在LimitedMemoryCache的基礎上，當超過緩存上限的時候，将記憶體中最大的圖檔删掉。
源碼：
/**
* 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 the bitmap which has the largest size is deleted from
* cache.<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 LargestLimitedMemoryCache extends LimitedMemoryCache {
/**
* Contains strong references to stored objects (keys) and sizes of the objects. If hard cache
* size will exceed limit then object with the largest size is deleted (but it continue exist at
* {@link #softMap} and can be collected by GC at any time)
*/
private final Map<Bitmap, Integer> valueSizes = Collections.synchronizedMap(new HashMap<Bitmap, Integer>());
public LargestLimitedMemoryCache(int sizeLimit) {
super(sizeLimit);
}
@Override
public boolean put(String key, Bitmap value) {
if (super.put(key, value)) {
valueSizes.put(value, getSize(value));
return true;
} else {
return false;
}
}
@Override
public Bitmap remove(String key) {
Bitmap value = super.get(key);
if (value != null) {
valueSizes.remove(value);
}
return super.remove(key);
}
@Override
public void clear() {
valueSizes.clear();
super.clear();
}
@Override
protected int getSize(Bitmap value) {
return value.getRowBytes() * value.getHeight();
}
@Override
protected Bitmap removeNext() {//該類的核心，找到最大的圖檔删掉
Integer maxSize = null;
Bitmap largestValue = null;
Set<Entry<Bitmap, Integer>> entries = valueSizes.entrySet();
synchronized (valueSizes) {
for (Entry<Bitmap, Integer> entry : entries) {
if (largestValue == null) {
largestValue = entry.getKey();
maxSize = entry.getValue();
} else {
Integer size = entry.getValue();
if (size > maxSize) {
maxSize = size;
largestValue = entry.getKey();
}
}
}
}
valueSizes.remove(largestValue);
return largestValue;
}
@Override
protected Reference<Bitmap> createReference(Bitmap value) {
return new WeakReference<Bitmap>(value);
}
}