Question

我正在尝试创建一个简单的文件管理器，我在缩略图（位图）加载方面遇到了问题。我想使用这些提示来使用AsyncTask和Lru缓存：

http://developer.android.com/training/displaying-bitmaps/index.html

一切顺利，直到我尝试实现lru缓存。我的意思是，没有lru缓存位图正在加载但滚动它并不顺利。使用lru缓存，滚动很平滑，但位图不想立即加载。我必须向下和向上向下滚动，然后位图正在加载。

这就是我的意思（抱歉质量不好）：

http://www.youtube.com/watch?v=Xfkd6Esx7D0

这是我的ArrayAdapter：

public class AdapterFiles extends ArrayAdapter<String>{
private int resource;
private static final String PREFERENCES_NAME = "Preferences";
private static final String CHECKBOX_FIELD = "thumbnails";
private static final String LIST_FIELD = "colorlist";

private SharedPreferences preferences;
private boolean thumbnails;
private OnClickListener onItemMenuClickListener;
private String item;
private ViewHolder viewHolder;
public static ArrayList<Integer> selectedIds = new ArrayList<Integer>();
private String colorrow;
private final ThumbnailLoader tnloader = new ThumbnailLoader();


public AdapterFiles(Context context, int textViewResourceId, int label, List<String> objects) {
        super(context, textViewResourceId, objects);
        preferences = context.getSharedPreferences(PREFERENCES_NAME, Activity.MODE_PRIVATE);
        thumbnails = preferences.getBoolean(CHECKBOX_FIELD, false);
        resource = textViewResourceId;           
}

static class ViewHolder {
    TextView label;
    ImageView ikonka;
    TextView size;
    TextView date;
    ImageButton context_menu;

}


@Override
public View getView(int position, View convertView, ViewGroup parent) {
    RelativeLayout RowView;
        item = getItem(position);
        preferences.getString(LIST_FIELD, "#FF0099CC");



        if(convertView == null) {
        RowView = new RelativeLayout(getContext());
        LayoutInflater inflater = (LayoutInflater)getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        inflater.inflate(resource, RowView, true);
        viewHolder = new ViewHolder();
        viewHolder.label = (TextView)RowView.findViewById(R.id.label);
        viewHolder.ikonka = new ImageView(getContext());
        viewHolder.ikonka = (ImageView)RowView.findViewById(R.id.icon);
        viewHolder.ikonka.setTag(item);
        viewHolder.size = (TextView)RowView.findViewById(R.id.size);
        viewHolder.date = (TextView)RowView.findViewById(R.id.date);
        viewHolder.context_menu = (ImageButton)RowView.findViewById(R.id.context_menu);
        viewHolder.context_menu.setFocusable(false);
        viewHolder.context_menu.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                if(onItemMenuClickListener != null) onItemMenuClickListener.onClick(v);
            }
        });
        RowView.setTag(viewHolder);
        } else {
            RowView = (RelativeLayout)convertView;
            viewHolder = (ViewHolder) RowView.getTag();
        }


            colorrow = "#FF99D6EB"; 

        RowView.setBackgroundColor(selectedIds.contains(position) ? Color.parseColor(colorrow) : android.R.color.transparent);  


        File file = new File(item);
        if (file.isDirectory()){
            if(file.canRead()){
            viewHolder.ikonka.setImageResource(R.drawable.folder);
            }
            else{
            viewHolder.ikonka.setImageResource(R.drawable.foldernoway); 
            }
        }else if(item.endsWith(".doc") || item.endsWith(".docx")){
             viewHolder.ikonka.setImageResource(R.drawable.docs);}

        else if(item.endsWith(".xls") || item.endsWith(".xlsx")){
            viewHolder.ikonka.setImageResource(R.drawable.xls);}

        else if(item.endsWith(".ppt") || item.endsWith(".pptx")){
            viewHolder.ikonka.setImageResource(R.drawable.ppt);}

        else if(item.endsWith(".txt")){
            viewHolder.ikonka.setImageResource(R.drawable.txt);}

        else if(item.endsWith(".mp3") || item.endsWith(".wma") || item.endsWith(".m4a") || item.endsWith(".ogg")){
            viewHolder.ikonka.setImageResource(R.drawable.music);}

        else if(item.endsWith(".apk")){
            viewHolder.ikonka.setImageResource(R.drawable.android);}

        else if(item.endsWith(".pdf")){
            viewHolder.ikonka.setImageResource(R.drawable.adobe);}

        else if(item.endsWith(".jpg") || item.endsWith(".JPG") || item.endsWith(".png") || item.endsWith(".jpeg")){



            if(thumbnails == false){
            viewHolder.ikonka.setImageResource(R.drawable.image);   
            }else{

                tnloader.loadBitmap(item, viewHolder.ikonka);
            }
            }           
        else if(item.endsWith(".avi") || item.endsWith(".3gp") || item.endsWith(".mp4")){


                viewHolder.ikonka.setImageResource(R.drawable.video);   

