I need help understanding androids LruCache. I want to use to load images into my gridview in order make the loading/scrolling better. Can someone post an example code using LruCache please. Thanks in advance.
ePeace
Below is a class I made for using LruCache, this is based on the presentation Doing More With Less: Being a Good Android Citizen given at Google I/O 2012.
Check out the movie for more information about what I'm doing in the TCImageLoader class:
public class TCImageLoader implements ComponentCallbacks2 {
private TCLruCache cache;
public TCImageLoader(Context context) {
ActivityManager am = (ActivityManager) context.getSystemService(
Context.ACTIVITY_SERVICE);
int maxKb = am.getMemoryClass() * 1024;
int limitKb = maxKb / 8; // 1/8th of total ram
cache = new TCLruCache(limitKb);
}
public void display(String url, ImageView imageview, int defaultresource) {
imageview.setImageResource(defaultresource);
Bitmap image = cache.get(url);
if (image != null) {
imageview.setImageBitmap(image);
}
else {
new SetImageTask(imageview).execute(url);
}
}
private class TCLruCache extends LruCache<String, Bitmap> {
public TCLruCache(int maxSize) {
super(maxSize);
}
@Override
protected int sizeOf(ImagePoolKey key, Bitmap value) {
int kbOfBitmap = value.getByteCount() / 1024;
return kbOfBitmap;
}
}
private class SetImageTask extends AsyncTask<String, Void, Integer> {
private ImageView imageview;
private Bitmap bmp;
public SetImageTask(ImageView imageview) {
this.imageview = imageview;
}
@Override
protected Integer doInBackground(String... params) {
String url = params[0];
try {
bmp = getBitmapFromURL(url);
if (bmp != null) {
cache.put(url, bmp);
}
else {
return 0;
}
} catch (Exception e) {
e.printStackTrace();
return 0;
}
return 1;
}
@Override
protected void onPostExecute(Integer result) {
if (result == 1) {
imageview.setImageBitmap(bmp);
}
super.onPostExecute(result);
}
private Bitmap getBitmapFromURL(String src) {
try {
URL url = new URL(src);
HttpURLConnection connection
= (HttpURLConnection) url.openConnection();
connection.setDoInput(true);
connection.connect();
InputStream input = connection.getInputStream();
Bitmap myBitmap = BitmapFactory.decodeStream(input);
return myBitmap;
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
}
@Override
public void onConfigurationChanged(Configuration newConfig) {
}
@Override
public void onLowMemory() {
}
@Override
public void onTrimMemory(int level) {
if (level >= TRIM_MEMORY_MODERATE) {
cache.evictAll();
}
else if (level >= TRIM_MEMORY_BACKGROUND) {
cache.trimToSize(cache.size() / 2);
}
}
}
I've found a really easy way that work perfectly for me...
This is the Cache.java class. In this class, the static getInstance() method enables us to create only one cache instance in the whole application. getLru() method is used to retrieve the cached object, it will be shown later how to use it. This cache is generic, meaning you can save any Object type into it. The cache memory size here is set to 1024. It can be changed if it is too small:
import android.support.v4.util.LruCache;
public class Cache {
private static Cache instance;
private LruCache<Object, Object> lru;
private Cache() {
lru = new LruCache<Object, Object>(1024);
}
public static Cache getInstance() {
if (instance == null) {
instance = new Cache();
}
return instance;
}
public LruCache<Object, Object> getLru() {
return lru;
}
}
This is the code in your activity where you save the bitmap to the cache:
public void saveBitmapToCahche(){
//The imageView that you want to save it's bitmap image resourse
ImageView imageView = (ImageView) findViewById(R.id.imageViewID);
//To get the bitmap from the imageView
Bitmap bitmap = ((BitmapDrawable)imageview.getDrawable()).getBitmap();
//Saving bitmap to cache. it will later be retrieved using the bitmap_image key
Cache.getInstance().getLru().put("bitmap_image", bitmap);
}
This is the code where you retrieve the bitmap from the cache, then set an imageView to this bitmap:
public void retrieveBitmapFromCache(){
//The imageView that you want to set to the retrieved bitmap
ImageView imageView = (ImageView) findViewById(R.id.imageViewID);
//To get bitmap from cache using the key. Must cast retrieved cache Object to Bitmap
Bitmap bitmap = (Bitmap)Cache.getInstance().getLru().get("bitmap_image");
//Setting imageView to retrieved bitmap from cache
imageView.setImageBitmap(bitmap));
}
THAT'S ALL! As you can see this is rather easy and simple.
