java：如何使用内部类实现手绘绘图

Question

您好，我正在尝试一个绘画应用程序，并试图弄清楚内部类如何访问主要的graphic2D函数来实现徒手​​绘制选择？还是我找错了树？

 import javax.swing.*; // For JPanel, etc.
   import java.awt.*; // For Graphics, etc.
   import java.awt.geom.*; // For Ellipse2D, etc.
   import java.awt.event.*;
   import java.util.ArrayList;
   import java.awt.Shape;
   import java.awt.Graphics2D;
   import java.lang.Math;
   import javax.swing.event.ChangeListener; 
   import javax.swing.event.ChangeEvent; 

   public class DrawingPanel extends JPanel 
   {
      private double x1=0;
      private double x2=0;
      private double y1=0;
      private double y2=0;
        private double x3=0;
      private double x4=0;
      private double y3=0;
      private double y4=0;
      private double tx=0;
      private double ty=0;
      private double tz=0;
      double width = Math.abs(x1 -x2);
      double height = Math.abs(y1-y2);

      private Point start, end;
      private ArrayList<Shape> myArr = new ArrayList<Shape>();
      private ArrayList<Shape> myArr2 = new ArrayList<Shape>();
      ButtonPanel buttonPress;

      protected void paintComponent(Graphics g) { 
         super.paintComponent(g);//  let panel draw itself 
         Graphics2D g2d = (Graphics2D)g; 
         g2d.setPaint(Color.blue);
         g2d.setStroke(new BasicStroke(4));
         for (Shape i : myArr) 
         { 
            g2d.draw(i); 
         } 
         for(int j = 0;j<myArr2.size();j++)
         {
            //g2d.setColor(shapeTransColor.get(i));// get the colour from the colour array
            g2d.fill(myArr2.get(j));// fill the shape from the shape array                                  
         }

      }     
        //inner class

      class Listener1 extends MouseAdapter
      {
                     public void mousePressed(MouseEvent e)
         {

            x1=e.getX();
            y1=e.getY();
            System.out.println("Mouse Pressed");
                if (buttonPress.buttonType.equals("Clear"))
            {                        
               System.out.println("ArrayList Size :"+myArr.size());
               System.out.println("ArrayList2 Size :"+myArr2.size());                   
               myArr.clear();
               myArr2.clear(); // clears all elements from arraylists 
               System.out.println("ArrayList Size :"+myArr.size()); 
               System.out.println("ArrayList2 Size :"+myArr2.size());
               repaint();    
            } 
         }

         public void mouseReleased(MouseEvent e)
         {
            x2=e.getX();
            y2=e.getY();
            Shape shape = null;
            if (buttonPress.buttonType.equals("Rectangle"))
            {
            // Rectangles cannot have a zero width or height
               if (x1 != x2 || y1 != y2)
               {
                  double width = Math.abs(x1 - x2);
                  double height = Math.abs(y1 - y2);
                  Rectangle2D.Double rect = new Rectangle2D.Double(Math.min(x1,x2),Math.min(y1,y2), width, height);
                  myArr.add(rect);
                  repaint();
               }
            } 
            if (buttonPress.buttonType.equals("Eclipse"))
            {
               double width = Math.abs(x1 - x2);
               double height = Math.abs(y1 - y2);
               Ellipse2D.Double elli = new Ellipse2D.Double(Math.min(x1,x2),Math.min(y1,y2), width, height);
               myArr.add(elli);
               repaint();
            } 
            if (buttonPress.buttonType.equals("Lines"))
            {
               Line2D.Double nuLine = new Line2D.Double(x1, y1, x2, y2);    
               myArr.add(nuLine);   
               repaint();        
            } 
            if (buttonPress.buttonType.equals("Triangle"))
            {/*

                *
                *
                *
                repaint();    */    
            }
            if (buttonPress.buttonType.equals("FillRectangle"))
            {               
               if (x1 != x2 || y1 != y2)
               {
                  double width = Math.abs(x1 - x2);
                  double height = Math.abs(y1 - y2);
                  Rectangle2D.Double fillRect = new      Rectangle2D.Double(Math.min(x1,x2),Math.min(y1,y2), width, height);
                  myArr2.add(fillRect); 
                  repaint();
               }
            }
            if (buttonPress.buttonType.equals("FillEclipse"))
            {               
               double width = Math.abs(x1 - x2);
               double height = Math.abs(y1 - y2);
               Ellipse2D.Double fillElli = new Ellipse2D.Double(Math.min(x1,x2),Math.min(y1,y2), width, height);
               myArr2.add(fillElli); 
               repaint();
            }    
        if (buttonPress.buttonType.equals("Freehand"))
            {    
                    System.out.println("test free");

               //*
                    //*
                    //*               
                    repaint();  
               //myArr2.add(nuLine2);                                                            
            }             

            if (shape != null)
            {
               myArr.add(shape);    
               myArr2.add(shape);
            }
            repaint();
         }                          
      }
    //end of inner class   
      public DrawingPanel(ButtonPanel reference)
      {
         buttonPress = reference;
         setBorder(BorderFactory.createLineBorder(Color.LIGHT_GRAY,2));
         addMouseListener(new Listener1());  
         repaint();      
      }             
   }

Answer 1

我使用了两种解决方案来解决这个问题：

• 一种解决方案是让外部类将 BufferedImage 对象作为类字段保存并在其 PaintComponent 方法中显示它，然后内部类可以从 BufferedImage 中提取 Graphics 或 Graphcis2D 对象，绘制它，释放 Graphics 对象，并在外部类上调用重绘。
• 另一种选择是使用从内部类中填充的 Point（或其他 Shape）对象的类 ArrayLists 在外部类的 PaintComponent 方法中进行绘制。在后一种情况下，内部类与 Graphics 对象无关，而是填充外部类的数组列表并调用重绘。

Answer 2

您可以将：

private Graphics2D g2d;

作为面板的类成员，并且在第一次调用 PaintComponent 后，它将拥有可由内部类访问的主图形对象。