        }
        else if(item.endsWith(".rar") || item.endsWith(".zip") || item.endsWith(".tar")){
            viewHolder.ikonka.setImageResource(R.drawable.zip);}

        else{
            viewHolder.ikonka.setImageResource(R.drawable.noname);
        }



        viewHolder.label.setText(file.getName());

        if (file.isDirectory()){
        viewHolder.size.setText(R.string.folder);}
        else{
            double bytes = file.length();
            double kilobytes = (bytes / 1024);
            double megabytes = (kilobytes / 1024);
            if (bytes < 6000){
        viewHolder.size.setText(bytes + " b");  
            }else{
        viewHolder.size.setText(String.format( "%.2f MB", megabytes ));}    
        }

        Date lastModDate = new Date(file.lastModified());
        SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm");  
        String formattedDateString = formatter.format(lastModDate);

        viewHolder.date.setText(formattedDateString);

        viewHolder.context_menu.setTag(new Integer(position));          

        return RowView;


    } 

    public void setOnItemMenuClickListener(
        OnClickListener onItemMenuClickListner) {
    this.onItemMenuClickListener = onItemMenuClickListner;
    }
}

和ThumbnailLoader：

public class ThumbnailLoader {

Context context;
int memClass = 80;


public void loadBitmap(String filePath, ImageView imageView) {
    final String imageKey = String.valueOf(filePath);

    final Bitmap bitmap = getBitmapFromMemCache(imageKey);
    if (bitmap != null) {
        imageView.setImageBitmap(bitmap);
    } else {
        imageView.setImageResource(R.drawable.image);
        BitmapWorkerTask task = new BitmapWorkerTask(imageView);
        task.execute(filePath);
    }

}



public static boolean cancelPotentialWork(String data, ImageView imageView) {
    final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView);

    if (bitmapWorkerTask != null) {
        final String bitmapData = bitmapWorkerTask.getFilePath();
        if (bitmapData != data) {
            // Cancel previous task
            bitmapWorkerTask.cancel(true);
        } else {
            // The same work is already in progress
            return false;
        }
    }
    // No task associated with the ImageView, or an existing task was cancelled
    return true;
}

private static BitmapWorkerTask getBitmapWorkerTask(ImageView imageView) {
       if (imageView != null) {
           final Drawable drawable = imageView.getDrawable();
           if (drawable instanceof AsyncDrawable) {
               final AsyncDrawable asyncDrawable = (AsyncDrawable) drawable;
               return asyncDrawable.getBitmapWorkerTask();
           }
        }
        return null;
    }

public Bitmap loadImageFromSdCard(String filePath, int reqWidth, int reqHeight) {

    // First decode with inJustDecodeBounds=true to check dimensions
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeFile(filePath, options);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    return BitmapFactory.decodeFile(filePath, options);
} 

public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;

if (height > reqHeight || width > reqWidth) {
    if (width > height) {
        inSampleSize = Math.round((float)height / (float)reqHeight);
    } else {
        inSampleSize = Math.round((float)width / (float)reqWidth);
    }
}
return inSampleSize;}

class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> {

    private String mFilePath;
    private final WeakReference<ImageView> imageViewReference;

    public BitmapWorkerTask(ImageView imageView) {
        // Use a WeakReference to ensure the ImageView can be garbage collected
        imageViewReference = new WeakReference<ImageView>(imageView);
    }

    public String getFilePath() {
        return mFilePath;
    }

    // Decode image in background.
    @Override
    protected Bitmap doInBackground(String... params) {
        mFilePath = params[0];       
        final Bitmap bitmap = loadImageFromSdCard(mFilePath, 72, 72);
        addBitmapToMemoryCache(String.valueOf(mFilePath), bitmap);
        return bitmap;
    }

    // Once complete, see if ImageView is still around and set bitmap.
    @Override
    protected void onPostExecute(Bitmap bitmap) {
        if (isCancelled()) {
            bitmap = null;
        }

        if (imageViewReference != null && bitmap != null) {
            final ImageView imageView = imageViewReference.get();
            final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView);
            if (this == bitmapWorkerTask && imageView != null) {
                imageView.setImageBitmap(bitmap);
            }
        }
    }
}

static class AsyncDrawable extends BitmapDrawable {
    private final WeakReference<BitmapWorkerTask> bitmapWorkerTaskReference;

    public AsyncDrawable(BitmapWorkerTask bitmapWorkerTask) {
        super();
        bitmapWorkerTaskReference = new WeakReference<BitmapWorkerTask>(bitmapWorkerTask);
    }

    public BitmapWorkerTask getBitmapWorkerTask() {
        return bitmapWorkerTaskReference.get();
    }
}

// Get memory class of this device, exceeding this amount will throw an
// OutOfMemory exception.

