Android image caching

Question

How can I cache images after they are downloaded from web

User · Answer

As Thunder Rabbit suggested  ImageDownloader is the best one for the job  I also found a slight variation of the class at   http   theandroidcoder com utilities android-image-download-and-caching   The main difference between the two is that the ImageDownloader uses the Android caching system  and the modified one uses internal and external storage as caching  keeping the cached images indefinitely or until the user removes it manually  The author also mentions Android 2 1 compatibility

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This is a good catch by Joe  The code example above has two problems - one - the response object isn t an instance of Bitmap  when my URL references a jpg  like http  website com image jpg  its a  org apache harmony luni internal net www protocol http HttpURLConnectionImpl LimitedInputStream    Second  as Joe points out  no caching occurs without a response cache being configured  Android developers are left to roll their own cache  Here s an example for doing so  but it only caches in memory  which really isn t the full solution   http   codebycoffee com 2010 06 29 using-responsecache-in-an-android-app   The URLConnection caching API is described here   http   download oracle com javase 6 docs technotes guides net http-cache html  I still think this is an OK solution to go this route - but you still have to write a cache  Sounds like fun  but I d rather write features

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I would consider using droidfu s image cache  It implements both an in-memory and disk-based image cache  You also get a WebImageView that takes advantage of the ImageCache library   Here is the full description of droidfu and WebImageView  http   brainflush wordpress com 2009 11 23 droid-fu-part-2-webimageview-and-webgalleryadapter

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Late answer  but I figured I should add a link to my site because I have written a tutorial how to make an image cache for android  http   squarewolf nl 2010 11 android-image-cache  Update  the page has been taken offline as the source was outdated  I join  elenasys in her advice to use Ignition   So to all the people who stumble upon this question and haven t found a solution  hope you enjoy   D

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Google s libs-for-android has a nice libraries for managing image and file cache   http   code google com p libs-for-android

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Consider using Universal Image Loader library by Sergey Tarasevich  It comes with    Multithread image loading  It lets you can define the thread pool size Image caching in memory  on device s file sytem and SD card  Possibility to listen to loading progress and loading events   Universal Image Loader allows detailed cache management for downloaded images  with the following cache configurations    UsingFreqLimitedMemoryCache  The least frequently used bitmap is deleted when the cache size limit is exceeded  LRULimitedMemoryCache  The least recently used bitmap is deleted when the cache size limit is exceeded  FIFOLimitedMemoryCache  The FIFO rule is used for deletion when the cache size limit is exceeded  LargestLimitedMemoryCache  The largest bitmap is deleted when the cache size limit is exceeded  LimitedAgeMemoryCache  The Cached object is deleted when its age exceeds defined value  WeakMemoryCache  A memory cache with only weak references to bitmaps    A simple usage example   ImageView imageView   groupView findViewById R id imageView   String imageUrl    http   site com image png     ImageLoader imageLoader   ImageLoader getInstance    imageLoader init ImageLoaderConfiguration createDefault context    imageLoader displayImage imageUrl  imageView     This example uses the default UsingFreqLimitedMemoryCache

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There is a special entry on the official training section of Android about this  http   developer android com training displaying-bitmaps cache-bitmap html  The section is quite new  it was not there when the question was asked   The suggested solution is to use a LruCache  That class was introduced on Honeycomb  but it is also included on the compatibility library   You can initialize a LruCache by setting the maximum number or entries and it will automatically sort them your you and clean them less used ones when you go over the limit  Other than that it is used as a normal Map   The sample code from the official page   private LruCache mMemoryCache    Override protected void onCreate Bundle savedInstanceState                   Get memory class of this device  exceeding this amount will throw an        OutOfMemory exception      final int memClass     ActivityManager  context getSystemService              Context ACTIVITY SERVICE   getMemoryClass            Use 1 8th of the available memory for this memory cache      final int cacheSize   1024   1024   memClass   8       mMemoryCache   new LruCache cacheSize             Override         protected int sizeOf String key  Bitmap bitmap                   The cache size will be measured in bytes rather than number of items              return bitmap getByteCount                                public void addBitmapToMemoryCache String key  Bitmap bitmap        if  getBitmapFromMemCache key     null            mMemoryCache put key  bitmap            public Bitmap getBitmapFromMemCache String key        return mMemoryCache get key       Previously SoftReferences were a good alternative  but not anymore  quoting from the official page      Note  In the past  a popular memory cache implementation was a   SoftReference or WeakReference bitmap cache  however this is not   recommended  Starting from Android 2 3  API Level 9  the garbage   collector is more aggressive with collecting soft weak references   which makes them fairly ineffective  In addition  prior to Android 3 0    API Level 11   the backing data of a bitmap was stored in native   memory which is not released in a predictable manner  potentially   causing an application to briefly exceed its memory limits and crash

