Question

所以我想通过循环绘制几个矩形来表示JPanel上图形条形图中的值。

我已经扩展了JPanel以包含我的绘画命令，并且我有一个循环，它调用数组中的值并沿轴的点绘制它们。但是，当我运行我的程序时，它只绘制最后一个？

.repaint()会重置我的画布吗？它只是重新绘制我的缓冲图像，然后只在循环结束时更新我的面板吗？

我对JPanel的扩展：

class myJPanel extends JPanel 
{

     private Rectangle2D.Double rectangle;

     /**
      * Override paintComnponent method with our draw commands
      * 
      */
     public void paintComponent(Graphics g) 
     {

         super.paintComponent(g);

         // Change the dimension and location of the rectangle 
         // obtained from the user interface.
         rectangle = new Rectangle2D.Double(iX, iY, iWidth, iHeight);

         // Set the drawing colour, then draw a filled rectangle
         // on the graphics context of the BufferedImage object
         g2dImg.setPaint(Color.black);
         g2dImg.fill(rectangle);


         // Transfer the image from the BufferedImage to the JPanel to make it visible.
         g.drawImage(img, 0, 0, null);
     }

     // super.paintComponent clears off screen pixmap,
     // since we're using double buffering by default.
     protected void clear(Graphics g) {
         super.paintComponent(g);

         // Also clear the BufferedImage object by drawing a white coloured filled rectangle all over.
         g2dImg.setPaint(Color.WHITE);
         g2dImg.fill(new Rectangle2D.Double(0, 0, img.getWidth(), img.getHeight()));
     }
}

这是我的面板代码：

        final myJPanel jPanelDraw = new myJPanel();
        jPanelDraw.setLayout(new GridBagLayout());
        jPanelDraw.setBounds(248, 152, 604, 257);
        jPanelDraw.setBackground(Color.white);
        jPanelDraw.setEnabled(false);
        jPanelDraw.setPreferredSize(new Dimension(281, 155));
        jPanelDraw.setBorder(BorderFactory.createBevelBorder(BevelBorder.LOWERED));
        frmUSnowboarding.getContentPane().add(jPanelDraw);

        //Instantiate the BufferedImage object and give it the same width 
        // and height as that of the drawing area JPanel
        img = new BufferedImage(jPanelDraw.getWidth(), 
                                jPanelDraw.getHeight(), 
                                BufferedImage.TYPE_INT_RGB);

        //Get its graphics context. 
        g2dImg = (Graphics2D)img.getGraphics();

        //Draw a filled white coloured rectangle on the entire area to clear it.
        g2dImg.setPaint(Color.WHITE);
        g2dImg.fill(new Rectangle2D.Double(0, 0, img.getWidth(), img.getHeight()));

这是我的循环，它位于我的绘图按钮的动作监听器中：

            for (int iI = 0; iI < 6; iI++) {
                iHeight = (double) iaRun1[iI];
                iX = 0 + (iI * 40);
                iY = (double) (jPanelDraw.getHeight() - iHeight);
                jPanelDraw.repaint();
            }

Answer 1

并不是它只重画一次，它只是在循环结束后重新绘制。

repaint方法不会立即重新绘制，而是标记要尽快重新绘制的面板（但现在不是）。

Swing不使用线程，所以一次只能运行。 Swing在幕后做了很多任务，在调用你的听众之间，其中一个任务是重新绘制需要重新绘制的窗口。在听众运行时，Swing不会重新绘制窗口。

此外，即使repaint立即重绘，动画也会发生得太快，任何人都无法注意到。

Answer 2

您可能在事件调度线程中运行该代码，在这种情况下，UI不会在循环之后重新绘制。如果您调试代码，您会发现jPanelDraw.repaint();被多次调用，但UI的实际更新被放入被阻止的同一事件队列中通过你的循环。

尝试在SwingWorker或Timer中执行该循环。

Java jPanel.repaint（）;在一个循环内只涂一次？

2 个答案: