Question

我需要帮助，我会创建一个动态的LazyList，但运行时会出现错误。我已经尝试了各种方法来修复它，请指导我的方法是否错误。

代码：

public class ImageLoader {

MemoryCache memoryCache = new MemoryCache();
FileCache fileCache;
private Map<ImageView, String> imageViews = Collections
        .synchronizedMap(new WeakHashMap<ImageView, String>());
ExecutorService executorService;

public ImageLoader(Context context) {
    fileCache = new FileCache(context);
    executorService = Executors.newFixedThreadPool(5);
}

final int stub_id = R.drawable.no_image;

public void DisplayImage(String url, ImageView imageView) {
    imageViews.put(imageView, url);
    Bitmap bitmap = memoryCache.get(url);
    if (bitmap != null)
        imageView.setImageBitmap(bitmap);
    else {
        queuePhoto(url, imageView);
        imageView.setImageResource(stub_id);
    }
}

private void queuePhoto(String url, ImageView imageView) {
    PhotoToLoad p = new PhotoToLoad(url, imageView);
    executorService.submit(new PhotosLoader(p));
}

private Bitmap getBitmap(String url) {
    File f = fileCache.getFile(url);

    Bitmap b = decodeFile(f);
    if (b != null)
        return b;

    try {
        Bitmap bitmap = null;
        URL imageUrl = new URL(url);
        HttpURLConnection conn = (HttpURLConnection) imageUrl
                .openConnection();
        conn.setConnectTimeout(30000);
        conn.setReadTimeout(30000);
        conn.setInstanceFollowRedirects(true);
        InputStream is = conn.getInputStream();
        OutputStream os = new FileOutputStream(f);
        Utils.CopyStream(is, os);
        os.close();
        bitmap = decodeFile(f);
        return bitmap;
    } catch (Exception ex) {
        ex.printStackTrace();
        return null;
    }
}

private Bitmap decodeFile(File f) {
    try {

        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(new FileInputStream(f), null, o);

        final int REQUIRED_SIZE = 70;
        int width_tmp = o.outWidth, height_tmp = o.outHeight;
        int scale = 1;
        while (true) {
            if (width_tmp / 2 < REQUIRED_SIZE
                    || height_tmp / 2 < REQUIRED_SIZE)
                break;
            width_tmp /= 2;
            height_tmp /= 2;
            scale *= 2;
        }


        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize = scale;
        return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
    } catch (FileNotFoundException e) {
    }
    return null;
}

private class PhotoToLoad {
    public String url;
    public ImageView imageView;

    public PhotoToLoad(String u, ImageView i) {
        url = u;
        imageView = i;
    }
}

class PhotosLoader implements Runnable {
    PhotoToLoad photoToLoad;

    PhotosLoader(PhotoToLoad photoToLoad) {
        this.photoToLoad = photoToLoad;
    }

    @Override
    public void run() {
        if (imageViewReused(photoToLoad))
            return;
        Bitmap bmp = getBitmap(photoToLoad.url);
        memoryCache.put(photoToLoad.url, bmp);
        if (imageViewReused(photoToLoad))
            return;
        BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad);
        Activity a = (Activity) photoToLoad.imageView.getContext();
        a.runOnUiThread(bd);
    }
}

boolean imageViewReused(PhotoToLoad photoToLoad) {
    String tag = imageViews.get(photoToLoad.imageView);
    if (tag == null || !tag.equals(photoToLoad.url))
        return true;
    return false;
}


class BitmapDisplayer implements Runnable {
    Bitmap bitmap;
    PhotoToLoad photoToLoad;

    public BitmapDisplayer(Bitmap b, PhotoToLoad p) {
        bitmap = b;
        photoToLoad = p;
    }

    public void run() {
        if (imageViewReused(photoToLoad))
            return;
        if (bitmap != null)
            photoToLoad.imageView.setImageBitmap(bitmap);
        else
            photoToLoad.imageView.setImageResource(stub_id);
    }
}

public void clearCache() {
    memoryCache.clear();
    fileCache.clear();
}

}

public class FileCache {

private File cacheDir;

public FileCache(Context context) {

    if (android.os.Environment.getExternalStorageState().equals(
            android.os.Environment.MEDIA_MOUNTED))
        cacheDir = new File(android.os.Environment
                .getExternalStorageDirectory(), "LazyList");
    else
        cacheDir = context.getCacheDir();
    if (!cacheDir.exists())
        cacheDir.mkdirs();
}

public File getFile(String url) {

    String filename = String.valueOf(url.hashCode());

    File f = new File(cacheDir, filename);
    return f;

}

public void clear() {
    File[] files = cacheDir.listFiles();
    if (files == null)
        return;
    for (File f : files)
        f.delete();
}

}

Logcat输出：

03-10 20:05:22.772: E/AndroidRuntime(411): FATAL EXCEPTION: main
03-10 20:05:22.772: E/AndroidRuntime(411): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.dharma.aplikasilokomedia/com.dharma.aplikasilokomedia.DetailLoko}: java.lang.NullPointerException
03-10 20:05:22.772: E/AndroidRuntime(411):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
03-10 20:05:22.772: E/AndroidRuntime(411):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
03-10 20:05:22.772: E/AndroidRuntime(411):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
03-10 20:05:22.772: E/AndroidRuntime(411):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
03-10 20:05:22.772: E/AndroidRuntime(411):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-10 20:05:22.772: E/AndroidRuntime(411):  at android.os.Looper.loop(Looper.java:123)
03-10 20:05:22.772: E/AndroidRuntime(411):  at android.app.ActivityThread.main(ActivityThread.java:4627)
03-10 20:05:22.772: E/AndroidRuntime(411):  at java.lang.reflect.Method.invokeNative(Native Method)
03-10 20:05:22.772: E/AndroidRuntime(411):  at java.lang.reflect.Method.invoke(Method.java:521)
03-10 20:05:22.772: E/AndroidRuntime(411):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
03-10 20:05:22.772: E/AndroidRuntime(411):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
03-10 20:05:22.772: E/AndroidRuntime(411):  at dalvik.system.NativeStart.main(Native Method)
03-10 20:05:22.772: E/AndroidRuntime(411): Caused by: java.lang.NullPointerException
03-10 20:05:22.772: E/AndroidRuntime(411):  at com.dharma.aplikasilokomedia.FileCache.<init>(FileCache.java:17)
03-10 20:05:22.772: E/AndroidRuntime(411):  at com.dharma.aplikasilokomedia.ImageLoader.<init>(ImageLoader.java:32)
03-10 20:05:22.772: E/AndroidRuntime(411):  at com.dharma.aplikasilokomedia.DetailLoko.<init>(DetailLoko.java:28)
03-10 20:05:22.772: E/AndroidRuntime(411):  at java.lang.Class.newInstanceImpl(Native Method)
03-10 20:05:22.772: E/AndroidRuntime(411):  at java.lang.Class.newInstance(Class.java:1429)
03-10 20:05:22.772: E/AndroidRuntime(411):  at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
03-10 20:05:22.772: E/AndroidRuntime(411):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577)
03-10 20:05:22.772: E/AndroidRuntime(411):  ... 11 more

Answer 1

DetailLoko是一个活动，在构造函数/初始化（不在onCreate中）中，您使用ImageLoader（活动）作为上下文创建this。

你做不到。您需要等到调用onCreate才允许将活动用作context，因为在此之前它尚未完全初始化。

在ImageLoader中移动onCreate的创建。

带图像加载器的LazyList

1 个答案: