Question

我的应用程序中有一个自定义列表视图，它显示图像和文本（Json）。我从URL获取的图像正在工作，但listview是滞后的（滚动滞后）。也许我的问题是ImageLoader.java类这是我的代码：

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.aaaaaaaaaaaaaaa;

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);

    // from SD cache
    Bitmap b = decodeFile(f);
    if (b != null)
        return b;

    // from web
    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 (Throwable ex) {
        ex.printStackTrace();
        if (ex instanceof OutOfMemoryError)
            memoryCache.clear();
        return null;
    }
}

// decodes image and scales it to reduce memory consumption
private Bitmap decodeFile(File f) {
    try {
        // decode image size
        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        FileInputStream stream1 = new FileInputStream(f);
        BitmapFactory.decodeStream(stream1, null, o);
        stream1.close();

        // Find the correct scale value. It should be the power of 2.
        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;
        }

        // decode with inSampleSize
        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize = scale;
        FileInputStream stream2 = new FileInputStream(f);
        Bitmap bitmap = BitmapFactory.decodeStream(stream2, null, o2);
        stream2.close();
        return bitmap;
    } catch (FileNotFoundException e) {
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

// Task for the queue
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() {
        try {
            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);
        } catch (Throwable th) {
            th.printStackTrace();
        }
    }
}

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

// Used to display bitmap in the UI thread
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();
}

}

这也是我的BaseAdapter.java类

public class BRIgeAdapter extends BaseAdapter {
private LayoutInflater inflater;
private Activity activity;
public ArrayList<HashMap<String, String>> data;
public ViewHolder holder;
public ImageLoader imageLoader;
HashMap<String, String> itemList;
private int screenSize;
MainActivity main;
public BRIgeAdapter(Activity a, ArrayList<HashMap<String, String>> d,int screenSize) {
    this.activity = a;
    this.data = d;
    this.screenSize = screenSize;
    inflater = (LayoutInflater) activity
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    imageLoader = new ImageLoader(activity.getApplicationContext());
}
public int getCount() {
    return data.size();
}
public Object getItem(int position) {
    return data.get(position);
}
public long getItemId(int position) {
    return (long) position;
}
@Override
public int getViewTypeCount() {
    return data.size();
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
    if (convertView == null) {
        holder = new ViewHolder();
        main = new MainActivity();
        convertView = inflater.inflate(R.layout.list_row, parent, false);

        holder.journal = (TextView) convertView
                .findViewById(R.id.smalljournal);
        holder.statId = (TextView) convertView
                .findViewById(R.id.smallstatID);

        holder.smallDescription1 = (TextView) convertView
        .findViewById(R.id.smallDescription1);
        holder.DateTime = (TextView) convertView
                .findViewById(R.id.smallDateTime);
        holder.thumb_image = (ImageView) convertView
                .findViewById(R.id.smallthumb);
        holder.title = (TextView) convertView.findViewById(R.id.smalltitle);
        holder.description = (TextView) convertView
                .findViewById(R.id.smallDescription);
        convertView.setTag(holder);
    } else {
        holder = (ViewHolder) convertView.getTag();
    }
    itemList = data.get(position);
    if (itemList != null) {
        holder.journal.setText(itemList.get(MainActivity.KEY_journal));
        // holder.DateTime.setText(itemList.get(MainActivity.KEY_pubDate));
        holder.statId.setText(itemList.get(MainActivity.KEY_statID));
        holder.smallDescription1.setText(itemList.get(MainActivity.KEY_description));
        holder.journal.setTypeface(MainActivity.tf2);
        String titleString = itemList.get(MainActivity.KEY_title);
        Calendar cal = new GregorianCalendar(2013, 11, 20);
        DateFormat df = new SimpleDateFormat("dd.MM.yyyy");
        // DateFormat df = new SimpleDateFormat("yyyy-MM-dd");
        String date = df.format(cal.getTime());
        String DateTime = itemList.get(MainActivity.KEY_pubDate);
        DateTime = date;
        holder.DateTime.setText(DateTime);
        holder.title.setText(titleString);
        holder.title.setTypeface(MainActivity.tf2);

        holder.title.setLineSpacing(2, 1.2f);
        holder.description.setLineSpacing(2, 1.2f);

        if(screenSize == Configuration.SCREENLAYOUT_SIZE_NORMAL)
            holder.description.setVisibility(View.INVISIBLE);
        else
            holder.description.setText(itemList.get(MainActivity.KEY_description));

        holder.description.setTypeface(MainActivity.tf2);
        imageLoader.DisplayImage(itemList.get(MainActivity.KEY_image),
                holder.thumb_image);
    }
    return convertView;
}
static class ViewHolder {
    public TextView journal, title, description,smallDescription1, DateTime, statId;
    ImageView thumb_image;
}
 }

有没有办法减少或消除这种滞后？

Answer 1

如果您使用的是xml，请将ListView的宽度和高度设置为match_parent。

Answer 2

我看到您使用线程从网址加载图片。我建议您使用Android Universal Image Loader Library。它非常灵活，而且不那么迟钝。您可以找到所有信息Here

Answer 3

此外，您似乎在getView方法中创建对象。这意味着在绘制每个视图时，操作系统必须完成为您创建这些对象的所有工作。如果使用大型列表（或小型ram），您将强制垃圾收集器运行，导致应用程序断断续续。尝试将所有对象创建移动到构造函数方法，以便它只运行一次。然后根据需要在get view方法中重新分配它们。这应该提供明显的速度提升。

祝你好运;）

ListView滚动滞后在android中

3 个答案: