how to judge which child send the eventScrollChangePosition

I know there are five children in the scrollbar.

Button* mWidgetStart;
Button* mWidgetEnd;
Button* mWidgetTrack;
// куски между кнопками
Widget* mWidgetFirstPart;
Widget* mWidgetSecondPart;



I have make the scrollbar's event(eventScrollChangePosition) true.But I don't know which child send the event.
the following is my event hand function:

void BBBPopMenu::scrollChangePosition( MyGUI::ScrollBar* _sender, size_t _position )
{

MYGUI_LOG(Info, " _position = " << _position<<"name : "<< _sender->getName());

}


Now, how to judget that which children sent the event really when I go to "scrollChangePosition" function.

Child do not send event, it is scrollBar itself, who send event and it is stored in _sender, while _position is new scroll bar position, that can be changes using those buttons or by mouse drag.

But in the source code of ScrollBar, the event is sent by the children.
in fact, the event is sent by the chlidren.

the part of the source in MyGUI_ScrollBar.cpp
========================================================================================================

void ScrollBar::initialiseOverride()
{
Base::initialiseOverride();

// при нуле, будет игнорировать кнопки
mScrollPage = 1;
mScrollViewPage = 1;
mMinTrackSize = 0;
mSkinRangeStart = 0;
mSkinRangeEnd = 0;

assignWidget(mWidgetStart, "Start");
if (mWidgetStart != nullptr)
{
mWidgetStart->eventMouseButtonPressed += newDelegate(this, &ScrollBar::notifyMousePressed);
mWidgetStart->eventMouseWheel += newDelegate(this, &ScrollBar::notifyMouseWheel);
}

assignWidget(mWidgetEnd, "End");
if (mWidgetEnd != nullptr)
{
mWidgetEnd->eventMouseButtonPressed += newDelegate(this, &ScrollBar::notifyMousePressed);
mWidgetEnd->eventMouseWheel += newDelegate(this, &ScrollBar::notifyMouseWheel);
}

assignWidget(mWidgetTrack, "Track");
if (mWidgetTrack)
{
mWidgetTrack->eventMouseDrag += newDelegate(this, &ScrollBar::notifyMouseDrag);
mWidgetTrack->eventMouseButtonPressed += newDelegate(this, &ScrollBar::notifyMousePressed);
mWidgetTrack->eventMouseButtonReleased += newDelegate(this, &ScrollBar::notifyMouseReleased);
mWidgetTrack->eventMouseWheel += newDelegate(this, &ScrollBar::notifyMouseWheel);
mWidgetTrack->setVisible(false);
}

assignWidget(mWidgetFirstPart, "FirstPart");
if (mWidgetFirstPart != nullptr)
{
mWidgetFirstPart->eventMouseButtonPressed += newDelegate(this, &ScrollBar::notifyMousePressed);
mWidgetFirstPart->eventMouseWheel += newDelegate(this, &ScrollBar::notifyMouseWheel);
}

assignWidget(mWidgetSecondPart, "SecondPart");
if (mWidgetSecondPart != nullptr)
{
mWidgetSecondPart->eventMouseButtonPressed += newDelegate(this, &ScrollBar::notifyMousePressed);
mWidgetSecondPart->eventMouseWheel += newDelegate(this, &ScrollBar::notifyMouseWheel);
}

if (isUserString("MinTrackSize"))
mMinTrackSize = utility::parseValue<int>(getUserString("MinTrackSize"));
if (isUserString("TrackRangeMargins"))
utility::parseComplex<size_t>(getUserString("TrackRangeMargins"), mSkinRangeStart, mSkinRangeEnd);

if (mWidgetTrack != nullptr)
{
if (mWidgetTrack->isUserString("MinTrackSize"))
mMinTrackSize = utility::parseValue<int>(mWidgetTrack->getUserString("MinTrackSize"));
}
}

//////////////////////////////////////////////////
////////////////////////////////////////////////////

void ScrollBar::notifyMousePressed(Widget* _sender, int _left, int _top, MouseButton _id)
{
// диспечерезируем нажатие своих детей как свое
eventMouseButtonPressed(this, _left, _top, _id);

if (MouseButton::Left != _id)
return;

if (mMoveToClick &&
_sender != mWidgetTrack &&
_sender != mWidgetStart &&
_sender != mWidgetEnd)
{
if (mWidgetTrack != nullptr)
{
mPreActionOffset = InputManager::getInstance().getLastPressedPosition(MouseButton::Left);
const IntPoint& point = InputManager::getInstance().getMousePositionByLayer() - mWidgetTrack->getParent()->getAbsolutePosition();

mPreActionOffset.left -= getTrackSize() / 2;
mPreActionOffset.top -= getTrackSize() / 2;

TrackMove(point.left, point.top);
}
}
else if (_sender == mWidgetStart)
{
// минимальное значение
if (mScrollPosition == 0)
return;

// расчитываем следующее положение
if (mScrollPosition > mScrollPage)
mScrollPosition -= mScrollPage;
else
mScrollPosition = 0;

// оповещаем
eventScrollChangePosition(this, (int)mScrollPosition);
updateTrack();
}
else if (_sender == mWidgetEnd)
{
// максимальное значение
if ((mScrollRange < 2) || (mScrollPosition >= (mScrollRange - 1)))
return;

// расчитываем следующее положение
if ((mScrollPosition + mScrollPage) < (mScrollRange - 1))
mScrollPosition += mScrollPage;
else
mScrollPosition = mScrollRange - 1;

// оповещаем
eventScrollChangePosition(this, (int)mScrollPosition);
updateTrack();
}
else if (_sender == mWidgetFirstPart)
{
// минимальное значение
if (mScrollPosition == 0)
return;

// расчитываем следующее положение
if (mScrollPosition > mScrollViewPage)
mScrollPosition -= mScrollViewPage;
else
mScrollPosition = 0;

// оповещаем
eventScrollChangePosition(this, (int)mScrollPosition);
updateTrack();
}
else if (_sender == mWidgetSecondPart)
{
// максимальное значение
if ((mScrollRange < 2) || (mScrollPosition >= (mScrollRange - 1)))
return;

// расчитываем следующее положение
if ((mScrollPosition + mScrollViewPage) < (mScrollRange - 1))
mScrollPosition += mScrollViewPage;
else
mScrollPosition = mScrollRange - 1;

// оповещаем
eventScrollChangePosition(this, (int)mScrollPosition);
updateTrack();
}
else if (_sender == mWidgetTrack)
{
mPreActionOffset.left = _sender->getLeft();
mPreActionOffset.top = _sender->getTop();
}
}