QMetaObject之invokeMethod 点滴记录（有时间在看看）
QMetaObject之invokeMethod 点滴记录
2010-10-18 16:53
起源C++ GUI Qt4 编程 一书多线程部分提到invokeMethod的用法 QMetaObject::invokeMethod(label, SLOT(setText(const QString&)), Q_ARG(QString, "Hello")); 而 Qt Manual 中介绍却是
QMetaObject::invokeMethod(pushButton, "animateClick"); 这可怎么办？一个是官方的图书，一个是官方的Manual。是否意味着两种方式都可以呢，还是说Qt的早期版本用的是前者？ 查 Qt4.7/Qt4.6/Qt4.5/Qt4.4/Qt4.3/Qt4.2/Qt4.1/Qt4.0 ，结果发现都没有提到前面的用法。是不是书的出错呢？网上搜一下：确实有人抱怨它不工作 测试本着事实就是的精神，还是先写个程序测试一下： #include <QtCore/QObject> #include <QtCore/QDebug> #include <QtCore/QCoreApplication> class Test : public QObject { Q_OBJECT public: Test(QObject * parent):QObject(parent) { connect(this, SIGNAL(sig1(QString)), SLOT(slot1(QString))); QMetaObject::invokeMethod(this, "sig1", Q_ARG(QString, "constructor")); } Q_INVOKABLE void method1(const QString& t) { qDebug()<<"from method:"<<t; } signals: void sig1(const QString& t); public slots: void slot1(const QString& t) { qDebug()<<"from slot:"<<t; } }; #include "main.moc" int main(int argc, char *argv[]) { QCoreApplication a(argc, argv); Test obj(0); QMetaObject::invokeMethod(&obj, "slot1", Q_ARG(QString, "Hello")); QMetaObject::invokeMethod(&obj, "method1", Q_ARG(QString, "Hello")); QMetaObject::invokeMethod(&obj, SLOT(slot1(QString)), Q_ARG(QString, "Hello with SLOT")); QMetaObject::invokeMethod(&obj, METHOD(method1(QString)), Q_ARG(QString, "Hello with METHOD")); return a.exec(); } 确实如他人所说，SLOT这种用法不工作 from slot: "constructor" from slot: "Hello" from method: "Hello" QMetaObject::invokeMethod: No such method Test::1slot1(QString)(QString) QMetaObject::invokeMethod: No such method Test::0method1(QString)(QString) 源码顺便看看源码吧
bool QMetaObject::invokeMethod(QObject *obj, const char *member, Qt::ConnectionType type, QGenericReturnArgument ret, QGenericArgument val0, QGenericArgument val1, QGenericArgument val2, QGenericArgument val3, QGenericArgument val4, QGenericArgument val5, QGenericArgument val6, QGenericArgument val7, QGenericArgument val8, QGenericArgument val9) { if (!obj) return false; QVarLengthArray<char, 512> sig; int len = qstrlen(member); if (len <= 0) return false; 生成函数原型字符串(从这儿可以看到书中方法不工作的原因) sig.append(member, len); sig.append('('); const char *typeNames[] = {ret.name(), val0.name(), val1.name(), val2.name(), val3.name(), val4.name(), val5.name(), val6.name(), val7.name(), val8.name(), val9.name()}; int paramCount; for (paramCount = 1; paramCount < MaximumParamCount; ++paramCount) { len = qstrlen(typeNames[paramCount]); if (len <= 0) break; sig.append(typeNames[paramCount], len); sig.append(','); } if (paramCount == 1) sig.append(')'); // no parameters else sig[sig.size() - 1] = ')'; sig.append('\0'); 在元对象系统中看该函数信息是否存在 int idx = obj->metaObject()->indexOfMethod(sig.constData()); if (idx < 0) { QByteArray norm = QMetaObject::normalizedSignature(sig.constData()); idx = obj->metaObject()->indexOfMethod(norm.constData()); } if (idx < 0 || idx >= obj->metaObject()->methodCount()) { qWarning("QMetaObject::invokeMethod: No such method %s::%s", obj->metaObject()->className(), sig.constData()); return false; } 获得相应的 QMetaMethod,调用其 invoke 方法 QMetaMethod method = obj->metaObject()->method(idx); return method.invoke(obj, type, ret, val0, val1, val2, val3, val4, val5, val6, val7, val8, val9); } QMetaMethod::invoke接着看看它的源码，首先： * 如果指定了返回值，检查返回值的类型是否和QMetaMethod 的中的一致 if (returnValue.data()) {
const char *retType = typeName();
if (qstrcmp(returnValue.name(), retType) != 0) {
// normalize the return value as well
// the trick here is to make a function signature out of the return type
// so that we can call normalizedSignature() and avoid duplicating code
QByteArray unnormalized;
int len = qstrlen(returnValue.name());
unnormalized.reserve(len + 3);
unnormalized = "_(";
// the function is called "_"
unnormalized.append(returnValue.name());
unnormalized.append(')');
QByteArray normalized = QMetaObject::normalizedSignature(unnormalized.constData());
normalized.truncate(normalized.length() - 1); // drop the ending ')'
if (qstrcmp(normalized.constData() + 2, retType) != 0)
return false;
}
}
* 检查参数个数，传递的参数是否不少于需要的参数 * 检查Connection的类型，处理AutoConnection // check connection type
QThread *currentThread = QThread::currentThread();
QThread *objectThread = object->thread();
if (connectionType == Qt::AutoConnection) {
connectionType = currentThread == objectThread
? Qt::DirectConnection
: Qt::QueuedConnection;
}
if (connectionType == Qt::DirectConnection) {
return QMetaObject::metacall(object, QMetaObject::InvokeMetaMethod, methodIndex, param) < 0;
if (connectionType == Qt::QueuedConnection) {
QCoreApplication::postEvent(object, new QMetaCallEvent(methodIndex,
0,
-1,
nargs,
types,
args));
QSemaphore semaphore;
QCoreApplication::postEvent(object, new QMetaCallEvent(methodIndex,
0,
-1,
nargs,
types,
args,
&semaphore));
semaphore.acquire();
|