深⼊探究connect函数
connect，是QT中的连接函数，将信号发送者nder对象中的信号signal与接受者receiver中的member槽函数联系起来。
QObject::connect的定义是这样的：
static bool connect(const QObject *nder, const char *signal,
const QObject *receiver, const char *member, Qt::ConnectionType =
#ifdef qdoc
购买咖啡豆Qt::AutoConnection
#el
#ifdef QT3_SUPPORT
Qt::AutoCompatConnection
#el
Qt::AutoConnection
#endif
#endif
);
inline bool connect(const QObject *nder, const char *signal,
const char *member, Qt::ConnectionType type =
#ifdef qdoc
Qt::AutoConnection
#el
#ifdef QT3_SUPPORT
Qt::AutoCompatConnection
#el
Qt::AutoConnection
#endif
#endif
) const;
其中第⼆个connect的实现其实只有⼀句话：urgent怎么读
{ return connect(ander, 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。
在使⽤connect函数的时候⼀般是这样调⽤的：
connect(nder,SIGNAL(signal()),receiver,SLOT(slot()));
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：
1. #ifndef QT_NO_DEBUG
2. # define QLOCATION "\0"__FILE__":"QTOSTRING(__LINE__)
3. # define METHOD(a) qFlagLocation("0"#a QLOCATION)
4. # define SLOT(a) qFlagLocation("1"#a QLOCATION)
5. # define SIGNAL(a) qFlagLocation("2"#a QLOCATION)
6. #el
7. # define METHOD(a) "0"#a
8. # define SLOT(a) "1"#a
9. # define SIGNAL(a) "2"#a
10. #endif
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()"。connect(nder,SIGNAL(signal()),receiver,SLOT(slot()));
实际上就是connect(nder,“2signal()”,receiver,“1slot())”;
在QObject.cpp⽂件中可以找到connect的实现代码，下⾯是去除了debug代码的connect实现。
1. bool QObject::connect(const QObject *nder, const char *signal,你来自哪里用英语怎么说
2. const QObject *receiver, const char *method,
3. Qt::ConnectionType type)
4. {
5. {
6. const void *cbdata[] = { nder, signal, receiver, method, &type };
7. if (QInternal::activateCallbacks(QInternal::ConnectCallback, (void **) cbdata))
8. return true;
9. }
10.
11. if (nder == 0 || receiver == 0 || signal == 0 || method == 0) {
12. qWarning("QObject::connect: Cannot connect %s::%s to %s::%s",
13. nder ? nder->metaObject()->className() : "(null)",
14. (signal && *signal) ? signal+1 : "(null)",
15. receiver ? receiver->metaObject()->className() : "(null)",
16. (method && *method) ? method+1 : "(null)");
17. return fal;
18. }
19. QByteArray tmp_signal_name;
20.
21. if (!check_signal_macro(nder, signal, "connect", "bind"))
22. return fal;
23. const QMetaObject *smeta = nder->metaObject();托福学习
24. const char *signal_arg = signal;
25. ++signal; //skip code
26. int signal_index = smeta->indexOfSignal(signal);
27. if (signal_index < 0) {
28. // check for normalized signatures
29. tmp_signal_name = QMetaObject::normalizedSignature(signal - 1);
30. signal = tmp_stData() + 1;
31.
32. signal_index = smeta->indexOfSignal(signal);
33. if (signal_index < 0) {
34. err_method_notfound(nder, signal_arg, "connect");
35. err_info_about_objects("connect", nder, receiver);
36. return fal;
37. }
38. }
39.
40. QByteArray tmp_method_name;
2014年巴西世界杯赛程41. int membcode = extract_code(method);
42.
43. if (!check_method_code(membcode, receiver, method, "connect"))
44. return fal;
45. const char *method_arg = method;
46. ++method; // skip code
47.
48. const QMetaObject *rmeta = receiver->metaObject();
49. int method_index = -1;
50. switch (membcode) {
51. ca QSLOT_CODE:
52. method_index = rmeta->indexOfSlot(method);
53. break;
54. ca QSIGNAL_CODE:
55. method_index = rmeta->indexOfSignal(method);
56. break;
57. }
58. if (method_index < 0) {
59. // check for normalized methods
60. tmp_method_name = QMetaObject::normalizedSignature(method);
61. method = tmp_stData();
62. switch (membcode) {
63. ca QSLOT_CODE:
64. method_index = rmeta->indexOfSlot(method);
64. method_index = rmeta->indexOfSlot(method);
65. break;
66. ca QSIGNAL_CODE:
67. method_index = rmeta->indexOfSignal(method);
68. break;
69. }
70. }
71.
72. if (method_index < 0) {
73. err_method_notfound(receiver, method_arg, "connect");
74. err_info_about_objects("connect", nder, receiver);
75. return fal;
76. }
77. if (!QMetaObject::checkConnectArgs(signal, method)) {
78. qWarning("QObject::connect: Incompatible nder/receiver arguments"
79. "\n %s::%s --> %s::%s",
80. nder->metaObject()->className(), signal,
81. receiver->metaObject()->className(), method);
82. return fal;
83. }
84.
85. int *types = 0;
86. if ((type == Qt::QueuedConnection || type == Qt::BlockingQueuedConnection)
87. && !(types = queuedConnectionTypes(smeta->method(signal_index).parameterTypes())))
88. return fal;
89.
90. QMetaObject::connect(nder, signal_index, receiver, method_index, type, types);
91. const_cast<QObject*>(nder)->connectNotify(signal - 1);
92. return true;
93. }
判断连接是否已经建⽴：
1. const void *cbdata[] = { nder, signal, receiver, method, &type };
cctv news在线直播2. if (QInternal::activateCallbacks(QInternal::ConnectCallback, (void **) cbdata))
3. return true;
QInternal：：ConnectCallback在qglobal.cpp中实现：
1. bool QInternal::activateCallbacks(Callback cb, void **parameters)
2. {
3. Q_ASSERT_X(cb >= 0, "QInternal::activateCallback()", "Callback id must be a valid id");
4.
5. QInternal_CallBackTable *cbt = global_callback_table();
6. if (cbt && cb < cbt->callbacks.size()) {
7. QList<qInternalCallback> callbacks = cbt->callbacks[cb];
bored怎么读
8. bool ret = fal;
9. for (int i=0; i<callbacks.size(); ++i)
10. ret |= (callbacks.at(i))(parameters);
racer
11. return ret;
12. }
13. return fal;
14. }
QInternal_CallBackTable 定义为(qglobal.cpp)：
1. struct QInternal_CallBackTable {
shapeofmyheart2. QVector<QList<qInternalCallback> > callbacks;
3. };
qInternalCallback定义为(qnamespace.h)：
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。
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。
判断signal是否合法
1. if (!check_signal_macro(nder, signal, "connect", "bind"))
2. return fal;hoho
在QObject.cpp⽂件中可以找到check_signal_macro的实现
