从类对象获取窗格的宽度和高度时出现问题- Javafx

Question

好了，我理解了调整窗格中对象大小的绑定原则，这个问题有点不同。我很困惑，我试图创建一个扩展Pane的类，在我的main中创建一条线，将它的startX和startY坐标绑定到窗格的中心。问题是，当使用getWidth() / 2或getHeight() /2时，当我按下箭头键时，坐标被放置在起始坐标(0，0)的左上某处，当按下箭头键时，它会创建另一条线，该线在按下的给定方向上绘制，并从最后一条线的末端开始。

就像我说的，当我使用getWidth() / 2和getHeight / 2作为新行的startX和startY坐标时，作为回报，该行被放置在一个负坐标中，将其放置在屏幕上方窗格起始坐标(0，0)的左侧。

下面是我的代码的一部分，其中包含我遇到问题的默认构造函数，在非默认构造函数上，我可以手动输入起始坐标，当我这样做时，该行正好位于我想要的位置。

public class LineDrawingObject extends Pane {
    // ArrayList to store the Line Object's
    ArrayList<Line> lines = new ArrayList<>();
    Line line;
    private Color lineColor;
    private double lineLength;
    private int lineCount = 0;
    private double startX;
    private double startY;
    private double endX;
    private double endY;

    /** Default Constructor */
    public LineDrawingObject() {
        this.lineLength = 20;
        line = new Line(this.getWidth() / 2, this.getHeight() / 2,
            (this.getWidth() / 2), (this.getHeight() / 2) - this.lineLength);
        this.lineColor = Color.BLACK;
        line.setStroke(this.lineColor);
        this.lineCount++;
        this.lines.add(line);
        getChildren().add(line);
    }

编辑：我想我可能需要添加更多信息

另外，我想补充一点，我的窗格大小是在新场景中设置的（窗格，250,250），所以中心坐标是（125,125）……如果窗格上使用getWidth和getHeight方法会返回尚未绘制的无效大小吗？我尝试在开始方法中设置首选大小，但似乎不起作用。如果是这种情况，我该如何解决这个问题？

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

/**
 * Created by John on 7/24/2014.
 */
public class DrawLines extends Application {
    @Override // Override the start method in the Application class
    public void start(Stage primaryStage) {
        // Create a pane
        Pane pane = new Pane();

        // Create object to draw lines upon KeyEvent
        LineDrawingObject lineDrawingObject = new LineDrawingObject(20, Color.BLACK,
            pane.getWidth() / 2, pane.getWidth() / 2);
        pane.getChildren().add(lineDrawingObject);
        lineDrawingObject.setOnKeyPressed(e -> {
            lineDrawingObject.paintLine(e.getCode());
        });

        // Create a scene and place it in the pane
        Scene scene = new Scene(pane, 250, 250);
        primaryStage.setTitle("DrawLines"); // Set the stage title
        primaryStage.setScene(scene); // Place the scene in the stage
        primaryStage.show(); // Display the stage

        // Allow object to receive key input
        lineDrawingObject.requestFocus();
    }
}

这是LineDrawing对象：

import javafx.scene.input.KeyCode;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Line;

import java.util.ArrayList;

/** This object will draw lines inside of a Pane when an arrow key is
 *  pressed and will draw it in that direction from the current line */
public class LineDrawingObject extends Pane {
    // ArrayList to store the Line Object's
    ArrayList<Line> lines = new ArrayList<>();
    Line line;
    private Color lineColor;
    private double lineLength;
    private int lineCount = 0;
    private double startX;
    private double startY;
    private double endX;
    private double endY;

    /** Default Constructor */
    public LineDrawingObject() {
        this.lineLength = 20;
        line = new Line(this.getWidth() / 2, this.getHeight() / 2,
            (this.getWidth() / 2), (this.getHeight() / 2) - this.lineLength);
        this.lineColor = Color.BLACK;
        line.setStroke(this.lineColor);
        this.lineCount++;
        this.lines.add(line);
        getChildren().add(line);
    }

