JavaFX 进度指示器未正确更新

Question

我正在创建一个 JavaFX 桌面应用程序，在其中模拟一些工作负载。我希望应用程序有一个动态更新的进度指示器(随着时间的流逝)以显示加载过程的进展情况。这是我的应用程序类:

public class App extends Application {

@Override
public void init() throws InterruptedException{
    //Simulation of time consuming code.
    for(int i = 0; i<=10; i++) {
        notifyPreloader(new Preloader.ProgressNotification(i/10));
        System.out.println("Progress is being set by the app to: " + (i/10));
        Thread.sleep(500);
    }
}

@Override
public void start(Stage primaryStage) {
    Parent root;
    try {
        root = FXMLLoader.load(getClass().getResource("/gui/fxml/App.fxml"));
        Scene scene = new Scene(root, 600, 400);

        scene.getStylesheets().add("/gui/style/app.css");

        primaryStage.setScene(scene);
        primaryStage.setTitle("Hello World!");
        primaryStage.show();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
}

这是我的预加载器类:

public class AppPreloader extends Preloader {
private Stage preloaderStage;
private Parent root;
private Scene scene;
private ProgressIndicator progress_indicator;

@Override
public void start(Stage primaryStage) throws Exception {
    this.preloaderStage = primaryStage;
    this.preloaderStage.setScene(this.scene);
    this.preloaderStage.show();
    this.progress_indicator = (ProgressIndicator) scene.lookup("#progressIndicator");
}


@Override
public void init() throws Exception {
    root = FXMLLoader.load(getClass().getResource("/gui/fxml/AppPreloader.fxml"));
    Platform.runLater(new Runnable() { 
        @Override
        public void run() {
            scene = new Scene(root, 600, 400);
            scene.getStylesheets().add("/gui/style/appPreloader.css");
        }
    });
}

@Override
public void handleProgressNotification(ProgressNotification pn) {
    if(pn instanceof ProgressNotification){
        progress_indicator.setProgress(pn.getProgress());
        System.out.println("Progress is being set by the handle method to: " + pn.getProgress());
    }
}

@Override
public void handleStateChangeNotification(StateChangeNotification evt) {
    if (evt.getType() == StateChangeNotification.Type.BEFORE_START) {
        preloaderStage.hide();
    }
}    
}

通过打印句子，我发现了两个问题:首先，在 App 类的 init 方法循环开始之前，handleProgressNotification 方法被调用两次，一次设置为 0，另一次设置为 1。 谁在打电话？我怎样才能避免它？

第二个问题是app类的init方法中的打印语句总是打印0.0。 这怎么可能？是并发问题吗？

此外，我需要说的是，我已经检查了这两个问题( progressbar in preloader does not update 和 javafx preloader not updating progress )，但没有找到解决我的问题的方法。

非常感谢您的宝贵时间。

Answer 1

首先，您没有看到预期的进度值，因为您使用的是整数算术:i和10都是整数，所以 i/10是 0对于 0 <= i < 10和1当i=10 .

第二，handleProgressNotification和handleStateChangeNotification方法是与加载资源相关的应用程序生命周期的一部分。这些确实是 JavaFX 仍然支持 Web 部署时代的遗留物，现在可能用途有限。

要接收来自应用程序的通知，您需要覆盖 handleApplicationNotification(...)方法代替。这是两个类的更正版本(也修改为独立的，以便可以复制和运行它们:请在您的问题中提供这些类型的示例)，可以使用:

package application;

import javafx.application.Application;
import javafx.application.Preloader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class App extends Application {

    @Override
    public void init() throws InterruptedException{
        //Simulation of time consuming code.
        for(int i = 0; i<=10; i++) {
            notifyPreloader(new Preloader.ProgressNotification(i/10.0));
            System.out.println("Progress is being set by the app to: " + (i/10.0));
            Thread.sleep(500);
        }
        notifyPreloader(new Preloader.StateChangeNotification(Preloader.StateChangeNotification.Type.BEFORE_START));
    }

    @Override
    public void start(Stage primaryStage) {
        Parent root;
            root = new StackPane(new Label("Hello World"));
            Scene scene = new Scene(root, 600, 400);

            primaryStage.setScene(scene);
            primaryStage.setTitle("Hello World!");
            primaryStage.show();

    }

}

package application;

import javafx.application.Preloader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.ProgressIndicator;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class AppPreloader extends Preloader {
    private Stage preloaderStage;
    private Parent root;
    private Scene scene;
    private ProgressIndicator progress_indicator;

    @Override
    public void start(Stage primaryStage) throws Exception {
        progress_indicator = new ProgressIndicator();
        root = new StackPane(progress_indicator);
        scene = new Scene(root, 600, 400);
        this.preloaderStage = primaryStage;
        this.preloaderStage.setScene(this.scene);
        this.preloaderStage.show();
    }


    @Override
    public void handleApplicationNotification(PreloaderNotification pn) {
        if (pn instanceof ProgressNotification) {
           //expect application to send us progress notifications 
           //with progress ranging from 0 to 1.0
           double v = ((ProgressNotification) pn).getProgress();
           progress_indicator.setProgress(v);            
        } else if (pn instanceof StateChangeNotification) {
            StateChangeNotification scn = (StateChangeNotification) pn ;
            if (scn.getType() == StateChangeNotification.Type.BEFORE_START) {
                preloaderStage.hide();
            }
        }
    } 
}