有没有办法在JLabel上设置锚点？

Question

我希望能够为中心的JLabel设置定位点，所以我可以根据它移动它。

Answer 1

如果您试图将JLabel居中在某个点上，那么您只需要简单的数学就可以完成此操作，仅此而已。

假设您有一个JLabel或任何我们将其命名为“component”的组件，它保存在JPanel中，或者我们将称之为“container”的任何容器，并且假设有一个鼠标Point 在屏幕上，说叫“mousePoint”，那么数学也很简单：

Point mousePoint = e.getLocationOnScreen(); 
Point containerLocation = container.getLocationOnScreen(); 
Dimension componentSize = component.getSize(); 

int x = mousePoint.x - componentSize.width/2 - containerLocation.x; 
int y = mousePoint.y - componentSize.height/2 - containerLocation.y; 
component.setLocation(x, y); 

就是这样。例如，假设您有两个JLabel，一个带有图像，另一个带有一些文本，那么您可以将两个相同的MouseListener和MouseMotionListener添加到这两个JLabel，并且这可以让您将它们拖放到它们的中心点。下面是我在我的上述评论提到MCVE的例子：具有登载

import java.awt.Color; 
import java.awt.Container; 
import java.awt.Dimension; 
import java.awt.Image; 
import java.awt.Point; 
import java.awt.event.MouseAdapter; 
import java.awt.event.MouseEvent; 
import java.io.IOException; 
import java.net.URL; 

import javax.imageio.ImageIO; 
import javax.swing.*; 

public class ClickDragLabel extends JPanel { 
    public static final String IMG_PATH = "https://upload.wikimedia.org/wikipedia/commons/thumb/4/43/" 
      + "Theodore_Comnenus-Ducas_cropped.jpg/133px-Theodore_Comnenus-Ducas_cropped.jpg"; 
    private static final int PREF_W = 1000; 
    private static final int PREF_H = 850; 
    private JLabel imageLabel; 
    private JLabel textLabel = new JLabel("Some Random Text"); 

    public ClickDragLabel(Icon icon) { 
     setBackground(Color.WHITE); 
     imageLabel = new JLabel(icon); 

     setLayout(null); 
     imageLabel.setSize(imageLabel.getPreferredSize()); 
     textLabel.setSize(textLabel.getPreferredSize()); 

     imageLabel.setLocation(250, 250); 
     textLabel.setLocation(10, 10); 

     MyMouse myMouse = new MyMouse(); 
     imageLabel.addMouseListener(myMouse); 
     imageLabel.addMouseMotionListener(myMouse); 
     textLabel.addMouseListener(myMouse); 
     textLabel.addMouseMotionListener(myMouse); 

     add(imageLabel); 
     add(textLabel); 

    } 

    @Override 
    public Dimension getPreferredSize() { 
     if (isPreferredSizeSet()) { 
      return super.getPreferredSize(); 
     } 
     return new Dimension(PREF_W, PREF_H); 
    } 

    private class MyMouse extends MouseAdapter { 
     @Override 
     public void mousePressed(MouseEvent e) { 
      center(e); 
     } 

     @Override 
     public void mouseReleased(MouseEvent e) { 
      center(e); 
     } 

     @Override 
     public void mouseDragged(MouseEvent e) { 
      center(e); 
     } 

     private void center(MouseEvent e) { 
      JComponent component = (JComponent) e.getSource(); 
      Container container = component.getParent(); 

      Point mousePoint = e.getLocationOnScreen(); 
      Point containerLocation = container.getLocationOnScreen(); 
      Dimension componentSize = component.getSize(); 

      int x = mousePoint.x - componentSize.width/2 - containerLocation.x; 
      int y = mousePoint.y - componentSize.height/2 - containerLocation.y; 
      component.setLocation(x, y); 
      container.repaint(); 
     } 

    } 

    private static void createAndShowGui() { 
     Image img = null; 
     try { 
      URL imgUrl = new URL(IMG_PATH); 
      img = ImageIO.read(imgUrl); 
     } catch (IOException e) { 
      e.printStackTrace(); 
      System.exit(-1); 
     } 

