Android 哈希映射返回空值
我正在尝试下载图像并将所有下载的图像保存在哈希映射中。我尝试了以下代码：Android 哈希映射返回空值,android,bitmap,Android,Bitmap,我正在尝试下载图像并将所有下载的图像保存在哈希映射中。我尝试了以下代码： public class ImageAdapter extends BaseAdapter{ private final Context mContext; final String[] mImages; private LayoutInflater mInflater; private static final String TAG = ImageActivity.class.getSimp
public class ImageAdapter extends BaseAdapter{
private final Context mContext;
final String[] mImages;
private LayoutInflater mInflater;
private static final String TAG = ImageActivity.class.getSimpleName();
public ImageAdapter(Context context, String[] images){
mContext=context;
mImages=images;
mInflater=(LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return mImages.length;
}
@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return mImages[position];
}
@Override
public long getItemId(int arg0) {
// TODO Auto-generated method stub
return 0;
}
private static class ViewHolder {
ImageView imageView;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder viewHolder;
if(convertView==null){
viewHolder=new ViewHolder();
convertView=mInflater.inflate(R.layout.image_layout, parent, false);
viewHolder.imageView=(ImageView) convertView.findViewById(R.id.image_View);
convertView.setTag(viewHolder);
}
else{
viewHolder=(ViewHolder) convertView.getTag();
}
String imageUrl=mImages[position];
ImageDownloader downloader=new ImageDownloader();
Bitmap value=downloader.urlMap.get(imageUrl);
Log.d(TAG, "Print Url:" + value);
if(value==null){
downloader.download(imageUrl,viewHolder.imageView);
}
else
viewHolder.imageView.setImageBitmap(value);
return convertView;
}
}
public class ImageDownloader {
private static final int IO_BUFFER_SIZE = 8 * 1024;
private static final String TAG = ImageActivity.class.getSimpleName();
final HashMap<String, Bitmap> urlMap=new HashMap<String, Bitmap>();
public void download(String url, ImageView imageView) {
downloadBitmap(url, imageView);
}
private void downloadBitmap(final String url,final ImageView imageView) {
new AsyncTask<Void, Void, Bitmap>() {
@Override
protected Bitmap doInBackground(Void... params) {
return downloadUrlToStream(url, imageView);
}
protected void onPostExecute(Bitmap bitmap) {
imageView.setImageBitmap(bitmap);
urlMap.put(url, bitmap);
Log.d(TAG, "Print value:" + urlMap);
};
}.execute();
}
公共类ImageDownloader{
专用静态最终输入输出缓冲区大小=8*1024；
私有静态最终字符串标记=ImageActivity.class.getSimpleName（）；
final HashMap urlMap=新HashMap（）；
公共void下载（字符串url，ImageView）{
下载位图（url、imageView）；
}
私有void下载位图（最终字符串url，最终图像视图）{
新建异步任务（）{
@凌驾
受保护位图doInBackground（无效…参数）{
返回downloadUrlToStream（url，imageView）；
}
受保护的void onPostExecute（位图）{
设置图像位图（位图）；
放置（url，位图）；
Log.d（标签，“打印值：”+urlMap）；
};
}.execute（）；
}
为什么不从哈希映射中检索值？每次下载都会创建一个新的下载程序：
ImageDownloader downloader=new ImageDownloader();
downloader.download(imageUrl,viewHolder.imageView);
final HashMap<String, Bitmap> urlMap=new HashMap<String, Bitmap>();
final HashMap urlMap=new HashMap（）；
sizeOf}如果要尝试LRU缓存，可以使用此代码
public class GalleryAdapter extends BaseAdapter {
AlertDialog alertDialog = null;
List<GalleryDTO> mDatalist;
Activity context;
private LruCache<String, Bitmap> mMemoryCache;
LocationHandler mLocationHandler = null;
public GalleryAdapter(Activity context, List<GalleryDTO> mDatalist) {
this.context = context;
this.mDatalist = mDatalist;
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
final int cacheSize = maxMemory / 8;
mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
@Override
protected int sizeOf(String key, Bitmap bitmap) {
return (int) (getSizeInBytes(bitmap) / 1024);
}
};
}
