Android：Lmap带有Bitmap的问题
我有一个使用LruCache类的全局位图缓存。加载列表视图的缩略图时，首先使用缓存。它工作正常。
但有一个问题是：有时缓存中的Bitmap实例无法显示在listview上。似乎缓存中的这种位图不再有效。我已经从缓存中检查了位图，如果它不是空的并且它没有被回收，但它似乎仍然无法显示这样的位图（即使它不是空的并且它不被回收）。
缓存类：
public class ImageCache {
private LruCache<String, Bitmap> mMemoryCache;
private static ImageCache instance;
public static ImageCache getInstance() {
if(instance != null) {
return instance;
}
instance = new ImageCache();
instance.initializeCache();
return instance;
}
protected void initializeCache() {
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
// Use 1/8th of the available memory for this memory cache.
final int cacheSize = maxMemory / 8;
mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
@Override
protected int sizeOf(String key, Bitmap bitmap) {
// The cache size will be measured in kilobytes rather than
// number of items.
return bitmap.getByteCount() / 1024;
}
};
}
public Bitmap getImage(String url) {
return this.mMemoryCache.get(url);
}
public void cacheImage(String url, Bitmap image) {
this.mMemoryCache.put(url, image);
}
}
并且使用缓存的代码在Adapter类中，它是CursorAdapter的子类：
final ImageCache cache = ImageCache.getInstance();
// First get from memory cache
final Bitmap bitmap = cache.getImage(thumbnailUrl);
if (bitmap != null && !bitmap.isRecycled()) {
Log.d(TAG, "The bitmap is valid");
viewHolder.imageView.setImageBitmap(bitmap);
}
else {
Log.d(TAG, "The bitmap is invalid, reload it.");
viewHolder.imageView.setImageResource(R.drawable.thumbnail_small);
// use the AsyncTask to download the image and set in cache
new DownloadImageTask(context, viewHolder.imageView, thumbnailUrl, dir, filepath).execute();
}
DownloadImageTask的代码：
public class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {
private ImageView mImageView;
private String url;
private String dir;
private String filename;
private Context context;
public DownloadImageTask(Context context, ImageView imageView, String url, String dir, String filename) {
this.mImageView = imageView;
this.url = url;
this.filename = filename;
this.dir = dir;
this.context = context;
this.cache = cache;
}
protected Bitmap doInBackground(String... urls) {
// String urldisplay = urls[0];
final Bitmap bitmap = FileUtils.readImage(context, dir, filename, url);
return bitmap;
}
protected void onPostExecute(Bitmap result) {
final ImageCache cache = ImageCache.getInstance();
if(result != null) {
cache.put(url, result);
mImageView.setImageBitmap(result);
}
}
}
任何帮助将不胜感激。谢谢！
更新：我遵循了greywolf82建议的link：“处理配置更改”部分。我在我的activity类和两个片段类中添加了以下属性：
public LruCache mMemoryCache;
在activity类中，我尝试在调用片段时初始化缓存：
// Get the cache
mMemoryCache = mIndexFragment.mRetainedCache;
if (mMemoryCache == null) {
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
// Use 1/8th of the available memory for this memory cache.
final int cacheSize = maxMemory / 8;
// Initialize the cache
mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
@Override
protected int sizeOf(String key, Bitmap bitmap) {
// The cache size will be measured in kilobytes rather than
// number of items.
