java - 模拟器中 InfiniteScrollAdapter 中的 URLImage 显示 NPE (CodenameOne)

标签 java codenameone

我的应用程序具有一个 InfiniteScrollAdapter，通过 URLImage 和 URLImage.ImageAdapter 填充图像。

在模拟器(Iphone3GS、Xoom 或 GoogleNexus7)中，第一次出现 InfiniteScrollAdapter 时会显示 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。因此，在下图中，您应该看到同一行(图像 + 文本)重复了 3 次。

NPE in InfiniteScrollAdapter

请注意，未显示的图标中的顺序可能不同

NPE with different order in the undisplayed icons

我用来下载图像的代码是:

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 似乎源于重写的 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$1.lambda$adaptImage$0(ParametresGeneraux.java:564) at com.codename1.ui.RunnableWrapper.run(RunnableWrapper.java:95) at com.codename1.ui.Display.processSerialCalls(Display.java:1154) at com.codename1.ui.Display.edtLoopImpl(Display.java:1098) at com.codename1.ui.Display.invokeAndBlock(Display.java:1207) at com.codename1.ui.Display.invokeAndBlock(Display.java:1244) at com.codename1.ui.URLImage$DownloadCompleted.actionPerformed(URLImage.java:233) at com.codename1.ui.URLImage$4.onSucess(URLImage.java:301) at com.codename1.ui.URLImage$4.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$71.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$1.lambda$adaptImage$0(ParametresGeneraux.java:564) at com.codename1.ui.RunnableWrapper.run(RunnableWrapper.java:95) at com.codename1.ui.Display.processSerialCalls(Display.java:1154) at com.codename1.ui.Display.edtLoopImpl(Display.java:1098) at com.codename1.ui.Display.invokeAndBlock(Display.java:1207) at com.codename1.ui.Display.invokeAndBlock(Display.java:1244) at com.codename1.ui.URLImage$DownloadCompleted.actionPerformed(URLImage.java:233) at com.codename1.ui.URLImage$4.onSucess(URLImage.java:301) at com.codename1.ui.URLImage$4.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)

此外，浏览 .cn1 目录会发现 URLImage 存储文件名带有后缀“ImageURLTMP”，在没有 NPE 的情况下一切正常时不会出现。

最后，如果我稍后返回此表单，一切都会按预期进行(显示了图像，没有 NPE)。我尝试在 imageAdapter 中测试 downloadImage 是否为空，但 EncodedImage 不为空。

如何避免这种 NPE？

2017 年 3 月 1 日编辑

根据@Diamond和@Shai的回答，我相信发生NPE是因为InfiniteScrollAdapter想要用行填充屏幕，从而同时启动同一图像的下载(因为它不在缓存中)。因此，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。但是图像不应该被下载 3 次，不是吗？

No 404

最佳答案

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，并在逻辑结束时，在 callSerially() 中调用您的 URLImage > 方法:

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，您可以检查当前是否正在下载相同的图像并防止拉取另一个图像。因为这通常会导致冲突:

//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();
});

关于java - 模拟器中 InfiniteScrollAdapter 中的 URLImage 显示 NPE (CodenameOne)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/42500815/

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