java - ListView 和图像 : I'm going crazy

Question

我有一个大问题让我发疯。我有一个安装了所有应用程序的 ListView，但滚动速度非常慢，所以我想改进它。我尝试放置一个线程，但它不能解决问题。这是代码

应用程序适配器

public class ApplicationAdapter extends ArrayAdapter<ApplicationInfo> {
    private List<ApplicationInfo> appsList = null;
    private Context context;
    private PackageManager packageManager;
    Holder holder;

    public ApplicationAdapter(Context context, int textViewResourceId,
            List<ApplicationInfo> appsList) {
        super(context, textViewResourceId, appsList);
        this.context = context;
        this.appsList = appsList;
        packageManager = context.getPackageManager();
    }


    @Override
    public View getView(int position, View convertView, ViewGroup parent){
        View view = convertView;
        final Holder holder;
        if (null == view) {
            LayoutInflater layoutInflater = (LayoutInflater) context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            view = layoutInflater.inflate(R.layout.snippet_list_row, null);
            holder = new Holder();
            holder.appName = (TextView) view.findViewById(R.id.app_name);
            holder.packageName = (TextView) view.findViewById(R.id.app_paackage);
            holder.iconview = (ImageView) view.findViewById(R.id.app_icon);


            view.setTag(holder);
        }
        else
        {
            holder = (Holder)view.getTag();
        }




        final ApplicationInfo data = appsList.get(position);
        if (null != data) {

            holder.appName.setText(data.loadLabel(packageManager));
            holder.packageName.setText(data.packageName);
            holder.iconview.setImageDrawable(data.loadIcon(packageManager));



        }







        return view;
    }

    static class Holder
    {
        TextView appName, packageName;
        ImageView iconview;
    }



}

Activity

public class Activity_Eclair extends ListActivity {

    public PackageManager packageManager = null;
    public List<ApplicationInfo> applist = null;
    public ApplicationAdapter listadaptor = null;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_eclair);

        ListView lv = getListView();
        lv.setFastScrollEnabled(true);
        lv.setScrollingCacheEnabled(false);
        registerForContextMenu(lv);

        packageManager = getPackageManager();


        new LoadApplications().execute();


    Button bottone1 = (Button)findViewById(R.id.button1);
    bottone1.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {

            new LoadApplications().execute();


        }
    });};



    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        super.onListItemClick(l, v, position, id);

        ApplicationInfo app = applist.get(position);

        Uri packageUri = Uri.parse("package:"+app.packageName);
        Intent uninstallIntent = new Intent(Intent.ACTION_DELETE, packageUri);
        startActivity(uninstallIntent);
    }


    public List<ApplicationInfo> checkForLaunchIntent(List<ApplicationInfo> list) {
        ArrayList<ApplicationInfo> applist = new ArrayList<ApplicationInfo>();
        for (ApplicationInfo info : list) {
            try {
                if (null != packageManager.getLaunchIntentForPackage(info.packageName)) {
                    applist.add(info);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        return applist;
    }


    private class LoadApplications extends AsyncTask<Void, Void, Void> {        

        public ProgressDialog progress = null;

        @Override
        protected Void doInBackground(Void... params) {
            applist = checkForLaunchIntent(packageManager.getInstalledApplications(PackageManager.GET_META_DATA));
            listadaptor = new ApplicationAdapter(Activity_Eclair.this,
                    R.layout.snippet_list_row, applist);

            return null;
        }

        @Override
        protected void onCancelled() {
            super.onCancelled();
        }

        protected void onDestroy() {
            if(progress!=null)
                if(progress.isShowing()){
                progress.dismiss();
                }

        }

        @Override
        protected void onPostExecute(Void result) {
            setListAdapter(listadaptor);
            progress.dismiss();
            super.onPostExecute(result);
        }

        @Override
        protected void onPreExecute() {
            progress = ProgressDialog.show(Activity_Eclair.this, null,
                    "Loading...");
            super.onPreExecute();
        }

        @Override
        protected void onProgressUpdate(Void... values) {
            super.onProgressUpdate(values);
        }
    }

    private final static int UPDATE_MENU_OPTION = 1;
    private final static int DELETE_MENU_OPTION = 2;
    private final static int TRUNCATE_MENU_OPTION = 3;
    private final static int DELETE = 4;

