Universal-Image-Loader源码阅读（18）-memory/impl/FIFOLimitedMemoryCache

在原来LimitedMemoryCache的基础上，扩展了FIFO的策略进行图片的缓存策略。

源码：

/**
* Limited {@link Bitmap bitmap} cache. Provides {@link Bitmap bitmaps} storing. Size of all stored bitmaps will not to
* exceed size limit. When cache reaches limit size then cache clearing is processed by FIFO principle.<br />
* <br />
* <b>NOTE:</b> This cache uses strong and weak references for stored Bitmaps. Strong references - for limited count of
* Bitmaps (depends on cache size), weak references - for all other cached Bitmaps.
*
* @author Sergey Tarasevich (nostra13[at]gmail[dot]com)
* @since 1.0.0
*/
public class FIFOLimitedMemoryCache extends LimitedMemoryCache {

private final List<Bitmap> queue = Collections.synchronizedList(new LinkedList<Bitmap>());

public FIFOLimitedMemoryCache(int sizeLimit) {
super(sizeLimit);
}

@Override
public boolean put(String key, Bitmap value) {
if (super.put(key, value)) {
queue.add(value);
return true;
} else {
return false;
}
}

@Override
public Bitmap remove(String key) {
Bitmap value = super.get(key);
if (value != null) {
queue.remove(value);
}
return super.remove(key);
}

@Override
public void clear() {
queue.clear();
super.clear();
}

@Override
protected int getSize(Bitmap value) {
return value.getRowBytes() * value.getHeight();
}

@Override
protected Bitmap removeNext() {
return queue.remove(0);
}

@Override
protected Reference<Bitmap> createReference(Bitmap value) {
return new WeakReference<Bitmap>(value);
}
}