[英]How do I change the background color of a frame in Java from another class?
我有以下几点:
import javax.swing.JFrame;
public class Directions {
public Directions(){
JFrame frame = new JFrame("Direction");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new DirectionPanel());
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
Directions myTest = new Directions();
}
}
第二类:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class DirectionPanel extends JPanel{
public DirectionPanel(){
addKeyListener(new DirectionListener());
setBackground(Color.yellow);
}
private class DirectionListener implements KeyListener{
@Override
public void keyPressed(KeyEvent e) {
//JOptionPane.showMessageDialog(null, "Hello Johnny");
int keyCode = e.getKeyCode();
if (keyCode == KeyEvent.VK_LEFT){
setBackground(Color.red);
}
repaint();
}
@Override
public void keyReleased(KeyEvent e) {
// TODO Auto-generated method stub
}
@Override
public void keyTyped(KeyEvent e) {
// TODO Auto-generated method stub
}
}
}
当我按下向左箭头时,为什么框架没有变成红色? 我也没有进行键码测试就认为它无论键是否有效都可以,但是没有用。 谢谢。
public DirectionPanel(){
addKeyListener(new DirectionListener());
setFocusable(true);// INSERT THIS
setBackground(Color.yellow);
}
JPanel
需要专注于接收KeyEvent
当使用键盘时,Swing组件应使用键绑定 (而不是KeyListeners)来调用Action。 这样做的附带好处是,您不必担心可聚焦性。
Action left = new AbstractAction()
{
public void actionPerformed(ActionEvent e)
{
System.out.println( "Left" );
}
};
Object key1 = "left";
KeyStroke ks1 = KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0);
panel.getInputMap(JPanel.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT).put(ks1, key1);
panel.getActionMap().put(key1, left);
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