// Use 1/8th of the available memory for this memory cache.
final int cacheSize = 1024 * 1024 * memClass / 8;

public LruCache<String, Bitmap> mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {

    @Override
    protected int sizeOf(String key, Bitmap bitmap) {
        // The cache size will be measured in bytes rather than number of items.
        return bitmap.getByteCount();
    }
};

public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
    if (getBitmapFromMemCache(key) == null) {
        mMemoryCache.put(key, bitmap);
    }
}

public Bitmap getBitmapFromMemCache(String key) {
    return mMemoryCache.get(key);
}}

我该如何解决？

更新

我找到了解决方案。也许它会帮助别人。

public class ThumbnailLoader{
static Context context;
int memClass = 80;

public ThumbnailLoader(Context context) {
    ThumbnailLoader.context = context;
}

public void loadBitmap(String filePath, ImageView imageView) {
    final String imageKey = String.valueOf(filePath);
    final Bitmap bitmap = getBitmapFromMemCache(imageKey);
    Bitmap preloadbitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.image);

    if (bitmap != null) {
        imageView.setImageBitmap(bitmap);
    }else if (cancelPotentialWork(filePath, imageView)) {
        BitmapWorkerTask task = new BitmapWorkerTask(imageView);
        final AsyncDrawable asyncDrawable = new AsyncDrawable(context.getResources(), preloadbitmap, task);
        imageView.setImageDrawable(asyncDrawable);
        task.execute(filePath);
    }

}

public static boolean cancelPotentialWork(String data, ImageView imageView) {
    final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView);

    if (bitmapWorkerTask != null) {
        final String bitmapData = bitmapWorkerTask.getFilePath();
        if (bitmapData != data) {
            // Cancel previous task
            bitmapWorkerTask.cancel(true);
        } else {
            // The same work is already in progress
            return false;
        }
    }
    // No task associated with the ImageView, or an existing task was cancelled
    return true;
}

private static BitmapWorkerTask getBitmapWorkerTask(ImageView imageView) {
       if (imageView != null) {
           final Drawable drawable = imageView.getDrawable();
           if (drawable instanceof AsyncDrawable) {
               final AsyncDrawable asyncDrawable = (AsyncDrawable) drawable;
               return asyncDrawable.getBitmapWorkerTask();
           }
        }
        return null;
    }

public Bitmap loadImageFromSdCard(String filePath, int reqWidth, int reqHeight) {

    // First decode with inJustDecodeBounds=true to check dimensions
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeFile(filePath, options);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    return BitmapFactory.decodeFile(filePath, options);
} 

public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;

if (height > reqHeight || width > reqWidth) {
    if (width > height) {
        inSampleSize = Math.round((float)height / (float)reqHeight);
    } else {
        inSampleSize = Math.round((float)width / (float)reqWidth);
    }
}
return inSampleSize;}

class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> {

    private String mFilePath;
    private final WeakReference<ImageView> imageViewReference;

    public BitmapWorkerTask(ImageView imageView) {
        // Use a WeakReference to ensure the ImageView can be garbage collected
        imageViewReference = new WeakReference<ImageView>(imageView);
    }

    public String getFilePath() {
        return mFilePath;
    }

    // Decode image in background.
    @Override
    protected Bitmap doInBackground(String... params) {
        mFilePath = params[0];       
        final Bitmap bitmap = loadImageFromSdCard(mFilePath, 68, 68);
        addBitmapToMemoryCache(String.valueOf(mFilePath), bitmap);
        return bitmap;
    }

    // Once complete, see if ImageView is still around and set bitmap.
    @Override
    protected void onPostExecute(Bitmap bitmap) {
        if (isCancelled()) {
            bitmap = null;
        }

        if (imageViewReference != null && bitmap != null) {
            final ImageView imageView = imageViewReference.get();
            final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView);
            if (this == bitmapWorkerTask && imageView != null) {
                imageView.setImageBitmap(bitmap);
            }
        }
    }
}

static class AsyncDrawable extends BitmapDrawable {
    private final WeakReference<BitmapWorkerTask> bitmapWorkerTaskReference;

    public AsyncDrawable(Resources res, Bitmap bitmap, BitmapWorkerTask bitmapWorkerTask) {
        super(res, bitmap);
        bitmapWorkerTaskReference = new WeakReference<BitmapWorkerTask>(bitmapWorkerTask);
    }

    public BitmapWorkerTask getBitmapWorkerTask() {
        return bitmapWorkerTaskReference.get();
    }
}

final int cacheSize = 1024 * 1024 * memClass / 8;

public LruCache<String, Bitmap> mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {

    @Override
    protected int sizeOf(String key, Bitmap bitmap) {
        // The cache size will be measured in bytes rather than number of items.
        return bitmap.getByteCount();
    }
};

public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
    if (getBitmapFromMemCache(key) == null) {
        mMemoryCache.put(key, bitmap);
    }
}

public Bitmap getBitmapFromMemCache(String key) {
    return mMemoryCache.get(key);
}
}

此代码应粘贴到您要查看位图的位置：

ThumbnailLoader tnloader = new ThumbnailLoader(getContext());
tnloader.loadBitmap(filepath, imageView);

Answer 1

检查此问题：

Lazy load of images in ListView

PS。我有几乎相同的问题，因为我记得图像只是在从网络加载后才出现 - 可能是因为缓存或其他。这个链接对我有帮助。

<强>更新

您还可以在标记字段（setteag \ gettag）中存储每个图像视图的网址。有关此教程，您可以找到here：

位图不会使用lrucache和asynctask显示

1 个答案: