Android api level-22中android.support.v4.util.LruCache和android.util.LruCache的行為不一樣問題

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今天發現一個問題，ApiLevel-22的Android源碼，兩個版本的LruCache：android.support.v4.util.LruCache和android.util.LruCache在移除舊的緩衝對象時的行為完全不一樣。

android.support.v4.util.LruCache在移除緩衝的時候是移除最近最少訪問的，符合LruCache的設計初衷。

android.util.LruCache在緩衝滿了的情況下，會把當前加入的直接移除掉，不符合LruCache的設計初衷。

關鍵代碼如下:

android.support.v4.util.LruCache,第15行代碼

 1     private void trimToSize(int maxSize) { 2         while (true) { 3             K key; 4             V value; 5             synchronized (this) { 6                 if (size < 0 || (map.isEmpty() && size != 0)) { 7                     throw new IllegalStateException(getClass().getName() 8                             + ".sizeOf() is reporting inconsistent results!"); 9                 }10 11                 if (size <= maxSize) {12                     break;13                 }14 15                 Map.Entry<K, V> toEvict = map.eldest();16                 if (toEvict == null) {17                     break;18                 }19 20                 key = toEvict.getKey();21                 value = toEvict.getValue();22                 map.remove(key);23                 size -= safeSizeOf(key, value);24                 evictionCount++;25             }26 27             entryRemoved(true, key, value, null);28         }29     }

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android.util.LruCache,第20行代碼

 1     private void trimToSize(int maxSize) { 2         while (true) { 3             K key; 4             V value; 5             synchronized (this) { 6                 if (size < 0 || (map.isEmpty() && size != 0)) { 7                     throw new IllegalStateException(getClass().getName() 8                             + ".sizeOf() is reporting inconsistent results!"); 9                 }10 11                 if (size <= maxSize) {12                     break;13                 }14 15                 // BEGIN LAYOUTLIB CHANGE16                 // get the last item in the linked list.17                 // This is not efficient, the goal here is to minimize the changes18                 // compared to the platform version.19                 Map.Entry<K, V> toEvict = null;20                 for (Map.Entry<K, V> entry : map.entrySet()) {21                     toEvict = entry;22                 }23                 // END LAYOUTLIB CHANGE24 25                 if (toEvict == null) {26                     break;27                 }28 29                 key = toEvict.getKey();30                 value = toEvict.getValue();31                 map.remove(key);32                 size -= safeSizeOf(key, value);33                 evictionCount++;34             }35 36             entryRemoved(true, key, value, null);37         }38     }

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 所以最好使用Support包中的LruCache。

Android api level-22中android.support.v4.util.LruCache和android.util.LruCache的行為不一樣問題