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For signal and slot of below type
signals: void textChanged(const QString &); public slots: void setText(const QString & text) the type of argument of textChanged and setText seems to work invarable of const and &. Does the constant and reference qualification make any difference compared to just using QString ?
QObject::connect(a,SIGNAL(textChanged(QString)),b,SLOT(setText(QString))); QObject::connect(a,SIGNAL(textChanged(const QString &)),b,SLOT(setText(const QString &))); EDIT: I did not notice the output window showing error messages when there is incompatible type being used in SIGNAL or SLOT. I thought the signal slot mechanism is capable of detecting argument type error at compile time.
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In Qt, we have an alternative to the callback technique: We use signals and slots. A signal is emitted when a particular event occurs. Qt's widgets have many predefined signals, but we can always subclass widgets to add our own signals to them. A slot is a function that is called in response to a particular signal.
Queued Connection The slot is invoked when control returns to the event loop of the receiver's thread. The slot is executed in the receiver's thread. Blocking Queued Connection The slot is invoked as for the Queued Connection, except the current thread blocks until the slot returns.
Event loop of another thread is started by default implementation of QThread::run . When Qt decides it's time to process an event, it executes its event handler. While event handler is working, Qt has no chance to process any other event (unless given directly by QApplication::processEvents() or some other methods).
Qt checks a normalized signature, meaning
Normalization reduces whitespace to a minimum, moves 'const' to the front where appropriate, removes 'const' from value types and replaces const references with values.
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