我正在使用自制的LruDiskCache构建应用程序以减少加载时间。 LruDiskCache下载文件（如果该文件尚不存在）并通过回调返回。我有一个非常奇怪的问题，第一张图像没有正确加载。这仅在活动第一次启动时发生。如果您打开相同的活动，则可以正确加载图像。
调试后我发现我收到以下调试信息：--- SkImageDecoder Factory returned null。我已经阅读了有关此问题的多个问题，但都涉及通过输入流下载图像，而我首先将图像下载到持久存储。
我的缓存类：
public class LruDiskCache {
private static final String LOGTAG = "LruDiskCache";
//Cache size
private final long cacheMaxSize;
private volatile long currentCacheSize;
public static final int DEFAULT_CACHE_SIZE_KB = 1024;
public static final int MINIMUM_CACHE_SIZE_KB = 128;
//Preferences
private final String cachePreferencesName;
private final String chachePreferencesSize = "cacheSize";
private final SharedPreferences cachePreferences;
//Lock
private final Object mDiskCacheLock = new Object();
//Cache Path
private final File cachePath;
//Initialisation
private boolean openingCache;
//Static variables
private static final long BYTES_IN_KB = 1024;
public LruDiskCache (Context c, String cacheName, int cacheMaxSizeKB){
//Preferences
cachePreferencesName = cacheName + "CachePreferences";
cachePreferences = c.getSharedPreferences(cachePreferencesName, Context.MODE_PRIVATE);
//Paths
cachePath = new File(c.getFilesDir().getPath()+"/"+cacheName);
//Cache size
if(cacheMaxSizeKB < MINIMUM_CACHE_SIZE_KB){
throw new IllegalArgumentException
("Invalid cache size, size must be bigger than "
+ MINIMUM_CACHE_SIZE_KB + "kb.");
}
cacheMaxSize = cacheMaxSizeKB * BYTES_IN_KB;
//Initialize
openingCache = true;
new InitializeCache().execute();
}
//PUBLIC METHODS
public synchronized void getRemoteFile(URL remoteFile, Callback c){
if(openingCache){
try {
mDiskCacheLock.wait(1000);
} catch (InterruptedException e) {
c.onRequestedFileRetrieved(null, false);
}
}
String path = createFilePath(remoteFile);
File f = new File(path);
if(f.exists() && f.isFile()){
f.setLastModified(System.currentTimeMillis());
c.onRequestedFileRetrieved(f, true);
} else {
new RemoteFileDownloadTask(remoteFile, f, c).execute();
}
}
//PRIVATE METHODS
private String createFilePath(URL key){
return cachePath + "/" + key.getHost() + key.getPath();
}
private synchronized void cleanUpCache(){
long cacheSize = getDirSize(cachePath);
int failedToDeleteCounter = 0;
while(cacheSize > cacheMaxSize){
File toDelete = getFirstRequestedFile(cachePath);
Log.w("LruDiskCache", "File to be deleted: " + toDelete.getName() + ".");
long toDeleteSize = toDelete.length();
if(!toDelete.delete()){
failedToDeleteCounter++;
} else {
Log.w("LruDiskCache", "Deleted file to clean cache.");
cacheSize -= toDeleteSize;
}
if(failedToDeleteCounter > 100){
Log.w("LruDiskCache", "Failed to clean cache, could not delete files.");
break;
}
}
}
private File getFirstRequestedFile(File directory){
File first = null;
for(File f : directory.listFiles()){
if(f.isFile()){
if(first == null){
first = f;
} else {
if(f.lastModified() < first.lastModified()){
first = f;
}
}
} else if (f.isDirectory()) {
File firstReqInDir = getFirstRequestedFile(f);
if(first == null){
first = firstReqInDir;
} else if (firstReqInDir.lastModified() < first.lastModified()){
first = firstReqInDir;
}
}
}
return first;
}
private long getDirSize(File dir) {
long bytes = 0;
for (File f : dir.listFiles()) {
if (f.isDirectory()) {
bytes += getDirSize(f);
} else {
bytes += f.length();
}
}
return bytes;
}
//ASYNC TASKS
private class InitializeCache implements Runnable{
public void execute(){
new Thread(this).start();
}
@Override
public void run() {
synchronized (mDiskCacheLock) {
Log.d("Initialize cache", "Starting init...");
if (!cachePath.exists()) {
if (!cachePath.mkdirs()) {
mDiskCacheLock.notifyAll();
openingCache = false;
}
}
currentCacheSize = getDirSize(cachePath);
Log.d("LruDiskCache", "Cache size: " + currentCacheSize / BYTES_IN_KB + "kb.");
if(currentCacheSize > cacheMaxSize){
cleanUpCache();
}
Log.d("Initialize cache", "Did init...");
mDiskCacheLock.notifyAll();
openingCache = false;
}
}
}
private class RemoteFileDownloadTask extends AsyncTask<Void, Void, File> {
private final Callback c;
private URL remoteFile;
private File localFile;
protected RemoteFileDownloadTask(URL remoteFile, File localFile, Callback c){
this.c = c;
this.remoteFile = remoteFile;
this.localFile = localFile;
}
@Override
protected File doInBackground(Void... params) {
if(retrieveRemoteFile(remoteFile, localFile)){
return localFile;
} else {
return null;
}
}
@Override
protected void onPostExecute(File file) {
super.onPostExecute(file);
currentCacheSize += file.length();
if(currentCacheSize > cacheMaxSize){
cleanUpCache();
}
c.onRequestedFileRetrieved(file, true);
}
public boolean retrieveRemoteFile(URL remote, File filePath) {
try {
if (filePath.exists() && filePath.isFile()) {
return true;
} else {
if (!filePath.getParentFile().exists()) {
if (!filePath.getParentFile().mkdirs()) {
return false;
}
}
}
} catch (Exception e){
return false;
}
Log.w("LruDiskCache", "Created empty file: " + filePath.getPath());
Log.w("LruDiskCache", "Downloading source from: " + remote.toString());
try {
FileOutputStream fos;
InputStream is;
BufferedInputStream bis;
fos = new FileOutputStream(filePath);
HttpURLConnection con = (HttpURLConnection) remote.openConnection();
if(con.getResponseCode() != HttpURLConnection.HTTP_OK){
Log.e("Receiver", "HTTP Response code is not OK");
return false;
}
is = con.getInputStream();
bis = new BufferedInputStream(is);
while(bis.available() > 0){
fos.write(bis.read());
}
bis.close();
is.close();
fos.close();
} catch (Exception e) {
return false;
}
Log.d("LruDiskCacheReceiver", filePath.getPath() + " received, " + filePath.length() + " bytes.");
return true;
}
}
//CALLBACK INTERFACE
public interface Callback{
public abstract void onRequestedFileRetrieved(File f, boolean success);
}
}
这里的实现如下：
URL emblemURL = new URL(data[position].getEmblemUrl());
cache.getRemoteFile(emblemURL, new LruDiskCache.Callback() {
@Override
public void onRequestedFileRetrieved(File f, boolean success) {
if (success && f.exists()) {
Drawable bitmap = Drawable.createFromPath(f.getAbsolutePath());
emblem.setImageDrawable(bitmap);
}
}
});
感谢任何帮助。