User · Answer

To download an image and save to the memory card you can do it like this     First create a new URL object  URL url   new URL  http   www google co uk logos holiday09 2 gif      Next create a file  the example below will save to the SDCARD using JPEG format File file   new File   sdcard example jpg       Next create a Bitmap object and download the image to bitmap Bitmap bitmap   BitmapFactory decodeStream url openStream        Finally compress the bitmap  saving to the file previously created bitmap compress CompressFormat JPEG  100  new FileOutputStream file      Don t forget to add the Internet permission to your manifest    lt uses-permission android name  android permission INTERNET    gt

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What  actually worked for me was setting ResponseCache on my Main class   try      File httpCacheDir   new File getApplicationContext   getCacheDir     http       long httpCacheSize   10   1024   1024     10 MiB    HttpResponseCache install httpCacheDir  httpCacheSize     catch  IOException e         and   connection setUseCaches true     when downloading bitmap   http   practicaldroid blogspot com 2013 01 utilizing-http-response-cache html

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Use LruCache to cache images efficiently  You can read about LruCache from Android Developer site   I ve used below solution for Images download and caching in android  You can follow steps below   STEP 1  make Class Named ImagesCache  I ve used Singleton object for this class  import android graphics Bitmap  import android support v4 util LruCache   public class ImagesCache        private  LruCache lt String  Bitmap gt  imagesWarehouse       private static ImagesCache cache       public static ImagesCache getInstance                 if cache    null                        cache   new ImagesCache                       return cache             public void initializeCache                 final int maxMemory    int   Runtime getRuntime   maxMemory    1024            final int cacheSize   maxMemory   8           System out println  cache size     cacheSize            imagesWarehouse   new LruCache lt String  Bitmap gt  cacheSize                                        protected int sizeOf String key  Bitmap value                                                    The cache size will be measured in kilobytes rather than number of items                           int bitmapByteCount   value getRowBytes     value getHeight                             return bitmapByteCount   1024                                                      public void addImageToWarehouse String key  Bitmap value                       if imagesWarehouse    null  amp  amp  imagesWarehouse get key     null                        imagesWarehouse put key  value                        public Bitmap getImageFromWarehouse String key                if key    null                        return imagesWarehouse get key                     else                       return null                       public void removeImageFromWarehouse String key                imagesWarehouse remove key              public void clearCache                 if imagesWarehouse    null                        imagesWarehouse evictAll                                STEP 2   make another class named DownloadImageTask which is used if bitmap is not available in cache it will download it from here   public class DownloadImageTask extends AsyncTask lt String  Void  Bitmap gt           private int inSampleSize   0       private String imageUrl       private BaseAdapter adapter       private ImagesCache cache       private int desiredWidth  desiredHeight       private Bitmap image   null       private ImageView ivImageView       public DownloadImageTask BaseAdapter adapter  int desiredWidth  int desiredHeight                 this adapter   adapter           this cache   ImagesCache getInstance             this desiredWidth   desiredWidth           this desiredHeight   desiredHeight             public DownloadImageTask ImagesCache cache  ImageView ivImageView  int desireWidth  int desireHeight                this cache   cache           this ivImageView   ivImageView           this desiredHeight   desireHeight           this desiredWidth   desireWidth              Override     protected Bitmap doInBackground String    params                 imageUrl   params 0            return getImage imageUrl               Override     protected void onPostExecute Bitmap result                 super onPostExecute result            if result    null                        cache addImageToWarehouse imageUrl  result                if ivImageView    null                                ivImageView setImageBitmap result                             else if adapter    null                                adapter notifyDataSetChanged                                       private Bitmap getImage String imageUrl                   if cache getImageFromWarehouse imageUrl     null                        BitmapFactory Options options   new BitmapFactory Options                 options inJustDecodeBounds   true               options inSampleSize   inSampleSize               try                               URL url   new URL imageUrl                    HttpURLConnection connection    HttpURLConnection url openConnection                     InputStream stream   connection getInputStream                     image   BitmapFactory decodeStream stream  null  options                    int imageWidth   options outWidth                   int imageHeight   options outHeight                   if imageWidth  gt  desiredWidth    imageHeight  gt  desiredHeight                                           System out println  imageWidth   imageWidth    imageHeight   imageHeight                        inSampleSize   inSampleSize   2                       getImage imageUrl                                     else                                          options inJustDecodeBounds   false                       connection    HttpURLConnection url openConnection                         stream   connection getInputStream                         image   BitmapFactory decodeStream stream  null  options                        return image                                               catch Exception e                                Log e  getImage   e toString                                      return image          STEP 3  Usage from your Activity or Adapter  Note  If you want to load image from url from Activity Class  Use the second Constructor of DownloadImageTask  but if you want to display image from Adapter use first Constructor of DownloadImageTask  for example you have a image in ListView and you are setting image from  Adapter    USAGE FROM ACTIVITY   ImageView imv    ImageView  findViewById R id imageView   ImagesCache cache   ImagesCache getInstance     Singleton instance handled in ImagesCache class  cache initializeCache     String img    your image url here    Bitmap bm   cache getImageFromWarehouse img    if bm    null      imv setImageBitmap bm     else     imv setImageBitmap null      DownloadImageTask imgTask   new DownloadImageTask cache  imv  300  300    Since you are using it from  Activity  call second Constructor     imgTask execute img       USAGE FROM ADAPTER   ImageView imv    ImageView  rowView findViewById R id imageView   ImagesCache cache   ImagesCache getInstance    cache initializeCache     String img    your image url here    Bitmap bm   cache getImageFromWarehouse img    if bm    null      imv setImageBitmap bm     else     imv setImageBitmap null      DownloadImageTask imgTask   new DownloadImageTask this  300  300    Since you are using it from  Adapter  call first Constructor     imgTask execute img       Note    cache initializeCache   you can use this statement in the very first Activity of your application  Once you ve initialized the cache you would never need to initialized it every time if you are using ImagesCache instance   I am never good at explaining things but hope this will help the beginners that how to cache using LruCache and its usage      EDIT   Now a days there are very famous libraries known as Picasso and Glide which can be used to load images very efficiently in android app  Try this very simple and usefull library Picasso for android and Glide For Android  You do not need to worry about cache images       Picasso allows for hassle-free image loading in your application   often   in one line of code       Glide  just like Picasso  can load and display images from many   sources  while also taking care of caching and keeping a low memory   impact when doing image manipulations  It has been used by official   Google apps  like the app for Google I O 2015  and is just as popular   as Picasso  In this series  we re going to explore the differences and   advantages of Glide over Picasso    You can also visit blog for difference between Glide and Picasso

