Question

In my Qt application in the event handler for mouse press events I have such ugly code

void Render::Viewer::mousePressEvent(QMouseEvent* e)
{
  switch (e->button())
  {
  case Qt::LeftButton:
    switch (mode_)
    {
    case Render::Viewer::ModeView:
      switch (e->modifiers())
      {
      case Qt::NoModifier:
        ...
        break;
      ...
      default:
        break;
      }
      break;
    case Render::Viewer::ModeEdit:
      ...
      break;
    }
    break;
  case Qt::RightButton:
    ...
    break;
  }
}

Even without switching on mode_ variable the code looks terrible. =( Two many degrees of freedom: button type, modifiers, … Absolutely unreadable.

Is there any ways to overcome such a “heap of switches”?

Answer 1

It would be easier to read and maintain if you broke up tasks into their own functions:

void Render::Viewer::mousePressEvent(QMouseEvent* e) 
{ 
  switch (e->button()) 
  { 
  case Qt::LeftButton: 
    handleLeftButton(e);
    break;
  case Qt::RightButton: 
    handleRightButton(e);
    break; 
  } 
}

void Render::Viewer::handleLeftButton(QMouseEvent* e)
{
    switch (mode_) 
    { 
    case Render::Viewer::ModeView: 
      switch (e->modifiers()) 
      { 
      case Qt::NoModifier: 
        ... 
        break; 
      ... 
      default: 
        break; 
      } 
      break; 
    case Render::Viewer::ModeEdit: 
      ... 
      break; 
    } 
}

void Render::Viewer::handleRightButton(QMouseEvent* e)
{
  ...
}

Break it up into however many functions you need to make it readable.