Question

我希望能够将使用图形对象创建的形状存储为变量，但是输出的类型为void，并且将其转换为无效。

目前我只能使用paintComponent方法使用Graphics引用。但是我希望能够将一个形状（碰巧是void类型）存储为Graphic类型的实例变量...

请考虑以下事项：

test class{
      Graphics instanceOfGraphics;

      public void createShape(Graphics g1){
             g1.setPaint(new Color(255, 0, 0));
             instanceOfGraphics = g1.fillOval(//xPosition, //yPosition,
                                              //width, //height);

             }
          }

上面的源代码不起作用，因为fillOval方法的返回类型是void，即使我尝试转换静默返回值它也不起作用。

我如何将创建的形状保存/存储为变量。

将来我希望能够在Shape上注册一个Listener，并允许我创建的形状成为事件源。

Answer 1

上面的源代码不起作用，因为fillOval方法的返回类型是void，即使我尝试转换静默返回值它也不起作用。

您正在考虑存储效果，这是不可能的，您要做的是存储数据。如果要存储椭圆型数据，只需使用Ellipse2D字段并将信息存储在那里。

Ellipse2D ellipse = new Ellipse2D.Double(//xPosition, //yPosition,
                                          //width, //height);

然后在paintComponent中使用Graphics2D对象绘制它。

Swing具有有用的Shape接口，该接口已经实现为几个可以很好地满足您目的的具体类。

如，

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.Shape;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Rectangle2D;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.swing.*;

public class GraphicsEg extends JPanel {
   private static final int PREF_W = 400;
   private static final int PREF_H = PREF_W;
   private List<Shape> shapes = new ArrayList<>();
   private Map<Shape, Color> shapeColorMap = new HashMap<>();

   public GraphicsEg() {
      Shape shape = new Ellipse2D.Double(10, 10, 30, 30);
      shapeColorMap.put(shape, Color.RED);
      shapes.add(shape);

      shape = new Rectangle2D.Double(140, 140, 200, 200);
      shapeColorMap.put(shape, Color.BLUE);
      shapes.add(shape);

      shape = new RoundRectangle2D.Double(200, 200, 80, 80, 10, 10);
      shapeColorMap.put(shape, Color.GREEN);
      shapes.add(shape);
   }

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      Graphics2D g2 = (Graphics2D) g;
      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
      for (Shape shape : shapes) {
         Color color = shapeColorMap.get(shape);
         g2.setColor(color);
         g2.fill(shape);
      }
   }

   @Override
   public Dimension getPreferredSize() {
      if (isPreferredSizeSet()) {
         return super.getPreferredSize();
      }
      return new Dimension(PREF_W, PREF_H);
   }
   private static void createAndShowGui() {
      JFrame frame = new JFrame("GraphicsEg");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(new GraphicsEg());
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

这里有几个不同的形状（Ellipse2D，Rectangle2D，RoundRectangle2D）存储在Shape对象的ArrayList中，然后在第一次将Graphics对象强制转换为Graphics2D之后，在JPanel的paintComponent方法中绘制这些形状。我还添加了一个HashMap<Shape, Color>，以便将Shape与颜色轻松关联。

另外，您在评论中说明，

将其用作事件来源

为所有实现Shape的类带来了另一个有用的功能 - 它们有一个contains(...)方法，如果与MouseListener一起使用，可以让你轻松地看到鼠标是否在你的一个形状内部被点击。 / p>

例如：

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.Shape;
import java.awt.Stroke;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.swing.*;

@SuppressWarnings("serial")
public class GraphicsEg extends JPanel {
   private static final int PREF_W = 400;
   private static final int PREF_H = PREF_W;
   private static final Color SELECTED_COLOR = Color.RED;
   private static final Stroke SELECTED_STROKE = new BasicStroke(8f);
   private List<Shape> shapes = new ArrayList<>();
   private Map<Shape, Color> shapeColorMap = new HashMap<>();
   private Shape selectedShape = null;

   public GraphicsEg() {
      Shape shape = new Ellipse2D.Double(10, 10, 90, 90);
      shapeColorMap.put(shape, Color.GRAY);
      shapes.add(shape);

      shape = new Rectangle2D.Double(140, 140, 200, 200);
      shapeColorMap.put(shape, Color.BLUE);
      shapes.add(shape);

      shape = new RoundRectangle2D.Double(200, 200, 80, 80, 10, 10);
      shapeColorMap.put(shape, Color.GREEN);
      shapes.add(shape);

      addMouseListener(new MyMouseListener());
   }

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      Graphics2D g2 = (Graphics2D) g;
      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
      for (Shape shape : shapes) {
         Color color = shapeColorMap.get(shape);
         g2.setColor(color);
         g2.fill(shape);
      }

      if (selectedShape != null) {
         Graphics2D newG2 = (Graphics2D) g2.create();
         newG2.setColor(SELECTED_COLOR);
         newG2.setStroke(SELECTED_STROKE);
         newG2.draw(selectedShape);
         newG2.dispose(); // because this is a created Graphics object
      }
   }

   @Override
   public Dimension getPreferredSize() {
      if (isPreferredSizeSet()) {
         return super.getPreferredSize();
      }
      return new Dimension(PREF_W, PREF_H);
   }

   private class MyMouseListener extends MouseAdapter {
      @Override
      public void mousePressed(MouseEvent e) {
         for (int i = shapes.size() - 1; i >= 0; i--) {
            if (shapes.get(i).contains(e.getPoint())) {
               selectedShape = shapes.get(i);
               repaint();
               return;
            }
         }
      }
   }

   private static void createAndShowGui() {
      JFrame frame = new JFrame("GraphicsEg");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(new GraphicsEg());
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

保存信息 - 摆动形状

1 个答案: