Qt控件焦點切換

們日常切換控件，例如QQ登陸的賬號和密碼輸入框就可以通過Tab鍵切換焦點。 
 
圖1 qq切換焦點 
Qt中QWidget提供了一個靜態方式實現該效果 
其中也包含介紹使用

[static] void QWidget::setTabOrder(QWidget *first, QWidget *second)
Puts the second widget after the first widget in the focus order. Note that since the tab order of the second widget is changed, you should order a chain like this: setTabOrder(a, b); // a to b setTabOrder(b, c); // a to b to c setTabOrder(c, d); // a to b to c to d not like this: // WRONG setTabOrder(c, d); // c to d setTabOrder(a, b); // a to b AND c to d setTabOrder(b, c); // a to b to c, but not c to d If first or second has a focus proxy, setTabOrder() correctly substitutes the proxy.

實現效果如下 
 
圖2 Tab切換焦點 
主要部分源碼

    QPushButton *p = new QPushButton("按鈕"); QLineEdit *l = new QLineEdit("輸入框"); QCheckBox *c = new QCheckBox("復選框"); QComboBox *b = new QComboBox; setTabOrder(p, l); setTabOrder(l, c); setTabOrder(c, b);

當然也可以讓控件屏蔽焦點的使用，或者接受響應其他類型的焦點方式 
主要使用

void setFocusPolicy(Qt::FocusPolicy policy)

其中Qt::FocusPolicy 這個枚舉類型定義了一個控件可以用來獲取鍵盤焦點的各種策略。

Constant	Value	Description
Qt::TabFocus	0x1	the widget accepts focus by tabbing.
Qt::ClickFocus	0x2	the widget accepts focus by clicking.
Qt::StrongFocus	TabFocus | ClickFocus | 0x8	he widget accepts focus by both tabbing and clicking. On macOS this will also be indicate that the widget accepts tab focus when in ‘Text/List focus mode’.
Qt::WheelFocus	StrongFocus | 0x4	like Qt::StrongFocus plus the widget accepts focus by using the mouse wheel.
Qt::NoFocus	0	the widget does not accept focus.

例如設置 
QCheckBox為NoFouse

c->setFocusPolicy(Qt::NoFocus);

效果如下 
 
圖3 復選框設置NoFocuse 
函數

[slot] void QWidget::setFocus() //可通過信號槽方式設置 This is an overloaded function. Gives the keyboard input focus to this widget (or its focus proxy) if this widget or one of its parents is the active window.

可直接設置焦點

接下來可以看一下Qt是怎么實現焦點切換的，查看qwidget.cpp源碼

void QWidget::setTabOrder(QWidget* first, QWidget *second) { //如果這兩個控件都設置為沒有焦點則不進行焦點設置，如圖3中所示 if (!first || !second || first->focusPolicy() == Qt::NoFocus || second->focusPolicy() == Qt::NoFocus) return; /****************************************************************** QWidget *QWidget::window() const { QWidget *w = const_cast<QWidget *>(this); QWidget *p = w->parentWidget(); while (!w->isWindow() && p) { w = p; p = p->parentWidget(); } return w; } ******************************************************************/ //查看當前控件“祖先”(ancestor widget)窗口，見上面代碼 if (Q_UNLIKELY(first->window() != second->window())) { qWarning("QWidget::setTabOrder: 'first' and 'second' must be in the same window"); return; } //找到first或其子類中焦點的控件(不是很懂) QWidget *fp = first->focusProxy(); if (fp) { QList<QWidget *> l = first->findChildren<QWidget *>(); for (int i = l.size()-1; i >= 0; --i) { QWidget * next = l.at(i); if (next->window() == fp->window()) { fp = next; if (fp->focusPolicy() != Qt::NoFocus) break; } } first = fp; } if (fp == second) return; if (QWidget *sp = second->focusProxy()) second = sp; //雙向鏈表存儲焦點觸發控件順序 // QWidget *fp = first->d_func()->focus_prev; QWidget *fn = first->d_func()->focus_next; if (fn == second || first == second) return; QWidget *sp = second->d_func()->focus_prev; QWidget *sn = second->d_func()->focus_next; fn->d_func()->focus_prev = second; first->d_func()->focus_next = second; second->d_func()->focus_next = fn; second->d_func()->focus_prev = first; sp->d_func()->focus_next = sn; sn->d_func()->focus_prev = sp; //查錯 Q_ASSERT(first->d_func()->focus_next->d_func()->focus_prev == first); Q_ASSERT(first->d_func()->focus_prev->d_func()->focus_next == first); Q_ASSERT(second->d_func()->focus_next->d_func()->focus_prev == second); Q_ASSERT(second->d_func()->focus_prev->d_func()->focus_next == second); }

 

http://blog.csdn.net/gx864102252/article/details/72731992