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) {

    }

    @Override
    public boolean onContextItemSelected(MenuItem item) {
            AdapterContextMenuInfo info = (AdapterContextMenuInfo) item.getMenuInfo();
            final long examId = info.id;
            ApplicationInfo app = applist.get((int) info.id);

            switch (item.getItemId()) {

            case UPDATE_MENU_OPTION:
                try {
                    Intent intent = packageManager
                            .getLaunchIntentForPackage(app.packageName);

                    if (null != intent) {
                        startActivity(intent);
                    }
                } catch (ActivityNotFoundException e) {
                    Toast.makeText(Activity_Eclair.this, e.getMessage(),
                            Toast.LENGTH_LONG).show();
                } catch (Exception e) {
                    Toast.makeText(Activity_Eclair.this, e.getMessage(),
                            Toast.LENGTH_LONG).show();
                }
                return true;

            case DELETE_MENU_OPTION:
                Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse("https://play.google.com/store/apps/details?id="+app.packageName));
                startActivity(browserIntent);
                return true;

            case TRUNCATE_MENU_OPTION:
                try {
                    //Open the specific App Info page:
                    Intent intent = new Intent(android.provider.Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
                    intent.setData(Uri.parse("package:" + app.packageName));
                    startActivity(intent);

                } catch ( ActivityNotFoundException e ) {
                    //e.printStackTrace();

                    //Open the generic Apps page:
                    Intent intent = new Intent(android.provider.Settings.ACTION_MANAGE_APPLICATIONS_SETTINGS);
                    startActivity(intent);

                }
                return true;

            case DELETE:
            {
                 Uri packageUri = Uri.parse("package:"+app.packageName);
                 Intent uninstallIntent = new Intent(Intent.ACTION_DELETE, packageUri);
                 startActivity(uninstallIntent);

            }
            return true;

            default:
                    return super.onContextItemSelected(item);
            }
    }

我声明我已经尝试过 StackOverflow 和 Web 上的大量代码 fragment ，但不起作用。 }

Answer 1

1 - 编辑 list 文件添加到 Activity

android:hardwareAccelerated="true"

2- 缓存并绘制图标到 ImageView oneByOne 我们需要 4 个类:

Utils.class

public class Utils {
    public static void CopyStream(InputStream is, OutputStream os)
    {
        final int buffer_size=1024;
        try
        {
            byte[] bytes=new byte[buffer_size];
            for(;;)
            {
              int count=is.read(bytes, 0, buffer_size);
              if(count==-1)
                  break;
              os.write(bytes, 0, count);
            }
        }
        catch(Exception ex){}
    }
}

MemoryCache.class

public class MemoryCache {

    private static final String TAG = "MemoryCache";
    private Map<String, Bitmap> cache=Collections.synchronizedMap(
            new LinkedHashMap<String, Bitmap>(10,1.5f,true));//Last argument true for LRU ordering
    private long size=0;//current allocated size
    private long limit=1000000;//max memory in bytes

    public MemoryCache(){
        //use 25% of available heap size
        setLimit(Runtime.getRuntime().maxMemory()/4);
    }

    public void setLimit(long new_limit){
        limit=new_limit;
        Log.i(TAG, "MemoryCache will use up to "+limit/1024./1024.+"MB");
    }

    public Bitmap get(String id){
        try{
            if(!cache.containsKey(id))
                return null;
            return cache.get(id);
        }catch(NullPointerException ex){
            ex.printStackTrace();
            return null;
        }
    }

    public void put(String id, Bitmap bitmap){
        try{
            if(cache.containsKey(id))
                size-=getSizeInBytes(cache.get(id));
            cache.put(id, bitmap);
            size+=getSizeInBytes(bitmap);
            checkSize();
        }catch(Throwable th){
            th.printStackTrace();
        }
    }

    private void checkSize() {
        Log.i(TAG, "cache size="+size+" length="+cache.size());
        if(size>limit){
            Iterator<Entry<String, Bitmap>> iter=cache.entrySet().iterator(); 
            while(iter.hasNext()){
                Entry<String, Bitmap> entry=iter.next();
                size-=getSizeInBytes(entry.getValue());
                iter.remove();
                if(size<=limit)
                    break;
            }
            Log.i(TAG, "Clean cache. New size "+cache.size());
        }
    }

    public void clear() {
        try{
            cache.clear();
            size=0;
        }catch(NullPointerException ex){
            ex.printStackTrace();
        }
    }

    long getSizeInBytes(Bitmap bitmap) {
        if(bitmap==null)
            return 0;
        return bitmap.getRowBytes() * bitmap.getHeight();
    }
}

