javafx显示image_JavaFX技巧20：有很多要显示的吗？使用画布！

朴灿烈づ我的快乐病毒、 2023-02-25 03:45 1阅读 0赞

javafx显示image

JavaFX应用程序似乎有两种：第一种使用带有节点和CSS样式的场景图，第二种使用单个画布。 但是，将这两种方法混合使用是完全合法的。 尤其是当您的应用程序必须显示大量详细信息时，您很容易最终创建成千上万个节点。 即使JavaFX的整体性能非常出色，当所有这些节点都需要样式设置时（特别是由于可视化的动态性质而需要反复进行样式设置时），您很有可能会使系统崩溃。

对我来说，这是一个顿悟，当我意识到在[FlexGanttFX中][FlexGanttFX]保证高性能的唯一方法是对每个包含画布的单元使用ListView。 不幸的是，该框架的代码太复杂，无法在一个小博客中与您共享。因此，我写了一个小例子来说明基本概念。 下图显示了运行示例时的结果。 ListView显示的数据涵盖了我生命中的岁月，并且每年的每一天都有随机生成的值。

![bildschirmfoto-2015-06-15-um-19-25-50][]

最重要的类称为**CanvasCell** 。 它是一个专门的列表视图单元，其中包含标签和画布。 标签用于显示年份，画布用于绘制图表。

import java.util.Collections;
    import java.util.List;
    
    import javafx.geometry.Pos;
    import javafx.scene.canvas.Canvas;
    import javafx.scene.canvas.GraphicsContext;
    import javafx.scene.control.ContentDisplay;
    import javafx.scene.control.Label;
    import javafx.scene.control.ListCell;
    import javafx.scene.layout.StackPane;
    import javafx.scene.paint.Color;
    import javafx.scene.paint.CycleMethod;
    import javafx.scene.paint.LinearGradient;
    import javafx.scene.paint.Stop;
    
    public class CanvasCell extends ListCell<YearEntry> {
    
    	private Label yearLabel;
    	private ResizableCanvas canvas;
    
    	public CanvasCell() {
    		/*
    		 * Important, otherwise we will keep seeing a horizontal scrollbar.
    		 */
    		setStyle("-fx-padding: 0px;");
    
    		yearLabel = new Label();
    		yearLabel
    		  .setStyle("-fx-padding: 10px; -fx-font-size: 1.2em; -fx-font-weight: bold;");
    		StackPane.setAlignment(yearLabel, Pos.TOP_LEFT);
    
    		/*
    		 * Create a resizable canvas and bind its width and height to the width
    		 * and height of the table cell.
    		 */
    		canvas = new ResizableCanvas();
    		canvas.widthProperty().bind(widthProperty());
    		canvas.heightProperty().bind(heightProperty());
    
    		StackPane pane = new StackPane();
    		pane.getChildren().addAll(yearLabel, canvas);
    
    		setGraphic(pane);
    		setContentDisplay(ContentDisplay.GRAPHIC_ONLY);
    	}
    
    	@Override
    	protected void updateItem(YearEntry entry, boolean empty) {
    		if (empty || entry == null) {
    			yearLabel.setText("");
    			canvas.setData(Collections.emptyList());
    			canvas.draw();
    		} else {
    			yearLabel.setText(Integer.toString(entry.getYear()));
    			canvas.setData(entry.getValues());
    			canvas.draw();
    		}
    	}
    
    	/*
    	 * Canvas is normally not resizable but by overriding isResizable() and
    	 * binding its width and height to the width and height of the cell it will
    	 * automatically resize.
    	 */
    	class ResizableCanvas extends Canvas {
    
    		private List<Double> data = Collections.emptyList();
    
    		public ResizableCanvas() {
    
    			/*
    			 * Make sure the canvas draws its content again when its size
    			 * changes.
    			 */
    			widthProperty().addListener(it -> draw());
    			heightProperty().addListener(it -> draw());
    		}
    
