在Java中拖动形状

Question

public class DragPanel extends JPanel implements MouseListener, MouseMotionListener
{
Graphics2D g2;
Rectangle2D square;
Color colour;

double x1, y1, x2, y2, size;
double offsetX, offsetY;

boolean dragging = false;

构造函数方法：

public DragPanel()
{

x1 = 10.0;
y1 = 10.0;
size = 40.0;
x2 = x1 + size;
y2 = y1 + size;

square = new Rectangle2D.Double(x1, y1, size, size);
colour = Color.BLUE;

setFocusable(true);
addMouseListener(this);
addMouseMotionListener(this);
this.requestFocus();

}

PaintComponent方法和MouseDlold、MousePressed和MouseReleased方法：

public void paintComponent(Graphics g)
{

super.paintComponent(g);
g2 = (Graphics2D) g;
g2.draw(square);
g2.setColor(colour);
g2.draw(square);

}

@Override
public void mouseDragged(MouseEvent ev) 
{
    if (dragging)
    {
    double mx = ev.getX();
    double my = ev.getY();

    x1 = mx - offsetX;
    y1 = mx - offsetY;
    square = new Rectangle2D.Double(x1, y1, size, size);
    repaint();  
    }

}

@Override
public void mousePressed(MouseEvent ev) 
{
double mx = ev.getX();
double my = ev.getY();

if (mx > x1 && mx < x2 && my > y1 && my < y2)
{
    dragging = true;
    offsetX  = mx - x1;
    offsetY = my - y1;
}

}

@Override
public void mouseReleased(MouseEvent arg0) 
{
dragging = false;
}

Answer 1

在MouseDlowed（）中

x1 = mx - offsetX;
y1 = mx - offsetY;

应该是

x1 = mx - offsetX;
y1 = my - offsetY;
x2 = x1 + size;
y2 = y1 + size;

每次移动方块时，都需要更新方块的所有边界。不是将它们显式存储在实例变量中，而是使用内置的矩形2D方法，如getMinX（）和getMaxX（）