    /** Secondary Constructor, allows you to control the line length and color */
    public LineDrawingObject(double lineLength, Color lineColor, double startX, double startY) {
        this.lineLength = lineLength;
        line = new Line(startX, startY,
                startX, startY - this.lineLength);
        this.lineColor = lineColor;
        line.setStroke(this.lineColor);
        this.lineCount++;
        this.lines.add(line);
        getChildren().add(line);
    }

    public ArrayList<Line> getLines() {
        return lines;
    }

    public void setLines(ArrayList<Line> lines) {
        this.lines = lines;
    }

    public Line getLine() {
        return this.line;
    }

    public void setLine(Line line) {
        this.line = line;
    }

    public Color getLineColor() {
        return this.lineColor;
    }

    public void setLineColor(Color lineColor) {
        this.lineColor = lineColor;
    }

    public double getLineLength() {
        return this.lineLength;
    }

    public void setLineLength(double lineLength) {
        this.lineLength = lineLength;
    }

    public int getLineCount() {
        return this.lineCount;
    }

    public void setLineCount(int lineCount) {
        this.lineCount = lineCount;
    }

    public double getStartX() {
        return this.startX;
    }

    public void setStartX(double startX) {
        this.startX = startX;
    }

    public double getStartY() {
        return this.startY;
    }

    public void setStartY(double startY) {
        this.startY = startY;
    }

    public double getEndX() {
        return this.endX;
    }

    public void setEndX(double endX) {
        this.endX = endX;
    }

    public double getEndY() {
        return this.endY;
    }

    public void setEndY(double endY) {
        this.endY = endY;
    }

    public void paintLine(KeyCode keyCode) {
        // Set line start coordinates to the end of the last line
        setStartX(line.getEndX());
        setStartY(line.getEndY());

        // Set line end coordinates
        switch (keyCode) {
            case UP: goUp(); break;
            case LEFT: goLeft(); break;
            case DOWN: goDown(); break;
            case RIGHT: goRight(); break;
        }

        // Create line
        line = new Line(getStartX(), getStartY(), getEndX(), getEndY());
        line.setStroke(lineColor);
        this.lines.add(line);
        getChildren().add(line);
    }

    public void goLeft() {
        setEndX(getStartX() - this.lineLength);
        setEndY(getStartY());
    }

    public void goRight() {
        setEndX(getStartX() + this.lineLength);
        setEndY(getStartY());
    }

    public void goUp() {
        setEndX(getStartX());
        setEndY(getStartY() - this.lineLength);
    }

    public void goDown() {
        setEndX(getStartX());
        setEndY(getStartY() + this.lineLength);
    }
}

Answer 1

为了解决这个问题，我决定用一种更简单的方法，为构造函数设置一个预设的size属性，并设置一些额外的构造函数来允许你自己设置大小。

import javafx.scene.input.KeyCode;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Line;

import java.util.ArrayList;

/** This object will draw lines inside of a Pane when an arrow key is
 *  pressed and will draw it in that direction from the current line */
public class LineDrawingObject extends Pane {
    // ArrayList to store the Line Object's
    ArrayList<Line> lines = new ArrayList<>();
    Line line;
    private Color lineColor;
    private double lineLength;
    private double startX;
    private double startY;
    private double endX;
    private double endY;

    /** Default Constructor */
    public LineDrawingObject() {
        // Set a default size for this Pane
        this.setWidth(350);
        this.setHeight(350);
        // Set Line properties
        this.startX = getWidth() / 2;
        this.startY = getHeight() / 2;
        this.lineLength = 20;
        this.lineColor = Color.BLACK;
        // Create line and set it's Stroke
        line = new Line(this.startX, this.startY,
                this.startX, this.startY - this.lineLength);
        line.setStroke(this.lineColor);
        // Add line to ArrayList and Pane
        lines.add(line);
        getChildren().add(line);
    }

    /** Second Constructor, allows you to control the line length, color and center it */
    public LineDrawingObject(double lineLength, Color lineColor) {
        // Set a default size for this Pane
        this.setWidth(350);
        this.setHeight(350);
        // Set line properties
        this.startX = getWidth() / 2;
        this.startY = getHeight() / 2;
        this.lineLength = lineLength;
        this.lineColor = lineColor;
        // Create line and set it's Stroke
        line = new Line(this.startX, this.startY,
                this.startX, this.startY - this.lineLength);
        line.setStroke(this.lineColor);
        // Add line to ArrayList and Pane
        lines.add(line);
        getChildren().add(line);
    }

