JavaFX - 处理窗口

Question

我在 JavaFX 中有一个窗口，我需要“清理”IE:重置所有字段的值并将其设置回初始化时的状态。我想我可以做类似 window.dispose() 的事情，但事实证明这样的事情似乎并不存在。

这似乎是对窗口引擎的重大疏忽，因为我将打开多个我不想保留的窗口。如果我执行 stage.close() 它只是隐藏窗口而不释放内存，可能导致内存泄漏。

Answer 1

当您在一个窗口上调用 close()(或等效地调用 hide())时，FX 工具包将释放它持有的对该窗口的所有引用。因此，只要您不保留对窗口的引用，一旦调用了 close()，它就可以进行垃圾回收。在垃圾回收方面，它的行为与任何其他 Java 对象一样 - 一旦垃圾被回收，与窗口关联的资源就会被释放。

这是一个每秒打开一个新窗口并关闭前一个窗口的演示。该窗口在标签中显示图像，因此它消耗了合理的内存块。初级阶段显示内存统计信息(也是每秒更新一次)。这完全符合您的预期，内存逐渐增加，直到垃圾收集器启动，此时内存使用率回落。 (在我的系统上，它在 ~7MB 和 ~65MB 之间循环；您的里程可能因操作系统、JDK 版本和系统资源而异。)您可以插入对 System.gc(); 的调用onSucceeded 处理程序的末尾(仅用于演示目的；我不建议在实际代码中这样做)如果您想更清楚地看到垃圾收集释放了所有资源。

import java.util.Random;
import java.util.concurrent.atomic.AtomicInteger;

import javafx.animation.Animation;
import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.beans.binding.NumberBinding;
import javafx.beans.property.LongProperty;
import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleLongProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.concurrent.ScheduledService;
import javafx.concurrent.Task;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.chart.LineChart;
import javafx.scene.chart.NumberAxis;
import javafx.scene.chart.XYChart.Data;
import javafx.scene.chart.XYChart.Series;
import javafx.scene.control.ContentDisplay;
import javafx.scene.control.Label;
import javafx.scene.image.ImageView;
import javafx.scene.image.PixelWriter;
import javafx.scene.image.WritableImage;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Pane;
import javafx.scene.layout.StackPane;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.stage.Screen;
import javafx.stage.Stage;
import javafx.util.Duration;

public class ConstantlyOpenWindows extends Application {

    @Override
    public void start(Stage primaryStage) {

        ScheduledService<?> service = periodicallyShowNewWindow();

        Pane root = createMemoryMonitor();
        primaryStage.setScene(new Scene(root, 800, 600));

        primaryStage.show();

        service.start();

    }


    private ScheduledService<Integer> periodicallyShowNewWindow() {

        Screen screen = Screen.getPrimary();
        double maxX = screen.getBounds().getMaxX();

        AtomicInteger count = new AtomicInteger();
        ObjectProperty<Stage> visibleStage = new SimpleObjectProperty<>();
        ScheduledService<Integer> service = new ScheduledService<Integer>() {
            @Override
            protected Task<Integer> createTask() {
                Task<Integer> task = new Task<Integer>() {
                    @Override 
                    public Integer call() {
                        return count.incrementAndGet();
                    }
                };
                return task ;
            }
        };

        service.setOnSucceeded(event -> {
            Stage lastStage = visibleStage.get();
            Stage stage = createWindowWithImage(service.getValue());
            visibleStage.set(stage);
            stage.setX(maxX - 480);
            stage.show();
            if (lastStage != null) {
                lastStage.close();
            }
//            System.gc();
        });

        service.setPeriod(Duration.seconds(1));
        return service;
    }


    private Stage createWindowWithImage(int count) {
        Stage stage = new Stage();
        ImageView image = createImage();
        Label label = new Label("Window "+count);
        label.setGraphic(image);
        label.setContentDisplay(ContentDisplay.BOTTOM);
        stage.setScene( new Scene(new StackPane(label), 480, 500) );
        return stage;
    }

    private ImageView createImage() {
        WritableImage img = new WritableImage(400, 400);
        Random rng = new Random();
        int x = rng.nextInt(40);
        int y = rng.nextInt(40);
        PixelWriter pw = img.getPixelWriter();
        for (int i = 0; i < 400; i++) {
            for (int j = 0 ; j < 400 ; j++) {
                if (i >= x*10 && i < (x+1)*10 && j >= y*10 && j < (y+1) * 10) {
                    pw.setColor(i, j, Color.CORNFLOWERBLUE);
                } else {
                    pw.setColor(i, j, Color.ANTIQUEWHITE);
                }
            }
        }
        return new ImageView(img);
    }

    private Pane createMemoryMonitor() {
        LongProperty totalMemory = new SimpleLongProperty(Runtime.getRuntime().totalMemory());
        LongProperty freeMemory = new SimpleLongProperty(Runtime.getRuntime().freeMemory());
        LongProperty maxMemory = new SimpleLongProperty(Runtime.getRuntime().maxMemory());
        NumberBinding usedMemory = totalMemory.subtract(freeMemory);

        Label usedMemoryLabel = new Label();
        usedMemoryLabel.textProperty().bind(usedMemory.asString("Used memory: %,d"));
        Label freeMemoryLabel = new Label();
        freeMemoryLabel.textProperty().bind(freeMemory.asString("Free memory: %,d"));
        Label totalMemoryLabel = new Label();
        totalMemoryLabel.textProperty().bind(totalMemory.asString("Total memory: %,d"));
        Label maxMemoryLabel = new Label();
        maxMemoryLabel.textProperty().bind(maxMemory.asString("Max memory: %,d"));

        Series<Number, Number> series = new Series<>();
        series.setName("Used memory");

        AtomicInteger time = new AtomicInteger();

        Timeline updateMemory = new Timeline(new KeyFrame(Duration.seconds(1), event -> {
            totalMemory.set(Runtime.getRuntime().totalMemory());
            freeMemory.set(Runtime.getRuntime().freeMemory());
            maxMemory.set(Runtime.getRuntime().maxMemory());
            series.getData().add(new Data<>(time.incrementAndGet(), usedMemory.getValue()));
            if (series.getData().size() > 100) {
                series.getData().subList(0, series.getData().size() - 100).clear();
            }    
        }));
        updateMemory.setCycleCount(Animation.INDEFINITE);
        updateMemory.play();

        VBox labels = new VBox(usedMemoryLabel, freeMemoryLabel, totalMemoryLabel, maxMemoryLabel);
        labels.setAlignment(Pos.CENTER);

        NumberAxis xAxis = new NumberAxis();
        xAxis.setLabel("Time");
        xAxis.setForceZeroInRange(false);
        NumberAxis yAxis = new NumberAxis();
        yAxis.setLabel("Memory");
        LineChart<Number, Number> chart = new LineChart<Number, Number>(xAxis, yAxis);
        chart.setAnimated(false);
        chart.getData().add(series);

        BorderPane root = new BorderPane(chart, labels, null, null, null);

        return root;
    }

    public static void main(String[] args) {
        launch(args);
    }
}