实例化状态机

动态创建状态机和编译状态机两者行为方式相同，拥有相同特性、状态、数据模型等。它们仅实例化方式有所不同。要从 SCXML 文件以 C++ 动态创建一个，可以使用：

auto *stateMachine = QScxmlStateMachine::fromFile("MyStatemachine.scxml");
					

或，以 QML：

import QtScxml 5.8
Item {
    property StateMachine stateMachine: scxmlLoader.stateMachine
    StateMachineLoader {
        id: scxmlLoader
        source: "statemachine.scxml"
    }
}
					

编译状态机的实例化方式如同任何 C++ 对象：

auto *stateMachine = new MyStatemachine;
					

或：

MyStatemachine stateMachine;
					

要在 QML 中使用编译状态机，可以将其注册成 QML 类型：

qmlRegisterType<MyStateMachine>("MyStateMachine", 1, 0, "MyStateMachine");
					

然后，可以在 QML 中实例化它，像这样：

import MyStateMachine 1.0
MyStateMachine {
    id: stateMachine
}
					

要编译状态机，必须将以下行添加到 .pro 文件：

QT += scxml
STATECHARTS = MyStatemachine.scxml
					

This will tell qmake to run qscxmlc which generates MyStatemachine.h and MyStatemachine.cpp, and adds them to HEADERS and SOURCES variables. By default, the generated files are saved in the build directory. The QSCXMLC_DIR variable can be set to specify another directory. The QSCXMLC_NAMESPACE variable can be set to put the state machine code into a C++ namespace.

After instantiating a state machine, you can connect to any state's active property as follows. For example, if the state machine for a traffic light has a state indicating that the light is red (which has the convenient id "red" in the scxml file), you can write:

stateMachine->connectToState("red", [](bool active) {
    qDebug() << (active ? "entered" : "exited") << "the red state";
					

And in QML:

Light {
    id: greenLight
    color: "green"
    visible: stateMachine.green
}
					

If you want to be notified when a state machine sends out an event, you can connect to the corresponding signal. For example, for a media player state machine which indicates that playback has stopped by sending an event, you can write:

stateMachine->connectToEvent("playbackStopped", [](const QScxmlEvent &){
    qDebug() << "Stopped!";
});
					

And in QML:

import QtScxml 5.8
EventConnection {
    stateMachine: stateMachine
    events: ["playbackStopped"]
    onOccurred: console.log("Stopped!")
}
					

Sending events to a state machine is equally simple:

stateMachine->submitEvent("tap", QVariantMap({
    { "artist", "Fatboy Slim" },
    { "title", "The Rockafeller Skank" }
});
					

This will generate a "tap" event with the map contents available in _event.data inside the state machine. In QML:

stateMachine.submitEvent("tap", {
    "artist": "Fatboy Slim"
    "title": "The Rockafeller Skank"
})
					

注意： 状态机需要 QEventLoop to work correctly. The event loop is used to implement the delay attribute for events and to schedule the processing of a state machine when events are received from nested (or parent) state machines. A QML application or a widget application will always have an event loop running, so nothing extra is needed. For other applications, QApplication::run will have to be called to start the event loop processing.