Qt：實現平移的正確方法（拖動）

Question

QGraphicsview有一個方法setDragMode(ScrollHandDrag)，用於通過單擊鼠標左鍵來啓用平移。但我想啓用平移單擊鼠標滾輪時（中間的按鈕），並創建以下定製實現鍋：

//Within a custom derived class of QGraphicsView 
//pan is true when wheel is clicked and false when released 
//last Pos is defined somewhere else in the class 

void GridView::mouseMoveEvent(QMouseEvent *event){ 
    if(pan){ 
     QPointF currentPos = event->pos(); 
     QPointF relPos = currentPos - lastPos; 
     lastPos = currentPos; 

     //this is what creates the panning effect 
     translate(relPos.x(), relPos.y()); 
    } 
    QGraphicsView::mouseMoveEvent(event); 
} 

也能正常工作的大部分。但是，例如，如果我將單位矩陣縮放1,000,000，則此方法失敗並停止平移（就像視圖卡住了一樣）。當我使用setDragMode()

時，不會出現這個問題setDragMode()正確的自定義實現是什麼，所以它通過輪子點擊來啓用？

Answer 1

這對我很有用...它讓人想到用戶在按下鼠標左鍵的時候按下了鼠標左鍵。

void GridView :: mousePressEvent(QMouseEvent * e) 
{ 
    if (e->button() == MidButton) 
    { 
     QMouseEvent fake(e->type(), e->pos(), LeftButton, LeftButton, e->modifiers()); 
     QGraphicsView::mousePressEvent(&fake); 
    } 
    else QGraphicsView::mousePressEvent(e); 
} 

void GridView :: mouseReleaseEvent(QMouseEvent * e) 
{ 
    if (e->button() == MidButton) 
    { 
     QMouseEvent fake(e->type(), e->pos(), LeftButton, LeftButton, e->modifiers()); 
     QGraphicsView::mouseReleaseEvent(&fake); 
    } 
    else QGraphicsView::mouseReleaseEvent(e); 
}