FileCache.class

public class FileCache {

    private File cacheDir;
    String cacheFile  = "cachefolder"; 

    public FileCache(Context context, String subfolder ){
        //Find the dir to save cached images
        if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
            cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),cacheFile+"/"+subfolder);
        else
            cacheDir=context.getCacheDir();
        if(!cacheDir.exists())
            cacheDir.mkdirs();
    }

    public FileCache(Context context){
        //Find the dir to save cached images
        if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
            cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),cacheFile);
        else
            cacheDir=context.getCacheDir();
        if(!cacheDir.exists())
            cacheDir.mkdirs();
    }
    public File getFile(String url){
        //I identify images by hashcode. Not a perfect solution, good for the demo.
        String filename = String.valueOf(url.hashCode());
        //Another possible solution (thanks to grantland)
        //String filename = URLEncoder.encode(url);
        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();
    }

}

ImageLoader.class:

public class ImageLoader {

    public static int REQUIRED_SIZE=100;
    public MemoryCache memoryCache = new MemoryCache();
    FileCache fileCache;
    private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
    ExecutorService executorService; 
    int stub_id = R.drawable.drawing_image; 


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

    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 Bitmap bitmap_to_circel( Bitmap bitmap)
    {

        return bitmap;
        Bitmap circleBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), Bitmap.Config.ARGB_8888);

        BitmapShader shader = new BitmapShader (bitmap,  TileMode.CLAMP, TileMode.CLAMP);
        Paint paint = new Paint();
              paint.setShader(shader); 
              paint.setAntiAlias(true);
              paint.setFilterBitmap(true);
              paint.setDither(true);      

       Canvas c = new Canvas(circleBitmap);
       c.drawCircle(bitmap.getWidth()/2, bitmap.getHeight()/2, bitmap.getWidth()/2, paint);

       return circleBitmap;
    }*/

    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.
            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(stub_id);
        }
    }

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

}

3 - 将 ImageLoader 添加到您的 ApplicationAdapter 并开始显示图像

public class ApplicationAdapter extends ArrayAdapter<ApplicationInfo> {
    private List<ApplicationInfo> appsList = null;
    private Context context;
    private PackageManager packageManager;
    Holder holder;
//added imageloader here <<------------------
    ImageLoader imgLoader; 

    public ApplicationAdapter(Context context, int textViewResourceId,
            List<ApplicationInfo> appsList) {
        super(context, textViewResourceId, appsList);
        this.context = context;
        this.appsList = appsList;
        packageManager = context.getPackageManager();
//Register image loader class <<---------------------
imgLoader      = new ImageLoader(context);
    }


    @Override
    public View getView(int position, View convertView, ViewGroup parent){
        View view = convertView;
        final Holder holder;
        if (null == view) {
            LayoutInflater layoutInflater = (LayoutInflater) context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            view = layoutInflater.inflate(R.layout.snippet_list_row, null);
            holder = new Holder();
            holder.appName = (TextView) view.findViewById(R.id.app_name);
            holder.packageName = (TextView) view.findViewById(R.id.app_paackage);
            holder.iconview = (ImageView) view.findViewById(R.id.app_icon);


            view.setTag(holder);
        }
        else
        {
            holder = (Holder)view.getTag();
        }




        final ApplicationInfo data = appsList.get(position);
        if (null != data) {

            holder.appName.setText(data.loadLabel(packageManager));
            holder.packageName.setText(data.packageName);

//now load icon provide Url and ImageView only and keep the rest to the class
//provide fill link url to the icon the class will download it , cache it , display it
//next time when scroll again to this position the icon will be displayed from cache file 
imgLoader.DisplayImage(data.icon_link_url_with_http, holder.iconview);




        }







        return view;
    }

    static class Holder
    {
        TextView appName, packageName;
        ImageView iconview;
    }



}

现在你的 ListView 将快速滚动，即使它有 1k ImageView