如何在Java Applet中立即显示图像？

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我在Java Applet中创建了一个简单的内存游戏.卡有问题.在第一次出现时,图像需要一些额外的加载时间.如何解决？我需要在卡片翻转后立即显示图像.

我显示加载屏幕,直到应用程序不在AppStates.READY或AppStates.WAIT_FOR_START状态,但它没有帮助.

Memo.cs – 带图像加载的主类

public class Memo extends JApplet {

    //...   

    public void init() {
        //...   
        try {
            SwingUtilities.invokeAndWait(new Runnable() { @Override public void run() { createGUI(); }});
        } 
        catch(Exception e) {
            e.printStackTrace();
        }
    }

    private void createGUI() {
        final Model model = new Model(...);
        final View view = new View(model);

        getContentPane().add(view, BorderLayout.CENTER);
        setBackground(backgroundColor);
        setPreferredSize(new Dimension(width, height));

        model.setLoading(loadImages(loadingPath, format, 1));
        model.setCardsImages(loadImages(cardImagePath, format, 13));
        //...
        model.setAppState(AppStates.PROCESS);

        model.startNewGame();
        view.repaint();
    }

    private Image[] loadImages(String path1, String path2, int count) {
        Image[] imgs = new Image[count];        
        for(int i = 0; i < count; ++i) {
            imgs[i] = getImage(getCodeBase(), path1 + i + path2);
        }
        return imgs;
    }
}

Model.cs – 保存图像和应用程序状态,init板

public class Model {

    //...

    private AppStates appState;
    private Image[] cardsImages;

    public Model(...) {
        //...
        appState = AppStates.INIT;
    }

    public void startNewGame() {
        setAppState(AppStates.PROCESS);

        //... - init board - table with images' id

        setAppState(AppStates.WAIT_FOR_START);
    }

    public void setCardsImages(Image[] cardsImages) {
        this.cardsImages = cardsImages;
    }

    public Image getCardsImage(int v) {
        return cardsImages[v];
    }

    public AppStates getAppState() {
        return appState;
    }

    public void setAppState(AppStates appState) {
        this.appState = appState;
        //...
    }

    //...
}

View.cs – 显示板

public class View extends JPanel {

    //...

    private Model model;

    public View(Model model) {
        this.model = model;
        //...
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        if(model != null) {
            switch (model.getAppState()) {

            //...

            case WAIT_FOR_START:            
            case READY:
                //...
                drawBoard(g2d, model.getBoard(), model.getStates(), model.getFrontTypes());
                break;

            }
        }
        repaint();
    }

    private void drawBoard(Graphics2D g2d, int[][] board, int[][] states, int[][] frontTypes) {
        if(board != null && states != null && board.length > 0 && states.length > 0) {
            for(int x = 0; x < board.length; x++) {
                for(int y = 0; y < board[x].length; y++) {  
                    if(states[x][y] != Model.HIDE) {
                        Image img = null;

                        //...
                        img = model.getCardsImage(board[x][y]);

                        g2d.drawImage(
                                img,
                                model.getFirstCardX() + x * model.getCardDistance() + x * model.getCardWidth(), 
                                model.getFirstCardY() + y * model.getCardDistance() + y * model.getCardHeight(), 
                                model.getCardWidth(), 
                                model.getCardHeight(),
                                null);

                        //...
                    }
                }
            }
        }
    }
}

解决方法:

来自JavaDocs ..

public Image getImage(URL url)

..

This method always returns immediately, whether or not the image exists. When this applet attempts to draw the image on the screen, the data will be loaded.

请改用ImageIO.read(URL).此方法将“阻止”(它将停在该代码行),直到读取图像.所以当应用程序.去使用图像,它已经完全加载.

解决问题的另一种方法(不是你想要的方式)是改变..

g2d.drawImage(
    img,
    model.getFirstCardX() + x * model.getCardDistance() + x * model.getCardWidth(), 
    model.getFirstCardY() + y * model.getCardDistance() + y * model.getCardHeight(), 
    model.getCardWidth(), 
    model.getCardHeight(),
    null);

至..

g2d.drawImage(
    img,
    model.getFirstCardX() + x * model.getCardDistance() + x * model.getCardWidth(), 
    model.getFirstCardY() + y * model.getCardDistance() + y * model.getCardHeight(), 
    model.getCardWidth(), 
    model.getCardHeight(),
    this);

如果图像是异步加载的(例如,使用Applet.getImage(URL)),GUI会在更多可用时通知重绘.

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