public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
if (getBitmapFromMemCache(key) == null) {
mMemoryCache.put(key, bitmap);
}
}
public Bitmap getBitmapFromMemCache(String key) {
return mMemoryCache.get(key);
}
public long getSizeInBytes(Bitmap bitmap) {
if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.HONEYCOMB) {
return bitmap.getByteCount();
} else {
return bitmap.getRowBytes() * bitmap.getHeight();
}
}
@Override
public int getCount() {
return mDatalist.size();
}
@Override
public Object getItem(int position) {
return mDatalist.get(position);
}
@Override
public long getItemId(int position) {
return mDatalist.get(position).photoId;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = context.getLayoutInflater().inflate(
R.layout.list_item_gallery, parent, false);
holder = new ViewHolder();
holder.mPhoto = (ImageView) convertView
.findViewById(R.id.img_photo);
holder.mProgress = (ProgressBar) convertView
.findViewById(R.id.pg_list_item);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
GalleryDTO data = (GalleryDTO) getItem(position);
loadBitmap(data.photoName, holder);
return convertView;
}
private static class ViewHolder {
protected ImageView mPhoto;
protected ProgressBar mProgress;
}
public void loadBitmap(String respath, ViewHolder holder) {
final String imageKey = respath;
final Bitmap bitmap = getBitmapFromMemCache(imageKey);
if (bitmap != null) {
holder.mPhoto.setImageBitmap(bitmap);
holder.mProgress.setVisibility(View.GONE);
} else {
if (cancelPotentialWork(respath, holder.mPhoto, holder.mProgress)) {
final BitmapWorkerTask task = new BitmapWorkerTask(
holder.mPhoto, holder.mProgress);
final AsyncDrawable asyncDrawable = new AsyncDrawable(
context.getResources(), holder.mPlaceHolderBitmap, task);
holder.mPhoto.setImageDrawable(asyncDrawable);
task.execute(respath);
}
}
}
class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> {
private final WeakReference<ImageView> imageViewReference;
private final WeakReference<ProgressBar> progressbarReference;
private String data = "";
public BitmapWorkerTask(ImageView imageView, ProgressBar progressBar) {
imageViewReference = new WeakReference<ImageView>(imageView);
progressbarReference = new WeakReference<ProgressBar>(progressBar);
}
@Override
protected Bitmap doInBackground(String... params) {
data = params[0];
final Bitmap bitmap = downloadUrlToStream(url);
addBitmapToMemoryCache(String.valueOf(params[0]), bitmap);
return bitmap;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
if (isCancelled()) {
bitmap = null;
}
if (imageViewReference != null && bitmap != null) {
final ImageView imageView = imageViewReference.get();
final ProgressBar mProgressBar = progressbarReference.get();
final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(
imageView, mProgressBar);
if (this == bitmapWorkerTask && imageView != null) {
imageView.setImageBitmap(bitmap);
if (mProgressBar != null)
mProgressBar.setVisibility(View.GONE);
}
}
}
}
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();
}
}
public static boolean cancelPotentialWork(String data, ImageView imageView,
ProgressBar progressBar) {
final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(
imageView, progressBar);
if (bitmapWorkerTask != null) {
final String bitmapData = bitmapWorkerTask.data;
if (bitmapData != data) {
bitmapWorkerTask.cancel(true);
} else {
return false;
}
}
return true;
}
private static BitmapWorkerTask getBitmapWorkerTask(ImageView imageView,
ProgressBar progressBar) {
if (imageView != null) {
final Drawable drawable = imageView.getDrawable();
if (drawable instanceof AsyncDrawable) {
