Question

我绘制了一些形状，我想从屏幕上清理屏幕。所以我做了一个按钮并将其命名为clearButton并在我的actionPreformed中清理它们。它根本不是清洁。所以我想要的是我的cleanButton来清理我画的东西。只要看看cleanButton以及我做了什么来使它干净。它很长但我不得不发布整个事情，所以它更清楚。只需忽略它，只查看cleanButton正在做什么。谢谢。

主类：

package kal;

import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList; 
import javax.swing.*;
import kal.Box;

public class Kal extends JFrame implements MouseListener, MouseMotionListener,
  ActionListener
{
   int x=0, y=0; // last mouse location
   int pressx, pressy; // coords where the mouse is pressed

   JButton boxButton; // press this to put program in box-drawing mode
   JButton ovalButton;
   JButton triButton;
   JButton clearButton; 

   int mode = 0; // 0=ovals, 1=boxes, 2=triangles ..... 

   Oval theOval;
   Box theBox;
   Triangle theTriangle;
   Shape theShape;
   ColorPicker3 theColorPicker;

  public static void main( String[] args )
  {
     System.out.println("hi there.");
     new Kal();
  }

     // constructor, add MouseListener and MouseMotionListener
     public Kal()
     {
       setDefaultCloseOperation( EXIT_ON_CLOSE );

       setLayout( new FlowLayout() );

       boxButton = new JButton("box");
       add(boxButton);
       boxButton.addActionListener(this);

       ovalButton = new JButton("oval");
       add(ovalButton);
       ovalButton.addActionListener(this);

       triButton = new JButton("Triangle");
       add(triButton);
       triButton.addActionListener(this);

       clearButton = new JButton("Clear");
       add(clearButton);
       clearButton.addActionListener(this);

      addMouseListener(this);
      addMouseMotionListener(this);

      setSize( 500,500);
      setVisible( true);

      theColorPicker = new ColorPicker3();

    } 
     // returns a random color
     public Color randomColor()
     {
      int red = (int)(Math.random()*255);
      int green = (int)(Math.random()*255);
      int blue = (int)(Math.random()*255);
      return new Color(red,green,blue);
     }


      // note position of mouse xy globally, when clicked
      public void mouseClicked( MouseEvent e )
      {
        x = e.getX(); y = e.getY();
       System.out.println("click at x="+x+" y="+y);
      }
       public void mouseEntered( MouseEvent e ) {}

       // record where the mouse gets pressed
       public void mousePressed( MouseEvent e )
       {
         x = pressx = e.getX(); y = pressy = e.getY();

         Point p0 = new Point( x, y );
         Point p1 = new Point( pressx, pressy );

         if      ( mode==0 ) { theShape = theOval = new Oval( p0, p1, randomColor() );   }
         else if ( mode==1 ) { theShape = theBox = (new Box(p0 ,p1, randomColor()));}
         else if ( mode==2 ) { theShape = theTriangle = new Triangle( p0, p1,randomColor() ); }

         theShape.color = theColorPicker.b.color;
       }
          public void mouseExited( MouseEvent e ) {}
          public void mouseReleased( MouseEvent e ){}
          public void mouseMoved( MouseEvent e ) {}
          // note postion of mouse xy globally, when dragging
          public void mouseDragged( MouseEvent e )
       {
          x = e.getX(); y = e.getY();

          theShape.ends[0].x = x;
          theShape.ends[0].y = y;

         if ( mode==0 ) // Oval
         {
           theOval.ends[0].x = x; 
           theOval.ends[0].y = y; 
         }
         else if ( mode==1 ) // Box
         {
           theBox.ends[0].x = x;
           theBox.ends[0].y = y;
         }   

         else if ( mode==2) // Triangle 
         {
           theTriangle.ends[0].x = x;
           theTriangle.ends[0].y = y;
         }

           System.out.println("dragged to x="+x+" y="+y);
           repaint();
         }

          public void actionPerformed( ActionEvent e )
         {
             if ( e.getSource()==ovalButton) { mode = 0; }
             else if ( e.getSource()==boxButton ) { mode = 1; }
             else if ( e.getSource()==triButton ) { mode = 2; }

        //clear all
    else if (e.getSource() == clearButton)
    {
        //theOval.clear();
            //theBox.clear();
            //theTriangle.clear();
    }
  repaint();   

     }

       public void paint(Graphics g )
       {
          super.paint(g); // is no super.paint(), then lines stay on screen 
          if ( theShape != null ) { theShape.drawMe(g); }

       }

    }

Answer 1

绘画方法有什么用？ theShape，就是这样。所有其他变量，包括Oval，theBox和Triangle，都只是完全独立于一个重要变量theShape Variable的引用变量。因此，请在actionPerformed方法中放置要清除绘图的内容：

theShape = null;
repaint();

就是这样。

更重要的是：永远不要直接在JFrame中绘制。而是在JPanel的paintComponent方法中绘制，因为教程都会告诉你这样做。

如何让我的clearButton撤消一切

1 个答案: