- Qt 5.15
- Qt Core
- C++ Classes
- QState
- Qt 5.15.19 Reference Documentation

# QState Class

The QState class provides a general-purpose state for QStateMachine. More...

Header: | #include <QState>
qmake: | QT += core
Since: | Qt 4.6
Inherits: | QAbstractState
Inherited By: | QStateMachine

This class was introduced in Qt 4.6.

- List of all members, including inherited members

## Public Types

enum | ChildMode { ExclusiveStates, ParallelStates }
enum | RestorePolicy { DontRestoreProperties, RestoreProperties }

## Properties

- childMode : ChildMode
- errorState : QAbstractState*
- initialState : QAbstractState*

## Public Functions

| QState(ChildMode childMode, QState *parent = nullptr)
| QState(QState *parent = nullptr)
virtual | ~QState()
void | addTransition(QAbstractTransition *transition)
QSignalTransition * | addTransition(const QObject *sender, const char *signal, QAbstractState *target)
QSignalTransition * | addTransition(const QObject *sender, PointerToMemberFunction signal, QAbstractState *target)
QAbstractTransition * | addTransition(QAbstractState *target)
void | assignProperty(QObject *object, const char *name, const QVariant &value)
ChildMode | childMode() const
QAbstractState * | errorState() const
QAbstractState * | initialState() const
void | removeTransition(QAbstractTransition *transition)
void | setChildMode(ChildMode mode)
void | setErrorState(QAbstractState *state)
void | setInitialState(QAbstractState *state)
QList<QAbstractTransition *> | transitions() const

## Signals

void | childModeChanged(QPrivateSignal)
void | errorStateChanged(QPrivateSignal)
void | initialStateChanged(QPrivateSignal)

## Reimplemented Protected Functions

virtual bool | event(QEvent *e) override
virtual void | onEntry(QEvent *event) override
virtual void | onExit(QEvent *event) override

## Detailed Description

QState objects can have child states, and can have transitions to other states. QState is part of The State Machine Framework.

The addTransition() function adds a transition. The removeTransition() function removes a transition. The transitions() function returns the state's outgoing transitions.

The assignProperty() function is used for defining property assignments that should be performed when a state is entered.

Top-level states must be passed a QStateMachine object as their parent state, or added to a state machine using QStateMachine::addState().

### States with Child States

The childMode property determines how child states are treated. For non-parallel state groups, the setInitialState() function must be called to set the initial state. The child states are mutually exclusive states, and the state machine needs to know which child state to enter when the parent state is the target of a transition.

The state emits the QState::finished() signal when a final child state (QFinalState) is entered.

The setErrorState() sets the state's error state. The error state is the state that the state machine will transition to if an error is detected when attempting to enter the state (e.g. because no initial state has been set).

## Member Type Documentation

### enum QState::ChildMode

This enum specifies how a state's child states are treated.

Constant | Value | Description
--- | --- | ---
`QState::ExclusiveStates` | `0` | The child states are mutually exclusive and an initial state must be set by calling QState::setInitialState().
`QState::ParallelStates` | `1` | The child states are parallel. When the parent state is entered, all its child states are entered in parallel.

### enum QState::RestorePolicy

This enum specifies the restore policy type. The restore policy takes effect when the machine enters a state which sets one or more properties. If the restore policy is set to RestoreProperties, the state machine will save the original value of the property before the new value is set.

Later, when the machine either enters a state which does not set a value for the given property, the property will automatically be restored to its initial value.

Only one initial value will be saved for any given property. If a value for a property has already been saved by the state machine, it will not be overwritten until the property has been successfully restored.

Constant | Value | Description
--- | --- | ---
`QState::DontRestoreProperties` | `0` | The state machine should not save the initial values of properties and restore them later.
`QState::RestoreProperties` | `1` | The state machine should save the initial values of properties and restore them later.

See also QStateMachine::globalRestorePolicy and QState::assignProperty().

