为什么repaint(long)会立即重绘？
根据 Javadoc， JComponent .repaint(long) 应该在将来的某个时间安排 repaint() 。当我尝试使用它时，它总是会立即触发重新绘制。我做错了什么？
import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
public class Repaint
{
public static final boolean works = false;
private static class CustomComponent extends JPanel
{
private float alpha = 0;
@Override
protected void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setComposite(
AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha));
g2d.setPaint(Color.BLACK);
g2d.fillRect(0, 0, getWidth(), getHeight());
alpha += 0.1;
if (alpha > 1)
alpha = 1;
System.out.println("alpha=" + alpha);
if (!works)
repaint(1000);
}
}
public static void main(String[] args)
{
final JFrame frame = new JFrame();
frame.getContentPane().add(new CustomComponent());
frame.setSize(800, 600);
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.setVisible(true);
if (works)
{
new Timer(1000, new ActionListener()
{
@Override
public void actionPerformed(ActionEvent e)
{
frame.repaint();
}
}).start();
}
}
}
According to the Javadoc, JComponent.repaint(long) is supposed to schedule a repaint() sometime in the future. When I try using it it always triggers an immediate repaint. What am I doing wrong?
import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
public class Repaint
{
public static final boolean works = false;
private static class CustomComponent extends JPanel
{
private float alpha = 0;
@Override
protected void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setComposite(
AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha));
g2d.setPaint(Color.BLACK);
g2d.fillRect(0, 0, getWidth(), getHeight());
alpha += 0.1;
if (alpha > 1)
alpha = 1;
System.out.println("alpha=" + alpha);
if (!works)
repaint(1000);
}
}
public static void main(String[] args)
{
final JFrame frame = new JFrame();
frame.getContentPane().add(new CustomComponent());
frame.setSize(800, 600);
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.setVisible(true);
if (works)
{
new Timer(1000, new ActionListener()
{
@Override
public void actionPerformed(ActionEvent e)
{
frame.repaint();
}
}).start();
}
}
}
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请注意，Javadoc 表示该方法将导致在指定时间内（而不是之后）发生重绘。
Note that the Javadoc says the method will cause a repaint to happen within (not after) the specified time.
如果您想安排重新绘制某些内容，那么您应该使用 Swing Timer。您不应该使用 PaintComponnt(..) 方法来安排绘制。您无法控制何时调用paintComponent() 方法。
If you want to schedule something to be repainted, then you should be using a Swing Timer. You should not be scheduling painting from withing the paintComponnt(..) method. You can't control when the paintComponent() method is called.
该参数表示 tm - 更新前的最长时间（以毫秒为单位），但它并没有说它不会立即执行更新，javadocs 也说
The parameter says tm - maximum time in milliseconds before update it does not say it won't do so immediately also the javadocs say
如果你稍微搜索一下，你会发现这个参数在派生类中被忽略。 ;)
If you search a little bit you find that this parameter is ignored in derived classes. ;)