QT connect函数的用法.docx

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1、QT connect函数的用法QT QObject：connect函数的学习 从Qobject(QObject.h)源码中可以看到QObject:connect的定义是这样的： cpp view plaincopy 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. static bool connect(const QObject *sender, const char *signal, const QObject *receiver, const char *membe

2、r, Qt:ConnectionType = #ifdef qdoc Qt:AutoConnection #else #ifdef QT3_SUPPORT Qt:AutoCompatConnection #else Qt:AutoConnection #endif #endif ); inline bool connect(const QObject *sender, const char *signal, const char *member, Qt:ConnectionType type = #ifdef qdoc Qt:AutoConnection #else #ifdef QT3_SU

3、PPORT Qt:AutoCompatConnection #else Qt:AutoConnection #endif #endif ) const; 其中第二个connect的实现其实只有一句话： cpp view plaincopy 1. return connect(asender, asignal, this, amember, atype); 所以对于connect函数的学习其实就是研究第一个connect函数。 我们在使用connect函数的时候一般是这样调用的： cpp view plaincopy 1. connect(sender,SIGNAL(signal),receiv

4、er,SLOT(slot); 这里用到了两个宏：SIGNAL 和SLOT；通过connect声明可以知道这两个宏最后倒是得到一个const char*类型。 在qobjectdefs.h中可以看到SIGNAL 和SLOT的宏定义： cpp view plaincopy 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. #ifndef QT_NO_DEBUG # define QLOCATION 0_FILE_:QTOSTRING(_LINE_) # define METHOD(a) qFlagLocation(0#a QLOCATION) # define SLOT(a) qFla

5、gLocation(1#a QLOCATION) # define SIGNAL(a) qFlagLocation(2#a QLOCATION) #else # define METHOD(a) 0#a # define SLOT(a) 1#a # define SIGNAL(a) 2#a #endif 所以这两个宏的作用就是把函数名转换为字符串并且在前面加上标识符。 比如：SIGNAL(read)展开后就是2read；同理SLOT(read)展开后就是1read。 cpp view plaincopy 1. 2. connect(sender,SIGNAL(signal),receiver,

6、SLOT(slot); 实际上就是connect(sender,“2signal”,receiver,“1slot)”; 搞明白了实际的参数就可以来看connect的真正实现过程了，在QObject.cpp文件中可以找到connect的实现代码。 cpp view plaincopy 1. 2. 3. 4. 5. bool QObject:connect(const QObject *sender, const char *signal, const QObject *receiver, const char *method, Qt:ConnectionType type) 6. const

7、void *cbdata = sender, signal, receiver, method, &type ; if (QInternal:activateCallbacks(QInternal:ConnectCallback, (void *) cbdata) return true; if (sender = 0 | receiver = 0 | signal = 0 | method = 0) qWarning(QObject:connect: Cannot connect %s:%s to %s:%s, sender ? sender-metaObject-className : (

8、null), (signal & *signal) ? signal+1 : (null), receiver ? receiver-metaObject-className : (null), (method & *method) ? method+1 : (null); return false; QByteArray tmp_signal_name; if (!check_signal_macro(sender, signal, connect, bind) return false; const QMetaObject *smeta = sender-metaObject; const

9、 char *signal_arg = signal; +signal; /skip code int signal_index = smeta-indexOfSignal(signal); if (signal_index indexOfSignal(signal); if (signal_index metaObject; int method_index = -1; switch (membcode) case QSLOT_CODE: method_index = rmeta-indexOfSlot(method); break; case QSIGNAL_CODE: method_in

10、dex = rmeta-indexOfSignal(method); break; if (method_index indexOfSlot(method); break; case QSIGNAL_CODE: method_index = rmeta-indexOfSignal(method); break; if (method_index %s:%s, sender-metaObject-className, signal, receiver-metaObject-className, method); return false; int *types = 0; if (type = Q

11、t:QueuedConnection | type = Qt:BlockingQueuedConnectio & !(types = queuedConnectionTypes(smeta-method(signal_index).p79. 80. 81. 82. 83. 84. 85. 86. n) 87. arameterTypes) 88. 89. 90. 91. 92. 93. return false; QMetaObject:connect(sender, signal_index, receiver, method_index, type, const_cast(sender)-

12、connectNotify(signal - 1); return true; types); 上面是去除了debug代码的connect实现。 cpp view plaincopy 1. 2. a) const void *cbdata = sender, signal, receiver, method, &type ; if (QInternal:activateCallbacks(QInternal:ConnectCallback, (void *) cbdat return true; 3. 判断连接是否已经建立。 QInternal：ConnectCallback在qglobal.

