单击鼠标后在JPanel上绘制圆圈

我只想在鼠标点击后绘制圆圈。 由于paintComponent方法调用自身，因此首先绘制圆圈而不单击。

public class DrawPanel extends JPanel implements MouseListener { private static final long serialVersionUID = 1L; int x, y; public DrawPanel() { setBackground(Color.WHITE); addMouseListener(this); } public void paintComponent(Graphics g) { Graphics2D g2 = (Graphics2D) g; g2.setColor(Color.red); g2.fillOval(x, y, 20, 20); } @Override public void mouseClicked(MouseEvent e) { x = e.getX(); y = e.getY(); repaint(); } } 

Answer 1

您的代码存在一些问题：

1. 你永远不会调用super.paintComponent();
2. 你只有一个x和y
3. 请注意，当您调整框架大小时，某些圆圈将消失，整体表现得很奇怪。
4. 我将存储用户在ArrayList单击的所有Point ，然后在paintComponent方法中循环遍历该列表。 这样你就可以调用super.paintComponent(); 没有圆圈消失。

改变了，工作代码：

 import java.awt.Color; import java.awt.EventQueue; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.Point; import java.awt.RenderingHints; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; import java.util.ArrayList; import javax.swing.JFrame; import javax.swing.JPanel; public class DrawPanel extends JPanel { private static final long serialVersionUID = 1L; private ArrayList points; public DrawPanel() { points = new ArrayList(); setBackground(Color.WHITE); addMouseListener(new MouseAdapter() { @Override public void mousePressed(MouseEvent e) { points.add(new Point(e.getX(), e.getY())); repaint(); } }); } @Override public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D) g; g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g2.setColor(Color.red); for (Point point : points) { g2.fillOval(point.x, point.y, 20, 20); } } public static void main(String[] args) { EventQueue.invokeLater(new Runnable() { @Override public void run() { JFrame frame = new JFrame(); frame.add(new DrawPanel()); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(400, 400); frame.setVisible(true); } }); } } 

Answer 2

你应该有一些初始状态，所以你知道在设置时不要绘制。

这可以通过一个简单的布尔变量来完成，当用户按下屏幕时，您将其设置为true。

 public class DrawPanel extends JPanel implements MouseListener { private static final long serialVersionUID = 1L; int x, y; boolean mustDraw = false; public DrawPanel() { setBackground(Color.WHITE); addMouseListener(this); } public void paintComponent(Graphics g) { if(!mustDraw) return; Graphics2D g2 = (Graphics2D) g; g2.setColor(Color.red); g2.fillOval(x, y, 20, 20); } @Override public void mouseClicked(MouseEvent e) { x = e.getX(); y = e.getY(); mustDraw = true; repaint(); } } 

Answer 3

你应该把你的圈放在自己的class级里。 该课程将保存有关其位置，半径和颜色的信息。 您可以抽象形状并在面板上绘制要绘制的形状列表。 这将使以后易于实现三角形，正方形，六边形等。

您可以稍后向形状对象添加更多方法和属性，只需更改其内部实现的THEIRWO paintComponent(g)方法。 这使得DrawPanel依赖于每个Shape如何进行自己的绘制。

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App.java

 import java.awt.Dimension; import javax.swing.JFrame; import javax.swing.SwingUtilities; public class App { public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { @Override public void run() { JFrame f = new JFrame("Circle Click Application"); DrawPanel p = new DrawPanel(10f); p.setPreferredSize(new Dimension(300, 200));; f.setContentPane(p); f.pack(); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.setLocationRelativeTo(null); f.setVisible(true); } }); } } 

DrawPanel.java

 import java.awt.Color; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.RenderingHints; import java.awt.event.MouseEvent; import java.awt.event.MouseListener; import java.util.ArrayList; import java.util.List; import javax.swing.JPanel; public class DrawPanel extends JPanel implements MouseListener { private static final long serialVersionUID = -6817035652787391530L; private List shapes; protected float radius; private float sat = 0.7f; private float bri = 0.8f; public DrawPanel(float radius) { this.shapes = new ArrayList(); this.radius = radius; setBackground(Color.WHITE); addMouseListener(this); } public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D) g; g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); for (Shape shape : shapes) { shape.paintComponent(g); } } @Override public void mouseClicked(MouseEvent e) { shapes.add(new Circle(e.getX(), e.getY(), radius, ColorUtils.randHue(sat, bri))); repaint(); } @Override public void mousePressed(MouseEvent e) { // TODO Auto-generated method stub } @Override public void mouseReleased(MouseEvent e) { // TODO Auto-generated method stub } @Override public void mouseEntered(MouseEvent e) { // TODO Auto-generated method stub } @Override public void mouseExited(MouseEvent e) { // TODO Auto-generated method stub } } 

