在Java中的JFrame中拖动矩形 [英] Drag rectangle on JFrame in Java

问题描述

我想根据mousedrag事件绘制矩形。如果用户拖动鼠标，然后在小程序中的矩形应该增加或减少立足当前鼠标的坐标。
我有以下code。

I want to draw rectangle based on mousedrag event. if user dragging the mouse, then the rectangle on the applet should increase or decrease basing on current mouse coordinates. i have the following code.

在以下code我使用延伸上对此我进行绘图操作的画布SelectionArea类。我正在使用本类双缓冲图像变量减少闪烁并保存applet的previous状态（即绘图小程序的内容）

in the following code i am using SelectionArea class which extends a canvas on which i am performing drawing operation. i am using image variable in this class for double buffering to reduce flickering and to save the applet's previous state(i.e drawing content of applet)

但是，如果我画一个矩形的code是工作的罚款。如果我开始绘制第二个矩形的previously绘制的矩形正在消失。我想previously绘制的矩形要在屏幕上

but the code is working fine if i draw first rectangle. if i start to draw second rectangle the previously drawn rectangle is disappearing. i want the previously drawn rectangle to be on the screen

PLZ告诉我怎么解决这个问题。

plz tell me how to solve this.

推荐答案

您需要做的，是的保存previously绘制的矩形在某些类型的数据结构上，这样你就可以画再次更新版本。

What you need to do, is save the previously drawn rectangle in some sort of data structure, so you can draw it again later.

这code（约长不好意思，会做类似于你所描述的东西。

要使用它，只是巴掌的JP​​anel 内部的的JFrame 。

This code (sorry about the length, will do something similar to what you are describing.
To use it, just slap the JPanel inside of a JFrame.

public class DrawPane extends JPanel {

    private List<DrawnShape> drawings;
    private DrawnShape curShape;

    public DrawPane() {
    	drawings = new ArrayList<DrawnShape>();
    	setBackground(Color.WHITE);
    	setPreferredSize(new Dimension(300, 300));
    	addMouseListener(clickListener);
    	addMouseMotionListener(moveListener);
    }

    @Override
    protected void paintComponent(Graphics g2) {
    	super.paintComponent(g2);
    	Graphics2D g = (Graphics2D) g2;
    	for (DrawnShape s : drawings) {
    		s.draw(g);
    	}
    	g.setColor(Color.BLACK);
    	g.setStroke(new BasicStroke(2));

    	if (curShape == null)
    		return;
    	curShape.draw(g);
    }

    private MouseListener clickListener = new MouseAdapter() {

    	@Override
    	public void mousePressed(MouseEvent e) {
    		curShape = new DrawnShape(e.getPoint(), e.getPoint());
    	}

    	@Override
    	public void mouseReleased(MouseEvent e) {
    		drawings.add(new DrawnShape(curShape.getClickP(), e.getPoint()));
    		curShape = null;
    	}
    };

    private MouseMotionListener moveListener = new MouseMotionListener() {

    	@Override
    	public void mouseDragged(MouseEvent e) {
    		curShape = new DrawnShape(curShape.getClickP(), e.getPoint());
    		repaint();
    	}
    	@Override
    	public void mouseMoved(MouseEvent e) {
    	}
    };
}

class DrawnShape {

    private Point p1, p2;

    public DrawnShape(Point p1, Point p2) {
    	this.p1 = p1;
    	this.p2 = p2;
    }

    public Point getClickP() {
    	return p1;
    }

    public void draw(Graphics2D g) {
    	g.drawLine(p1.x, p1.y, p2.x, p1.y);
    	g.drawLine(p1.x, p1.y, p1.x, p2.y);
    	g.drawLine(p2.x, p2.y, p2.x, p1.y);
    	g.drawLine(p2.x, p2.y, p1.x, p2.y);
    }
}

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