在用户拖动鼠标时收听 JFrame 调整大小事件？

Question

当用户单击 JFrame 的角以调整大小并拖动鼠标时，JFrame 在用户拖动时根据鼠标的当前位置重绘。你怎么能听到这些事件？

以下是我目前尝试过的：

public final class TestFrame extends JFrame {
    public TestFrame() {
        this.addComponentListener(new ComponentAdapter() {
            public void componentResized(ComponentEvent e) {
                // This is only called when the user releases the mouse button.
                System.out.println("componentResized");
            }
        });
    }

    // These methods do not appear to be called at all when a JFrame
    // is being resized.
    @Override
    public void setSize(int width, int height) {
        System.out.println("setSize");
    }

    @Override
    public void setBounds(Rectangle r) {
        System.out.println("setBounds A");
    }

    @Override
    public void setBounds(int x, int y, int width, int height) {
        System.out.println("setBounds B");
    }
}

当用户在鼠标周围拖动时，如何确定和限制用户如何调整窗口大小（基于窗口的当前纵横比）？

Answer 1

你可以添加一个组件监听器并像这样实现 componentResized 函数：

JFrame component = new JFrame("My Frame");

component.addComponentListener(new ComponentAdapter() 
{  
        public void componentResized(ComponentEvent evt) {
            Component c = (Component)evt.getSource();
            //........
        }
});

编辑： 显然，对于 JFrame，componentResized 事件与 mouseReleased 事件挂钩。这就是释放鼠标按钮时调用该方法的原因。

实现您想要的一种方法是添加一个 JPanel，它将覆盖您的 JFrame 的整个区域。然后将 componentListener 添加到 JPanel（即使您的鼠标仍在拖动，也会调用 JPanel 的 componentResized）。当您的框架调整大小时，您的面板也将调整大小。

我知道，这不是最优雅的解决方案，但它确实有效！

Answer 2

public class MouseDrag extends Component implements MouseListener,
    MouseMotionListener {
  /** The Image we are to paint */
  Image curImage;

  /** Kludge for showStatus */
  static Label status;

  /** true if we are in drag */
  boolean inDrag = false;

  /** starting location of a drag */
  int startX = -1, startY = -1;

  /** current location of a drag */
  int curX = -1, curY = -1;

  // "main" method
  public static void main(String[] av) {
    JFrame f = new JFrame("Mouse Dragger");
    Container cp = f.getContentPane();

    if (av.length < 1) {
      System.err.println("Usage: MouseDrag imagefile");
      System.exit(1);
    }
    Image im = Toolkit.getDefaultToolkit().getImage(av[0]);

    // create a MouseDrag object
    MouseDrag j = new MouseDrag(im);

    cp.setLayout(new BorderLayout());
    cp.add(BorderLayout.NORTH, new Label(
        "Hello, and welcome to the world of Java"));
    cp.add(BorderLayout.CENTER, j);
    cp.add(BorderLayout.SOUTH, status = new Label());
    status.setSize(f.getSize().width, status.getSize().height);
    f.pack();
    f.setVisible(true);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }

  // "Constructor" - creates the object
  public MouseDrag(Image i) {
    super();
    curImage = i;
    setSize(300, 200);
    addMouseListener(this);
    addMouseMotionListener(this);
  }

  public void showStatus(String s) {
    status.setText(s);
  }

  // Five methods from MouseListener:
  /** Called when the mouse has been clicked on a component. */
  public void mouseClicked(MouseEvent e) {
  }

  /** Called when the mouse enters a component. */
  public void mouseEntered(MouseEvent e) {
  }

  /** Called when the mouse exits a component. */
  public void mouseExited(MouseEvent e) {
  }


  // And two methods from MouseMotionListener:
  public void mouseDragged(MouseEvent e) {
    Point p = e.getPoint();
    // System.err.println("mouse drag to " + p);
    showStatus("mouse Dragged to " + p);
    curX = p.x;
    curY = p.y;
    if (inDrag) {
      repaint();
    }
  }

  public void paint(Graphics g) {
    int w = curX - startX, h = curY - startY;
    Dimension d = getSize();
    g.drawImage(curImage, 0, 0, d.width, d.height, this);
    if (startX < 0 || startY < 0)
      return;
    System.err.println("paint:drawRect @[" + startX + "," + startY
        + "] size " + w + "x" + h);
    g.setColor(Color.red);
    g.fillRect(startX, startY, w, h);
  }

}

Answer 3

另一种解决方法（与 Alex 的非常相似，但更简单一点）是从 JFrame 的根窗格中监​​听事件：

public final class TestFrame extends JFrame {
    public TestFrame() {
        this.getRootPane().addComponentListener(new ComponentAdapter() {
            public void componentResized(ComponentEvent e) {
                // This is only called when the user releases the mouse button.
                System.out.println("componentResized");
            }
        });
    }
}

根据其他实现细节，根窗格可能会更改。如果这是一种可能性，那么您可以覆盖 setRootPane() 并处理它。由于setRootPane() 受到保护并且只能从构造函数中调用，因此您不太可能需要这样做。

Answer 4

您可能需要覆盖 validate 之类的内容（不要忘记调用 super）。当然，如果您使用窗口系统配置为拖动轮廓，这仍然可能不起作用。