Java FX 将函数作为参数发送到方法

Question

更新 2019.05.14 4:54PM EST - 好的 - 这是说明我的问题的代码 - 可能花了我太长时间才得到这个，而且可能太长了，但同样，我是 Java 新手。无论如何 - 它有效，打开表单，但无法让第二个按钮看到“事件”并对“事件”使用react。我想我现在正在“引发”事件，好吧 - 至少它击中了事件中的代码。但是，它仍然运行类代码，而不是通过 setOnFormStateChange 传入的“自定义”代码？？？我不确定出了什么问题。

所有导入

import java.util.ArrayList;
import java.util.Date;
import javafx.application.Application;
import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.event.Event;
import javafx.event.EventHandler;
import javafx.event.EventType;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.AnchorPane;
import javafx.stage.Stage;

MyApp.java

public class MyApp extends Application {

    public static void main(String[] args) {
        launch(args); // this method will hang here until main form is closed!
    }

    @Override
    public void start(Stage stage) throws Exception {
        Form myForm = new Form();
        myForm.ShowForm();
    }

}

Form.java

class Form {

    private boolean modified;
    private ArrayList<FormStateChangeListener> registry = new ArrayList<>();

    public void setModified(boolean m) {
        modified = m;
        this.throwStateChange(m);
    }

    public void throwStateChange(boolean m) {
        for (FormStateChangeListener o : registry) {
          //  o.onFormStateChange(m);         
            FormStateChangeEvent.fireEvent(o,m);
        }
    }

    public void ShowForm() {

        Label lbl = new Label("NORMAL STATE");
        lbl.setLayoutX(50);
        lbl.setLayoutY(20);

        Btn myBtn1 = new Btn(this);
        myBtn1.setLayoutX(100);
        myBtn1.setLayoutY(100);
        myBtn1.setPrefWidth(200);

        myBtn1.setText("Press To Change State");
        myBtn1.setOnAction(e -> {
            lbl.setText("CHANGED STATE:" + new Date().toString());
            this.setModified(true);
        });

        Btn myBtn2 = new Btn(this);
        myBtn2.setLayoutX(100);
        myBtn2.setLayoutY(200);
        myBtn2.setPrefWidth(200);
        myBtn2.setText("And This Should React");

        myBtn2.setOnFormStateChange(e -> {
            myBtn2.setText("I REACTED!");
        });


        Stage stage = new Stage();
        AnchorPane root = new AnchorPane();
        Scene scene = new Scene(root, 430, 400);
       // root.getChildren().add(lbl);
       // root.getChildren().add(myBtn1);
       // root.getChildren().add(myBtn2);
        root.getChildren().addAll(lbl,myBtn1,myBtn2);
        stage.setScene(scene);
        stage.showAndWait();
    }

    void registerForEvent(FormStateChangeListener t) {
        registry.add(t);

    }

}

FormStateChangeListener.java

interface FormStateChangeListener {
    public void onFormStateChange(boolean mod);
}

FormState.java

enum FormState {
    NORMAL, MODIFIED, NEW
}

Btn.java

class Btn extends Button implements FormStateChangeListener {

    private final ObjectProperty<EventHandler<? super FormStateChangeEvent>> onFormStateChange
            = new SimpleObjectProperty<EventHandler<? super FormStateChangeEvent>>(this, "onFormStateChange") {

        @Override
        protected void invalidated() {
            setEventHandler(FormStateChangeEvent.FORM_STATE_CHANGE, get());
        }
    };

    public Btn(Form f) { // constructor
        f.registerForEvent(this); // register for the event
    }

    public final void setOnFormStateChange(EventHandler<? super FormStateChangeEvent> handler) {
        onFormStateChange.set(handler);
    }

    public final EventHandler<? super FormStateChangeEvent> getOnFormStateChange() {
        return onFormStateChange.get();
    }

    public final ObjectProperty<EventHandler<? super FormStateChangeEvent>> onFormStateChangeProperty() {
        return onFormStateChange;
    }

    public void onFormStateChange(boolean mod) {
        //in reality nothing would be here, but is just for testing
       System.out.println("Code from class.");
    }
;

}

FormStateChangeEvent.java

class FormStateChangeEvent extends Event {

    public static final EventType<FormStateChangeEvent> ANY = new EventType<>(Event.ANY, "MY_EVENT");
    public static final EventType<FormStateChangeEvent> FORM_STATE_CHANGE = new EventType<>(ANY, "FORM_STATE_CHANGE");

    static void fireEvent(FormStateChangeListener o, boolean mod) {
        //throw new UnsupportedOperationException("Not supported yet."); 
        o.onFormStateChange(mod);
    }

    public FormStateChangeEvent(EventType<? extends FormStateChangeEvent> eventType) {
        super(eventType);
    }
}

Answer 1

诸如setOnMouseClicked之类的方法接受javafx.event.EventHandler，它是一个函数式接口(interface)。换句话说，它有一个抽象方法，这意味着它可以用作 lambda 表达式或方法引用的目标。如果您的目标是拥有自己的具有相应 onXXX 属性的 Event 类，那么您的 setOnXXX 方法必须接受 EventHandler 像所有其他人一样。

但是，如果您希望在正常事件分派(dispatch)期间调用 EventHandler，仅仅设置该属性是不够的。您必须向事件调度程序注册它，这可以通过 protected Node.setEventHandler(EventType,EventHandler) 方法来完成。

例如，假设以下是您的事件类:

import javafx.event.Event;
import javafx.event.EventType;

public class MyEvent extends Event {

    public static final EventType<MyEvent> ANY = new EventType<>(Event.ANY, "MY_EVENT");
    public static final EventType<MyEvent> AWESOME_THING = new EventType<>(ANY, "AWESOME_THING");

    public MyEvent(EventType<? extends MyEvent> eventType) {
        super(eventType);
    }

}

那么您的自定义节点将类似于:

import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.event.EventHandler;
import javafx.scene.control.Button;

public class MyButton extends Button {

    private final ObjectProperty<EventHandler<? super MyEvent>> onAwesomeThing 
            = new SimpleObjectProperty<>(this, "onAwesomeThing") {
            @Override protected void invalidated() {
                setEventHandler(MyEvent.AWESOME_THING, get());
            }
    };

    public final void setOnAwesomeThing(EventHandler<? super MyEvent> handler) {
        onAwesomeThing.set(handler);
    }

    public final EventHandler<? super MyEvent> getOnAwesomeThing() {
        return onAwesomeThing.get();
    }

    public final ObjectProperty<EventHandler<? super MyEvent>> onAwesomeThingProperty() {
        return onAwesomeThing;
    }

}

通常，与事件关联的每个 EventType 都有一个属性，“常规”事件类型(例如 MyEvent.ANY)除外。

现在您可以调用 myBtn.fireEvent(new MyEvent(MyEvent.AWESOME_THING)) 并且您注册的 EventHandler 将被调用。您还可以通过 addEventFilter 或 addEventHandler 注册处理程序。