将矩形向下移动一个JFrame

Question

我想让程序移动一个JFrame的矩形，任何人都可以解释为什么这不起作用？

public class DrawingComponent extends JLabel { 

public static int x = 0; 

public void paintComponent(Graphics g){ 
    Graphics2D g2 = (Graphics2D) g; 
    Rectangle rect = new Rectangle(50,x,50,50); 
    g2.draw(rect); 
    x = x+100; 
} 
} 

public class GameL { 

javax.swing.JFrame frame = new javax.swing.JFrame(); 

public static void main(String[] args) { 
     GameL tetris = new GameL(); 
     tetris.start();  
} 

public void start(){ 
    //setup frame 
    frame.setSize(800,600); 
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    frame.setVisible(true); 

    TimerEH timereh = new TimerEH(); 
    Timer timer = new Timer(5000,timereh); 
    timer.start();   
} 

class TimerEH implements ActionListener{   
    public void actionPerformed(ActionEvent e){ 
     DrawingComponent dc = new DrawingComponent(); 
     frame.add(dc); 
    }  
} 
} 

Answer 1

你正在创建一个新的DrawingComponent并将其添加到每个刻度周期的框架。这是很多DrawComponent s

尽管可以通过移动组件来动画，但您需要提供更多信息来说明为什么要这样做。首选的方法是使用类似JPanel的东西，将其添加到使用BorderLayout的框架并覆盖面板paintComponent方法。

尝试“移动”组件的问题是组件有一个已定义的空间，可以在其中渲染，从您的代码外观来看，标签很可能具有0x0的大小，在所有油漆中......

已更新，例如

所以，下面的例子使用布局管理器演示WITHIN组件的范围矩形的画就是将尝试大小分量到可用的可用空间。

它还显示用户getPreferredSize向布局管理器提供有用的大小提示。

import java.awt.BorderLayout; 
import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.EventQueue; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.GridLayout; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.Timer; 
import javax.swing.UIManager; 
import javax.swing.UnsupportedLookAndFeelException; 

public class CreppyRectangle { 

    public static void main(String[] args) { 
     new CreppyRectangle(); 
    } 

    public CreppyRectangle() { 
     EventQueue.invokeLater(new Runnable() { 
      @Override 
      public void run() { 
       try { 
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); 
       } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { 
       } 

       JFrame frame = new JFrame("Testing"); 
       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
       frame.setLayout(new GridLayout(0, 6)); 
       frame.add(new TestPane(Color.RED)); 
       frame.add(new TestPane(Color.GREEN)); 
       frame.add(new TestPane(Color.BLUE)); 
       frame.add(new TestPane(Color.ORANGE)); 
       frame.add(new TestPane(Color.PINK)); 
       frame.add(new TestPane(Color.MAGENTA)); 
       frame.pack(); 
       frame.setLocationRelativeTo(null); 
       frame.setVisible(true); 
      } 
     }); 
    } 

    public class TestPane extends JPanel { 

     private int yPos; 
     private int size = 25 + (int)Math.round(Math.random() * 50); 
     private int yDelta = 5 + (int)Math.round(Math.random() * 10); 

     public TestPane(Color foreground) { 
      setForeground(foreground); 
      Timer timer = new Timer(40, new ActionListener() { 
       @Override 
       public void actionPerformed(ActionEvent e) { 
        yPos += yDelta; 
        if (yPos < 0) { 
         yPos = 0; 
         yDelta *= -1; 
         System.out.println(yDelta); 
        } else if (yPos + size > getHeight()) { 
         yPos = getHeight() - size; 
         yDelta *= -1; 
        } 
        repaint(); 
       } 
      }); 
      timer.setRepeats(true); 
      timer.setCoalesce(true); 
      timer.start(); 
     } 

     @Override 
     public Dimension getPreferredSize() { 
      return new Dimension(50, 200); 
     } 

     @Override 
     protected void paintComponent(Graphics g) { 
      super.paintComponent(g); 
      Graphics2D g2d = (Graphics2D) g.create(); 
      g2d.setColor(getForeground()); 
      g2d.drawRect(0, yPos, getWidth() - 1, size); 
      g2d.dispose(); 
     } 
    } 

}