Android 可抽出式韩元'；不能使用异步任务加载

我有一个queryAppIcon（）方法，可以在数组appIconDrawable中查询和存储图像。然而，我只是在应该弹出图像的地方变得空白。请让我知道我是否应该发布任何其他相关代码

这是ViewActivity中的相关代码：

// global vars
final Drawable[] appIconDrawable = null;
int i;

public Drawable[] queryAppIcon() throws ParseException, IOException {
    ParseQuery<ParseObject> query = ParseQuery.getQuery("AndroidStoreContent");
    query.whereExists("appIcon");
    List<ParseObject> ParseResult = query.find();
    // Drawable array
    appIconDrawable = new Drawable[ParseResult.size()];

    for (i = 0; i < ParseResult.size(); i++) {
        ParseFile pf = (ParseFile) ParseResult.get(i).get("appIcon");
        startDownload(pf);
    }
    return appIconDrawable;
}

public void startDownload(ParseFile pf) {
    new DownloadImageTask(this).execute(pf);
}

public class DownloadImageTask extends AsyncTask<ParseFile, Void, Drawable> {

    private AsyncResponse ar;

    DownloadImageTask(AsyncResponse ar) {
        this.ar = ar;
    }

    @Override
    protected Drawable doInBackground(ParseFile... pf) {
        return fetchDrawable(pf[0]);
    }

    protected void onPostExecute(Drawable result) {
        ar.processFinish(result);
    }

    public Drawable fetchDrawable(ParseFile pf) {
        InputStream is;
        try {
            is = (InputStream) new URL(pf.getUrl()).getContent();
            return Drawable.createFromStream(is,null);
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}

@Override
public void processFinish(Drawable d) {
    appIconDrawable[i] = d; // i also tried testing appIconDrawable[1] = d and the app loaded with all blank images and then crashes
}

---

看起来你需要一点重构

您希望从

queryAppIcon（）

下载

Drawable[]

，但您将始终得到一个空集，因为您在单独的线程中启动下载，然后更新返回值

您应该从

processFinish

中将

Drawable

设置为

ImageView

出错的迹象：异步方法（如下载图像）永远不会有返回值

更新

这是一个非常简单的异步下载任务，但是缺少很多检查、优化等，比如缓存！另外，下载ImageTask中的ImageView应该由

WeakReference

（谷歌it）持有，否则它会泄露你的活动

public class DownloadImageTask extends AsyncTask<String, Void, Drawable> {

    private static final String TAG = DownloadImageTask.class.getSimpleName();
    private ImageView mImageView;

    DownloadImageTask(ImageView imageView) {
        mImageView = imageView;
    }

    @Override
    protected Drawable doInBackground(String... url) {
        return fetchDrawable(url[0]);
    }

    @Override
    protected void onPostExecute(Drawable result) {
        if (result != null) {
            mImageView.setImageDrawable(result);
        } else {
            Log.w(TAG, "Could download image!");
        }
    }

    public static Drawable fetchDrawable(String url) {
        Log.v(TAG, "Downloading: " + url);
        InputStream is;
        try {
            is = (InputStream) new URL(url).getContent();
            return Drawable.createFromStream(is, null);
        } catch (MalformedURLException e) {
            Log.e(TAG, e.getMessage(), e);
        } catch (IOException e) {
            Log.e(TAG, e.getMessage(), e);
        }

        return null;
    }
}

---

谢谢我试图这样做，但是ImageView是在

ViewAdapter

类中设置的，而AsyncTask是在

ViewActivity

类中设置的。有办法解决这个问题吗？我应该发布我的适配器和活动类吗？你反对使用库吗？看：是的，我见过，但我不想用图书馆来做这个project@ErmiasAsghedom添加了一个示例类，但将其作为一个概念，而不是复制和粘贴代码。

public class DownloadImageTask extends AsyncTask<String, Void, Drawable> {

    private static final String TAG = DownloadImageTask.class.getSimpleName();
    private ImageView mImageView;

    DownloadImageTask(ImageView imageView) {
        mImageView = imageView;
    }

    @Override
    protected Drawable doInBackground(String... url) {
        return fetchDrawable(url[0]);
    }

    @Override
    protected void onPostExecute(Drawable result) {
        if (result != null) {
            mImageView.setImageDrawable(result);
        } else {
            Log.w(TAG, "Could download image!");
        }
    }

    public static Drawable fetchDrawable(String url) {
        Log.v(TAG, "Downloading: " + url);
        InputStream is;
        try {
            is = (InputStream) new URL(url).getContent();
            return Drawable.createFromStream(is, null);
        } catch (MalformedURLException e) {
            Log.e(TAG, e.getMessage(), e);
        } catch (IOException e) {
            Log.e(TAG, e.getMessage(), e);
        }

        return null;
    }
}

public class ImageDownloadAdapter extends ArrayAdapter<String>{

    public ImageDownloadAdapter(Context context, String[] objects) {
        super(context, R.layout.item_image_download, R.id.txt_url, objects);
    }

    @SuppressLint("NewApi")
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View view = super.getView(position, convertView, parent);

        String url = getItem(position);

        ImageView imageView = (ImageView) view.findViewById(R.id.img_download);
        DownloadImageTask downloadImageTask = new DownloadImageTask(imageView);
        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
            downloadImageTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, url);
        } else {
            downloadImageTask.execute(url);
        }
        return view;
    }
}

    ListView listView = (ListView) findViewById(android.R.id.list);
    listView.setAdapter(new ImageDownloadAdapter(this, new String[]{
        "http://www.beautystat.com/site/wp-content/uploads/2011/02/happy-faces-small.jpg",
        "http://www.ducthide.com/new_wallet_pics/happy_face.JPG"
    }));