A Qt Quick application that uses a compiled state machine to implement a simplified traffic light.
Traffic Light QML Example (Simple) demonstrates how to connect to the active properties of a state in a state machine that is compiled to a class.
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We link against the Qt SCXML module by adding the following line to the .pro 文件：
QT += qml scxml
接着，指定要编译的状态机：
STATECHARTS = ../trafficlight-common/statemachine.scxml
Qt SCXML 编译器
qscxmlc
, is run automatically to generate
statemachine.h
and
statemachine.cpp
, and to add them to the
HEADERS
and
SOURCES
variables for compilation.
We instantiate the state machine as follows:
TrafficLightStateMachine {
id: stateMachine
running: true
}
In the SCXML file, we specify states for each light: red, yellow, and green. In the
<onentry>
element, we specify the event to send when entering the state and the delay in seconds before sending the event. In the
<transition>
element, we specify the event that triggers the transition to the state specified by the
target
属性：
<state id="red">
<onentry>
<send event="startGoingGreen" delay="3s"/>
</onentry>
<transition event="startGoingGreen" target="redGoingGreen"/>
</state>
<state id="yellow" initial="greenGoingRed">
<state id="redGoingGreen">
<onentry>
<send event="goGreen" delay="1s"/>
</onentry>
<transition event="goGreen" target="green"/>
</state>
<state id="greenGoingRed">
<onentry>
<send event="goRed" delay="1s"/>
</onentry>
<transition event="goRed" target="red"/>
</state>
</state>
<state id="green">
<onentry>
<send event="startGoingRed" delay="3s"/>
</onentry>
<transition event="startGoingRed" target="greenGoingRed"/>
</state>
We connect to the states as follows:
Light {
anchors.top: parent.top
anchors.horizontalCenter: parent.horizontalCenter
color: "red"
visible: stateMachine.red || stateMachine.redGoingGreen
}
Light {
anchors.centerIn: parent
color: "yellow"
visible: stateMachine.yellow || stateMachine.blinking
}
Light {
anchors.bottom: parent.bottom
anchors.horizontalCenter: parent.horizontalCenter
color: "green"
visible: stateMachine.green
}
}