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私は現在、リストビューを持つアプリケーションを開発しています。このリストビューには、XMLファイルからオンラインで取得されたテキストとイメージが挿入されます。ただし、スクロールするたびに、現在画面に表示されていないものはリロードし、ビットマップのサイズを再計算してリストビューに表示します。これは、スクロールが流動的で厄介なことにつながります。どのようにして、リストビューに画像を取り込み、そこにとどまるために1回読み込むためにアクティビティを取得できますか？永久にListViewに画像を取り込みますか？
ImageLoader：
public class ImageLoader {
MemoryCache memoryCache = new MemoryCache();
FileCache fileCache;
private Map<ImageView, String> imageViews = Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
ExecutorService executorService;
int size;
int placeholderpic;
public ImageLoader(Context context, int size, int placeholderpic) {
fileCache = new FileCache(context);
executorService = Executors.newFixedThreadPool(5);
this.size = size;
this.placeholderpic = placeholderpic;
}
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(placeholderpic);
}
}
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;
BitmapFactory.decodeStream(new FileInputStream(f),null,o);
//Find the correct scale value. It should be the power of 2.
final int REQUIRED_SIZE = size;
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;
return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
} catch (FileNotFoundException e) {}
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() {
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;
}
//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(placeholderpic);
}
}
public void clearCache() {
memoryCache.clear();
fileCache.clear();
}
ListViewコントロールアダプタ：
public class LazyNewsAdapter extends BaseAdapter {
private Activity activity;
private ArrayList<News> listData;
private LayoutInflater inflater = null;
public LazyNewsAdapter(Activity activity, ArrayList<News> listData) {
this.activity = activity;
this.listData = listData;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
public int getCount() {
return listData.size();
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
News newsItem = listData.get(position);
View view = convertView;
if(convertView == null)
view = inflater.inflate(R.layout.news_cell, null);
TextView newsTitle = (TextView) view.findViewById(R.id.newsTitle);
TextView newsDate = (TextView) view.findViewById(R.id.newsDate);
ImageView image = (ImageView) view.findViewById(R.id.newsImage);
newsTitle.setText(newsItem.getNewsTitle());
newsDate.setText(newsItem.getNewsDate());
String url = newsItem.getNewsImageUrl();
ImageLoader imageLoader = new ImageLoader(activity, 600, R.drawable.placeholder);
imageLoader.displayImage(url, image);
return view;
}
リストビューやスクロールビューを正確に混同しているので、リストビューをスクロールビュー内に置くことは恐ろしい考えです。 –
私はただリストビューだと嘘をついた – MattyK14