return bitmap.getByteCount() / 1024;
}
};
Log.d(TAG, "Initialized the memory cache");
mIndexFragment.mRetainedCache = mMemoryCache;
}
： setRetainInstance（真）;
我将缓存实例传递给适配器构造函数，以便适配器可以使用缓存。
但我仍然遇到同样的问题。
更新2：
两个适配器类，其中包含更改以接受LruCache实例：
NewsCursorAdapter：
public class NewsCursorAdapter extends CursorAdapter {
private static final String TAG = "NewsCursorAdapter";
private LruCache<String, Bitmap> cache;
private Context mContext;
public NewsCursorAdapter(Context context, LruCache<String, Bitmap> cache) {
super(context, null, false);
this.mContext = context;
this.cache = cache;
}
@Override
public void bindView(View view, Context context, Cursor cursor) {
final Setting setting = ApplicationContext.getSetting();
// Get the view holder
ViewHolder viewHolder = (ViewHolder) view.getTag();
final String thumbnail = cursor.getString(NewsContract.Entry.THUMBNAIL_CURSOR_INDEX);
if(thumbnail != null) {
String pictureDate = cursor.getString(NewsContract.Entry.PIC_DATE_CURSOR_INDEX);
final String dir = "thumbnails/" + pictureDate + "/";
final String filepath = thumbnail + "-small.jpg";
final String thumbnailUrl = setting.getCdnUrl() + dir + filepath;
//final ImageCache cache = ImageCache.getInstance();
// First get from memory cache
final Bitmap bitmap = cache.get(thumbnailUrl);
if (bitmap != null && !bitmap.isRecycled()) {
Log.d(TAG, "The bitmap is valid: " + bitmap.getWidth());
viewHolder.imageView.setImageBitmap(bitmap);
}
else {
Log.d(TAG, "The bitmap is invalid, reload it.");
viewHolder.imageView.setImageResource(R.drawable.thumbnail_small);
new DownloadImageTask(viewHolder.imageView, thumbnailUrl, dir, filepath).execute();
}
}
else {
viewHolder.imageView.setVisibility(View.GONE);
}
}
@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View view = inflater.inflate(R.layout.listview_item_row, parent,
false);
// Initialize the view holder
ViewHolder viewHolder = new ViewHolder();
viewHolder.titleView = (TextView) view.findViewById(R.id.title);
viewHolder.timeView = (TextView) view.findViewById(R.id.news_time);
viewHolder.propsView = (TextView) view.findViewById(R.id.properties);
viewHolder.imageView = (ImageView) view.findViewById(R.id.icon);
view.setTag(viewHolder);
return view;
}
static class ViewHolder {
TextView titleView;
TextView timeView;
TextView propsView;
ImageView imageView;
}
private class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {
private ImageView mImageView;
private String url;
private String dir;
private String filename;
public DownloadImageTask(ImageView imageView, String url, String dir, String filename) {
this.mImageView = imageView;
this.url = url;
this.filename = filename;
this.dir = dir;
}
protected Bitmap doInBackground(String... urls) {
final Bitmap bitmap = FileUtils.readImage(mContext, dir, filename, url);
return bitmap;
}
protected void onPostExecute(Bitmap result) {
//final ImageCache cache = ImageCache.getInstance();
if(result != null) {
cache.put(url, result);
mImageView.setImageBitmap(result);
}
}
}
}
列表适配器，NewsTopicItemAdapter：
public class NewsTopicItemAdapter extends ArrayAdapter<NewsTopicItem> {
private Context context = null;
private EntryViewHolder viewHolder;
private HeaderViewHolder headerViewHolder;
private LruCache<String, Bitmap> mCache;
public NewsTopicItemAdapter(Context context, List<NewsTopicItem> arrayList, LruCache<String, Bitmap> cache) {
super(context, 0, arrayList);
this.context = context;
this.mCache = cache;
}
public void setItems(List<NewsTopicItem> items) {
this.addAll(items);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
final NewsTopicItem item = getItem(position);
View view;
if(!item.isHeader()) {
view = this.getEntryView((NewsTopicEntry)item, convertView, parent);