final AsyncDrawable asyncDrawable = (AsyncDrawable) drawable;
return asyncDrawable.getBitmapWorkerTask();
}
}
return null;
}
}
公共类GalleryAdapter扩展了BaseAdapter{
AlertDialog AlertDialog=null；
列出mDatalist；
活动语境；
私人LruCache-mMemoryCache；
LocationHandler mlLocationHandler=null；
公共GalleryAdapter（活动上下文，列表mDatalist）{
this.context=上下文；
this.mDatalist=mDatalist；
final int maxMemory=（int）（Runtime.getRuntime（）.maxMemory（）/1024）；
最终int cacheSize=maxMemory/8；
mMemoryCache=新的LruCache（缓存大小）{
@凌驾
受保护的int-sizeOf（字符串键、位图）{
返回（int）（getSizeInBytes（位图）/1024）；
}
};
}
public void addBitmapToMemoryCache（字符串键、位图）{
if（getBitmapFromMemCache（key）==null）{
mMemoryCache.put（键，位图）；
}
}
公共位图getBitmapFromMemCache（字符串键）{
返回mMemoryCache.get（key）；
}
公共长getSizeInBytes（位图）{
if（android.os.Build.VERSION.SDK\u INT>=android.os.Build.VERSION\u code.HONEYCOMB）{
返回bitmap.getByteCount（）；
}否则{
返回bitmap.getRowBytes（）*bitmap.getHeight（）；
}
}
@凌驾
public int getCount（）{
返回mDatalist.size（）；
}
@凌驾
公共对象getItem（int位置）{
返回mDatalist.get（位置）；
}
@凌驾
公共长getItemId（int位置）{
返回mDatalist.get（position）.photoId；
}
@凌驾
公共视图getView（int位置、视图转换视图、视图组父视图）{
视窗座；
if（convertView==null）{
convertView=context.GetLayoutFlater（）.充气(
R.layout.list\u item\u gallery，父项，false）；
holder=新的ViewHolder（）；
holder.mPhoto=（图像视图）convertView
.findviewbyd（R.id.img_照片）；
holder.mProgress=（进度条）convertView
.findViewById（R.id.pg\U列表项目）；
convertView.setTag（支架）；
}否则{
holder=（ViewHolder）convertView.getTag（）；
}
GalleryDTO数据=（GalleryDTO）获取项目（位置）；
加载位图（data.photoName，holder）；
返回视图；
}
私有静态类视图持有者{
受保护的图像视图mPhoto；
受保护的进程条进程；
}
公共void加载位图（字符串响应、视图持有者）{
最终字符串imageKey=respath；
最终位图=getBitmapFromMemCache（imageKey）；
if（位图！=null）{
holder.mPhoto.setImageBitmap（位图）；
holder.mProgress.setVisibility（View.GONE）；
}否则{
if（取消潜在工作（respath，holder.mPhoto，holder.mProgress））{
最终BitmapWorkerTask任务=新建BitmapWorkerTask(
holder.mPhoto，holder.mProgress）；
最终AsyncDrawable AsyncDrawable=新的AsyncDrawable(
context.getResources（），holder.mPlaceHolderBitmap，task）；
holder.mPhoto.setImageDrawable（异步Drawable）；
task.execute（respath）；
}
}
}
类BitmapWorkerTask扩展了AsyncTask{
私有最终WeakReference imageViewReference；
私人最终WeakReference progressbarReference；
私有字符串数据=”；
公共位图工作任务（ImageView ImageView、ProgressBar ProgressBar）{
imageViewReference=新的WeakReference（imageView）；
progressbarReference=新的WeakReference（progressBar）；
}
@凌驾
受保护位图doInBackground（字符串…参数）{
数据=参数[0]；
最终位图=下载URLTOStream（url）；
addBitmapToMemoryCache（String.valueOf（params[0]），位图）；
返回位图；
}
@凌驾
受保护的void onPostExecute（位图）{
如果（isCancelled（））{
位图=空；
}
if（imageViewReference！=null&&bitmap！=null）{
最终ImageView=imageViewReference.get（）；
final ProgressBar mProgressBar=progressbarReference.get（）；
最终BitmapWorkerTask BitmapWorkerTask=getBitmapWorkerTask(
图像视图，mProgressBar）；
if（this==bitmapWorkerTask&&imageView！=null）{
设置图像位图（位图）；
if（mProgressBar！=null）
public class GalleryAdapter extends BaseAdapter {
AlertDialog alertDialog = null;
List<GalleryDTO> mDatalist;
Activity context;
private LruCache<String, Bitmap> mMemoryCache;
LocationHandler mLocationHandler = null;
public GalleryAdapter(Activity context, List<GalleryDTO> mDatalist) {
this.context = context;
this.mDatalist = mDatalist;
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
final int cacheSize = maxMemory / 8;
mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
@Override
protected int sizeOf(String key, Bitmap bitmap) {
return (int) (getSizeInBytes(bitmap) / 1024);
}
};
}
public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
if (getBitmapFromMemCache(key) == null) {
mMemoryCache.put(key, bitmap);
}
}
