我在我的应用Using DiskLruCache in android 4.0 does not provide for openCache method
中使用了这种缓存位图我在onCreate（）
中使用该行DiskLruImageCache dlic=new DiskLruImageCache(getApplicationContext(),"bckgCache", CACHESIZE, CompressFormat.PNG, 70);
并且我很确定每次应用程序打开时都会覆盖我的DiskLruCache“as new”，所以我无法恢复一些Bitmaps，我抓住了用户打开应用程序的时间。所以这是问题
我如何检查我是否已经为特定应用程序创建了一个DislLruCache，所以我只创建它如果它不存在？
这是我在上面的网址中使用的课程
public class DiskLruImageCache {
private DiskLruCache mDiskCache;
private CompressFormat mCompressFormat = CompressFormat.PNG;
private int mCompressQuality = 70;
private static final int APP_VERSION = 1;
private static final int VALUE_COUNT = 1;
private static final String TAG = "DiskLruImageCache";
public DiskLruImageCache( Context context,String uniqueName, int diskCacheSize,
CompressFormat compressFormat, int quality ) {
try {
final File diskCacheDir = getDiskCacheDir(context, uniqueName );
mDiskCache = DiskLruCache.open( diskCacheDir, APP_VERSION, VALUE_COUNT, diskCacheSize );
mCompressFormat = compressFormat;
mCompressQuality = quality;
} catch (IOException e) {
e.printStackTrace();
}
}
private boolean writeBitmapToFile( Bitmap bitmap, DiskLruCache.Editor editor )
throws IOException, FileNotFoundException {
BufferedOutputStream out = null;
try {
out = new BufferedOutputStream( editor.newOutputStream( 0 ), Utils.IO_BUFFER_SIZE );
return bitmap.compress( mCompressFormat, mCompressQuality, out );
} finally {
if ( out != null ) {
out.close();
}
}
}
private File getDiskCacheDir(Context context, String uniqueName) {
// Check if media is mounted or storage is built-in, if so, try and use external cache dir
// otherwise use internal cache dir
final String cachePath =
Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) ||
!Utils.isExternalStorageRemovable() ?
Utils.getExternalCacheDir(context).getPath() :
context.getCacheDir().getPath();
return new File(cachePath + File.separator + uniqueName);
}
public void put( String key, Bitmap data ) {
DiskLruCache.Editor editor = null;
try {
editor = mDiskCache.edit( key );
if ( editor == null ) {
return;
}
if( writeBitmapToFile( data, editor ) ) {
mDiskCache.flush();
editor.commit();
if ( BuildConfig.DEBUG ) {
Log.d( "cache_test_DISK_", "image put on disk cache " + key );
}
} else {
editor.abort();
if ( BuildConfig.DEBUG ) {
Log.d( "cache_test_DISK_", "ERROR on: image put on disk cache " + key );
}
}
} catch (IOException e) {
if ( BuildConfig.DEBUG ) {
Log.d( "cache_test_DISK_", "ERROR on: image put on disk cache " + key );
}
try {
if ( editor != null ) {
editor.abort();
}
} catch (IOException ignored) {
}
}
}
public Bitmap getBitmap( String key ) {
Bitmap bitmap = null;
DiskLruCache.Snapshot snapshot = null;
try {
snapshot = mDiskCache.get( key );
if ( snapshot == null ) {
return null;
}
final InputStream in = snapshot.getInputStream( 0 );
if ( in != null ) {
final BufferedInputStream buffIn =
new BufferedInputStream( in, Utils.IO_BUFFER_SIZE );
bitmap = BitmapFactory.decodeStream( buffIn );
}
} catch ( IOException e ) {
e.printStackTrace();
} finally {
if ( snapshot != null ) {
snapshot.close();
}
}
if ( BuildConfig.DEBUG ) {
Log.d( "cache_test_DISK_", bitmap == null ? "" : "image read from disk " + key);
}
return bitmap;
}
public boolean containsKey( String key ) {
boolean contained = false;
DiskLruCache.Snapshot snapshot = null;
try {
snapshot = mDiskCache.get( key );
contained = snapshot != null;
} catch (IOException e) {
e.printStackTrace();
} finally {
if ( snapshot != null ) {
snapshot.close();
}
}
return contained;
}
public void clearCache() {
if ( BuildConfig.DEBUG ) {
Log.d( "cache_test_DISK_", "disk cache CLEARED");
}
try {
mDiskCache.delete();
} catch ( IOException e ) {
e.printStackTrace();
}
}
public File getCacheFolder() {
return mDiskCache.getDirectory();
}
这就是我正在为我的活动做的事情，但这不起作用。如果你第一次尝试离线工作，第二次它没有（OnPause中的空指针，因为它在文件夹中找不到任何位图）。如果您尝试在线总是有效，但是，如果您尝试在线，然后离线，而是加载以前下载的图像，则停止（空指针），因此，主要问题是它，无论出于何种原因，它不记录或读取缓存文件夹中的任何内容
public class Portada extends Activity {
private LinearLayout linearLayout;
private BitmapDrawable drawableBitmap;
private Bitmap b;
private DiskLruImageCache dlic;
private final String urlFondo="http://adapp.hostei.com/img/portada.jpg";
private final int MAXMEMORY = (int) (Runtime.getRuntime().maxMemory() / 1024);
private final int CACHESIZE = MAXMEMORY / 8;
private final String KEYPORTADA="bckportada";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_portada);
linearLayout=(LinearLayout)findViewById(R.id.fondoPortada);
Log.i("OnCreate","Starting");
File cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"bckgCache");
if(!cacheDir.exists()){ // check if it exits. if not create one
Log.i("OnCreate","Create not exsisting folder");
cacheDir.mkdirs();
dlic=new DiskLruImageCache(Portada.this,cacheDir.getName(), CACHESIZE, CompressFormat.PNG, 70);
