Question

我想使用paintComponent(Graphics g)使用for循环绘制一些图像。但是，JFrame只显示为白色屏幕，它只显示调整窗口大小后的黑色背景和图像。

import java.awt.*; 
import java.awt.event.*; 
import javax.swing.*;
import java.io.*; 
import javax.imageio.*; 
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.awt.Graphics;
import java.util.Scanner;

 public class SimpleAdventure {
         private JFrame frame;
         private CardLayout cards;
         private Container c;
         private DrawPanel1 gamepanel;
         private BufferedImage greentiles, pinktiles, sandtiles, charsprites;
         private Image left1, right1, left2, right2, front;
         private Image pinkbg, greenbg, sandbg;
         private Image pinktop, greentop, sandtop;
         private int charx, chary;

         public SimpleAdventure()
         {}
         public static void main (String [] args)
         {
                 SimpleAdventure retro = new SimpleAdventure();
                 retro.run();
         }
         public void run()
         {
                 frame = new JFrame("Simple Adventure");
                 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                 frame.setSize(576, 576);
                 frame.setVisible(true);
                 // frame.setResizable(false);
                 getImage();


                 c = frame.getContentPane();
                 cards = new CardLayout();
                 c.setLayout(cards);

                 gamepanel = new DrawPanel1();
                 gamepanel.setBackground(Color.black);
                 c.add(gamepanel, "Panel 1");
         }
         public void getImage()
         {

             try
             {
                 greentiles = ImageIO.read(new File("greenTiles.png"));
                 pinktiles = ImageIO.read(new File("pinkTiles.png"));
                 sandtiles = ImageIO.read(new File("sandTiles.png"));
                 charsprites = ImageIO.read(new File("charactersheet.png"));
             }
             catch(IOException e)
             {
                 e.printStackTrace();
             }


             left1 = charsprites.getSubimage(18, 0, 6, 6);
             left2 = charsprites.getSubimage(24, 0, 6, 6);
             right1 = charsprites.getSubimage(0, 0, 6, 6);
             right2 = charsprites.getSubimage(6, 0, 6, 6);
             front = charsprites.getSubimage(12, 0, 6, 6);

             greenbg = greentiles.getSubimage(240, 0, 16, 16);
             sandbg = sandtiles.getSubimage(240, 0, 16, 16);
             pinkbg = pinktiles.getSubimage(240, 0, 16, 16);

             greentop = greentiles.getSubimage(224, 0, 16, 16);
             sandtop = sandtiles.getSubimage(224, 0, 16, 16);
             pinktop = pinktiles.getSubimage(224, 0, 16, 16);
         }

         class DrawPanel1 extends JPanel implements KeyListener
         {
                 // private BottomPanel lower;
                 public DrawPanel1()
                 {
                     /*this.setLayout(new BorderLayout());
                     lower = new BottomPanel();
                     this.add(lower, BorderLayout.SOUTH);*/
                     addKeyListener(this);
                 }

                 public void paintComponent(Graphics g)
                 {
                         super.paintComponent(g);

                         for(int i = 0; i < 7; i++)
                         {
                             g.drawImage(greentop, 0 + (i * 96), 480, 96, 96, this);
                         }
                         System.out.println("check");
                 }
                 public void keyPressed(KeyEvent e)
                 {

                 }
                 public void keyReleased(KeyEvent e)
                 {

                 }
                 public void keyTyped(KeyEvent e)
                 {

                 }
         } }

Answer 1

您需要致电frame.pack()进行初始布局。自动调整窗口大小会导致布局被修复，但frame.setSize(...)不会*。

将frame.setVisible(true)移至run方法的末尾（即，在构建完所有UI元素之后）并将frame.pack()放在frame.setVisible(true)之前。（感谢Hovercraft和MadProgrammer指出这一点）

*至少，如果框架不可见则不会。如果框架已经可见，它可能会起作用;试一试，看看。

编辑：现在我重新阅读了javadoc，你可能根本不想要pack - 它会为你调整帧的大小。如果不对它进行测试，我想将setVisible移动到最后会起作用;如果没有，则使用revalidate而不是pack来运行布局引擎。

编辑2：现在我重新读取了javadoc，setVisible将验证窗口是否尚未显示。因此，您不需要显式调用revalidate。 setSize将使组件无效，但不会重新验证。

TL; DR：值得一提的是关于验证和可显示性如何在Swing中工作，这样你就不会犯错误。

Answer 2

仅在构建UI后调用setVisible ...

public void run()
{
    frame = new JFrame("Simple Adventure");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(576, 576);
    // frame.setResizable(false);
    getImage();


    c = frame.getContentPane();
    cards = new CardLayout();
    c.setLayout(cards);

    gamepanel = new DrawPanel1();
    gamepanel.setBackground(Color.black);
    c.add(gamepanel, "Panel 1");

    // Lucky last...   
    frame.setVisible(true);
}

否则您需要重新验证框架

paintComponent中的图像仅在调整窗口大小后显示

2 个答案: