单击 JButton 时,我的 JPanel 不显示。当我在 go() 方法中添加 JPanel 时,它确实会出现。但是,当我尝试通过单击 JButton 来执行它时,它不起作用。不过,程序确实进入了监听器的 actionPeformed() 方法的循环。
public class MyShape
{
JFrame frame;
JPanel panel;
JButton drawButton;
public static void main (String[] args)
{
MyShape test = new MyRandomShape();
test.go();
}
public void go()
{
drawButton = new JButton("Draw Shape!");
drawButton.addActionListener(new DrawListener());
frame = new JFrame();
frame.add(drawButton, BorderLayout.NORTH);
frame.setSize(500,500);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
private class DrawListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
if(empty)
{
System.out.print("IN");
panel = new DrawPanel();
frame.add(panel, BorderLayout.CENTER);
}
}
}
private class DrawPanel extends JPanel
{
public void paintComponent(Graphics g)
{
super.paintComponents(g);
int randNo = (int)(Math.random() * 3);
int width = (int)(Math.random() * getWidth());
int height = (int)(Math.random() * getHeight());
int xpos = getWidth()/2-width/2;
int ypos = getHeight()/2-height/2;
int v1 = (int)(Math.random() * 256);
int v2 = (int)(Math.random() * 256);
int v3 = (int)(Math.random() * 256);
g.setColor(new Color(v1, v2, v3));
if(randNo == 0)
{
g.fillOval(xpos, ypos, width, height);
}
else if(randNo == 1)
{
g.fillRect(xpos, ypos, width, height);
}
else
{
int startAngle = (int)(Math.random() * 360);
int arcAngle = (int)(Math.random() * 360);
g.fillArc(xpos, ypos, width, height, startAngle, arcAngle);
}
}
}
}
单击按钮后如何显示 JPanel?
最佳答案
每次执行一个或多个 parentComponent.add(childComponent)
时,您都必须调用 parentComponent.revalidate()
(或者以其他方式更改其子组件,例如重新排序或删除它们)。
就您而言,您的代码应该是
private class DrawListener implements ActionListener {
public void actionPerformed(ActionEvent event)
{
if(empty)
{
System.out.print("IN");
panel = new DrawPanel();
frame.add(panel, BorderLayout.CENTER);
frame.revalidate(); // <---------- important
}
}
}
关于java - 单击 JButton 后不出现 JPanel,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/19792276/