public Bitmap getBitmapFromMemCache(String key) {
return mMemoryCache.get(key);
}
public long getSizeInBytes(Bitmap bitmap) {
if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.HONEYCOMB) {
return bitmap.getByteCount();
} else {
return bitmap.getRowBytes() * bitmap.getHeight();
}
}
@Override
public int getCount() {
return mDatalist.size();
}
@Override
public Object getItem(int position) {
return mDatalist.get(position);
}
@Override
public long getItemId(int position) {
return mDatalist.get(position).photoId;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = context.getLayoutInflater().inflate(
R.layout.list_item_gallery, parent, false);
holder = new ViewHolder();
holder.mPhoto = (ImageView) convertView
.findViewById(R.id.img_photo);
holder.mProgress = (ProgressBar) convertView
.findViewById(R.id.pg_list_item);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
GalleryDTO data = (GalleryDTO) getItem(position);
loadBitmap(data.photoName, holder);
return convertView;
}
private static class ViewHolder {
protected ImageView mPhoto;
protected ProgressBar mProgress;
}
public void loadBitmap(String respath, ViewHolder holder) {
final String imageKey = respath;
final Bitmap bitmap = getBitmapFromMemCache(imageKey);
if (bitmap != null) {
holder.mPhoto.setImageBitmap(bitmap);
holder.mProgress.setVisibility(View.GONE);
} else {
if (cancelPotentialWork(respath, holder.mPhoto, holder.mProgress)) {
final BitmapWorkerTask task = new BitmapWorkerTask(
holder.mPhoto, holder.mProgress);
final AsyncDrawable asyncDrawable = new AsyncDrawable(
context.getResources(), holder.mPlaceHolderBitmap, task);
holder.mPhoto.setImageDrawable(asyncDrawable);
task.execute(respath);
}
}
}
class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> {
private final WeakReference<ImageView> imageViewReference;
private final WeakReference<ProgressBar> progressbarReference;
private String data = "";
public BitmapWorkerTask(ImageView imageView, ProgressBar progressBar) {
imageViewReference = new WeakReference<ImageView>(imageView);
progressbarReference = new WeakReference<ProgressBar>(progressBar);
}
@Override
protected Bitmap doInBackground(String... params) {
data = params[0];
final Bitmap bitmap = downloadUrlToStream(url);
addBitmapToMemoryCache(String.valueOf(params[0]), bitmap);
return bitmap;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
if (isCancelled()) {
bitmap = null;
}
if (imageViewReference != null && bitmap != null) {
final ImageView imageView = imageViewReference.get();
final ProgressBar mProgressBar = progressbarReference.get();
final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(
imageView, mProgressBar);
if (this == bitmapWorkerTask && imageView != null) {
imageView.setImageBitmap(bitmap);
if (mProgressBar != null)
mProgressBar.setVisibility(View.GONE);
}
}
}
}
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();
}
}
public static boolean cancelPotentialWork(String data, ImageView imageView,
ProgressBar progressBar) {
final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(
imageView, progressBar);
if (bitmapWorkerTask != null) {
final String bitmapData = bitmapWorkerTask.data;
if (bitmapData != data) {
bitmapWorkerTask.cancel(true);
} else {
return false;
}
}
return true;
}
private static BitmapWorkerTask getBitmapWorkerTask(ImageView imageView,
ProgressBar progressBar) {
if (imageView != null) {
final Drawable drawable = imageView.getDrawable();
if (drawable instanceof AsyncDrawable) {
final AsyncDrawable asyncDrawable = (AsyncDrawable) drawable;
return asyncDrawable.getBitmapWorkerTask();
}
}
return null;
}
}