模拟器中 InfiniteScrollAdapter 中的 URLImage 显示 NPE (CodenameOne)

Question

我的应用程序有一个 InfiniteScrollAdapter，通过 URLImage 和 URLImage.ImageAdapter 填充了图像。

在模拟器（Iphone3GS 或 Xoom 或 GoogleNexus7）中，首次出现 InfiniteScrollAdapter 时显示 NPE，尽管该文件确实存在于服务器上。

请注意：在此测试中，数据库中只有一个条目。所以在下图中，您应该看到同一行（图像 + 文本）重复了 3 次。

请注意，未显示图标中的顺序可能不同

我用来下载图片的代码是：

Image tempPlaceholder = Image.createImage(
            ParametresGeneraux.SIZE_OF_REPORT_PIC_IN_PX,
            ParametresGeneraux.SIZE_OF_REPORT_PIC_IN_PX,
            ParametresGeneraux.accentColor);
    Graphics gr = tempPlaceholder.getGraphics();
    gr.setAntiAliased(true);
    gr.setColor(ParametresGeneraux.accentColor);
    gr.fillArc(0, 0, ParametresGeneraux.SIZE_OF_REPORT_PIC_IN_PX, ParametresGeneraux.SIZE_OF_REPORT_PIC_IN_PX, 0, 360);

    EncodedImage roundPlaceholder = EncodedImage.createFromImage(tempPlaceholder, true);

    final Image reportImage = URLImage.createToStorage(
                            roundPlaceholder,
                            photoFilenameInStorage,
                            currentReport.getPhotoPath(),
                            ParametresGeneraux.RESIZE_SCALE_WITH_ROUND_MASK
                    );

这里是重写的 imageAdapter 方法：

    public final static URLImage.ImageAdapter RESIZE_SCALE_WITH_ROUND_MASK = new URLImage.ImageAdapter() {
    @Override
    public EncodedImage adaptImage(EncodedImage downloadedImage, EncodedImage placeholderImage) {
        final Image[] tmp = new Image[1];

        if (!Display.getInstance().isEdt()) {
            // The image scaling has to be called from EDT
            Display.getInstance().callSeriallyAndWait(() -> {

                tmp[0] = downloadedImage.scaledLargerRatio(placeholderImage.getWidth(), placeholderImage.getHeight());
                if (tmp[0].getWidth() > placeholderImage.getWidth()) {
                    int diff = tmp[0].getWidth() - placeholderImage.getWidth();
                    int x = diff / 2;
                    tmp[0] = tmp[0].subImage(x, 0, placeholderImage.getWidth(), placeholderImage.getHeight(), true);
                } else if (tmp[0].getHeight() > placeholderImage.getHeight()) {
                    int diff = tmp[0].getHeight() - placeholderImage.getHeight();
                    int y = diff / 2;
                    tmp[0] = tmp[0].subImage(0, y, Math.min(placeholderImage.getWidth(), tmp[0].getWidth()),
                            Math.min(placeholderImage.getHeight(), tmp[0].getHeight()), true);
                }
            });
        } else {
            tmp[0] = downloadedImage.scaledLargerRatio(placeholderImage.getWidth(), placeholderImage.getHeight());
            if (tmp[0].getWidth() > placeholderImage.getWidth()) {
                int diff = tmp[0].getWidth() - placeholderImage.getWidth();
                int x = diff / 2;
                tmp[0] = tmp[0].subImage(x, 0, placeholderImage.getWidth(), placeholderImage.getHeight(), true);
            } else if (tmp[0].getHeight() > placeholderImage.getHeight()) {
                int diff = tmp[0].getHeight() - placeholderImage.getHeight();
                int y = diff / 2;
                tmp[0] = tmp[0].subImage(0, y, Math.min(placeholderImage.getWidth(), tmp[0].getWidth()),
                        Math.min(placeholderImage.getHeight(), tmp[0].getHeight()), true);
            }
        }

        EncodedImage[] image2Return = new EncodedImage[1];
        if (!Display.getInstance().isEdt()) {
            // The image scaling has to be called from EDT
            Display.getInstance().callSeriallyAndWait(() -> {
                Image roundMask = Image.createImage(tmp[0].getWidth(), tmp[0].getHeight(), 0xff000000);
                Graphics gr = roundMask.getGraphics();
                gr.setColor(0xffffff);

                gr.fillArc(0, 0, tmp[0].getWidth(), tmp[0].getHeight(), 0, 360);
                Object mask = roundMask.createMask();
                tmp[0] = tmp[0].applyMask(mask);
                image2Return[0] = EncodedImage.createFromImage(tmp[0], false);
            });
        } else {
            Image roundMask = Image.createImage(tmp[0].getWidth(), tmp[0].getHeight(), 0xff000000);
            Graphics gr = roundMask.getGraphics();
            gr.setColor(0xffffff);

            gr.fillArc(0, 0, tmp[0].getWidth(), tmp[0].getHeight(), 0, 360);
            Object mask = roundMask.createMask();
            tmp[0] = tmp[0].applyMask(mask);
            image2Return[0] = EncodedImage.createFromImage(tmp[0], false);
        }

        return image2Return[0];