- EXAMPLE:
In my application, All the views are saved in class variables so they can be seen by all the methods in the class. In my first activity, I save the image bitmap to the cache in an onClickButton() method, right before I start a new activity using intent. I also save a string value in my cache:
public void onClickButton(View v){
Bitmap bitmap = ((BitmapDrawable)imageView.getDrawable()).getBitmap();
String name = textEdit.getText().toString();
Cache.getInstance().getLru().put("bitmap_image", bitmap);
Cache.getInstance().getLru().put("name", name);
Intent i = new Intent(FirstActivity.this, SecondActivity.class);
startActivity(i);
}
Then I navigate from the second activity to a third activity also using intents. In the last activity I save other objects into my cache, then go back to the first activity using an intent. Once I'm back in the first activity, the onCreate() method will start. In that method, I check if my cache has any bitmap value or any String value separately (based on my application business):
public ImageView imageView;
public EditText editText;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_first);
//...Other code...
//The imageView that you want to save it's bitmap image resourse
imageView = (ImageView) findViewById(R.id.imageViewID);
//The editText that I want to save it's text into cache
editText = (EditText)findViewById(R.id.editTextID);
if(Cache.getInstance().getLru().get("name")!=null){
editText.setText(Cache.getInstance().getLru().get("name").toString());
}
if(Cache.getInstance().getLru().get("bitmap_image")!=null){
imageView.setImageBitmap((Bitmap)Cache.getInstance().getLru().get("bitmap_image"));
}
//...Other code...
}
Take a look at Caching Bitmaps where the use of LruCache is demonstrated.
The relevant portion of the code from the page is as follows:-
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);
}
https://techienotes.info/2015/08/28/caching-bitmaps-in-android-using-lrucache/
This link has a full project having sample application to load images into Gridview using LruCache.
This class is using LruCache and taken from the code given in the link
public class ImageAdapter extends BaseAdapter{
private String TAG = getClass().getSimpleName();
Context mContext;
ArrayList<Uri> imageList;
private LruCache<String, Bitmap> mLruCache;
public ImageAdapter (Context context){
mContext = context;
//Find out maximum memory available to application
//1024 is used because LruCache constructor takes int in kilobytes
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
// Use 1/4th of the available memory for this memory cache.
final int cacheSize = maxMemory / 4;
Log.d(TAG, "max memory " + maxMemory + " cache size " + cacheSize);
// LruCache takes key-value pair in constructor
// key is the string to refer bitmap
// value is the stored bitmap
mLruCache = new LruCache<String, Bitmap>(cacheSize) {
@Override
protected int sizeOf(String key, Bitmap bitmap) {
// The cache size will be measured in kilobytes
return bitmap.getByteCount() / 1024;
}
};
imageList = new ArrayList<Uri>();
//Change this directory to where the images are stored
String imagesFolderPath = Environment.getExternalStorageDirectory().getPath()+"/backups/";
File imageSrcDir = new File (imagesFolderPath);
// if directory not present, build it
if (!imageSrcDir.exists()){
imageSrcDir.mkdirs();
}
ArrayList<File> imagesInDir = getImagesFromDirectory(imageSrcDir);
for (File file: imagesInDir){
// imageList will hold Uri of all images
imageList.add(Uri.fromFile(file));
}
}
@Override
public int getCount() {
return imageList.size();
}
@Override
public Object getItem(int position) {
return null;
}
@Override
public long getItemId(int position) {
return 0;
}
/**
*
* @param position The position of the item within the
* adapter's data set of the item whose view we want.
* @param convertView it is the view to be reused
* @param parent The parent that this view will eventually be attached to
* @return a View corresponding to the data at the specified position.
