java-JScrollPane不会在JPanel上滚动
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我有一个JFrame,在其中我要在一个大网格中绘制很多图像.我的窗口不够大,无法容纳整个网格,因此我想使用一个JScrollPane来让我在窗口中显示网格的某些部分.
我的问题是我无法滚动.当我使滚动条始终显示时,它们似乎已经覆盖了整个区域.
如您所见,滚动条给人的印象是整个区域都显示在窗口中.但是,如果我调整它的大小,您会发现根本不是这种情况!
滚动条继续说它们覆盖了整个区域.
(请注意,网格中的数字实际上是16 x 16 px的图像,但是为了制作一个Minimal,Complete和Verifiable的示例,我用坐标字符串替换了这些图像.)
这是我的最小,完整和可验证示例的代码:
import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
public class Main {
public static int[][] tiles;
public static void main(String[] args) {
Foo foo = new Foo();
foo.run();
}
}
class Foo {
public void run(){
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
Panel panel = new Panel();
panel.setPreferredSize(new Dimension(512,448));
JScrollPane scrollPane = new JScrollPane(panel);
scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
frame.add(scrollPane);
frame.setVisible(true);
frame.pack();
Main.tiles = new int[32][32];
while (true) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
panel.repaint();
}
}
}
class Panel extends JPanel {
public void paintComponent(Graphics g){
paintScreen(g);
}
private void paintScreen(Graphics g){
int x =0, y =0;
for (int i = 0; i < Main.tiles.length; i++) {
for (int j = 0; j < Main.tiles[i].length; j++){
g.drawString(i + " " + j, x*32, y*32);
y++;
}
y=0;
x++;
}
}
}
所以我的问题是:
问:为什么JScrollPane不允许我在JPanel上滚动?
解决方法:
您的问题似乎在这里:
panel.setPreferredSize(new Dimension(512,448));
在此处将JScrollPane持有的JPanel限制为特定大小,不允许其扩展.永远不要这样做.而是约束JScrollPane或其视图端口.
例如.,
import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
public class Main {
public static int[][] tiles;
public static void main(String[] args) {
Foo foo = new Foo();
foo.run();
}
}
class Foo {
public void run() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
Panel panel = new Panel();
// !! panel.setPreferredSize(new Dimension(512,448));
JScrollPane scrollPane = new JScrollPane(panel);
scrollPane.getViewport().setPreferredSize(new Dimension(512, 448));
scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
frame.add(scrollPane);
frame.setVisible(true);
frame.pack();
Main.tiles = new int[32][32];
while (true) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
panel.repaint();
}
}
}
class Panel extends JPanel {
private static final int PREF_W = 1200;
private static final int PREF_H = 1200;
public void paintComponent(Graphics g) {
super.paintComponent(g);
paintScreen(g);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
private void paintScreen(Graphics g) {
int x = 0, y = 0;
for (int i = 0; i < Main.tiles.length; i++) {
for (int j = 0; j < Main.tiles[i].length; j++) {
g.drawString(i + " " + j, x * 32, y * 32);
y++;
}
y = 0;
x++;
}
}
}
编辑
尝试根据MadProgrammer的建议改进版本:
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Rectangle;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.Scrollable;
public class Main {
public static int[][] tiles;
public static void main(String[] args) {
Foo foo = new Foo();
foo.run();
}
}
class Foo {
public void run() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
NumberPanel panel = new NumberPanel();
// !! panel.setPreferredSize(new Dimension(512,448));
JScrollPane scrollPane = new JScrollPane(panel);
// !! scrollPane.getViewport().setPreferredSize(new Dimension(512, 448));
scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
frame.add(scrollPane);
frame.setVisible(true);
frame.pack();
Main.tiles = new int[32][32];
while (true) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
panel.repaint();
}
}
}
class NumberPanel extends JPanel implements Scrollable {
private static final int PREF_W = 1200;
private static final int PREF_H = 1200;
private static final int VP_WIDTH = 512;
private static final int VP_HEIGHT = 448;
public void paintComponent(Graphics g) {
super.paintComponent(g);
paintScreen(g);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
private void paintScreen(Graphics g) {
int x = 0, y = 0;
for (int i = 0; i < Main.tiles.length; i++) {
for (int j = 0; j < Main.tiles[i].length; j++) {
g.drawString(i + " " + j, x * 32, y * 32);
y++;
}
y = 0;
x++;
}
}
@Override
public Dimension getPreferredScrollableViewportSize() {
return new Dimension(VP_WIDTH, VP_HEIGHT);
}
@Override
public int getScrollableBlockIncrement(Rectangle arg0, int arg1, int arg2) {
// TODO Consider improving
return 0;
}
@Override
public boolean getScrollableTracksViewportHeight() {
return false;
}
@Override
public boolean getScrollableTracksViewportWidth() {
return false;
}
@Override
public int getScrollableUnitIncrement(Rectangle arg0, int arg1, int arg2) {
// TODO Consider improving
return 0;
}
}
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