Qt之信號與槽
在遇到多信號問題的時候,你是否經常會連接多個槽函數呢?如果你的答案是絕對的,那麼你已經Out很久了。多信號連接多個槽,實現不同的槽就在潛意識的加大程序的開銷!那麼爲什麼不去鏈接同一個槽呢?
今天在次寫下這篇文章,感覺有些唐突,但是又不得不寫!因爲信號與槽是Qt裏面的最基礎而且是最重要的部分,有很多人問過我關於信號與槽的問題,就總結一下。Qt主要包括:Qt基礎部分(Qt入門、Qt對話框、Qt窗口、自定義窗口部件)、Qt中級(佈局管理、事件處理、二維繪圖、容器、數據庫、多線程、網絡等)、Qt高級(國際化、自定義樣式、三維繪圖、創建插件、嵌入式編程等)。
信號與槽的連接方式看起來會是這樣的:
Qt5之前:
connect(sender, SIGNAL(signal), receiver, SLOT(slot));
Qt5開始:
connect(sender, &Sender::signal, receiver, &Receiver::slot);
前者:
sender和receiver是指向QObject的指針,signal和slot是不帶參數的函數名。SIGNAL()宏和SLOT()宏會把他們的參數轉換成相應的字符串。
後者:
(1)編譯器,檢查信號與槽是否存在,參數類型檢查,Q_OBJECT宏是否存在
(2)信號可以和普通函數、類的普通成員函數、lambda函數連接(不在侷限於信號和槽函數)
(3)參數可以是typedef的或者使用不同的namespace specifier
(4)可以允許一些自動類型的轉換(即信號和槽函數類型不必完全匹配)
1、一個信號連接一個槽
connect(slider, &QSlider::valueChanged, spin_box, &QSpinBox::setValue);
2、一個信號連接多個槽
connect(slider, &QSlider::valueChanged, spin_box, &QSpinBox::setValue);
connect(slider, &QSlider::valueChanged, this, &QWidget::showValue);
3、多個信號連接同一個槽
connect(push_button, &QPushButton::clicked, this, &QWidget::show);
connect(tool_button, &QToolButton::clicked, this, &QWidget::show);
4、一個信號連接另一個信號
connect(push_button, &QPushlButton::clicked, this, &QWidget::buttonClicked);
5、斷開鏈接
disconnect(push_button); //斷開push_button的所有連接
disconnect(push_button, &QPushButton::clicked, this, &QWidget::show); //斷開此信號連接的槽
再說說disconnect,見名知意,肯定與connect是相反的關係。
1、bool QObject::disconnect(const QObject * receiver, const char * method = 0) const
斷開所有發送者的信號與接受者槽的連接
2、bool QObject::disconnect(const char * signal = 0, const QObject * receiver = 0, const char * method = 0) const
斷開發送者和接受者的連接
3、bool QObject::disconnect(const QObject * sender, const char * signal, const QObject * receiver, const char * method) [static]
斷開通常用於以下三種方式:
(1)斷開所有連接到該對象的信號
disconnect(myObject, 0, 0, 0);
相當於非靜態重載函數
myObject->disconnect();
(2)斷開一切連接到特定信號:
disconnect(myObject, SIGNAL(mySignal()), 0, 0);
相當於非靜態重載函數
myObject->disconnect(SIGNAL(mySignal()));
(3)斷開一個特定的接收者:
disconnect(myObject, 0, myReceiver, 0);
相當於非靜態重載函數
myObject->disconnect(myReceiver);
4、bool QObject::disconnect(const QObject * sender, const QMetaMethod & signal, const QObject * receiver, const QMetaMethod & method) [static]
5、bool QObject::disconnect(const QMetaObject::Connection & connection) [static]
6、bool QObject::disconnect(const QObject * sender, PointerToMemberFunction signal, const QObject * receiver, PointerToMemberFunction method) [static]
斷開通常用於以下三種方式:
(1)斷開所有連接到該對象的信號
disconnect(myObject, 0, 0, 0);
(2)斷開一切連接到特定信號:
disconnect(myObject, &MyObject::mySignal(), 0, 0);
(3)斷開一個特定的接收者:
disconnect(myObject, 0, myReceiver, 0);
(4)斷開一個特定信號到特定槽的連接:
QObject::disconnect(lineEdit, &QLineEdit::textChanged, label, &QLabel::setText);
好了,這些都是最基本的應用。那麼多個信號連接同一個槽的時候如何進行區分呢?