    /** Third Constructor, allows you to control the line length, color, and pane size */
    public LineDrawingObject(double lineLength, Color lineColor,
                             double paneWidth, double paneHeight) {
        // Set a default size for this Pane
        this.setWidth(paneWidth);
        this.setHeight(paneHeight);
        // Set line properties
        this.startX = getWidth() / 2;
        this.startY = getHeight() / 2;
        this.lineLength = lineLength;
        this.lineColor = lineColor;
        // Create line and set it's Stroke
        line = new Line(this.startX, this.startY,
                this.startX, this.startY - this.lineLength);
        line.setStroke(this.lineColor);
        // Add line to ArrayList and Pane
        lines.add(line);
        getChildren().add(line);
    }

    /** Third Constructor, allows you to control the line length and color, startX, and startY */
    public LineDrawingObject(double lineLength, double startX, double startY, Color lineColor) {
        // Set line properties
        this.startX = startX;
        this.startY = startY;
        this.lineLength = lineLength;
        this.lineColor = lineColor;
        // Create line and set it's Stroke
        line = new Line(this.startX, this.startY,
                this.startX, this.startY - this.lineLength);
        line.setStroke(this.lineColor);
        // Add line to ArrayList and Pane
        lines.add(line);
        getChildren().add(line);
    }

    /** Get the list of lines */
    public ArrayList<Line> getLines() {
        return lines;
    }

    /** Get the current line object */
    public Line getLine() {
        return this.line;
    }

    /** Manually set the current line object */
    public void setLine(Line line) {
        this.line = line;
    }

    /** Get the current line object's color */
    public Color getLineColor() {
        return this.lineColor;
    }

    /** Set the current line object's color */
    public void setLineColor(Color lineColor) {
        this.lineColor = lineColor;
    }

    /** Get length of the lines */
    public double getLineLength() {
        return this.lineLength;
    }

    /** Set a new length for the lines */
    public void setLineLength(double lineLength) {
        this.lineLength = lineLength;
    }

    /** Get the count of the number of line's currently in existence */
    public int getLineCount() {
        return this.lines.size();
    }

    /** Get the startX coordinates */
    public double getStartX() {
        return this.startX;
    }

    /** Set the startX coordinates */
    public void setStartX(double startX) {
        this.startX = startX;
    }

    /** Get the startY coordinates */
    public double getStartY() {
        return this.startY;
    }

    /** Set the startY coordinates */
    public void setStartY(double startY) {
        this.startY = startY;
    }

    /** Get the endX coordinates */
    public double getEndX() {
        return this.endX;
    }

    /** Set the endX coordinates */
    public void setEndX(double endX) {
        this.endX = endX;
    }

    /** Get the endY coordinates */
    public double getEndY() {
        return this.endY;
    }

    /** Set the endY coordinates */
    public void setEndY(double endY) {
        this.endY = endY;
    }

    /** Paint the next line based on the key pressed */
    public void paintLine(KeyCode keyCode) {
        // Set line start coordinates to the end of the last line
        setStartX(line.getEndX());
        setStartY(line.getEndY());

        // Set line end coordinates
        switch (keyCode) {
            case UP: goUp(); break;
            case LEFT: goLeft(); break;
            case DOWN: goDown(); break;
            case RIGHT: goRight(); break;
        }

        // Create line
        line = new Line(getStartX(), getStartY(), getEndX(), getEndY());
        line.setStroke(lineColor);
        this.lines.add(line);
        getChildren().add(line);
    }

    /** Set the end coordinates to the left of the last line */
    public void goLeft() {
        setEndX(getStartX() - this.lineLength);
        setEndY(getStartY());
    }

    /** Set the end coordinates to the right of the last line */
    public void goRight() {
        setEndX(getStartX() + this.lineLength);
        setEndY(getStartY());
    }

    /** Set the end coordinates above the last line */
    public void goUp() {
        setEndX(getStartX());
        setEndY(getStartY() - this.lineLength);
    }

    /** Set the end coordinates below the last line */
    public void goDown() {
        setEndX(getStartX());
        setEndY(getStartY() + this.lineLength);
    }
}

Answer 2

您正在构造函数中调用 getWidth（） 和 getHeight（），这必须在将窗格添加到任何实时场景之前执行。因此，这些将返回 0（因为窗格尚未布局）。

相反，将线的坐标绑定到基于< code>widthProperty和< code>heightProperty的值:

line = new Line();
line.startXProperty().bind(widthProperty().divide(2));
line.startYProperty().bind(heightProperty().divide(2));
line.endXProperty().bind(widthProperty().divide(2));
line.endYProperty().bind(heightProperty().divide(2).subtract(lineLength));