## Property Documentation

### childMode : ChildMode

This property holds the child mode of this state

The default value of this property is QState::ExclusiveStates.

Access functions:

ChildMode | childMode() const
void | setChildMode(ChildMode mode)

Notifier signal:

void | childModeChanged(QPrivateSignal)

### errorState : QAbstractState*

This property holds the error state of this state

Access functions:

QAbstractState * | errorState() const
void | setErrorState(QAbstractState *state)

Notifier signal:

void | errorStateChanged(QPrivateSignal)

### initialState : QAbstractState*

This property holds the initial state of this state (one of its child states)

Access functions:

QAbstractState * | initialState() const
void | setInitialState(QAbstractState *state)

Notifier signal:

void | initialStateChanged(QPrivateSignal)

## Member Function Documentation

### QState::QState(ChildMode childMode, QState *parent = nullptr)

Constructs a new state with the given childMode and the given parent state.

### QState::QState(QState *parent = nullptr)

Constructs a new state with the given parent state.

### `[virtual]` QState::~QState()

Destroys this state.

### void QState::addTransition(QAbstractTransition *transition)

Adds the given transition. The transition has this state as the source. This state takes ownership of the transition.

### QSignalTransition *QState::addTransition(const QObject *sender, const char *signal, QAbstractState *target)

Adds a transition associated with the given signal of the given sender object, and returns the new QSignalTransition object. The transition has this state as the source, and the given target as the target state.

### template <typename PointerToMemberFunction> QSignalTransition *QState::addTransition(const QObject *sender, PointerToMemberFunction signal, QAbstractState *target)

This is an overloaded function.

Adds a transition associated with the given signal of the given sender object, and returns the new QSignalTransition object. The transition has this state as the source, and the given target as the target state.

This function was introduced in Qt 5.5.

### QAbstractTransition *QState::addTransition(QAbstractState *target)

Adds an unconditional transition from this state to the given target state, and returns then new transition object.

### void QState::assignProperty(QObject *object, const char *name, const QVariant &value)

Instructs this state to set the property with the given name of the given object to the given value when the state is entered.

See also propertiesAssigned().

### ChildMode QState::childMode() const

Returns the child mode of this state.

Note: Getter function for property childMode.

See also setChildMode().

### QAbstractState *QState::errorState() const

Returns this state's error state.

Note: Getter function for property errorState.

See also setErrorState() and QStateMachine::error().

### `[override virtual protected]` bool QState::event(QEvent *e)

Reimplements: QAbstractState::event(QEvent *e).

### QAbstractState *QState::initialState() const

Returns this state's initial state, or `nullptr` if the state has no initial state.

Note: Getter function for property initialState.

See also setInitialState().

### `[override virtual protected]` void QState::onEntry(QEvent *event)

Reimplements: QAbstractState::onEntry(QEvent *event).

### `[override virtual protected]` void QState::onExit(QEvent *event)

Reimplements: QAbstractState::onExit(QEvent *event).

### void QState::removeTransition(QAbstractTransition *transition)

Removes the given transition from this state. The state releases ownership of the transition.

See also addTransition().

### void QState::setChildMode(ChildMode mode)

Sets the child mode of this state.

Note: Setter function for property childMode.

See also childMode().

### void QState::setErrorState(QAbstractState *state)

Sets this state's error state to be the given state. If the error state is not set, or if it is set to `nullptr`, the state will inherit its parent's error state recursively. If no error state is set for the state itself or any of its ancestors, an error will cause the machine to stop executing and an error will be printed to the console.

Note: Setter function for property errorState.

See also errorState().

### void QState::setInitialState(QAbstractState *state)

Sets this state's initial state to be the given state. state has to be a child of this state.

Note: Setter function for property initialState.

See also initialState().

### QList<QAbstractTransition *> QState::transitions() const

Returns this state's outgoing transitions (i.e. transitions where this state is the source state), or an empty list if this state has no outgoing transitions.

This function was introduced in Qt 4.7.

See also addTransition().