方法一:
typedef enum{
BUTTON_1,
BUTTON_2,
BUTTON_3,
BUTTON_4
}BUTTON;
push_button_1->setObjectName(QString::number(BUTTON_1, 10));
push_button_2->setObjectName(QString::number(BUTTON_2, 10));
tool_button_1->setObjectName(QString::number(BUTTON_3, 10));
tool_button_2->setObjectName(QString::number(BUTTON_4, 10));
connect(push_button_1, &QPushButton::clicked, this, &MyWidget::changeButton);
connect(push_button_2, &QPushButton::clicked, this, &MyWidget::changeButton);
connect(tool_button_1, &QToolButton::clicked, this, &MyWidget::changeButton);
connect(tool_button_2, &QToolButton::clicked, this, &MyWidget::changeButton);
void MyWidget::changeButton()
{
QObject *object = QObject::sender();
QPushButton *push_button = qobject_cast(object);
QToolButton *tool_button = qobject_cast<</span>QToolButton *>(object);
int index;
if(push_button)
{
QString object_name = push_button->objectName();
index = object_name.toInt();
}
else if(tool_button )
{
QString object_name = tool_button->objectName();
index = object_name.toInt();
}
QString information = QString("");
switch(index)
{
case BUTTON_1:
information = QString("clicked 1");
break;
case BUTTON_2:
information = QString("clicked 2");
break;
case BUTTON_3:
information = QString("clicked 3");
break;
case BUTTON_4:
information = QString("clicked 4");
break;
default:
information = QString("which is clicked?");
break;
}
QMessageBox::information(NULL, QString("Title"), information);
}
當然,setObjectName不是專門用來幹這事的,也可以使用text進行區分或者其它方法,這裏介紹的只是一種思路而已!
方法二:
QSignalMapper類可以簡單的理解爲信號的翻譯和轉發器, 它可以把一個無參數的信號翻譯成帶int參數、QString參數、QObject*參數或者QWidget*參數的信號,並將之轉發。
QSignalMapper *signal_mapper = new QSignalMapper(this);
connect(push_button_1, &QPushButton::clicked, signal_mapper, &QSignalMapper::map);
connect(push_button_2, &QPushButton::clicked, signal_mapper, &QSignalMapper::map);
connect(tool_button_1, &QToolButton::clicked, signal_mapper, &QSignalMapper::map);
connect(tool_button_2, &QToolButton::clicked, signal_mapper, &QSignalMapper::map);
signal_mapper->setMapping(push_button_1, QString::number(BUTTON_1, 10));
signal_mapper->setMapping(push_button_2, QString::number(BUTTON_2, 10));
signal_mapper->setMapping(tool_button_1, QString::number(BUTTON_3, 10));
signal_mapper->setMapping(tool_button_2, QString::number(BUTTON_4, 10));
connect(signal_mapper, &QSignalMapper::mapped, this, &MyWidget::changeButton);
void MyWidget::changeButton(QString text)
{
int index = text.toInt();
QString information = QString("");
switch(index)
{
case BUTTON_1:
information = QString("clicked 1");
break;
case BUTTON_2:
information = QString("clicked 2");
break;
case BUTTON_3:
information = QString("clicked 3");
break;
case BUTTON_4:
information = QString("clicked 4");
break;
default:
information = QString("which is clicked?");
break;
}
QMessageBox::information(NULL, QString("Title"), information);
}
執行順序
同一信號連接多個槽呢,槽函數執行沒有絕對的先後順序。
如:
connect(slider, &QSlider::valueChanged, spin_box, &QSpinBox::setValue);
connect(slider, &QSlider::valueChanged, this, &QWidget::showValue);
在Qt5之前,並不是setValue一定會比showValue先執行。
但在Qt5中,文檔中這樣介紹:
A signal can be connected to many slots and signals. Many signals can be connected to one slot.
If a signal is connected to several slots, the slots are activated in the same order in which the connections were made, when the signal is emitted.(一個信號連接多個槽,信號發射後,會按照鏈接順序執行)。
經過簡單測試的確如此:
connect(spin_box, &QSpinBox::valueChanged, this, &ListView::changeValue);
信號與槽連接看上去很正確,但是會出現如下錯誤:
connect(spin_box, static_cast(&QSpinBox::valueChanged), this, &ListView::changeValue);
總結就到這裏,都是很常用的東西,編程過程中多注意細節部分,多總結就好了。很多東西文檔裏都說的很清楚,write less,do more。。。
注:
技術在於交流、溝通,轉載請註明出處並保持作品的完整性。
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