如何检查 DiskLruCache 是否已经存在?(安卓) [英] How check if a DiskLruCache already exists? (Android)

问题描述

我在我的应用程序中使用这种缓存位图的方式 在android 4.0 中使用DiskLruCache 不提供openCache 方法

I´m using that way of cache Bitmaps in my app Using DiskLruCache in android 4.0 does not provide for openCache method

问题是我在 onCreate() 中使用了该行

Thing is that I´m using that line in onCreate()

DiskLruImageCache dlic=new DiskLruImageCache(getApplicationContext(),"bckgCache", CACHESIZE, CompressFormat.PNG, 70);

而且我很确定每次应用程序作为新的"打开时它都会覆盖我的 DiskLruCache，所以我无法恢复一些我在用户打开应用程序时捕捉到的位图.那么问题来了

and I´m pretty sure that It is overwriting my DiskLruCache everytime the app is opened "as new", so I´m not being able to recover some Bitmaps I catch las time user opened the app. So here is the question

我如何检查是否已经为特定应用创建了 DislLruCache，所以我只会在它不存在时创建它?

How can I check I there´s already a DislLruCache created for an specific App so I will only create It If It doesn´t exist?

这是我从上面的 URL 使用的类

That's the class I'm using from the above URL

 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();
}

这就是我在我的 Activity 中所做的，这不起作用.如果您第一次尝试离线工作，第二次它不会(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，而是加载先前下载的图像，则停止(空指针)，因此，主要问题是它无论出于何种原因都不会记录或读取缓存文件夹中的任何内容

And this is what I'm doing into my Activity, wich doesn't works. If you try offline works the first time, second It doesn't (null pointer in OnPause because It can't find any Bitmap in the folder). If you try Online always works, but, if you try online, and then offline, instead load the previous downloaded image, is stops (null pointer), so, main problem is that It, for whatever reason, doesn't records or reads anything in the cache folder

 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;
}

}

推荐答案

检查是否安装了 sd 卡.获取sdcard的路径.检查sdcard下的文件夹是否已经存在，如果没有则创建一个.

Check if sd card is mounted. Get the path of the sdcard. Check if the folder under sdcard already exists, if not create one.

记得在清单文件中添加权限

Remember to add permission in manifest file

 <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.在开发者网站上的以下链接中找到了这个

You can use the below. Found this on developer site in the below link

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);
}

欲了解更多信息，请查看以下链接

For more information check the link below

http://developer.android.com/training/displaying-bitmaps/cache-bitmap.html

我看到您使用了 getAppliactionContext().检查下面的链接

I see you have used getAppliactionContext(). Check the link below

何时调用活动上下文或应用程序上下文?.了解何时使用活动上下文和 getApplicationContext()

When to call activity context OR application context?. Get to know when to use activity context and getApplicationContext()

   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);
   } 

2

正如您在下面看到的，您只是传递文件而不是创建新文件.

As you can see below you are just passing the file not creating a new one.

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;
}

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