     Icon icon = new ImageIcon(img); 

     ClickDragLabel mainPanel = new ClickDragLabel(icon); 

     JFrame frame = new JFrame("Click-Drag Label"); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     frame.getContentPane().add(mainPanel); 
     frame.pack(); 
     frame.setLocationRelativeTo(null); 
     frame.setVisible(true); 
    } 

    public static void main(String[] args) { 
     SwingUtilities.invokeLater(() -> createAndShowGui()); 
    } 
} 

，如果我没有提到使用空布局的罪恶我会失职。虽然Swing的新手可能看起来像是创建复杂GUI的最简单也是最好的方式，但更多Swing GUI的创建使用它们时会遇到更严重的困难。它们不会在GUI大小调整时调整组件的大小，它们是增强或维护的皇室女巫，当它们放在滚动窗格中时它们会完全失败，在所有平台或屏幕分辨率与原始视图不同时，它们看起来会非常糟糕。我只将它们用于动画，比如上面的，没有别的。

Answer 2

有没有办法在JLabel上设置锚？

您似乎想要的设置可以通过将EmptyBorder设置并更改为标签来实现。

import java.awt.*; 
import javax.swing.*; 
import javax.swing.border.EmptyBorder; 
import javax.swing.event.*; 

public class MovableLabel { 

    private JComponent ui = null; 
    String anchorString = new String(Character.toChars(9875)); 
    private JLabel label = new JLabel(anchorString); 
    int pad = 200; 
    SpinnerNumberModel xModel = new SpinnerNumberModel(0, 0, pad, 1); 
    SpinnerNumberModel yModel = new SpinnerNumberModel(0, 0, pad, 1); 

    MovableLabel() { 
     initUI(); 
    } 

    public void initUI() { 
     if (ui != null) { 
      return; 
     } 

     ui = new JPanel(new BorderLayout(4, 4)); 
     ui.setBorder(new EmptyBorder(4, 4, 4, 4)); 

     Font[] fonts = GraphicsEnvironment.getLocalGraphicsEnvironment().getAllFonts(); 
     Font font = null; 
     for (Font f : fonts) { 
      if (f.canDisplayUpTo(anchorString) < 0) { 
       font = f.deriveFont(40f); 
       break; 
      } 
     } 
     label.setFont(font); 
     label.setBackground(Color.BLUE); 
     setBorder(); 
     ui.add(label); 

     JToolBar tb = new JToolBar(); 
     ui.add(tb, BorderLayout.PAGE_START); 

     ChangeListener changeListener = new ChangeListener() { 

      @Override 
      public void stateChanged(ChangeEvent e) { 
       setBorder(); 
      } 
     }; 

     tb.add(new JLabel("X")); 
     JSpinner xSpinner = new JSpinner(xModel); 
     xSpinner.addChangeListener(changeListener); 
     tb.add(xSpinner); 

     tb.add(new JLabel("Y")); 
     JSpinner ySpinner = new JSpinner(yModel); 
     ySpinner.addChangeListener(changeListener); 
     tb.add(ySpinner); 
    } 

    private void setBorder() { 
     int x = xModel.getNumber().intValue(); 
     int y = yModel.getNumber().intValue(); 
     EmptyBorder border = new EmptyBorder(x, y, pad - x, pad - y); 
     label.setBorder(border); 
    } 

    public JComponent getUI() { 
     return ui; 
    } 

    public static void main(String[] args) { 
     Runnable r = new Runnable() { 
      @Override 
      public void run() { 
       try { 
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); 
       } catch (Exception useDefault) { 
       } 
       MovableLabel o = new MovableLabel(); 

       JFrame f = new JFrame(o.getClass().getSimpleName()); 
       f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); 
       f.setLocationByPlatform(true); 

       f.setContentPane(o.getUI()); 
       f.pack(); 
       f.setMinimumSize(f.getSize()); 

       f.setVisible(true); 
      } 
     }; 
     SwingUtilities.invokeLater(r); 
    } 
}