滚动时JavaFX ScrollPane更新viewportBounds

Question

我有一个非常大的图像,我试图在JavaFX中显示.为此,我将图像分成几个较小的图像,并且仅加载/显示在我的图像中可见的部分ScrollPane.

为了检测可见区域ScrollPane,我正在添加监听器ScrollPane.viewportBounds.但是,viewportBounds仅在我调整窗口大小时更新,但在滚动滚动条时不会更新.

如果我要滚动我的大图像,我也需要viewportBounds在滚动滚动条时更新.我该怎么做呢？

---

我在下面有一些测试代码.点击Button作品,但不是通过ChangeListener- left和right仍然使用保持不变ChangeListener.

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Bounds;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ScrollPane;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

public class TestClass extends Application {
    @Override
    public void start(Stage stage) {
        VBox vbox = new VBox();

        ScrollPane scrollPane = new ScrollPane(new Rectangle(1000, 700, Color.GREEN));
        scrollPane.setPrefSize(500, 300);

        // Using a ChangeListener on viewportBounds doesn't work.
        scrollPane.viewportBoundsProperty().addListener(new ChangeListener<Bounds>() {
            @Override
            public void changed(ObservableValue<? extends Bounds> observable, Bounds oldBounds, Bounds bounds) {
                int left = -1 * (int) bounds.getMinX();
                int right = left + (int) bounds.getWidth();
                System.out.println("hval:" + scrollPane.getHvalue() + " left:" + left + " right:" + right);
            }
        });

        // Neither does this.
        scrollPane.hvalueProperty().addListener(new ChangeListener<Number>() {
            @Override
            public void changed(ObservableValue<? extends Number> observable, Number oldValue, Number newValue) {
                Bounds bounds = scrollPane.getViewportBounds();
                int left = -1 * (int) bounds.getMinX();
                int right = left + (int) bounds.getWidth();
                System.out.println("hval:" + scrollPane.getHvalue() + " left:" + left + " right:" + right);
            }
        });

        // Clicking the button works.
        Button printButton = new Button("Print");

        printButton.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                Bounds bounds = scrollPane.getViewportBounds();
                int left = -1 * (int) bounds.getMinX();
                int right = left + (int) bounds.getWidth();
                System.out.println("hval:" + scrollPane.getHvalue() + " left:" + left + " right:" + right);
                event.consume();
            }
        });

        vbox.getChildren().addAll(scrollPane, printButton);

        Scene scene = new Scene(vbox, 640, 480);
        stage.setScene(scene);

        stage.show();
    }

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

编辑更新了测试代码.

Answer 1

该viewportBounds是视口的只是界限,即滚动内容是可见的部分的边界.滚动时这些不会改变(但随着大小的改变,通常会随着窗口大小的改变而改变).

要以滚动内容被视口内移动做出反应,你需要观察hvalueProperty和vvalueProperty的ScrollPane.您可以使用相同的更改侦听器,只需对参数类型进行少量修改:

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.geometry.Bounds;
import javafx.scene.Scene;
import javafx.scene.control.ScrollPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

public class TestClass extends Application {
    @Override
    public void start(Stage stage) {
        ScrollPane scrollPane = new ScrollPane(new Rectangle(1000, 700, Color.GREEN));
        scrollPane.setPrefSize(500, 300);

        ChangeListener<Object> changeListener = new ChangeListener<Object>() {
            @Override
            public void changed(ObservableValue<? extends Object> observable, Object oldValue, Object newValue) {
                Bounds bounds = scrollPane.getViewportBounds();
                int left = -1 * (int) bounds.getMinX();
                int right = left + (int) bounds.getWidth();
                System.out.println("hval:" + scrollPane.getHvalue() + " left:" + left + " right:" + right);
            }
        };
        scrollPane.viewportBoundsProperty().addListener(changeListener);
        scrollPane.hvalueProperty().addListener(changeListener);
        scrollPane.vvalueProperty().addListener(changeListener);

        Scene scene = new Scene(scrollPane, 640, 480);
        stage.setScene(scene);

        stage.show();
    }

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

请注意,滚动时,视口(当然)不会在其父级中移动; 滚动窗格内容的可见部分会发生变化.我没有简单的方法来计算内容的可见部分:你只需要做一些数学运算.

(注意:可能有一种更简单的方法,但我无法看到它.)

适用于ScrollPane州的API文档

ScrollPane允许应用程序设置当前,最小和最大值,以便在水平和垂直方向上定位内容.这些值按比例映射到包含节点的layoutBounds.

所以你必须解释一下,但这意味着

(hvalue - hmin) / (hmax - hmin) = hoffset / freeHspace

其中hmin,hvalue和,hmax是滚动窗格属性值,hoffset是内容水平freeHspace移动的量,是内容可以移动的总水平量.这是

freeHspace = contentWidth - viewportWidth

(显然,如果contentWidth<= viewportWidth,则不能进行水平滚动,并且hoffset必须为零.)

所以如果你想要水平偏移

hoffset = Math.max(0, contentWidth - viewportWidth) * (hvalue - hmin) / (hmax - hmin)

并且类似的公式适用于垂直偏移.

所以你可以用上面的替换更改监听器

    ChangeListener<Object> changeListener = new ChangeListener<Object>() {
        @Override
        public void changed(ObservableValue<? extends Object> observable, Object oldValue, Object newValue) {
            double hmin = scrollPane.getHmin();
            double hmax = scrollPane.getHmax();
            double hvalue = scrollPane.getHvalue();
            double contentWidth = content.getLayoutBounds().getWidth();
            double viewportWidth = scrollPane.getViewportBounds().getWidth();

            double hoffset = 
                Math.max(0, contentWidth - viewportWidth) * (hvalue - hmin) / (hmax - hmin);

            double vmin = scrollPane.getVmin();
            double vmax = scrollPane.getVmax();
            double vvalue = scrollPane.getVvalue();
            double contentHeight = content.getLayoutBounds().getHeight();
            double viewportHeight = scrollPane.getViewportBounds().getHeight();

            double voffset = 
                Math.max(0,  contentHeight - viewportHeight) * (vvalue - vmin) / (vmax - vmin);

            System.out.printf("Offset: [%.1f, %.1f] width: %.1f height: %.1f %n", 
                    hoffset, voffset, viewportWidth, viewportHeight);
        }
    };