13、cpp中实现。 cpp view plaincopy 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. bool QInternal:activateCallbacks(Callback cb, void *parameters) Q_ASSERT_X(cb = 0, QInternal:activateCallback, Callback id must be a valid id); QInternal_CallBackTable *cbt = global_callback_table; if (cbt & cb callbacks.size)

14、 QList callbacks = cbt-callbackscb; bool ret = false; for (int i=0; icallbacks.size; +i) ret |= (callbacks.at(i)(parameters); return ret; return false; QInternal_CallBackTable 定义为(qglobal.cpp) cpp view plaincopy 1. 2. 3. struct QInternal_CallBackTable QVectorQList callbacks; ; qInternalCallback定义为(q

15、namespace.h) cpp view plaincopy 1. typedef bool (*qInternalCallback)(void *);这是一个函数指针 返回值是bool，只有一个参数为void*。这个指针在调用registerCallback加入列表。 cpp view plaincopy 1. 2. if (!check_signal_macro(sender, signal, connect, bind) return false; 判断signal是否合法。 在QObject.cpp文件中可以找到check_signal_macro的实现 cpp view plain

16、copy 1. 2. 3. 4. 5. 6. 7. 8. static bool check_signal_macro(const QObject *sender, const char *signal, const char *func, const char *op) int sigcode = extract_code(signal); if (sigcode != QSIGNAL_CODE) if (sigcode = QSLOT_CODE) qWarning(Object:%s: Attempt to %s non-signal %s:%s, func, op, sender-met

17、aObject-className, signal+1);9. 10. 11. 12. 13. 14. 15. else qWarning(Object:%s: Use the SIGNAL macro to %s %s:%s, func, op, sender-metaObject-className, signal); return false; return true; extract的实现也在QObject中，它就是去字符串第一个字符，并且只取低2位的值。 cpp view plaincopy 1. 2. 3. 4. 5. static int extract_code(const c

18、har *member) / extract code, ensure QMETHOD_CODE = code metaObject; const char *signal_arg = signal; +signal; /skip code int signal_index = smeta-indexOfSignal(signal); if (signal_index indexOfSignal(signal); if (signal_index metaObject ? QObject:d_ptr-metaObject : &staticMetaObject; 其中staticMetaObj

19、ect也是在moc文件中定义的 cpp view plaincopy 1. 2. 3. 4. const QMetaObject MainWindow:staticMetaObject = &QMainWindow:staticMetaObject, qt_meta_stringdata_MainWindow, qt_meta_data_MainWindow, 0 ; qt_meta_stringdata_MainWindow就是staticconstchar类型。它记录了全部的signals和slots等的函数名、返回值和参数表的信息。 qt_meta_data_MainWindow是sta

20、ticconstuint类型。它记录了每一个函数的函数名、返回值和参数表在qt_meta_stringdata_MainWindow中的索引。同时它还记录了每一个函数的类型具体在qmetaobject.cpp文件中定义。 cpp view plaincopy 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. enum MethodFlags AccessPrivate = 0x00, AccessProtected = 0x01, AccessPublic = 0x02, AccessMask = 0x03, /mask Method

21、Method = 0x00, MethodSignal = 0x04, MethodSlot = 0x08, MethodConstructor = 0x0c, MethodTypeMask = 0x0c, MethodCompatibility = 0x10, MethodCloned = 0x20, MethodScriptable = 0x40 ; indexOfSignal(signal);的实现在qmetaobject.cpp中。其主要作用是利用qt_meta_stringdata_MainWindow 和qt_meta_data_MainWindow查找已经定义了的signal并返

22、回索引。 cpp view plaincopy 1. 2. 3. 4. 5. QByteArray tmp_method_name; int membcode = extract_code(method); if (!check_method_code(membcode, receiver, method, connect) return false; 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37

23、. const char *method_arg = method; +method; / skip code const QMetaObject *rmeta = receiver-metaObject; int method_index = -1; switch (membcode) case QSLOT_CODE: method_index = rmeta-indexOfSlot(method); break; case QSIGNAL_CODE: method_index = rmeta-indexOfSignal(method); break; if (method_index in

24、dexOfSlot(method); break; case QSIGNAL_CODE: method_index = rmeta-indexOfSignal(method); break; if (method_index %s:%s, 4. 5. 6. 7. sender-metaObject-className, signal, receiver-metaObject-className, method); return false; 判断signal和method是否兼容，checkConnectArgs函数的在qmetaObject.cpp文件中实现。这个函数校验了signal和me

25、thod的参数。当两者的参数一致或method参数比signal参数少的时候返回true，其它返回false。 cpp view plaincopy 1. 2. 3. 4. int *types = 0; if (type = Qt:QueuedConnection | type = Qt:BlockingQueuedConnection) & !(types = queuedConnectionTypes(smeta-method(signal_index).parameterTypes) return false; 如果是以发消息的方式执行method就需要对参数类型进行判断。queued

26、ConnectionTypes在QObject.cpp实现。实际上是在QMetatype.cpp中定义了一个 static conststruct constchar * typeName;int type; types；在这里记录了全部类型和名称如；Void在Qmetatype.h中定义。 cpp view plaincopy 1. es); QMetaObject:connect(sender, signal_index, receiver, method_index, type, typ调用QMetaObject的connect函数，再次不详细写出。 cpp view plaincopy 1. const_cast(sender)-connectNotify(signal - 1); 最后调用虚函数connectNotify表示connect已经执行完成。