我正在尝试创建一个简单的文件管理器，但在加载缩略图（位图）时遇到问题。我想使用这些技巧来使用 AsyncTask 和 Lru 缓存：
http://developer.android.com/training/displaying-bitmaps/index.html
一切都很顺利，直到我尝试实现 lru 缓存。我的意思是，如果没有 lru 缓存位图正在加载，但滚动它并不流畅。使用 lru 缓存，滚动很流畅，但位图不想立即加载。我必须向下和向上滚动，然后再加载位图。
这就是我的意思（对不起质量不好）：
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;
}
}
和缩略图加载器：
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。也许它会帮助某人。
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);
}
}
此代码应粘贴在您要查看位图的位置：
ThumbnailLoader tnloader = new ThumbnailLoader(getContext());
tnloader.loadBitmap(filepath, imageView);