点击QSlider直接跳转

Question

默认情况下，QSlider通过鼠标单击singleStep()支柱的值移动他的大拇指轨迹。要使拇指轨迹直接跳转到鼠标单击点，我们需要创建一个由QSlider继承的新类。

头文件(.h)：

#include <QWidget>
#include <QAbstractSlider>
#include <QSlider>
#include <QMouseEvent>
#include <QStyle>
#include <QStyleOptionSlider>
#ifndef QIMPROVEDSLIDER_H
#define QIMPROVEDSLIDER_H

class QImprovedSlider : public QSlider
{
    Q_OBJECT
protected:
    void mousePressEvent(QMouseEvent *event);

public:
    explicit QImprovedSlider(QWidget *parent = 0);

    ~QImprovedSlider();

public slots:

private:

private slots:

signals:
    void onClick(int value);
};

#endif // QIMPROVEDSLIDER_H

源文件(.cpp)：

#include "QImprovedSlider.h"


QImprovedSlider::QImprovedSlider(QWidget *parent) :
    QSlider(parent)
{

}

QImprovedSlider::~QImprovedSlider()
{
}

void QImprovedSlider::mousePressEvent(QMouseEvent *event) {
  QStyleOptionSlider opt;
  initStyleOption(&opt);
  QRect sr = style()->subControlRect(QStyle::CC_Slider, &opt, QStyle::SC_SliderHandle, this);

  if (event->button() == Qt::LeftButton &&
      !sr.contains(event->pos())) {
    int newVal;
    if (orientation() == Qt::Vertical) {
       double halfHandleHeight = (0.5 * sr.height()) + 0.5;
       int adaptedPosY = height() - event->y();
       if ( adaptedPosY < halfHandleHeight )
             adaptedPosY = halfHandleHeight;
       if ( adaptedPosY > height() - halfHandleHeight )
             adaptedPosY = height() - halfHandleHeight;
       double newHeight = (height() - halfHandleHeight) - halfHandleHeight;
       double normalizedPosition = (adaptedPosY - halfHandleHeight)  / newHeight ;

       newVal = minimum() + (maximum()-minimum()) * normalizedPosition;
    } else {
        double halfHandleWidth = (0.5 * sr.width()) + 0.5;
        int adaptedPosX = event->x();
        if ( adaptedPosX < halfHandleWidth )
              adaptedPosX = halfHandleWidth;
        if ( adaptedPosX > width() - halfHandleWidth )
              adaptedPosX = width() - halfHandleWidth;
        double newWidth = (width() - halfHandleWidth) - halfHandleWidth;
        double normalizedPosition = (adaptedPosX - halfHandleWidth)  / newWidth ;

        newVal = minimum() + ((maximum()-minimum()) * normalizedPosition);
    }

    if (invertedAppearance())
        this->setValue( maximum() - newVal );
    else
        this->setValue(newVal);

    event->accept();
  }
  else {
        QSlider::mousePressEvent(event);
  }
  emit onClick(this->value());
}

这段代码运行良好，所以不是坏代码。有什么办法可以改善这一点吗？也许是为了区分直接跳转和手柄拖动。

Answer 1

我看到的一个问题是，这与功能有关:因为您使用的是双值，但是您的结束值是整数，也许您应该舍入结果。

当您将鼠标放在末尾时，上面的代码将在结束前一步设置句柄。

若要修复，请绕过新位置:替换

newVal = minimum() + ((maximum()-minimum()) * normalizedPosition);

使用

newVal = minimum() + qRound((maximum()-minimum()) * normalizedPosition);

Answer 2

if (invertedAppearance()) {
        this->setValue( maximum() - newVal ); 
} else {
        this->setValue(newVal);
}

您不应该在没有Curly的情况下发布if/else语句。这种风格为您打开了大量的bug，而事后的想法是:让您或其他开发人员添加到这段代码中很麻烦。

例如，假设您正在编辑或调试代码，并决定注释掉一行：

if (invertedAppearance())
    this->setValue( maximum() - newVal );
else
    // this->setValue(newVal); 

event->accept();

你看到问题了吗？