QT5.6 QTableWidget Drag and drop mode can be used. only "InternalMove" mode has effect when use setDragDropMode

[cawlfj]

I try to made a class Inherited from QTableWidget and it's event.
The drag and drop can be used only on internalMove mode, why can be used by DragDrop mode.
Code:
h file
class MyListTabel:public QTableWidget
{ Q_OBJECT
public:
explicit MyListTabel(QWidget *parent=0);
protected:
void dragEnterEvent(QDragEnterEvent *e);
void dropEvent(QDropEvent *e);
// void dragMoveEvent(QDragMoveEvent *e);

};

cpp file

MyListTabel::MyListTabel(QWidget *parent){
this->setAcceptDrops(true);
this->setDragEnabled(true);
this->setDropIndicatorShown(true);
this->setDragDropMode(QAbstractItemView::InternalMove); //DragDrop
}

void MyListTabel::dragEnterEvent(QDragEnterEvent *e){
e->setAccepted(true);
e->setDropAction(Qt::MoveAction);
e->acceptProposedAction();
}
void MyListTabel::dropEvent(QDropEvent *e)
{
if(this!=e->source()){
MyPoint3d InsertP;
this->setFocus();
.....................