User · Answer

Convert them into Bitmaps and then either store them in a Collection HashMap List etc   or you can write them on the SDcard   When storing them in application space using the first approach  you might want to wrap them around a java lang ref SoftReference specifically if their numbers is large  so that they are garbage collected during crisis   This could ensue a Reload though   HashMap lt String SoftReference lt Bitmap gt  gt  imageCache           new HashMap lt String SoftReference lt Bitmap gt  gt       writing them on SDcard will not require a Reload  just a user-permission

User · Answer

Late answer but I think this library will help a lot with caching images   https   github com crypticminds ColdStorage   Simply annotate the ImageView with   LoadCache R id id of my image view   URL to downlaod image from  and it will take care of downloading the image and loading it into the image view  You can also specify a placeholder image and loading animation   Detailed documentation of the annotation is present here  - https   github com crypticminds ColdStorage wiki  LoadImage-annotation

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Regarding the elegant connection setUseCaches solution above  sadly  it won t work without some additional effort  You will need to install a ResponseCache using ResponseCache setDefault  Otherwise  HttpURLConnection will silently ignore the setUseCaches true  bit   See the comments at the top of FileResponseCache java for details   http   libs-for-android googlecode com svn reference com google android filecache FileResponseCache html   I d post this in a comment  but I apparently don t have enough SO karma

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I ve tried SoftReferences  they are too aggressively reclaimed in android that I felt there was no point using them

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Even later answer  but I wrote an Android Image Manager that handles caching transparently  memory and disk   The code is on Github https   github com felipecsl Android-ImageManager

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I suggest IGNITION this is even better than Droid fu  https   github com kaeppler ignition  https   github com kaeppler ignition wiki Sample-applications

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And now the punchline  use the system cache   URL url   new URL strUrl   URLConnection connection   url openConnection    connection setUseCaches true   Object response   connection getContent    if  response instanceof Bitmap      Bitmap bitmap    Bitmap response       Provides both memory and flash-rom cache  shared with the browser   grr  I wish somebody had told ME that before i wrote my own cache manager

User · Answer

I had been wrestling with this for some time  the answers using SoftReferences would lose their data too quickly   The answers that suggest instantiating a RequestCache were too messy  plus I could never find a full example   But ImageDownloader java works wonderfully for me    It uses a HashMap until the capacity is reached or until the purge timeout occurs  then things get moved to a SoftReference  thereby using the best of both worlds

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