java - 在调用 repaint() 之前，paintComponent 不会绘制所有内容

Question

我正在研究一个国际象棋引擎，我有以下问题：除非repaint()被调用，否则我的棋子不会被绘制。但是，正方形（= 国际象棋场）看起来很好。我读到我应该避免repaint()在内部使用，paintComponent因为这会使函数被连续调用。我怎样才能避免调用repaint()，但仍然绘制我的图像？这是代码：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.util.ArrayList;

import javax.swing.JFrame;
import javax.swing.JPanel;

@SuppressWarnings("serial")
public class ChessBoard extends JPanel {

    ArrayList<Square> squares = new ArrayList<Square>();
    Piece piece = new Piece("B", 0);
    
    public ChessBoard() {
        for (int i = 0; i < 8; i++) {
            for (int j = 0; j < 8; j++) {
                squares.add(new Square(i, j));
            }
        }
    }
    
    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        for (Square square : squares) {
            square.draw(g);
        }
        piece.draw(g);
        //repaint(); //Image only appears if this is called
    }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ChessBoard chessboard = new ChessBoard();
        chessboard.createFrame();
    }
    
    public void createFrame() {
        JFrame f = new JFrame("ChessBoard");
        f.getContentPane().setPreferredSize(new Dimension(squareSize()*8, squareSize()*8));
        f.setResizable(false);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setTitle("Chessboard");
        f.setLocation((int)(screenSize().width-squareSize()*8)/2, (int)(screenSize().height-squareSize()*8)/2);
        f.add(this);
        f.pack();
        Frame.getFrames();
        f.setVisible(true);
    }
    
    public static Dimension screenSize() {
        return Toolkit.getDefaultToolkit().getScreenSize();
    }
    
    public static int squareSize() {
        return (int)screenSize().height/12;
    }

}


class Square {
    int start_x, start_y;
    int square_size;
    Color color;
    
    public Square(int x, int y) {
        // constructor
        start_x = x*ChessBoard.squareSize();
        start_y = y*ChessBoard.squareSize();
        square_size = ChessBoard.squareSize();
        if ((x+y)%2 == 0) {
            // Color of the white squares
            color = new Color(209, 192, 148);
        } else {
            // Color of the black squares
            color = new Color(110, 83, 43);
        }
    }

    public void draw(Graphics g) {
        g.setColor(this.color);
        g.fillRect(this.start_x, this.start_y, square_size, square_size);
    }
}

class Piece {
    String type;
    int coordinate, square_size, piece_size;
    int[] draw_coordinates = {7, 6, 5, 4, 3, 2, 1, 0};
    Image image;
    
    public Piece(String type, int coordinate) {
        this.type = type;
        this.coordinate = coordinate;
        this.square_size = ChessBoard.squareSize();
        this.piece_size = (int)ChessBoard.squareSize()*2/3;
        this.image = Toolkit.getDefaultToolkit().getImage("src/pieces/black_bishop.png");
    }
    
    public int co_x_board() {
        return coordinate - ((int)coordinate/8)*8;
    }
    
    public int co_y_board() {
        return (int)coordinate/8;
    }
    
    public int co_x_draw() {
        return co_x_board()*square_size+((int)square_size/6);
    }
    
    public int co_y_draw() {
        return draw_coordinates[co_y_board()]*square_size+((int)square_size/6);
    }
    
    public void draw(Graphics g) {
        g.drawString(type, co_x_draw(), co_y_draw()); // does work
        g.drawImage(image, co_x_draw(), co_y_draw(), piece_size, piece_size, null); // does not work
    }
}

先感谢您！

标签： javaswingpaintcomponent

Answer 1

问题在于您没有提供方法调用的ImageObserver参数。drawImage

我可以重现您在 MRE 中看到的错误。

我曾通过Toolkit.getDefaultToolkit().getImage("...");(or ) 阅读图像，有时如果您不提供，或者在绘制图像之前不调用图像以及其他症状，Toolkit.getDefaultToolkit().createImage("...");则有时它不起作用，对此我没有知道原因。但是我所知道的是，如果您提供论点，那么它将起作用。ImageObservergetWidth(null)ImageObserver

请记住，Componentis an ImageObserver... 所以您需要将Component（Graphics对象所属的）实际提供给drawImage最后一个参数。

因此，您可以更改您的Piece#draw方法以接受Component绘制它的对象，如下所示：

public void draw(Graphics g, final Component observer) {
    g.drawString(type, co_x_draw(), co_y_draw());
    g.drawImage(image, co_x_draw(), co_y_draw(), piece_size, piece_size, observer);
}

然后记得通过改变这样的方式正确调用它ChessBoard#paintComponent：

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    for (Square square : squares) {
        square.draw(g);
    }
    piece.draw(g, this);
}

通常纠正错误的另一种方法null是ImageObserver使用一种ImageIO#read方法将图像读取为BufferedImage. 同样，我不知道为什么会这样，但确实如此。我也没有用 测试你的案例ImageIO#read，但我仍然用它测试它Toolkit.getDefaultTooklit().getImage("...");并且它有效（但你需要提供ImageObserver参数）。

一些建议：

在我看来，将一些JLabels 放在JPanelwith 中GridLayout（例如new GridLayout(0, 8);）然后将图像设置为Icons （via myLabel.setIcon(new ImageIcon(myImage));）到JLabels...