Qt中鏈接信號和槽的方法

人云E云 posted @ 2015年7月03日 16:07 in 信息技術 with tags Coding Qt , 1284 阅读

最近又在用Qt寫東西，順便翻了翻Qt的文檔，發現鏈接信號和槽的方法有不少，Qt5和C++11的組合也帶來了一些不小變化。

所以有此一篇文章，對其稍加總結。

文中約定

使用“鏈接”這一術語而非“連接”
默認所有對象都（直接或間接）繼承了QObject

Qt對信號和槽的鏈接有如下規則：

使用信號和槽機制需要在類聲明中加入Q_OBJECT宏
可以鏈接信號和槽
可以鏈接信號和信號
同一個信號或槽可鏈接或被鏈接多次
信號比槽中多出的參數會被忽略
鏈接可以通過disconnect斷開

其鏈接方法如下：

connect( 信號源, SIGNAL( 信號( 參數表 ) ), 接收者, SLOT( 槽( 參數表 ) ) )
- 目前最爲常用的一個方法，是static函數
- 在任何繼承了QObject且寫有Q_OBJECT宏的類中使用
- 其中SIGNAL()和SLOT()均爲宏
- 參數表中只需（）按順序寫出參數類型
- 其原型爲：
  - ```
  bool QObject::connect(const QObject * sender, const char * signal, const QObject * receiver, const char * method, Qt::ConnectionType type = Qt::AutoConnection)
```
- ```
QMetaObject::Connection QObject::connect(const QObject * sender, const char * signal, const QObject * receiver, const char * method, Qt::ConnectionType type = Qt::AutoConnection)
```
- 其還有幾個重載，常用的爲：
  - 接收者爲當前對象時可不寫接收者
connect( 信號源, &信號源類::信號, 接收者, &接收者類::信號 )
- 需要Qt5
- 編譯器會檢查信號和槽的參數類型是否匹配
- 不支持槽使用默認參數來填補信號中不足的參數
- 其原型爲：
```
QMetaObject::Connection QObject::connect(const QObject * sender, PointerToMemberFunction signal, const QObject * receiver, PointerToMemberFunction method, Qt::ConnectionType type = Qt::AutoConnection)
```
connect( 信號源, &信號源類::信號, lambda表達式 )
- 需要編譯器支持C++11且需要Qt5
- 若編譯器不支持可變參數模板，則最多允許信號攜帶6個參數
- 其原型爲：
```
QMetaObject::Connection QObject::connect(const QObject * sender, PointerToMemberFunction signal, Functor functor)
```

Qt5和Q4中，connect函數幾個主要不同點在於：

Qt5中返回值類型爲QMetaObject::Connection，而Qt4中爲bool
Qt5中支持槽爲lambda表達式，而Qt4中不支持

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