Java：mouseDragged并在图形界面中移动
新手程序员在这里。
我正在制作一个在笛卡尔坐标系中呈现用户输入方程式的程序。目前，让用户在坐标中自由移动视图时遇到一些问题。当前，在使用mouseDragged的情况下，用户可以拖动视图一点点，但是一旦用户释放鼠标并尝试再次移动视图，原点就会恢复到鼠标光标的当前位置。让用户自由移动的最佳方法是什么？提前致谢！
这是绘图区域的代码。
import java.awt.Color;import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import javax.swing.JPanel;
public class DrawingArea extends JPanel implements MouseMotionListener {
private final int x_panel = 350; // width of the panel
private final int y_panel = 400; // height of the panel
private int div_x; // width of one square
private int div_y; // height of one square
private int real_y;
private int real_x;
private Point origin; // the origin of the coordinate
private Point temp; // temporary point
private static int y = 0;
private static int x = 0;
DrawingArea() {
setBackground(Color.WHITE);
real_x = x_panel;
real_y = y_panel;
setDivisionDefault();
setOrigin(new Point((real_x / 2), (real_y / 2)));
setSize(x_panel, y_panel);
addMouseMotionListener(this);
}
DrawingArea(Point origin, Point destination) {
this.origin = origin;
this.destination = destination;
panel = new JPanel();
panel.setSize(destination.x, destination.y);
panel.setLocation(origin);
this.panel.setBackground(Color.red);
panel.setLayout(null);
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D line = (Graphics2D) g;
temp = new Point(origin.x, origin.y);
line.setColor(Color.red);
drawHelpLines(line);
line.setColor(Color.blue);
drawOrigin(line);
line.setColor(Color.green);
for (int i = 0; i < 100; i++) { // This is a test line
//temp = this.suora();
temp.x++;
temp.y++;
line.drawLine(temp.x, temp.y, temp.x, temp.y);
}
}
public void setOrigin(Point p) {
origin = p;
}
public void drawOrigin(Graphics2D line) {
line.drawLine(origin.x, 0, origin.x, y_panel);
line.drawLine(0, origin.y, x_panel, origin.y);
}
public void drawHelpLines(Graphics2D line) {
int xhelp= origin.x;
int yhelp= origin.y;
for (int i = 0; i < 20; i++) {
xhelp+= div_x;
line.drawLine(xhelp, 0, xhelp, y_panel);
}
xhelp= origin.x;
for (int i = 0; i < 20; i++) {
xhelp-= div_x;
line.drawLine(xhelp, 0, xhelp, y_panel);
}
for (int i = 0; i < 20; i++) {
yhelp-= div_y;
line.drawLine(0, yhelp,x_panel, yhelp);
}
yhelp= origin.y;
for (int i = 0; i < 20; i++) {
yhelp+= div_y;
line.drawLine(0, yhelp, x_panel, yhelp);
}
}
public void setDivisionDefault() {
div_x = 20;
div_y = 20;
}
@Override
public void mouseDragged(MouseEvent e) {
//Point temp_point = new Point(mouse_x,mouse_y);
Point coords = new Point(e.getX(), e.getY());
setOrigin(coords);
repaint();
}
@Override
public void mouseMoved(MouseEvent e) {
}
}
回答：
基于该示例，以下程序允许用户将轴的交点拖动到任意点origin，该点从面板的中心开始。
import java.awt.Cursor;import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import javax.swing.JFrame;
import javax.swing.JPanel;
/**
* @see https://stackoverflow.com/a/15576413/230513
* @see https://stackoverflow.com/a/5312702/230513
*/
public class MouseDragTest extends JPanel {
private static final String TITLE = "Drag me!";
private static final int W = 640;
private static final int H = 480;
private Point origin = new Point(W / 2, H / 2);
private Point mousePt;
public MouseDragTest() {
this.setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR));
this.addMouseListener(new MouseAdapter() {
@Override
public void mousePressed(MouseEvent e) {
mousePt = e.getPoint();
repaint();
}
});
this.addMouseMotionListener(new MouseMotionAdapter() {
@Override
public void mouseDragged(MouseEvent e) {
int dx = e.getX() - mousePt.x;
int dy = e.getY() - mousePt.y;
origin.setLocation(origin.x + dx, origin.y + dy);
mousePt = e.getPoint();
repaint();
}
});
}
@Override
public Dimension getPreferredSize() {
return new Dimension(W, H);
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawLine(0, origin.y, getWidth(), origin.y);
g.drawLine(origin.x, 0, origin.x, getHeight());
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
JFrame f = new JFrame(TITLE);
f.add(new MouseDragTest());
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.pack();
f.setLocationRelativeTo(null);
f.setVisible(true);
}
});
}
}
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