我想在点击按钮时更改Jpanel的背景颜色及其字体。
谁能告诉我我做错了什么？ 我可以将JPanel背景设置为透明吗？如果是，如何？
在按钮上单击test4.action方法，我需要更改Jpanel背景颜色？
以下是代码：
import java.applet.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.awt.event.*;
import javax.swing.*;
public class test3 extends Applet {
JPanel c;
JScrollPane s;
Button connect;
Panel controls;
Color back, fore;
public void init() {
back = Color.black;
fore = Color.white;
setBackground(Color.darkGray);
setLayout(new BorderLayout());
s = new JScrollPane(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
//s.setSize(100, 100);
add("Center", s);
c = new myCanvas11(this);
s.setOpaque(false);
s.setViewportView(c);
//s.add(c);
c.setSize(1000, 16000);
add("North", controls = new Panel());
controls.setLayout(new FlowLayout());
controls.add(connect = new Button("Change Color"));
}
public void start() {
// s.setScrollPosition(100, 100);
}
public boolean action(Event e, Object arg) {
back = Color.magenta;
fore = Color.blue;
//setBackground(back);
//invalidate();
//repaint();
c.setBackground(back);
c.repaint();
//s.getViewport().setBackground(back);
// s.getViewport().repaint();
//c.repaint();
c.setFocusable(true);
return true;
}
}
class myCanvas11 extends JPanel implements KeyListener {
Image buffImage;
Graphics offscreen;
boolean initDone = false;
int chw, chh; // size of a char (in pixels)
int chd; // offset of char from baseline
int width, height; // size of applet (in pixels)
int w, h; // size of applet (in chars)
Font fn;
Graphics gr;
int nh, nw;
test3 owner;
static int counter = 0;
myCanvas11(test3 t) {
super();
owner = t;
nh = 16000;
nw = 1000;
this.setOpaque(true);
this.setFocusable(true);
addKeyListener(this);
}
public void reshape(int nx, int ny, int nw1, int nh1) {
if (nw1 != width || nh1 != height) {
width = nw;
height = nh;
gr = getGraphics();
fn = new Font("Courier", Font.PLAIN, 11);
if (fn != null) {
gr.setFont(fn);
}
FontMetrics fnm = gr.getFontMetrics();
chw = fnm.getMaxAdvance();
chh = fnm.getHeight();
chd = fnm.getDescent();
// kludge for Windows NT and others which have too big widths
if (chw + 1 >= chh) {
chw = (chw + 1) / 2;
}
// work out size of drawing area
h = nh / chh;
w = nw / chw;
buffImage = this.createImage(nw, nh);
offscreen = buffImage.getGraphics();
//offscreen.setColor(Color.black);
//offscreen.fillRect(0, 0, nw, nh);
offscreen.setColor(Color.blue);
offscreen.setFont(fn);
if (initDone) {
offscreen.drawString("Hello World!", 0, 50);
} else {
offscreen.drawString("khushbu", 2, 50);
}
initDone = true;
offscreen.drawImage(buffImage, 0, 0, this);
}
super.reshape(nx, ny, nw, nh);
}
public void paint(Graphics g) {
// if (!initDone)
// initpaint(g);
// else
g.drawImage(buffImage, 0, 0, this);
//g.drawImage(buffImage, 0, 0, owner.back, this);
}
public void update(Graphics g) {
g.drawImage(buffImage, 0, 0, this);
super.update(g);
//g.drawImage(buffImage, 0, 0, owner.back, this);
}
public void initpaint(Graphics g) {
try {
nh = getHeight();
nw = getWidth();
gr = getGraphics();
fn = new Font("Courier", Font.PLAIN, 11);
if (fn != null) {
gr.setFont(fn);
}
FontMetrics fnm = gr.getFontMetrics();
chw = fnm.getMaxAdvance();
chh = fnm.getHeight();
chd = fnm.getDescent();
// kludge for Windows NT and others which have too big widths
if (chw + 1 >= chh) {
chw = (chw + 1) / 2;
}
// work out size of drawing area
h = nh / chh;
w = nw / chw;
buffImage = this.createImage(nw, nh);
offscreen = buffImage.getGraphics();
//offscreen.setColor(Color.black);
//offscreen.fillRect(0, 0, nw, nh);
offscreen.setColor(Color.white);
offscreen.setFont(fn);
if (initDone) {
offscreen.drawString("Hello World!", 0, 50);
} else {
offscreen.drawString("khushbu", 2, 50);
}
initDone = true;
g.drawImage(buffImage, 0, 0, this);
} catch (Exception e) {
e.printStackTrace();
}
}
/** Handle the key typed event from the text field. */
public void keyTyped(KeyEvent e) {
}
/** Handle the key pressed event from the text field. */
public void keyPressed(KeyEvent e) {
String s;
offscreen.setColor(owner.fore);
offscreen.setFont(fn);
for (int i = counter; i < counter + 25; ++i) {
s = Integer.toString(i);
offscreen.drawString(s, 3, i * chh);
offscreen.drawLine(10, i * chh, 160, i * chh);
}
//owner.s.setScrollPosition(0, counter * 16);
counter = counter + 25;
repaint();
}
/** Handle the key released event from the text field. */
public void keyReleased(KeyEvent e) {
}
public boolean keyDown(Event e, int k) {
String s;
offscreen.setColor(owner.fore);
offscreen.setFont(fn);
for (int i = counter; i < counter + 25; ++i) {
s = Integer.toString(i);
offscreen.drawString(s, 3, i * chh);
offscreen.drawLine(10, i * chh, 160, i * chh);
}
//owner.s.setScrollPosition(0, counter * 16);
counter = counter + 25;
repaint();
return true;
}
}
答案 0 :(得分：4)
我可以将JPanel背景设置为透明吗？如果是，如何？
是的，只需在该JPanel上调用setOpaque(false);即可。相反，如果您想要绘制背景，请在该面板上调用setOpaque(true);。
补充说明：
public boolean action(Event e, Object arg)已弃用。改为添加适当的侦听器。getGraphics(); public void paint(Graphics g)，但protected void paintComponent(Graphics g)。如果您想要绘制背景，请不要忘记致电super.paintComponent paint()，为什么还要覆盖update()？你两次做同样的工作。gr类变量，它没有任何意义。当您使用Graphics对象时，请使用作为paintComponent方法的参数提供的对象，但不要保留对它的引用，因为它将在稍后处理。 counter不一定是static。尽可能避免static。