    }

在堆栈跟踪中，NPE 似乎源于被覆盖的 URLImage.ImageAdapter :

java.lang.IllegalArgumentException: create image failed for the given image data of length: 0 at com.codename1.ui.Image.createImage(Image.java:654) at com.codename1.ui.EncodedImage.getInternal(EncodedImage.java:365) at com.codename1.ui.EncodedImage.getInternalImpl(EncodedImage.java:340) at com.codename1.ui.EncodedImage.getHeight(EncodedImage.java:522) at com.codename1.ui.Image.scaledLargerRatio(Image.java:899) at com.my.application.ParametresGeneraux.lambda$adaptImage[=18=](ParametresGeneraux.java:564) at com.codename1.ui.RunnableWrapper.run(RunnableWrapper.java:95) at com.codename1.ui.Display.processSerialCalls(Display.java:1154) at com.codename1.ui.Display.edtLoopImpl(Display.java:1098) at com.codename1.ui.Display.invokeAndBlock(Display.java:1207) at com.codename1.ui.Display.invokeAndBlock(Display.java:1244) at com.codename1.ui.URLImage$DownloadCompleted.actionPerformed(URLImage.java:233) at com.codename1.ui.URLImage.onSucess(URLImage.java:301) at com.codename1.ui.URLImage.onSucess(URLImage.java:297) at com.codename1.util.CallbackDispatcher.run(CallbackDispatcher.java:53) at com.codename1.ui.Display.processSerialCalls(Display.java:1154) at com.codename1.ui.Display.edtLoopImpl(Display.java:1098) at com.codename1.ui.Display.mainEDTLoop(Display.java:999) at com.codename1.ui.RunnableWrapper.run(RunnableWrapper.java:120) at com.codename1.impl.CodenameOneThread.run(CodenameOneThread.java:176) [EDT] 0:0:0,1 - Codename One revisions: e5c43877074c18b4b5c7748d000e5cfac75ab749 2318

[EDT] 0:0:0,1 - Exception: java.lang.NullPointerException - null java.lang.NullPointerException at com.codename1.impl.javase.JavaSEPort.scale(JavaSEPort.java:3996) at com.codename1.ui.Image.scale(Image.java:1007) at com.codename1.ui.Image.scaledImpl(Image.java:953) at com.codename1.ui.Image.scaled(Image.java:918) at com.codename1.impl.javase.JavaSEPort.save(JavaSEPort.java:7659) at com.codename1.ui.EncodedImage.scaledEncoded(EncodedImage.java:626) at com.codename1.ui.EncodedImage.scaled(EncodedImage.java:653) at com.codename1.ui.Image.scaledLargerRatio(Image.java:904) at com.my.application.ParametresGeneraux.lambda$adaptImage[=18=](ParametresGeneraux.java:564) at com.codename1.ui.RunnableWrapper.run(RunnableWrapper.java:95) at com.codename1.ui.Display.processSerialCalls(Display.java:1154) at com.codename1.ui.Display.edtLoopImpl(Display.java:1098) at com.codename1.ui.Display.invokeAndBlock(Display.java:1207) at com.codename1.ui.Display.invokeAndBlock(Display.java:1244) at com.codename1.ui.URLImage$DownloadCompleted.actionPerformed(URLImage.java:233) at com.codename1.ui.URLImage.onSucess(URLImage.java:301) at com.codename1.ui.URLImage.onSucess(URLImage.java:297) at com.codename1.util.CallbackDispatcher.run(CallbackDispatcher.java:53) at com.codename1.ui.Display.processSerialCalls(Display.java:1154) at com.codename1.ui.Display.edtLoopImpl(Display.java:1098) at com.codename1.ui.Display.mainEDTLoop(Display.java:999) at com.codename1.ui.RunnableWrapper.run(RunnableWrapper.java:120) at com.codename1.impl.CodenameOneThread.run(CodenameOneThread.java:176)

另外，在.cn1目录下一看，URLImage存储文件名后缀为"ImageURLTMP"，在没有NPE的情况下是不会出现的。

最后，如果我稍后再回到这个表格，一切都会按预期进行（显示图像，没有 NPE）。我试图在 imageAdapter 中测试 downloadedImage 是否为空，但 EncodedImage 不为空。

如何避免这种 NPE？

编辑 2017 年 3 月 1 日

根据@Diamond 和@Shai 的回答，我认为 NPE 的发生是因为 InfiniteScrollAdapter 想要用行填充屏幕并因此同时启动同一图像的下载（因为它不在缓存中）。因此，一个解决方案可能是防止 InfiniteScrollAdapter 循环（因此它变得有限）。我怎样才能做到这一点？

