Question

我有一个JFrame，我在大网格中绘制了大量图像。我的窗口不够大，无法包含整个网格，所以我想使用一个JScrollPane，它允许我在窗口中显示网格的某些部分。

我的问题是我无法滚动。当我这样滚动条总是出现时，它们似乎已经覆盖了整个区域。

enter image description here

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，如果我调整大小，你会注意到根本不是这样的情况！

enter image description here

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像素图像，但为了制作最小，完整和可验证的示例，我用坐标字符串替换了图像。）

这是我的Minimal，Complete和Verifiable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不允许我滚动JPanel？

Answer 1

你的问题似乎在这里：

panel.setPreferredSize(new Dimension(512,448));

将JScrollPane持有的JPanel约束到特定大小，不允许它扩展。永远不要这样做。而是约束JScrollPane或其视图端口。

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++;
      }
   }
}

修改
根据MadProgrammer的建议尝试改进版本：

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; } }

JScrollPane不会滚动JPanel

1 个答案: