JavaFX

Question

我正在尝试设置 BackgroundImage as background of BorderPane (pane) in JavaFX. I want that BackgroundImage covers BorderPane and that it is always positioned in the center. I want to do the same as in CSS (for web) with background-image。

我已经试过了：

使用CSS (fx-CSS)

package application;

import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;

public class ExternalCSS extends Application {
    @Override
    public void start(Stage primaryStage) {
        try {

            //BorderPane()
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BorderPane.html
            BorderPane borderPane = new BorderPane();


            //Button(String text)
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/control/Button.html
            Button btn = new Button("Center");

            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BorderPane.html#setCenter-javafx.scene.Node-
            borderPane.setCenter(btn);


            Scene scene = new Scene(borderPane, 600, 600);

            URL path = getClass().getResource("resources/BackgroundStyle.css");

            if(path != null) {
                scene.getStylesheets().add(path.toExternalForm());
            } else {
                scene.getStylesheets().add("https://raw.githubusercontent.com/4nds/CenteredBackgroundImage/master/Background/src/application/resources/BackgroundStyleExternalURL.css");
            }

            borderPane.setId("background_id");

            primaryStage.setScene(scene);
            primaryStage.show();

        } catch(Exception e) {
            e.printStackTrace();
        }
    }

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

此代码使用外部 CSS（您可以找到我的 CSS 代码 here）或者您可以将下面的代码与内联 CSS:

package application;

import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;

public class InlineCSS extends Application {
    @Override
    public void start(Stage primaryStage) {
        try {

            //BorderPane()
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BorderPane.html
            BorderPane borderPane = new BorderPane();


            //Button(String text)
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/control/Button.html
            Button btn = new Button("Center");

            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BorderPane.html#setCenter-javafx.scene.Node-
            borderPane.setCenter(btn);


            Scene scene = new Scene(borderPane, 600, 600);

            URL path = getClass().getResource("resources/black_clock.png");

            String image = null;
            if(path != null) {
                image = path.toExternalForm();
            } else {
                image = "https://raw.githubusercontent.com/4nds/CenteredBackgroundImage/master/Background/src/application/resources/black_clock.png";
            }                   

            borderPane.setStyle("-fx-background-image: url('" + image + "'); " +
                       "-fx-background-position: center center; " +
                       "-fx-background-repeat: no-repeat;" +
                       "-fx-background-size: cover");

            primaryStage.setScene(scene);
            primaryStage.show();

        } catch(Exception e) {
            e.printStackTrace();
        }
    }

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

仅使用 JavaFX：

package application;


import java.io.File;

import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.image.Image;
import javafx.scene.layout.Background;
import javafx.scene.layout.BackgroundImage;
import javafx.scene.layout.BackgroundPosition;
import javafx.scene.layout.BackgroundRepeat;
import javafx.scene.layout.BackgroundSize;
import javafx.scene.layout.BorderPane;


        public class OnlyJavaFX extends Application {
    @Override
    public void start(Stage primaryStage) {
        try {

            //BorderPane()
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BorderPane.html
            BorderPane borderPane = new BorderPane();


            //File(String pathname)
            //https://docs.oracle.com/javase/8/docs/api/java/io/File.html
            File file = new File("./src/application/resourcesa/black_clock.png");

            Image img = null;
            if(file.exists()) {
                //Image(InputStream is)
                //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/image/Image.html
                img = new Image(file.getAbsoluteFile().toURI().toString());
            } else {
                //Image(String url)
                //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/image/Image.html
                img = new Image("https://raw.githubusercontent.com/4nds/CenteredBackgroundImage/master/Background/src/application/resources/black_clock.png");
            }

            //BackgroundSize(double width, double height, boolean widthAsPercentage, boolean heightAsPercentage, boolean contain, boolean cover)
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BackgroundSize.html
            BackgroundSize bgSize = new BackgroundSize(0, 0, false, false, false, true);