Shape.java

 import java.awt.Color; import java.awt.Graphics; import java.awt.Point; public interface Shape { Point getOrigin(); void setOrigin(Point origin); Color getColor(); void setColor(Color color); void paintComponent(Graphics g); } 

Circle.java

 import java.awt.Color; import java.awt.Graphics; import java.awt.Point; public class Circle implements Shape { private Point origin; private float radius; private Color color; public Circle() { this(0, 0, 0.5f, Color.BLACK); } public Circle(int x, int y, float radius, Color color) { this(new Point(x, y), radius, color); } public Circle(Point origin, float radius, Color color) { this.origin = origin; this.radius = radius; this.color = color; } @Override public Point getOrigin() { return origin; } @Override public void setOrigin(Point origin) { this.origin = origin; } public float getRadius() { return radius; } public void setRadius(float radius) { this.radius = radius; } @Override public Color getColor() { return color; } @Override public void setColor(Color color) { this.color = color; } @Override public void paintComponent(Graphics g) { int diameter = (int) (this.radius * 2); int x = (int) (origin.x - this.radius); int y = (int) (origin.y - this.radius); g.setColor(this.color); g.fillOval(x, y, diameter, diameter); } } 

ColorUtils.java

 import java.awt.Color; import java.util.Random; public class ColorUtils { private static final Random RAND; static { RAND = new Random(System.currentTimeMillis()); } public static Color randHue(float saturation, float brightness) { return Color.getHSBColor(RAND.nextFloat(), saturation, brightness); } } 

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延期

您可以通过实现Shape接口轻松添加类，例如Triangle 。

DrawPanel＃的mouseClicked

 @Override public void mouseClicked(MouseEvent e) { long time = System.currentTimeMillis(); boolean isEven = time % 2 == 0; if (isEven) { shapes.add(new Circle(e.getX(), e.getY(), radius, ColorUtils.randHue(sat, bri))); } else { shapes.add(new Triangle(e.getX(), e.getY(), radius * 2, ColorUtils.randHue(sat, bri))); } repaint(); } 

Triangle.java

 import java.awt.Color; import java.awt.Graphics; import java.awt.Point; import java.awt.Polygon; import java.awt.geom.Point2D; public class Triangle implements Shape { private Point origin; private float side; private Color color; private Polygon poly; public Triangle(int x, int y, float side, Color color) { this(new Point(x, y), side, color); } public Triangle(Point origin, float side, Color color) { this.origin = origin; this.side = side; this.color = color; recalculate(); } protected void recalculate() { this.poly = createPolygon((float) origin.getX(), (float) origin.getY(), side, false); } protected Polygon createPolygon(float x, float y, float side, boolean invert) { float xOff = side / 2f; float yOff = (float) (xOff * Math.sqrt(3)); float r1 = 1f / 3f; float r2 = 2f / 3f; if (invert) { yOff *= -1; } return createPolygon(new Point2D.Float[] { new Point2D.Float(x, y - (yOff * r2)), // Top new Point2D.Float(x - xOff, y + (yOff * r1)), // Left new Point2D.Float(x + xOff, y + (yOff * r1)) // Right }); } protected Polygon createPolygon(Point2D.Float[] points) { int nPoints = points.length + 1; int xCoords[] = new int[nPoints]; int yCoords[] = new int[nPoints]; for (int i = 0; i < nPoints; i++) { xCoords[i] = (int) points[i % points.length].x; yCoords[i] = (int) points[i % points.length].y; } return new Polygon(xCoords, yCoords, nPoints); } @Override public Point getOrigin() { return origin; } @Override public void setOrigin(Point origin) { this.origin = origin; recalculate(); } public float getSide() { return side; } public void setSide(float side) { this.side = side; recalculate(); } @Override public Color getColor() { return color; } @Override public void setColor(Color color) { this.color = color; } @Override public void paintComponent(Graphics g) { g.setColor(this.color); g.fillPolygon(poly); } }