Qt控件焦点切换

们平常切换控件，例如QQ登录的帐号和密码输入框就能够经过Tab键切换焦点。 
 
图1 qq切换焦点 
Qt中QWidget提供了一个静态方式实现该效果 
其中也包含介绍使用

[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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实现效果以下 
 
图2 Tab切换焦点 
主要部分源码

QPushButton *p = new QPushButton("按钮"); QLineEdit *l = new QLineEdit("输入框"); QCheckBox *c = new QCheckBox("复选框"); QComboBox *b = new QComboBox; setTabOrder(p, l); setTabOrder(l, c); setTabOrder(c, b);

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固然也能够让控件屏蔽焦点的使用，或者接受响应其余类型的焦点方式 
主要使用

void setFocusPolicy(Qt::FocusPolicy policy)

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其中Qt::FocusPolicy 这个枚举类型定义了一个控件能够用来获取键盘焦点的各类策略。

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.

例如设置 
QCheckBox为NoFouse

c->setFocusPolicy(Qt::NoFocus);

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效果以下 
 
图3 复选框设置NoFocuse 
函数

[slot] void QWidget::setFocus() //可经过信号槽方式设置 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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可直接设置焦点

接下来能够看一下Qt是怎么实现焦点切换的，查看qwidget.cpp源码

void QWidget::setTabOrder(QWidget* first, QWidget *second) { //若是这两个控件都设置为没有焦点则不进行焦点设置，如图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; } ******************************************************************/ //查看当前控件“祖先”(ancestor widget)窗口，见上面代码 if (Q_UNLIKELY(first->window() != second->window())) { qWarning("QWidget::setTabOrder: 'first' and 'second' must be in the same window"); return; } //找到first或其子类中焦点的控件(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; //双向链表存储焦点触发控件顺序 // 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; //查错 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