• 5
name

A PHP Error was encountered

Severity: Notice

Message: Undefined index: userid

Filename: views/question.php

Line Number: 191

Backtrace:

File: /home/prodcxja/public_html/questions/application/views/question.php
Line: 191
Function: _error_handler

File: /home/prodcxja/public_html/questions/application/controllers/Questions.php
Line: 433
Function: view

File: /home/prodcxja/public_html/questions/index.php
Line: 315
Function: require_once

I am having trouble implementing Image cache using the new Volley library. In the presentation, code look like this

mRequestQueue = Volley.newRequestQueue(context);
mImageLoader = new ImageLoader(mRequestQueue, new BitmapLruCache());

The BitmapLruCache is obviously not included in the toolkit. Any idea how to implement it or point me to some resources?

http://www.youtube.com/watch?v=yhv8l9F44qo @14:38

Thanks!

import android.graphics.Bitmap;
import android.support.v4.util.LruCache;

public class BitmapLruCache extends LruCache<String, Bitmap> implements ImageCache {
    public static int getDefaultLruCacheSize() {
        final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
        final int cacheSize = maxMemory / 8;

        return cacheSize;
    }

    public BitmapLruCache() {
        this(getDefaultLruCacheSize());
    }

    public BitmapLruCache(int sizeInKiloBytes) {
        super(sizeInKiloBytes);
    }

    @Override
    protected int sizeOf(String key, Bitmap value) {
        return value.getRowBytes() * value.getHeight() / 1024;
    }

    @Override
    public Bitmap getBitmap(String url) {
        return get(url);
    }

    @Override
    public void putBitmap(String url, Bitmap bitmap) {
        put(url, bitmap);
    }
}
  • 50
Reply Report
      • 2
    • thanks a lot, by the way, how do you determine the proper size of your cache? he talks about that its a function of screen size, seems logical, but how do I make it more exact?
    • @Vlasto Benny Lava, I'm not sure, but something like N * screen_width * screen_height with N ~ 10 seems logical for me.
      • 1
    • because now what happens is works nicely, but image loads again if it goes off screen and comes back, so I presume it was kicked out of memory cache right? Any idea what that could be?
      • 1
    • @njzk2 to prevent int overflow. Runtime.maxMemory() returns long and casting to int can cuase an overflow. The division is just to minimize the possibility.

Here is an example of using a Disk based LRU cache with Volley. It is based on using a version of AOSP's DiskLruCache maintained by Jake Wharton. http://blogs.captechconsulting.com/blog/raymond-robinson/google-io-2013-volley-image-cache-tutorial

Edit: I have updated the project to include an in-memory LRU cache as the default implementation as this is the recommended method. Volley implicitly handles disk based cache in its own L2 cache. The image cache is just the L1 cache. I updated the original post and added some more detail here: http://www.thekeyconsultant.com/2013/06/update-volley-image-cache.html.

  • 5
Reply Report
    • In your library, you seem to be using url.hashCode() to generate the key required by the disk cache. Is that really safe? hashCodes aren't unique, so won't you risk getting false cache hits for URL's that randomly resolves to the same hash code? I've seen others use MD5 to reduce the risk of collisions, some even providing their own MD5 implementation to avoid Androids non-threadsafe MessageDigest class. Any suggestions regarding this (potential) issue?
    • You are correct, this was just put in place for the demo and works the majority of the time. I am testing the speed of UUID.fromString() as a viable alternative.

What I advise is using a Singleton Bitmap Cache so this cache is going to be available during all the life of your app.

public class BitmapCache implements ImageCache {
    private LruCache<String, Bitmap> mMemoryCache;

    private static BitmapCache mInstance;

    private BitmapCache(Context ctx) {
        final int memClass = ((ActivityManager) ctx
                .getSystemService(Context.ACTIVITY_SERVICE)).getMemoryClass();
        // Use 1/16th of the available memory for this memory cache.
        final int cacheSize = 1024 * 1024 * memClass / 16;
        mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
            @Override
            protected int sizeOf(String key, Bitmap value) {
                return value.getRowBytes() * value.getHeight();
            }
        };
    }

    public static BitmapCache getInstance(Context ctx) {
        if (mInstance == null) {
            mInstance = new BitmapCache(ctx);
        }
        return mInstance;
    }

    @Override
    public Bitmap getBitmap(String url) {
        return mMemoryCache.get(url);
    }

    @Override
    public void putBitmap(String url, Bitmap bitmap) {
        mMemoryCache.put(url, bitmap);
    }
}
  • 1
Reply Report

this is comes in new API to handle the OOM

public class BitmapMemCache extends LruCache<string, Bitmap> implements ImageCache {

    public BitmapMemCache() {
        this((int) (Runtime.getRuntime().maxMemory() / 1024) / 8);
    }

    public BitmapMemCache(int sizeInKiloBytes) {
        super(sizeInKiloBytes);
    }

    @Override
    protected int sizeOf(String key, Bitmap bitmap) {
        int size = bitmap.getByteCount() / 1024;
        return size;
    }

    public boolean contains(String key) {
        return get(key) != null;
    }

    public Bitmap getBitmap(String key) {
        Bitmap bitmap = get(key);
        return bitmap;
    }

    public void putBitmap(String url, Bitmap bitmap) {
        put(url, bitmap);
    }
}
  • 0
Reply Report