我有一个最简单的java gui的工作版本,带有一个按钮和一个圆圈,工作正常:
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
//a gui element shares its events only with classes that implement Actionlistener interface
public class SimpleGui1 implements ActionListener {
JButton button;
JFrame frame;
ppanel mypanel;
public static void main (String[] args) {
SimpleGui1 mywindow = new SimpleGui1();
mywindow.renderWindow();
}
public void renderWindow(){
frame = new JFrame();
button = new JButton("click me");
mypanel = new ppanel();
//register my interest to catch button events
button.addActionListener(this);
frame.getContentPane().add(BorderLayout.SOUTH, button);
frame.getContentPane().add(BorderLayout.CENTER, mypanel);
frame.setSize(300,300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
//button will call this method when clicked (its the callback)
public void actionPerformed(ActionEvent event)
{
frame.repaint();
button.setText("Clicked!!");
}
}
//i need this to override paintComponent
public class ppanel extends JPanel {
//draw something silly
public void paintComponent(Graphics g) {
//super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
int red = (int) (Math.random() * 255);
int green = (int) (Math.random() * 255);
int blue = (int) (Math.random() * 255);
Color startColor = new Color(red, green, blue);
red = (int) (Math.random() * 255);
green = (int) (Math.random() * 255);
blue = (int) (Math.random() * 255);
Color endColor = new Color(red, green, blue);
GradientPaint gradient = new GradientPaint(70,70,startColor, 150,150, endColor);
g2d.setPaint(gradient);
g2d.fillOval(70,70,100,100);
}
}
然后,为了好玩,我试图将这两个类聚合成一个这样的类:
public class SimpleGui1 extends JPanel implements ActionListener {
private JButton button;
private JFrame frame;
private JPanel mypanel;
public static void main (String[] args) {
SimpleGui1 mywindow = new SimpleGui1();
mywindow.renderWindow();
}
public void renderWindow(){
frame = new JFrame();
button = new JButton("click me");
mypanel = new JPanel();
frame.setSize(300,300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
// register my interest to catch button events
button.addActionListener(this);
frame.getContentPane().add(BorderLayout.SOUTH, button);
frame.getContentPane().add(BorderLayout.CENTER, mypanel);
//without this i see only the button
//frame.add(this);
}
//button will call this method when clicked (its the callback)
public void actionPerformed(ActionEvent event)
{
frame.repaint();
button.setText("Clicked!!");
}
public void paintComponent(Graphics g) {
//super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
int red = (int) (Math.random() * 255);
int green = (int) (Math.random() * 255);
int blue = (int) (Math.random() * 255);
Color startColor = new Color(red, green, blue);
red = (int) (Math.random() * 255);
green = (int) (Math.random() * 255);
blue = (int) (Math.random() * 255);
Color endColor = new Color(red, green, blue);
GradientPaint gradient = new GradientPaint(70,70,startColor, 150,150, endColor);
g2d.setPaint(gradient);
g2d.fillOval(70,70,100,100);
}
}
新类成功编译,但在运行时它只绘制按钮。由于某种原因,不调用paintComponent,并且正确工作的唯一方法是在renderwindow()中添加以下内容:
frame.add(this);
我的问题是为什么这种行为......为什么我必须明确添加 我的框架的对象,以使此版本正常工作?
几乎到处尝试重绘()和验证()。变化不大
我也知道我不应该在EDT上绘制内容,而内部类的版本也可以缓解问题
答案 0 :(得分:4)
实际上,您必须将此对象显式添加到内容窗格。我编译并测试了以下内容:
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
//a gui element shares its events only with classes that implement Actionlistener interface
public class SimpleGui1 extends JPanel implements ActionListener {
JButton button;
JFrame frame;
ppanel mypanel;
public void paintComponent(Graphics g)
{
//super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
int red = (int) (Math.random() * 255);
int green = (int) (Math.random() * 255);
int blue = (int) (Math.random() * 255);
Color startColor = new Color(red, green, blue);
red = (int) (Math.random() * 255);
green = (int) (Math.random() * 255);
blue = (int) (Math.random() * 255);
Color endColor = new Color(red, green, blue);
GradientPaint gradient = new GradientPaint(70,70,startColor, 150,150, endColor);
g2d.setPaint(gradient);
g2d.fillOval(70,70,100,100);
}
public static void main (String[] args) {
SimpleGui1 mywindow = new SimpleGui1();
mywindow.renderWindow();
}
public void renderWindow(){
frame = new JFrame();
button = new JButton("click me");
//register my interest to catch button events
button.addActionListener(this);
frame.getContentPane().add(BorderLayout.SOUTH, button);
frame.getContentPane().add(BorderLayout.CENTER, this);
frame.setSize(300,300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
//button will call this method when clicked (its the callback)
public void actionPerformed(ActionEvent event)
{
frame.repaint();
button.setText("Clicked!!");
}
}
你需要明确地添加组件才能绘制它,组件就是对象本身并不重要!
答案 1 :(得分:3)
这可能是你的问题:
public void renderWindow(){
//where everything is the same except ofcourse:
mypanel = new JPanel();
}
因为mypanel是JPanel类型,所以你要在框架中添加一个通用面板而不是覆盖的对象。
尝试:
public void renderWindow(){
//where everything is the same except ofcourse:
mypanel = new SimpleGui1(); // or possibly 'this'
}
这样,您的SimpleGui1类将被添加到框架中,并且可以参与Swing消息队列。
要回答关于“为什么”的问题,这是因为当您将面板附加到框架时,面板必须具有处理消息和覆盖的代码。当您包含JPanel对象时,您不会获得任何自定义行为。要告诉框架它应该向你的班级发送消息,你必须告诉框架,基本上用框架注册它。