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？
答案 0 :(得分：1)
如果您使用的是xml，请将ListView的宽度和高度设置为match_parent。
答案 1 :(得分：0)
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
答案 2 :(得分：0)
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;）