Question

eclipse麻烦帮我看看，感谢！ 就是我定义的类MyPanel中paint函数下if语句怎么才能进去，新手求解惑！

import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.util.ArrayList;
import java.awt.Point;

class Mouse extends MouseAdapter
{
protected ArrayList<Point> points=new ArrayList<Point>();
protected int endX=0,endY=0;
public void mouseClicked(MouseEvent e)
{
if(e.getClickCount()==1)
points.add(new Point(e.getX(),e.getY()));
else if(e.getClickCount()==2)
{
endX=e.getX();
endY=e.getY();
}
}
}

class MyPanel extends JPanel
{
private Mouse mouse=new Mouse();
public MyPanel()
{
this.addMouseListener(mouse);
}
public void paint(Graphics g)
{
Graphics2D gg=(Graphics2D)g;
if(mouse.points.size()>0)
{
for(int i=0;i<mouse.points.size()-1;i++)
gg.drawLine(mouse.points.get(i).x, mouse.points.get(i).y, mouse.points.get(i+1).x, mouse.points.get(i+1).y);
gg.drawLine(mouse.endX,mouse.endY,mouse.points.get(0).x, mouse.points.get(0).y);
}
}
}

public class Paint extends JFrame{
private MyPanel mpl=new MyPanel();
public Paint()
{
this.add(mpl);
this.setSize(400,400);
this.setVisible(true);
}
public static void main(String[] args) throws Exception
{
new Paint();
}
}
可能点了什么问题关闭了 。。。
求帮忙。。。

Answer 1

MyPanel 在new的时候父类JPanel 构造函数调用了paint，而你的mouseClicked还没执行，points.size()=0

追问

所以该怎么做才能触发那个鼠标事件，我知道原因不会解决啊。。。

追答

鼠标事件你是点击一下那个空面板就促发了呀，你在里面System.out.print(),打印输出就知道了鼠标点击事件有调用，但是paint在鼠标事件之前就调用了

追问

那么我的构造函数不是add了鼠标事件吗，为什么不触发呢

追答

你的add只是增加鼠标点击事件的监控，而你促发要点击那个mpl面板才可以

追问

我表达错意思了。。。我想在paint()前就调用鼠标点击事件，那是不是要把这个鼠标点击事件添加到MyPanel这个类中呢

追答

MyPanel：

public void paint(Graphics g)
{
mouse.setG(g);

}
Mouse：
class Mouse extends MouseAdapter
{
protected ArrayList points=new ArrayList();
protected int endX=0,endY=0;
private Graphics g;
public void mouseClicked(MouseEvent e)
{
System.out.println("kkkkk");
if(e.getClickCount()==1)
points.add(new Point(e.getX(),e.getY()));
else if(e.getClickCount()==2)
{
endX=e.getX();
endY=e.getY();
}
paint(g);
}

public Graphics getG() {
return g;
}

public void setG(Graphics g) {
this.g = g;
}

public void paint(Graphics g)
{
Graphics2D gg=(Graphics2D)g;

if(points.size()>0)
{System.out.println("6y"+gg);
for(int i=0;i<points.size()-1;i++)
gg.drawLine(points.get(i).x,points.get(i).y, points.get(i+1).x, points.get(i+1).y);
gg.drawLine(endX,endY,points.get(0).x, points.get(0).y);
}
}
}