《Java 核心技术卷1》笔记第八章事件处理(4)-CFANZ编程社区

8.3 鼠标事件

鼠标按下：mousePressed

鼠标释放：mouseReleased

鼠标点击：mouseClicked

点击次数：getClickCount===>可用于区分单击双击三击

鼠标光标形状：

《Java 核心技术卷1》笔记第八章事件处理(4)_swing

未按住鼠标是箭头，按住鼠标是十字,可通过 MouseEvent 的 getPoint() 确定是否按住鼠标，getPoint()不为空时按住鼠标，否则未按住。

原书例子：

绘制正方形

如果鼠标悬浮位置下方有正方形，则为拖拽模式，长按移动，可拖拽正方形
如果鼠标悬浮位置下方没有正方形，则为添加模式，点击添加一个新的正方形（发现点击后立即拖拽的情况，是识别不到的，这里做了一点小修改适应这个情况）
多次点击同一个小正方形，立刻删除小正方形

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.awt.geom.*;
import javax.swing.*;
public class Main {
    public static  void main(String[] args) {
        Main solution = new Main();
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                MouseFrame b = new MouseFrame();
                b.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                b.setVisible(true);
            }
        });
    }

}


class MouseFrame extends JFrame{
    public static final int W = 300;
    public static final int H = 200;
    public MouseFrame(){
        setTitle("MouseTest");
        setSize(W,H);

        MouseComponent component = new MouseComponent();
        add(component);

    }
}

class MouseComponent extends JComponent{
    private static final int SIDELENGTH = 10;
    private ArrayList<Rectangle2D> squares;
    private Rectangle2D current;

    public MouseComponent(){
        squares = new ArrayList<>();

        addMouseListener(new MouseHandler());
        addMouseMotionListener(new MouseMotionHandler());
    }

    public void paintComponent(Graphics g){
        Graphics2D g2 = (Graphics2D) g;

        for(Rectangle2D r:squares){
            g2.draw(r);
        }

    }

    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();
    }

    public Rectangle2D find(Point2D p){
        for(Rectangle2D r:squares){
            if(r.contains(p))
                return r;
        }
        return null;
    }
    private class MouseHandler extends MouseAdapter{
        public void mousePressed(MouseEvent event){
            current = find(event.getPoint());
            if(current == null)
                add(event.getPoint());
        }

        @Override
        public void mouseClicked(MouseEvent event) {
            current = find(event.getPoint());
            if(current!=null && event.getClickCount() >= 2)
                remove(current);
        }
    }
    private class MouseMotionHandler implements MouseMotionListener{
        @Override
        public void mouseMoved(MouseEvent event) {
            if(find(event.getPoint())==null){
                setCursor(Cursor.getDefaultCursor());
            }else{
                setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));
            }
        }

        @Override
        public void mouseDragged(MouseEvent event) {

            if(current != null){
                //点击立刻拖拽改光标
                if(getCursor()==Cursor.getDefaultCursor())
                    setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));
                int x = event.getX();
                int y = event.getY();

                current.setFrame(x-SIDELENGTH/2,y-SIDELENGTH/2, SIDELENGTH, SIDELENGTH);
                repaint();
            }
        }
    }
}