}
else{
dlic=new DiskLruImageCache(Portada.this,cacheDir.getName(), CACHESIZE, CompressFormat.PNG, 70);
}
}
@Override
protected void onResume() {
// TODO Auto-generated method stub
super.onResume();
Log.i("OnResume","Starting");
//checks if there's already a background image on cache
boolean hayportada=comprobarSiHayPortadaEnCache();
//creates a bckImage from R.drawable image if there's any already in cache
//this should only occurs once, the very first time the App runs
if(!hayportada){
b=BitmapFactory.decodeResource(getResources(), R.drawable.portada);
dlic.put(KEYPORTADA, b);
Log.i("onResume","Creates bckgImage from R.drawable");
}
//checks if there's any connection and if yes, loads the url image into cache and puts It as background
//if not load the image of the previous if
if(CheckOnline.isOnline(Portada.this)){
cargarPortadaUrl(urlFondo);//loads image from url and stores in cache
cargarImagenPortada(b);//put image as layout background
Log.i("onResume","there is online, down img");
}
else{
b=dlic.getBitmap(KEYPORTADA);
cargarImagenPortada(b);
Log.i("onResume","there's not online ");
}
}
@Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
dlic.put(KEYPORTADA, b);//just in case, It's already done in OnResume;
Log.i("onPause","stores Bitmap");
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_portada, menu);
return true;
}
/**
* Takes an image from url and stores It in cache
*
*/
public void cargarPortadaUrl(String urlFondo){
DownloadImageTask dit=new DownloadImageTask();//Async task that downloads an img
try {
b=dit.execute(urlFondo).get();
dlic.put(KEYPORTADA, b);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
//loads a Bitmap as Layout Background image
public void cargarImagenPortada(Bitmap bitm){
drawableBitmap=new BitmapDrawable(bitm);
linearLayout.setBackgroundDrawable(drawableBitmap);
}
//checks if there's any
public boolean comprobarSiHayPortadaEnCache(){
b=dlic.getBitmap(KEYPORTADA);
if(b==null)return false;
else return true;
}
}
答案 0 :(得分：2)
检查SD卡是否已安装。获取SD卡的路径。检查sdcard下的文件夹是否已存在，如果没有，则创建一个。
请记住在清单文件中添加权限
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
if(android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
{
File cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"MyFolder");
if(!cacheDir.exists())
cacheDir.mkdirs();
}
您可以使用以下内容。在以下链接的开发者网站上找到了这个
File cacheDir = getDiskCacheDir(ActivityName.this, "thumbnails");
if(!cacheDir.exists()) // check if it exits. if not create one
{
cacheDir.mkdirs();
}
public static File getDiskCacheDir(Context context, String uniqueName) {
// Check if media is mounted or storage is built-in, if so, try and use external cache dir
// otherwise use internal cache dir
final String cachePath =
Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) ||
!isExternalStorageRemovable() ? getExternalCacheDir(context).getPath() :
context.getCacheDir().getPath();
return new File(cachePath + File.separator + uniqueName);
}
有关更多信息，请查看以下链接
http://developer.android.com/training/displaying-bitmaps/cache-bitmap.html
我发现您使用了getAppliactionContext()。检查下面的链接
When to call activity context OR application context?。了解何时使用活动上下文和getApplicationContext（）
修改
File cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"MyFolder");
if(!cacheDir.exists()) // check if it exits. if not create one
{
cacheDir.mkdirs();
DiskLruImageCache dlic=new DiskLruImageCache(ActivityName.this,cacheDir, CACHESIZE, CompressFormat.PNG, 70);
}
else
{
DiskLruImageCache dlic=new DiskLruImageCache(ActivityName.this,cacheDir, CACHESIZE, CompressFormat.PNG, 70);
}
编辑：2
如下所示，您只是传递文件而不创建新文件。
private DiskLruCache(File directory, int appVersion, int valueCount, long maxSize) {
this.directory = directory;
this.appVersion = appVersion;
this.journalFile = new File(directory, JOURNAL_FILE);
this.journalFileTmp = new File(directory, JOURNAL_FILE_TMP);
this.valueCount = valueCount;
this.maxSize = maxSize;
}
public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize)
throws IOException {
if (maxSize <= 0) {
throw new IllegalArgumentException("maxSize <= 0");
}
if (valueCount <= 0) {
throw new IllegalArgumentException("valueCount <= 0");
}
// prefer to pick up where we left off
DiskLruCache cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
if (cache.journalFile.exists()) {
try {
cache.readJournal();
cache.processJournal();
cache.journalWriter = new BufferedWriter(new FileWriter(cache.journalFile, true),
IO_BUFFER_SIZE);
return cache;
} catch (IOException journalIsCorrupt) {
System.logW("DiskLruCache " + directory + " is corrupt: "
+ journalIsCorrupt.getMessage() + ", removing");
cache.delete();
}
}
// create a new empty cache
directory.mkdirs();
cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
cache.rebuildJournal();
return cache;
}