Doc: Restructure "Signal & Slots" article
Put sections with similar content together: - Put "A Small Example" next to "A Real Example". - Put "Signals and Slots", "Signals", and "Slots" together. Altogether, these 3 sections contain lots of repeated content and should be consolidated in a future commit. This patch only moves content around without adding, removing, or modifying content. Change-Id: Ic6bf6a8b51f4785a8bbe6d230c2934f2c952104d Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
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@ -113,76 +113,6 @@
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Together, signals and slots make up a powerful component programming
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mechanism.
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\section1 A Small Example
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A minimal C++ class declaration might read:
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\snippet signalsandslots/signalsandslots.h 0
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A small QObject-based class might read:
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\snippet signalsandslots/signalsandslots.h 1
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\codeline
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\snippet signalsandslots/signalsandslots.h 2
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\snippet signalsandslots/signalsandslots.h 3
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The QObject-based version has the same internal state, and provides
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public methods to access the state, but in addition it has support
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for component programming using signals and slots. This class can
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tell the outside world that its state has changed by emitting a
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signal, \c{valueChanged()}, and it has a slot which other objects
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can send signals to.
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All classes that contain signals or slots must mention
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Q_OBJECT at the top of their declaration. They must also derive
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(directly or indirectly) from QObject.
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Slots are implemented by the application programmer.
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Here is a possible implementation of the \c{Counter::setValue()}
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slot:
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\snippet signalsandslots/signalsandslots.cpp 0
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The \c{emit} line emits the signal \c valueChanged() from the
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object, with the new value as argument.
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In the following code snippet, we create two \c Counter objects
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and connect the first object's \c valueChanged() signal to the
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second object's \c setValue() slot using QObject::connect():
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\snippet signalsandslots/signalsandslots.cpp 1
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\snippet signalsandslots/signalsandslots.cpp 2
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\codeline
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\snippet signalsandslots/signalsandslots.cpp 3
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\snippet signalsandslots/signalsandslots.cpp 4
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Calling \c{a.setValue(12)} makes \c{a} emit a
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\c{valueChanged(12)} signal, which \c{b} will receive in its
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\c{setValue()} slot, i.e. \c{b.setValue(12)} is called. Then
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\c{b} emits the same \c{valueChanged()} signal, but since no slot
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has been connected to \c{b}'s \c{valueChanged()} signal, the
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signal is ignored.
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Note that the \c{setValue()} function sets the value and emits
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the signal only if \c{value != m_value}. This prevents infinite
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looping in the case of cyclic connections (e.g., if
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\c{b.valueChanged()} were connected to \c{a.setValue()}).
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By default, for every connection you make, a signal is emitted;
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two signals are emitted for duplicate connections. You can break
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all of these connections with a single disconnect() call.
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If you pass the Qt::UniqueConnection \a type, the connection will only
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be made if it is not a duplicate. If there is already a duplicate
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(exact same signal to the exact same slot on the same objects),
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the connection will fail and connect will return false
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This example illustrates that objects can work together without needing to
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know any information about each other. To enable this, the objects only
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need to be connected together, and this can be achieved with some simple
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QObject::connect() function calls, or with \c{uic}'s
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\l{Using a Designer UI File in Your Application#Automatic Connections}
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{automatic connections} feature.
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\section1 Signals
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@ -258,6 +188,77 @@
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#undef the offending preprocessor symbol.
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\section1 A Small Example
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A minimal C++ class declaration might read:
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\snippet signalsandslots/signalsandslots.h 0
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A small QObject-based class might read:
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\snippet signalsandslots/signalsandslots.h 1
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\codeline
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\snippet signalsandslots/signalsandslots.h 2
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\snippet signalsandslots/signalsandslots.h 3
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The QObject-based version has the same internal state, and provides
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public methods to access the state, but in addition it has support
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for component programming using signals and slots. This class can
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tell the outside world that its state has changed by emitting a
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signal, \c{valueChanged()}, and it has a slot which other objects
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can send signals to.
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All classes that contain signals or slots must mention
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Q_OBJECT at the top of their declaration. They must also derive
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(directly or indirectly) from QObject.
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Slots are implemented by the application programmer.
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Here is a possible implementation of the \c{Counter::setValue()}
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slot:
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\snippet signalsandslots/signalsandslots.cpp 0
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The \c{emit} line emits the signal \c valueChanged() from the
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object, with the new value as argument.
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In the following code snippet, we create two \c Counter objects
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and connect the first object's \c valueChanged() signal to the
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second object's \c setValue() slot using QObject::connect():
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\snippet signalsandslots/signalsandslots.cpp 1
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\snippet signalsandslots/signalsandslots.cpp 2
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\codeline
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\snippet signalsandslots/signalsandslots.cpp 3
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\snippet signalsandslots/signalsandslots.cpp 4
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Calling \c{a.setValue(12)} makes \c{a} emit a
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\c{valueChanged(12)} signal, which \c{b} will receive in its
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\c{setValue()} slot, i.e. \c{b.setValue(12)} is called. Then
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\c{b} emits the same \c{valueChanged()} signal, but since no slot
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has been connected to \c{b}'s \c{valueChanged()} signal, the
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signal is ignored.
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Note that the \c{setValue()} function sets the value and emits
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the signal only if \c{value != m_value}. This prevents infinite
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looping in the case of cyclic connections (e.g., if
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\c{b.valueChanged()} were connected to \c{a.setValue()}).
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By default, for every connection you make, a signal is emitted;
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two signals are emitted for duplicate connections. You can break
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all of these connections with a single disconnect() call.
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If you pass the Qt::UniqueConnection \a type, the connection will only
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be made if it is not a duplicate. If there is already a duplicate
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(exact same signal to the exact same slot on the same objects),
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the connection will fail and connect will return false
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This example illustrates that objects can work together without needing to
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know any information about each other. To enable this, the objects only
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need to be connected together, and this can be achieved with some simple
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QObject::connect() function calls, or with \c{uic}'s
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\l{Using a Designer UI File in Your Application#Automatic Connections}
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{automatic connections} feature.
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\section1 A Real Example
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Here is a simple commented example of a widget.
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