            //public BackgroundImage(Image image, BackgroundRepeat repeatX, BackgroundRepeat repeatY, BackgroundPosition position, BackgroundSize size)
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BackgroundImage.html
            BackgroundImage bgImg = new BackgroundImage(img,
                    BackgroundRepeat.NO_REPEAT,
                    BackgroundRepeat.NO_REPEAT,
                    BackgroundPosition.CENTER,
                    bgSize);

            //Background(BackgroundImage... images)
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/Background.html
            Background bg = new Background(bgImg);

            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/Region.html#setBackground-javafx.scene.layout.Background-
            borderPane.setBackground(bg);


            //Button(String text)
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/control/Button.html
            Button btn = new Button("Center");

            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BorderPane.html#setCenter-javafx.scene.Node-
            borderPane.setCenter(btn);


            Scene scene = new Scene(borderPane, 600, 600);
            primaryStage.setScene(scene);
            primaryStage.show();

        } catch(Exception e) {
            e.printStackTrace();
        }
    }

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

目前所有版本的代码 (InlineCSS, ExternalCSS and OnlyJavaFX) 都会产生这样的结果：

这是同一示例的 CSS 和 HTML 代码。这就是我想要的样子：

jsfidle examples: code, fullscreen
jsbin examples: code, fullscreen

编辑 1：

我意识到我已经发布了旧版本的代码，所以我会更新它。（代码中唯一的变化是，现在即使没有图像和 CSS 文件保存在您的计算机上，它也可以工作，而是程序会在线获取它。）

在 Jose Martinez's 之后编辑 2：

我已经测试了你的代码，但它不起作用。（我什至在 Y-axis 的方向添加了背景 ImageView 的翻译，在你的回答中它只是在 X-axis 的方向，而且我还设置了 borderPane 的大小以匹配场景的大小（app window) 但它仍然不起作用）。这是完整的代码（与您的回答相同，但有我已经提到的小修复）：

package application;


import java.io.File;

import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.BorderPane;

public class Try1 extends Application {
    @Override
    public void start(Stage primaryStage) {
        try {


            //BorderPane()
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BorderPane.html
            BorderPane borderPane = new BorderPane();

            //jot down the width and height of the scene
            double width = 600;
            double height = 600;

            //File(String pathname)
            //https://docs.oracle.com/javase/8/docs/api/java/io/File.html
            File file = new File("./src/application/resourcesa/black_clock.png");

            Image img = null;
            if(file.exists()) {
                //Image(InputStream is)
                //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/image/Image.html
                img = new Image(file.getAbsoluteFile().toURI().toString());
            } else {
                //Image(String url)
                //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/image/Image.html
                img = new Image("https://raw.githubusercontent.com/4nds/CenteredBackgroundImage/master/Background/src/application/resources/black_clock.png");
            }


            ImageView background = new ImageView(img);

            //..center the background
            double translateX = width/2 - img.getWidth()/2;
            System.out.println(translateX);
            background.setTranslateX(translateX);

            double translateY = height/2 - img.getHeight()/2;
            System.out.println(translateY);
            background.setTranslateY(translateY);

            //Button(String text)
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/control/Button.html
            Button btn = new Button("Center");

            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BorderPane.html#setCenter-javafx.scene.Node-
            borderPane.setCenter(btn);

            //make root with BorderPane and background image
            Group root = new Group (background, borderPane);

            Scene scene = new Scene(root, width, height);        

            primaryStage.setScene(scene);

            //this lines set borderPane's dimensions to be the same as scene
            borderPane.prefHeightProperty().bind(scene.heightProperty());
            borderPane.prefWidthProperty().bind(scene.widthProperty());

            primaryStage.show();

