java - 如何从主应用程序的 init() 方法调用 JavaFX 应用程序预加载器实例中的方法

Question

在 JavaFX 应用程序的 init() 方法中，我正在执行一些检查，其中之一是检查它是否可以使用 Http 响应代码连接到基于 Web 地址。该应用程序还有一个预加载器，可以在这些检查发生时运行。

根据响应代码，我希望它在预加载器应用程序的生命周期中显示警报窗口

我不确定使用当前的 javafx 预加载器类是否可以实现此目的，但是是否有任何解决方法可以实现此目的？

下面是我想要的 SSCCE

申请

public class MainApplicationLauncher extends Application implements Initializable{

    ...

    public void init() throws Exception {       
          
        for (int i = 1; i <= COUNT_LIMIT; i++) {
            double progress =(double) i/10;
            System.out.println("progress: " +  progress);         
            
            notifyPreloader(new ProgressNotification(progress));
            Thread.sleep(500);
        }
        
        try {
            URL url = new URL("https://example.com");
            HttpURLConnection connection = (HttpURLConnection)url.openConnection();
            connection.setRequestMethod("GET");
            connection.connect();           
            int code = connection.getResponseCode();
            System.out.println("Response code of the object is "+code);
            if (code==200) {
                System.out.println("Connected to the internet!");
            }else if (code==503){
                        //call the handleConnectionWarning() in preloader
                System.out.println("server down !");
            }
        } catch (UnknownHostException e) {
                //call the handleConnectionWarning() in preloader
            System.out.println("cannot connect to the internet!");
        }

    public static void main(String[] args) {        
       System.setProperty("javafx.preloader", MainPreloader.class.getCanonicalName());
        Application.launch(MainApplicationLauncher.class, args);
   }
}

预加载器

public class MyPreloader extends Preloader {

...

//Method that should be called from application method

public void handleConnectionWarning() {
        Alert alert = new Alert(AlertType.WARNING);
        alert.setTitle("Server is Offline");
        alert.setHeaderText("Cannot connect to service");
        alert.setContentText("Please check your connection");

        alert.showAndWait();
    }

}

有什么方法可以做到这一点吗？

Answer 1

预加载器

如果您想继续在启动画面中使用Preloader，那么您可以通过通知调用所需的方法。创建您自己的通知类:

// You can modify this class to carry information to the Preloader, such
// as a message indicating what kind of failure occurred.
public class ConnectionFailedNotification implements Preloader.PreloaderNotification {}

将其发送到您的预加载器:

notifyPreloader(new ConnectionFailedNotification());

并在所述预加载器中处理它:

@Override
public void handleApplicationNotification(PreloaderNotification info) {
    if (info instanceof ConnectionFailedNotification) {
        handleConnectionWarning();
    }
    // ...
}

---

无预加载器

当您通过 Java Web Start(即 Web 浏览器)部署应用程序时，Preloader 类更有意义，在使用代码之前必须下载代码。但 Java Web Start 不再受支持(尽管我认为可能有第三方维护至少类似的东西)。鉴于您的应用程序可能面向简单的桌面部署，使用 Preloader 可能会使事情变得不必要的复杂。相反，请考虑在初始化后简单地更新主要阶段的内容。

将您的 init() 内容移至 Task 实现中:

import java.io.IOException;
import javafx.concurrent.Task;

public class InitTask extends Task<Void> {

    private static final int COUNT_LIMIT = 10;

    private final boolean shouldSucceed;

    public InitTask(boolean shouldSucceed) {
        this.shouldSucceed = shouldSucceed;
    }

    @Override
    protected Void call() throws Exception {
        for (int i = 1; i <= COUNT_LIMIT; i++) {
            updateProgress(i, COUNT_LIMIT);
            Thread.sleep(500);
        }
        
        // could use a Boolean return type for this, but your real code seems
        // more complicated than a simple "yes" / "no" response. If you do
        // change the implementation to use a return value, note that you would
        // then need to check that return value in the 'onSucceeded' handler
        if (!shouldSucceed) {
            throw new IOException("service unavailable"); // failure
        }
        return null; // success
    }
    
}

然后在后台线程上启动该任务:

import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Scene;
import javafx.scene.control.Alert;
import javafx.scene.control.Label;
import javafx.scene.control.ProgressBar;
import javafx.scene.control.Alert.AlertType;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;;

public class App extends Application {
    
    @Override
    public void start(Stage primaryStage) throws Exception {
        var task = new InitTask(false); // change to 'true' to simulate success
        task.setOnSucceeded(e -> primaryStage.getScene().setRoot(createMainScreen()));
        task.setOnFailed(e -> {
            var alert = new Alert(AlertType.WARNING);
            alert.initOwner(primaryStage);
            alert.setTitle("Server Offline");
            alert.setHeaderText("Cannot connect to service");
            alert.setContentText("Please check your connection");
            alert.showAndWait();

            Platform.exit();
        });

        // Also see the java.util.concurrent.Executor framework
        var thread = new Thread(task, "init-thread");
        thread.setDaemon(true);
        thread.start();

        var scene = new Scene(createSplashScreen(task), 600, 400);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private StackPane createSplashScreen(InitTask task) {
        var bar = new ProgressBar();
        bar.progressProperty().bind(task.progressProperty());
        return new StackPane(bar);
    }

    private StackPane createMainScreen() {
        return new StackPane(new Label("Hello, World!"));
    }
}

---

附注

您的Application子类不应实现Initialized。该子类代表整个应用程序，并且永远不应该用作 FXML Controller 。