Java中如何监听鼠标事件

今天药忘吃喽~ 2022-05-28 11:39 580阅读 0赞

当点击鼠标按钮时，有三个监听器方法可以调用：①鼠标按下时调用mousePressed；②鼠标被释放时调用mouseReleased；③关注鼠标的最终点击事件时调用mouseClicked。鼠标点击可以由mouseClicked过程报告，该方法是MouseListener接口的一部分。通常大部分应用程序只对鼠标点击事件感兴趣，而对鼠标移动及拖动并不感兴趣，但是鼠标移动及拖动事件又经常发生，因此，鼠标移动与拖动事件定义在一个MouseMotionListener接口中。

因为MouseListener接口中有很多方法，而其中很多并不一定是我们需要的，但是我们在实现该接口的类时又必须实现MouseListener接口中所有的方法。庆幸的是，MouseAdapter类实现了MouseListener接口中的所有方法（就是空方法，并没有编写方法的具体执行过程），我们可以直接继承该类并重写我们需要的方法就可以了。下面的示例程序通过分别定义两个类MouseHandler和MouseMotionHandler演示了鼠标的点击监听、鼠标移动和拖动事件监听：

import java.awt.Cursor;
    import java.awt.Dimension;
    import java.awt.EventQueue;
    import java.awt.Graphics;
    import java.awt.Graphics2D;
    import java.awt.event.MouseAdapter;
    import java.awt.event.MouseEvent;
    import java.awt.event.MouseMotionListener;
    import java.awt.geom.Point2D;
    import java.awt.geom.Rectangle2D;
    import java.util.ArrayList;
    import javax.swing.JComponent;
    import javax.swing.JFrame;
    
    public class MouseDemo {
    	public static void main(String[] args){   
    		EventQueue.invokeLater(() -> {	         
    			JFrame frame = new MouseFrame();	         
    			frame.setTitle("MouseTest");	         
    			frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);	         
    			frame.setVisible(true);	      
    		});	   
    	}
    }
    
    class MouseFrame extends JFrame{ 
    	public MouseFrame(){    
    		add(new MouseComponent());    
    		pack();  
    	}
    }
    
    class MouseComponent extends JComponent{
    	private static final int DEFAULT_WIDTH = 300;
        private static final int DEFAULT_HEIGHT = 200;
        private static final int SIDELENGTH = 10;
        private ArrayList<Rectangle2D> squares;
        private Rectangle2D current; // the square containing the mouse cursor
        public MouseComponent(){
        	squares = new ArrayList<>();
        	current = null;
        	addMouseListener(new MouseHandler());   
        	addMouseMotionListener(new MouseMotionHandler()); 
        }
    
        public Dimension getPreferredSize() { return new Dimension(DEFAULT_WIDTH, DEFAULT_HEIGHT); }   
    
        public void paintComponent(Graphics g){     
        	Graphics2D g2 = (Graphics2D) g;      
        	for (Rectangle2D r : squares)        
        		g2.draw(r);
        }
       
        public Rectangle2D find(Point2D p){     
        	for (Rectangle2D r : squares){       
        		if (r.contains(p)) return r;     
        	}      
        	return null;   
        }
       
        public void add(Point2D p){      
        	double x = p.getX();     
        	double y = p.getY();   
        	current = new Rectangle2D.Double(x - SIDELENGTH / 2, y - SIDELENGTH / 2, SIDELENGTH, SIDELENGTH);      
        	squares.add(current);     
        	repaint();  
        }
       
        public void remove(Rectangle2D s){     
        	if (s == null) return;     
        	if (s == current) current = null;     
        	squares.remove(s); 
        	repaint(); 
        }
       
        private class MouseHandler extends MouseAdapter{   
        	public void mousePressed(MouseEvent event){    //鼠标按下时调用        
        		current = find(event.getPoint());     
        		if (current == null) add(event.getPoint());    
        	}
        
        	public void mouseClicked(MouseEvent event){   //鼠标点击时调用，点击两次则移除矩形    
        		current = find(event.getPoint());    
        		if (current != null && event.getClickCount() >= 2) remove(current);    
        	} 
        }
     
        private class MouseMotionHandler implements MouseMotionListener{   
        	public void mouseMoved(MouseEvent event){    //鼠标移动时调用
        		if (find(event.getPoint()) == null) setCursor(Cursor.getDefaultCursor());         
        		else setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));     
        	}
        
        	public void mouseDragged(MouseEvent event){  //鼠标按住拖动时调用      
        		if (current != null){           
        			int x = event.getX();           
        			int y = event.getY();         
        			current.setFrame(x - SIDELENGTH / 2, y - SIDELENGTH / 2, SIDELENGTH, SIDELENGTH);           
        			repaint();         
        		}      
        	} 
        }   
    }