StateMachine QML Type

Provides a hierarchical finite state machine. More...

• List of all members, including inherited members

Properties

• errorString : string
• globalRestorePolicy : enumeration
• running : bool

Signals

• started()
• stopped()

Methods

• start()
• stop()

Detailed Description

StateMachine is based on the concepts and notation of Statecharts. StateMachine is part of The Declarative State Machine Framework.

A state machine manages a set of states and transitions between those states; these states and transitions define a state graph. Once a state graph has been built, the state machine can execute it. StateMachine's execution algorithm is based on the State Chart XML (SCXML) algorithm. The framework's overview gives several state graphs and the code to build them.

Before the machine can be started, the initialState must be set. The initial state is the state that the machine enters when started. You can then set running property to true or start() the state machine. The started signal is emitted when the initial state is entered.

The state machine processes events and takes transitions until a top-level final state is entered; the state machine then emits the finished() signal. You can also stop() the state machine explicitly (you can also set running property to false). The stopped signal is emitted in this case.

Example Usage

The following snippet shows a state machine that will finish when a button is clicked:

import QtQuick 2.0
import QtQml.StateMachine 1.0 as DSM

Rectangle {
    Button {
        anchors.fill: parent
        id: button
        text: "Finish state"
        DSM.StateMachine {
            id: stateMachine
            initialState: state
            running: true
            DSM.State {
                id: state
                DSM.SignalTransition {
                    targetState: finalState
                    signal: button.clicked
                }
            }
            DSM.FinalState {
                id: finalState
            }
            onFinished: Qt.quit()
        }
    }
}

If an error is encountered, the machine will look for an errorState, and if one is available, it will enter this state. After the error state is entered, the type of the error can be retrieved with error(). The execution of the state graph will not stop when the error state is entered. If no error state applies to the erroneous state, the machine will stop executing and an error message will be printed to the console.

Warning: Setting the childMode of a StateMachine to anything else than QState::ExclusiveStates will result in an invalid state machine, and can lead to incorrect behavior.

See also QAbstractState, State, SignalTransition, TimeoutTransition, HistoryState, and The Declarative State Machine Framework.

Property Documentation

Signal Documentation

Method Documentation