}
else {
view = this.getHeaderView((NewsTopicHeader)item, convertView, parent);
}
return view;
}
protected View getEntryView(NewsTopicEntry newsItem, View convertView, ViewGroup parent) {
View view;
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
viewHolder = new EntryViewHolder();
view = inflater.inflate(R.layout.listview_item_row, parent,
false);
// Initialize the view holder
viewHolder.titleView = (TextView) view.findViewById(R.id.title);
viewHolder.timeView = (TextView) view.findViewById(R.id.news_time);
viewHolder.propsView = (TextView) view.findViewById(R.id.properties);
viewHolder.imageView = (ImageView) view.findViewById(R.id.icon);
view.setTag(viewHolder);
viewHolder.propsView.setText(newsItem.getSource());
if (newsItem.getThumbnail() != null) {
final String dir = "thumbnails/" + newsItem.getPictureDate() + "/";
final String filepath = newsItem.getThumbnail() + "-small.jpg";
final String thumbnailUrl = "http://www.oneplusnews.com/static/" + dir + filepath;
//final ImageCache cache = ImageCache.getInstance();
// First get from memory cache
final Bitmap bitmap = mCache.get(thumbnailUrl);
if (bitmap != null && !bitmap.isRecycled()) {
viewHolder.imageView.setImageBitmap(bitmap);
} else {
viewHolder.imageView.setImageResource(R.drawable.thumbnail_small);
new DownloadImageTask(viewHolder.imageView, thumbnailUrl, dir, filepath).execute();
}
}
else {
viewHolder.imageView.setVisibility(View.GONE);
}
viewHolder.titleView.setText(newsItem.getTitle());
viewHolder.timeView.setText(DateUtils.getDisplayDate(newsItem.getCreated()));
return view;
}
protected View getHeaderView(NewsTopicHeader header, View convertView, ViewGroup parent) {
View view;
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
headerViewHolder = new HeaderViewHolder();
view = inflater.inflate(R.layout.news_list_header, parent,
false);
// Initialize the view holder
headerViewHolder.topicView = (TextView) view.findViewById(R.id.topic);
view.setTag(headerViewHolder);
final View imageView = view.findViewById(R.id.more_icon);
imageView.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
// Start the Fragement
}
});
Topic topic = header.getTopic();
if(topic.isKeyword()) {
headerViewHolder.topicView.setText(topic.getName());
}
else {
// This is a hack to avoid error with - in android
headerViewHolder.topicView.setText(ResourceUtils.getStringByName(context, topic.getName()));
}
return view;
}
private class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {
private ImageView mImageView;
private String url;
private String dir;
private String filename;
public DownloadImageTask(ImageView imageView, String url, String dir, String filename) {
this.mImageView = imageView;
this.url = url;
this.filename = filename;
this.dir = dir;
}
protected Bitmap doInBackground(String... urls) {
final Bitmap mIcon11 = FileUtils.readImage(context, dir, filename, url);
return mIcon11;
}
protected void onPostExecute(Bitmap result) {
//final ImageCache cache = ImageCache.getInstance();
if(result != null) {
mCache.put(url, result);
mImageView.setImageBitmap(result);
}
}
}
static class EntryViewHolder {
TextView titleView;
TextView timeView;
TextView propsView;
ImageView imageView;
TextView topicView;
}
static class HeaderViewHolder {
TextView topicView;
}
}
更新3：我已经附加了eclipse的调试信息：第一张图片是工作位图，第二张图片是缓存中的非工作位图。我没有发现任何可疑之处。
来自缓存的工作位图的调试信息：
来自缓存的非工作位图的调试信息：
2 个答案:
答案 0 :(得分：3)
最后我弄明白了这个问题。这是适配器的原因。在适配器中，如果不需要缩略图，我将一些ImageView设置为不可见。当用户滚动列表视图时，将重用此类ImageView实例，但不会更新可见性。
所以缓存本身就可以了。解决方案是检查ImageView的可见性，并在需要时进行更新。
无论如何，感谢greywolf82的时间和关于单身人士模式的提示。
答案 1 :(得分：1)
单身模式是邪恶的:)请完全避免它并使用setReteainInstance(true)的片段，如here所述
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