如果无法继承QSlider，如何在滑块上添加刻度线 [英] How to add a tick mark to a slider if it cannot inherit QSlider

问题描述

我有一个Qt对话框，其中有一个滑块，初始化对话框时，滑块将被设置一个值.为了提醒用户默认值，我想在滑块上添加一个标记，只需在手柄上方绘制一条线或一个三角形即可.在这里，滑块应为QSlider类型，这意味着我无法实现从QSlider派生的自定义控件.有什么办法可以实现吗?

I have a Qt dialog and there is a slider in it, when the dialog is initialized the slider will be set a value. In order to remind the user what is the default value, I want to add a mark to the slider, just draw a line or a triangle above the handle. Here, the slider should be of QSlider type, that means I can't implement a customized control derived from QSlider. Is there any way to realize it ?

推荐答案

我不清楚您为什么不能从QSlider派生控件.您仍然可以将其视为QSlider，只需重写paintEvent方法即可.从视觉上来说，下面的示例很俗气，但是您可以使用QStyle中的方法使其看起来更自然:

I'm not clear why you can't derive a control from QSlider. You can still treat it like a QSlider, just override the paintEvent method. The example below is pretty cheesy, visually speaking, but you could use the methods from QStyle to make it look more natural:

#include <QtGui>

class DefaultValueSlider : public QSlider {
  Q_OBJECT

 public:
  DefaultValueSlider(Qt::Orientation orientation, QWidget *parent = NULL)
    : QSlider(orientation, parent),
      default_value_(-1) {
    connect(this, SIGNAL(valueChanged(int)), SLOT(VerifyDefaultValue(int)));
  }

 protected:
  void paintEvent(QPaintEvent *ev) {
    int position = QStyle::sliderPositionFromValue(minimum(),
                                                   maximum(),
                                                   default_value_,
                                                   width());
    QPainter painter(this);
    painter.drawLine(position, 0, position, height());
    QSlider::paintEvent(ev);
  }

 private slots:
  void VerifyDefaultValue(int value){
    if (default_value_ == -1) {
      default_value_ = value;
      update();
    }
  }

 private:
  int default_value_;
};

int main(int argc, char *argv[]) {
  QApplication app(argc, argv);

  DefaultValueSlider *slider = new DefaultValueSlider(Qt::Horizontal);
  slider->setValue(30);

  QWidget *w = new QWidget;
  QVBoxLayout *layout = new QVBoxLayout;
  layout->addWidget(slider);
  layout->addStretch(1);
  w->setLayout(layout);

  QMainWindow window;
  window.setCentralWidget(w);
  window.show();

  return app.exec();
}

#include "main.moc"

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