事件处理 – 如何在场景图的节点中监听WindowEvent.WINDOW_SHOWN

发布时间：2020-12-14 04:04:49 所属栏目：Windows 来源：网络整理

导读：似乎WindowEvent.WINDOW_SHOWN永远不会在场景图中的任何节点上调度,也无论如何(我可以找到)知道节点何时可见/呈现/显示.例如： TestLauncher.java package com.example.javafx.event;import javafx.application.Application;import javafx.fxml.FXMLLoader;i

似乎WindowEvent.WINDOW_SHOWN永远不会在场景图中的任何节点上调度,也无论如何(我可以找到)知道节点何时可见/呈现/显示.例如：

TestLauncher.java

package com.example.javafx.event;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class TestLauncher extends Application
{
    public static void main(String[] args)
    {
        Application.launch(TestLauncher.class,args);
    }

    @Override
    public void start(Stage stage) throws Exception
    {
        Parent root = FXMLLoader.load(TestController.class.getResource("TestView.fxml"));
        Scene scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
    }
}

TestController.java

package com.example.javafx.event;

import java.net.URL;
import java.util.ResourceBundle;
import javafx.event.EventHandler;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.Parent;
import javafx.scene.control.TextField;
import javafx.stage.WindowEvent;

public class TestController implements Initializable
{
    @FXML private Parent root;
    @FXML private TextField serverAddressInput;
    @FXML private TextField usernameInput;

    @Override
    public void initialize(URL url,ResourceBundle rb)
    {
        serverAddressInput.setText("127.0.0.1");

        //won't work because stage isn't visible yet
        trySetFocusOnUsernameInput1();

        //apparently Stage never passes on any WindowEvents to the children...
        trySetFocusOnUsernameInput2();
    }

    private void trySetFocusOnUsernameInput1()
    {
        usernameInput.requestFocus();
    }

    private void trySetFocusOnUsernameInput2()
    {
        root.addEventFilter(WindowEvent.WINDOW_SHOWN,new EventHandler<WindowEvent>()
        {
            @Override
            public void handle(WindowEvent window)
            {
                usernameInput.requestFocus();
            }
        });

        root.addEventHandler(WindowEvent.WINDOW_SHOWN,new EventHandler<WindowEvent>()
        {
            @Override
            public void handle(WindowEvent window)
            {
                usernameInput.requestFocus();
            }
        });
    }

    public void handleWindowShownEvent()
    {
        usernameInput.requestFocus();
    }
}

TestView.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import java.lang.*?>
<?import javafx.scene.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>

<VBox
    xmlns:fx="http://javafx.com/fxml"

    fx:id="root"
    fx:controller="com.example.javafx.event.TestController"

    prefHeight="150"
    prefWidth="200"
>
    <children>
        <TextField fx:id="serverAddressInput" />
        <TextField fx:id="usernameInput" />
    </children>
</VBox>

那么,实际上,节点如何才能意识到它是可见/渲染/显示的事实？

我想其中一个可能的解决方案是将以下方法添加到TestController.java中

public void handleWindowShownEvent()
    {
        usernameInput.requestFocus();
    }

然后将TestLauncher中的start方法更改为以下内容：

@Override
    public void start(Stage stage) throws Exception
    {
        FXMLLoader loader = new FXMLLoader();
        Parent root = (Parent)loader.load(TestController.class.getResourceAsStream("TestView.fxml"));
        final TestController controller = (TestController)loader.getController();
        stage.addEventHandler(WindowEvent.WINDOW_SHOWN,new EventHandler<WindowEvent>()
        {
            @Override
            public void handle(WindowEvent window)
            {
                controller.handleWindowShownEvent();
            }
        });
        Scene scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
    }

我真的很欢迎其他解决方案,因为这个看起来太笨重……

（编辑：李大同）

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