    		@Override
    		public boolean isResizable() {
    			return true;
    		}
    
    		@Override
    		public double prefWidth(double height) {
    			return getWidth();
    		}
    
    		@Override
    		public double prefHeight(double width) {
    			return getHeight();
    		}
    
    		public void setData(List<Double> data) {
    			this.data = data;
    		}
    
    		/*
    		 * Draw a chart based on the data provided by the model.
    		 */
    		private void draw() {
    			GraphicsContext gc = getGraphicsContext2D();
    			gc.clearRect(0, 0, getWidth(), getHeight());
    
    			Stop[] stops = new Stop[] { new Stop(0, Color.SKYBLUE),
    					new Stop(1, Color.SKYBLUE.darker().darker()) };
    			LinearGradient gradient = new LinearGradient(0, 0, 0, 300, false,
    					CycleMethod.NO_CYCLE, stops);
    
    			gc.setFill(gradient);
    
    			double availableHeight = getHeight() * .8;
    			double counter = 0;
    			for (Double value : data) {
    				double x = getWidth() / 365 * counter;
    				double barHeight = availableHeight * value / 100;
    				double barWidth = getWidth() / 365 + 1;
    				gc.fillRect(x, getHeight() - barHeight, barWidth, barHeight);
    				counter++;
    			}
    		}
    	}
    }

对于数据，我们使用一个非常简单的类来存储年份和值列表。

import java.util.ArrayList;
    import java.util.List;
    
    
    /**
     * Just some fake model object.
     */
    public class YearEntry {
    
    	private int year;
    
    	public YearEntry(int year) {
    		this.year = year;
    	}
    
    	public int getYear() {
    		return year;
    	}
    
    	private List<Double> values = new ArrayList<>();
    
    	/**
    	 * Stores the values shown in the chart.
    	 */
    	public List<Double> getValues() {
    		return values;
    	}
    }

以下清单显示了主类。

import javafx.application.Application;
    import javafx.collections.FXCollections;
    import javafx.collections.ObservableList;
    import javafx.scene.Scene;
    import javafx.scene.control.ListView;
    import javafx.stage.Stage;
    
    public class CanvasApp extends Application {
    
    	@Override
    	public void start(Stage stage) throws Exception {
    
    		/*
    		 * Create some random data for my life span.
    		 */
    		ObservableList<YearEntry> data = 
    			FXCollections.observableArrayList();
    		for (int year = 1969; year < 2015; year++) {
    			YearEntry entry = new YearEntry(year);
    			for (int day = 0; day < 365; day++) {
    				entry.getValues().add(Math.random() * 100);
    			}
    			data.add(entry);
    		}
    
    		ListView<YearEntry> listView = new ListView<>(data);
    		listView.setCellFactory(param -> new CanvasCell());
    		listView.setFixedCellSize(200);
    
    		Scene scene = new Scene(listView);
    
    		stage.setTitle("Canvas Cell");
    		stage.setScene(scene);
    		stage.setWidth(600);
    		stage.setHeight(600);
    		stage.show();
    	}
    
    	public static void main(String[] args) {
    		launch(args);
    	}
    }

> 翻译自: [https://www.javacodegeeks.com/2015/06/javafx-tip-20-a-lot-to-show-use-canvas.html][https_www.javacodegeeks.com_2015_06_javafx-tip-20-a-lot-to-show-use-canvas.html]

javafx显示image

[FlexGanttFX]: http://www.flexganttfx.com
[bildschirmfoto-2015-06-15-um-19-25-50]: /images/20230209/ad7ea5bc7b6f4e388b8dcb9fd95058c7.png
[https_www.javacodegeeks.com_2015_06_javafx-tip-20-a-lot-to-show-use-canvas.html]: https://www.javacodegeeks.com/2015/06/javafx-tip-20-a-lot-to-show-use-canvas.html