   void moveShot();
   void plotShot();
signals:
   void hit();
   void missed();
   void angleChanged(int);
   void forceChanged(int);
...
...
protected:
   paintEvent(QPaintEvent*);
private:
   int shotTimerCount;
   QTimer* autoShotTimer;
   float shotAngle;
   float shotForce;
};

以下是CannonShot构造函数的一个片段，以及它的update((的调用位置：

CannonShot::CannonShot(QWidget *parent): QWidget(parent)
{
   shotTimerCount = 0;
   autoShotTimer = new QTimer(this);
   connect(autoShotTimer, SIGNAL(timeout()), this, SLOT(moveShot()));
}
void CannonShot::shoot()
{
   if (autoShotTimer->isActive())
   return;
   shotTimerCount = 0;
   shotAngle = CannonField::angle();
   shotForce = CannonField::force();
   autoShotTimer->start(5);
}
void CannonShot::moveShot()
{
   QRegion region = shotRect();
   ++shotTimerCount;
   QRect shotR = shotRect();
   if (shotR.x() > width() || shotR.y() > height()) {
      autoShotTimer->stop();
      emit missed();
   }
   else {
      region = region.unite(shotR);
   }
   update(region); //-Checked that code reaches before and after this call!
}
void CannonShot::paintEvent(QPaintEvent*)
{
   //-Never gets here!!
   QPainter painter(this);
   QColor color;
   //-Do whatever
}

这里还有一个CannonField的简短片段，其中包含射击并调用shoot((来发射它们。

class CannonField : public QWidget
{
   Q_OBJECT
public:
   CannonField(QWidget *parent = 0);
   ~CannonField();
   static int angle() { return currentAngle; }
   static int force() { return currentForce; }
public slots:
   void setAngle(int angle);
   void setForce(int force);
   void shoot();
signals:
   void hit();
   void missed();
...
...
protected:
   void paintEvent(QPaintEvent *event);
public:
   static int currentAngle;
   static int currentForce;
private:
   QVector<CannonShot*> shots;
};

这里有一段CannonField的射击来源。

void CannonField::shoot()
{
   //-Added this argument since I though after searching that CannonShot 
   // needs to have a QWidget with some dimensions..
   shots.push_back(new CannonShot(this));
   (shots.back())->shoot();
}

最后，驾驶员看起来像：

class MyWidget : public QWidget {
public:
   MyWidget(QWidget *parent = 0);
};
MyWidget::MyWidget(QWidget *parent): QWidget(parent)
{
   QPushButton *quit = new QPushButton(tr("&Quit"));
   quit->setFont(QFont("Times", 18, QFont::Bold));
   connect(quit, SIGNAL(clicked()), qApp, SLOT(quit()));
   LCDRange *angle = new LCDRange(tr("&ANGLE"));
   angle->setRange(0, 90);
   LCDRange *force = new LCDRange(tr("&FORCE"));
   force->setRange(10, 50);
   CannonField *cannonField = new CannonField(this);
   connect(angle, SIGNAL(valueChanged(int)),
          cannonField, SLOT(setAngle(int)));
   connect(cannonField, SIGNAL(angleChanged(int)),
          angle, SLOT(setValue(int)));
   connect(force, SIGNAL(valueChanged(int)),
          cannonField, SLOT(setForce(int)));
   connect(cannonField, SIGNAL(forceChanged(int)),
          force, SLOT(setValue(int)));
   QPushButton *shoot = new QPushButton(tr("&Shoot"));
   shoot->setFont(QFont("Times", 18, QFont::Bold));
   connect(shoot, SIGNAL(clicked()), cannonField, SLOT(shoot()));      
   ...
   ...
   //-Other layout stuff
}
int main(int argc, char *argv[])
{
   QApplication app(argc, argv);
   MyWidget widget;
   widget.setMinimumSize(300, 300);
   widget.setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
   widget.setGeometry(100, 100, 500, 355);
   widget.show();
   return app.exec();
}

Answer 1

如果QRegion:：isEmpty((为true，则不会调用QWidget:：paintEvent((。我怀疑这可能发生在你身上。

Answer 2

paintEvent(QPaintEvent*)函数应在protected部分，函数签名为：

void QWidget::paintEvent ( QPaintEvent * event )   [virtual protected]

目前您有：

private:
paintEvent(QPaintEvent*);

应该是：

protected:
virtual void paintEvent(QPaintEvent*);

相反。

Answer 3

如果更新区域与帧区域不相交，则可能发生这种情况：

QRect frameRect = this->rect();
if( frameRect.intersected(updateRec).isEmpty())
{
}