另请注意，没有 404 错误，网络监视器显示响应代码 200，如下所示。但是图片应该不会下载3次吧？

Answer 1

在您的适配器中检查 downloadedImage.getData() 是否为 null。我假设它不是，它是一个 404 错误页面或类似的页面。

在这种情况下，您的适配器可以捕获异常，并且只是 return 与您在不存在图像时期望看到的内容相匹配的回退。

这是第二次工作，因为系统看到 tmp 文件并假设下载正在进行，因此它不会再次调用下载代码。 tmp 文件稍后重命名为最终可下载文件。

Answer 2

将您的 ImageAdapter 更改为以下内容：

public static final URLImage.ImageAdapter RESIZE_SCALE_WITH_ROUND_MASK = new URLImage.ImageAdapter() {
    @Override
    public EncodedImage adaptImage(EncodedImage downloadedImage, EncodedImage placeholderImage) {
        Image tmp = downloadedImage.scaledLargerRatio(placeholderImage.getWidth(), placeholderImage.getHeight());
        if (tmp.getWidth() > placeholderImage.getWidth()) {
            int diff = tmp.getWidth() - placeholderImage.getWidth();
            int x = diff / 2;
            tmp = tmp.subImage(x, 0, placeholderImage.getWidth(), placeholderImage.getHeight(), true);
        } else if (tmp.getHeight() > placeholderImage.getHeight()) {
            int diff = tmp.getHeight() - placeholderImage.getHeight();
            int y = diff / 2;
            tmp = tmp.subImage(0, y, Math.min(placeholderImage.getWidth(), tmp.getWidth()),
                    Math.min(placeholderImage.getHeight(), tmp.getHeight()), true);
        }
        Image roundMask = Image.createImage(tmp.getWidth(), tmp.getHeight(), 0xff000000);
        Graphics gr = roundMask.getGraphics();
        gr.setColor(0xffffff);
        gr.fillArc(0, 0, tmp.getWidth(), tmp.getHeight(), 0, 360);
        Object mask = roundMask.createMask();
        tmp = tmp.applyMask(mask);
        return EncodedImage.createFromImage(tmp, false);
    }

    @Override
    public boolean isAsyncAdapter() {
        return true;
    }
};

无需检查EDT。

确保您的 tempPlaceholder 图像首先应用于您的组件，并在您的逻辑结束时，在 callSerially() 方法中调用您的 URLImage：

Image tempPlaceholder = Image.createImage(
        ParametresGeneraux.SIZE_OF_REPORT_PIC_IN_PX,
        ParametresGeneraux.SIZE_OF_REPORT_PIC_IN_PX,
        ParametresGeneraux.accentColor);
Graphics gr = tempPlaceholder.getGraphics();
gr.setAntiAliased(true);
gr.setColor(ParametresGeneraux.accentColor);
gr.fillArc(0, 0, ParametresGeneraux.SIZE_OF_REPORT_PIC_IN_PX, ParametresGeneraux.SIZE_OF_REPORT_PIC_IN_PX, 0, 360);

myComponent.setIcon(tempPlaceholder);


...


//Then call this at the end of everything
Display.getInstance().callSerially(() -> {
    EncodedImage roundPlaceholder = EncodedImage.createFromImage(tempPlaceholder, true);

    final Image reportImage = URLImage.createToStorage(
                        roundPlaceholder,
                        photoFilenameInStorage,
                        currentReport.getPhotoPath(),
                        ParametresGeneraux.RESIZE_SCALE_WITH_ROUND_MASK
                );
    myComponent.setIcon(reportImage);
    myComponent.getComponentForm().repaint();
});

编辑：

根据@Shai 的回答，您可以检查您当前是否正在下载相同的图像并防止另一个图像被拉取。因为这通常会引起冲突：

//Declare this at the top of your class
final static private Map<String, Image> LOADED_URLS = new HashMap<>(); 

//Then change the URLImage image method to this
Display.getInstance().callSerially(() -> {
    EncodedImage roundPlaceholder = EncodedImage.createFromImage(tempPlaceholder, true);

    final Image reportImage = LOADED_URLS.containsKey(photoFilenameInStorage) ? LOADED_URLS.get(photoFilenameInStorage)
                        : URLImage.createToStorage(
                        roundPlaceholder,
                        photoFilenameInStorage,
                        currentReport.getPhotoPath(),
                        ParametresGeneraux.RESIZE_SCALE_WITH_ROUND_MASK
                );
    LOADED_URLS.put(photoFilenameInStorage, reportImage);
    myComponent.setIcon(reportImage);
    myComponent.getComponentForm().repaint();
});

模拟器中 InfiniteScrollAdapter 中的 URLImage 显示 NPE (CodenameOne)

URLImage in InfiniteScrollAdapter in Simulator shows NPE (CodenameOne)

java

codenameone

编辑：