        } catch(Exception e) {
            e.printStackTrace();
        }
    }

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

问题是此代码仅在您启动程序时有效

一旦您调整（应用程序）window，它就不再居中了。

Answer 1

我会通过不使用 BackGroundImage 来实现这一点，而只是有另一个区域可以包含背景 ImageView。然后平移背景 ImageView 使其居中。

我调整了你的代码来做到这一点。我使用一个组作为场景的根节点。在那个根目录中，我放置了背景的 ImageView 和 BorderPane。

        //BorderPane()
        //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BorderPane.html
        BorderPane borderPane = new BorderPane();

        //jot down the width and height of the scene
        double width = 600;
        double height = 600;

        //Image(InputStream is)
        //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/image/Image.html
        Image img = new Image(file.getAbsoluteFile().toURI().toString());
        ImageView background = new ImageView(img);
        //..center the background
        double translateX = width/2 - img.getWidth()/2;
        background.setTranslateX(translateX);

        //Button(String text)
        //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/control/Button.html
        Button btn = new Button("Center");

        //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BorderPane.html#setCenter-javafx.scene.Node-
        borderPane.setCenter(btn);

        //make root with BorderPane and background image
        Group root = new Group (background, borderPane);

        Scene scene = new Scene(root, width, height);

编辑：处理调整大小

1) 将背景ImageView移动为对象字段。 2) 创建使背景 ImageView 居中的方法。 3) 创建回调以在 window 调整大小时使背景 ImageView 居中。

public class Try1 extends Application {

    private ImageView background = new ImageView(img);

    private final ChangeListener<Number> windowWidthResized = (ObservableValue<? extends Number> ov, Number t, Number t1) -> {
    windowResized();
};

    private final ChangeListener<Number> windowHeightResized = (ObservableValue<? extends Number> ov, Number t, Number t1) -> {
    windowResized();
};

    private void windowResized(){
        double newHeight = scene.getHeight();
        double newWidth = scene.getWidth();
        centerBackgroundImage(newWidth, newHeight);
    }

    private void centerBackgroundImage(double width, double height) {
            double translateX = width/2 - img.getWidth()/2;
            System.out.println(translateX);
            background.setTranslateX(translateX);

            double translateY = height/2 - img.getHeight()/2;
            System.out.println(translateY);
            background.setTranslateY(translateY);
    }

    @Override
    public void start(Stage primaryStage) {
        try {


            //BorderPane()
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BorderPane.html
            BorderPane borderPane = new BorderPane();

            //jot down the width and height of the scene
            double width = 600;
            double height = 600;

            //File(String pathname)
            //https://docs.oracle.com/javase/8/docs/api/java/io/File.html
            File file = new File("./src/application/resourcesa/black_clock.png");

            Image img = null;
            if(file.exists()) {
                //Image(InputStream is)
                //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/image/Image.html
                img = new Image(file.getAbsoluteFile().toURI().toString());
            } else {
                //Image(String url)
                //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/image/Image.html
                img = new Image("https://raw.githubusercontent.com/4nds/CenteredBackgroundImage/master/Background/src/application/resources/black_clock.png");
            }


            background.setImage(img);

            //..center the background
            centerBackgroundImage(width, height);

            //Button(String text)
            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/control/Button.html
            Button btn = new Button("Center");

            //https://docs.oracle.com/javase/8/javafx/api/javafx/scene/layout/BorderPane.html#setCenter-javafx.scene.Node-
            borderPane.setCenter(btn);

            //make root with BorderPane and background image
            Group root = new Group (background, borderPane);

            Scene scene = new Scene(root, width, height);

            //add callbacks to handle window resize
            scene.heightProperty().addListener(windowResized);
            scene.widthProperty().addListener(windowWidthResized);        

            primaryStage.setScene(scene);

            //this lines set borderPane's dimensions to be the same as scene
            borderPane.prefHeightProperty().bind(scene.heightProperty());
            borderPane.prefWidthProperty().bind(scene.widthProperty());

            primaryStage.show();

        } catch(Exception e) {
            e.printStackTrace();
        }
    }

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

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