Qt控件焦點切換

們平常切換控件，例如QQ登錄的帳號和密碼輸入框就能夠經過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.

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實現效果以下 
 
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("複選框"); QComboBox *b = new QComboBox; setTabOrder(p, l); setTabOrder(l, c); setTabOrder(c, b);

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固然也能夠讓控件屏蔽焦點的使用，或者接受響應其餘類型的焦點方式 
主要使用

void setFocusPolicy(Qt::FocusPolicy policy)

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其中Qt::FocusPolicy 這個枚舉類型定義了一個控件能夠用來獲取鍵盤焦點的各類策略。

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爲NoFouse

c->setFocusPolicy(Qt::NoFocus);

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效果以下 
 
圖3 複選框設置NoFocuse 
函數

[slot] void QWidget::setFocus() //可經過信號槽方式設置 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.

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可直接設置焦點

接下來能夠看一下Qt是怎麼實現焦點切換的，查看qwidget.cpp源碼

void QWidget::setTabOrder(QWidget* first, QWidget *second) { //若是這兩個控件都設置爲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