为什么我的 JavaFX Preloader 偶尔会显示 gray/black 而其他时候它会正确加载？

Question

我正在尝试让我的 JavaFX Preloader 启动屏幕显示在我的应用程序之前。我正在使用 Eclipse IDE，当我单击 "run" 时，有一半时间启动画面会正确显示，而另一半时间我会得到一个灰色或黑色的屏幕，而不是图像应该显示的位置是。

我不确定是什么问题导致它有时只能正确显示。

SplashController:

public class SplashController extends Preloader {
  private static final double WIDTH = 676;
  private static final double HEIGHT = 227;
  private Stage preloaderStage;
  private Label progressText;
  private Pane splashScreen;

 public SplashController() {}    

 @Override
  public void init() throws Exception {
    ImageView splash =
        new ImageView(new Image(Demo.class.getResource("pic.png").toString()));
    progressText =
        new Label("VERSION: " + getVersion() + " ~~~ Loading plugins, please wait...");
    splashScreen = new VBox();
    splashScreen.getChildren().addAll(splash, progressText);
    progressText.setAlignment(Pos.CENTER);
  }

  @Override
  public void start(Stage primaryStage) throws Exception {
    this.preloaderStage = primaryStage;
    Scene splashScene = new Scene(splashScreen);
    this.preloaderStage.initStyle(StageStyle.UNDECORATED);
    final Rectangle2D bounds = Screen.getPrimary().getBounds();
    this.preloaderStage.setScene(splashScene);
    this.preloaderStage.setX(bounds.getMinX() + bounds.getWidth() / 2 - WIDTH / 2);
    this.preloaderStage.setY(bounds.getMinY() + bounds.getHeight() / 2 - HEIGHT / 2);
    this.preloaderStage.show();
  }
}

然后在我的主要 class Demo 中，我只有：

public class Demo extends Application {
  @Override
  public void start(Stage stage) throws Exception {
     FXMLLoader loader = new 
     FXMLLoader(Demo.class.getResource("FXMLDocument.fxml"));
     GridPane root = loader.load();

                  --------other app  code here---------
  }

  public static void main(String[] args) {
    LauncherImpl.launchApplication(Demo.class, SplashController.class, args);
  }

}

Answer 1

您可能正在 JavaFX 应用程序线程或涉及应用程序启动的线程上执行一些较长的 运行 进程，这会阻止预加载器的顺利运行。

我建议您正确复习 Oracle Preloader sample and compare to your application. Ensure that you are using concurrent features like Task，类似于 linked 示例。检查 linked 样本在您的环境中是否有效。

源代码（刚从 Oracle Preloader 示例 link 复制而来）

请注意如何在主 LongAppInit 应用程序 class 的启动方法中，应用程序的 Task and thread is spawned to ensure that the long application initiation does not take place on the JavaFX application thread. Also see how the notifyPreloader() 方法在长应用程序初始化的不同时间被调用，以使预加载器了解初始化过程的当前状态，以便它可以实时准确地反映 UI 中的进度。

LongAppInitPreloader.java

public class LongAppInitPreloader extends Preloader {
    ProgressBar bar;
    Stage stage;
    boolean noLoadingProgress = true;

    private Scene createPreloaderScene() {
        bar = new ProgressBar(0);
        BorderPane p = new BorderPane();
        p.setCenter(bar);
        return new Scene(p, 300, 150);
    }

    public void start(Stage stage) throws Exception {
        this.stage = stage;
        stage.setScene(createPreloaderScene());
        stage.show();
    }

    @Override
    public void handleProgressNotification(ProgressNotification pn) {
        //application loading progress is rescaled to be first 50%
        //Even if there is nothing to load 0% and 100% events can be
        // delivered
        if (pn.getProgress() != 1.0 || !noLoadingProgress) {
          bar.setProgress(pn.getProgress()/2);
          if (pn.getProgress() > 0) {
              noLoadingProgress = false;
          }
        }
    }

    @Override
    public void handleStateChangeNotification(StateChangeNotification evt) {
        //ignore, hide after application signals it is ready
    }

    @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();
           if (!noLoadingProgress) {
               //if we were receiving loading progress notifications 
               //then progress is already at 50%. 
               //Rescale application progress to start from 50%               
               v = 0.5 + v/2;
           }
           bar.setProgress(v);            
        } else if (pn instanceof StateChangeNotification) {
            //hide after get any state update from application
            stage.hide();
        }
    }  
 }

LongAppInit.java

public class LongInitApp extends Application {
    Stage stage;
    BooleanProperty ready = new SimpleBooleanProperty(false);

    private void longStart() {
        //simulate long init in background
        Task task = new Task<Void>() {
            @Override
            protected Void call() throws Exception {
                int max = 10;
                for (int i = 1; i <= max; i++) {
                    Thread.sleep(200);
                    // Send progress to preloader
                    notifyPreloader(new ProgressNotification(((double) i)/max));
                }
                // After init is ready, the app is ready to be shown
                // Do this before hiding the preloader stage to prevent the 
                // app from exiting prematurely
                ready.setValue(Boolean.TRUE);

                notifyPreloader(new StateChangeNotification(
                    StateChangeNotification.Type.BEFORE_START));

                return null;
            }
        };
        new Thread(task).start();
    }

    @Override
    public void start(final Stage stage) throws Exception {
        // Initiate simulated long startup sequence
        longStart();

        stage.setScene(new Scene(new Label("Application started"), 
            400, 400));

        // After the app is ready, show the stage
        ready.addListener(new ChangeListener<Boolean>(){
            public void changed(
                ObservableValue<? extends Boolean> ov, Boolean t, Boolean t1) {
                    if (Boolean.TRUE.equals(t1)) {
                        Platform.runLater(new Runnable() {
                            public void run() {
                                stage.show();
                            }
                        });
                    }
                }
        });;                
    }
}