*/
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ImageView imageView;
Bitmap thumbnailImage = null;
if (convertView == null){
imageView = new ImageView(mContext);
imageView.setLayoutParams(
//150,150 is size of imageview to display image
new GridView.LayoutParams(150, 150));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
}
else {
imageView = (ImageView)convertView;
}
// Use the path as the key to LruCache
final String imageKey = imageList.get(position).toString();
//thumbnailImage is fetched from LRU cache
thumbnailImage = getBitmapFromMemCache(imageKey);
if (thumbnailImage == null){
// if asked thumbnail is not present it will be put into cache
BitmapWorkerTask task = new BitmapWorkerTask(imageView);
task.execute(imageKey);
}
imageView.setImageBitmap(thumbnailImage);
return imageView;
}
/**
* This function returns the files from a directory
* @param parentDirPath source directory in which images are located
* @return list of Files
*/
private ArrayList<File> getImagesFromDirectory (File parentDirPath){
ArrayList <File> listOfImages = new ArrayList<File>();
File [] fileArray = null;
if ( parentDirPath.isDirectory() ){//parentDirPath.exists() &&
// &&
// parentDirPath.canRead()){
fileArray = parentDirPath.listFiles();
}
if (fileArray == null){
return listOfImages; // return empty list
}
for (File file: fileArray){
if (file.isDirectory()){
listOfImages.addAll(getImagesFromDirectory(file));
}
else {
// Only JPEG and PNG formats are included
// for sake of simplicity
if (file.getName().endsWith("png") ||
file.getName().endsWith("jpg")){
listOfImages.add(file);
}
}
}
return listOfImages;
}
/**
* This function will return the scaled version of original image.
* Loading original images into thumbnail is wastage of computation
* and hence we will take put scaled version.
*/
private Bitmap getScaledImage (String imagePath){
Bitmap bitmap = null;
Uri imageUri = Uri.parse (imagePath);
try{
BitmapFactory.Options options = new BitmapFactory.Options();
/**
* inSampleSize flag if set to a value > 1,
* requests the decoder to sub-sample the original image,
* returning a smaller image to save memory.
* This is a much faster operation as decoder just reads
* every n-th pixel from given image, and thus
* providing a smaller scaled image.
* 'n' is the value set in inSampleSize
* which would be a power of 2 which is downside
* of this technique.
*/
options.inSampleSize = 4;
options.inScaled = true;
InputStream inputStream = mContext.getContentResolver().openInputStream(imageUri);
bitmap = BitmapFactory.decodeStream(inputStream, null, options);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
return bitmap;
}
public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
if (getBitmapFromMemCache(key) == null) {
mLruCache.put(key, bitmap);
}
}
public Bitmap getBitmapFromMemCache(String key) {
return mLruCache.get(key);
}
class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> {
private final WeakReference<ImageView> imageViewReference;
public BitmapWorkerTask(ImageView imageView) {
// Use a WeakReference to ensure the ImageView can be garbage collected
imageViewReference = new WeakReference<ImageView>(imageView);
}
@Override
protected Bitmap doInBackground(String... params) {
final Bitmap bitmap = getScaledImage(params[0]);
addBitmapToMemoryCache(String.valueOf(params[0]), bitmap);
return bitmap;
}
// onPostExecute() sets the bitmap fetched by doInBackground();
@Override
protected void onPostExecute(Bitmap bitmap) {
if (imageViewReference != null && bitmap != null) {
final ImageView imageView = (ImageView)imageViewReference.get();
if (imageView != null) {
imageView.setImageBitmap(bitmap);
}
}
}
}
}
Utility Class to save and retrieve Bitmap from own Cache.
package com.roomco.android.utils;
import android.graphics.Bitmap;
import android.support.v4.util.LruCache;
public class MyCache {
private static MyCache instance;
private LruCache<Object, Object> lru;
private MyCache() {
lru = new LruCache<Object, Object>(1024);
}
public static MyCache getInstance() {
if (instance == null) {
instance = new MyCache();
}
return instance;
}
public LruCache<Object, Object> getLru() {
return lru;
}
public void saveBitmapToCahche(String key, Bitmap bitmap){
MyCache.getInstance().getLru().put(key, bitmap);
}
public Bitmap retrieveBitmapFromCache(String key){
Bitmap bitmap = (Bitmap)MyCache.getInstance().getLru().get(key);
return bitmap;
}
}
Usage:
//Save bitmap in cache
MyCache.getInstance().saveBitmapToCahche("your_key",bitmap);
// Get bitmap from cache
MyCache.getInstance().retrieveBitmapFromCache("your_key");
来源：https://stackoverflow.com/questions/11623994/example-using-androids-lrucache