android:persistentDrawingCache=”animation”

Defines the persistence of the drawing cache. The drawing cache might be enabled by a ViewGroup for all its children in specific situations (for instance
during a scrolling.) This property lets you persist the cache in memory after its initial usage. Persisting the cache consumes more memory but may prevent frequent garbage collection is the cache is created over and over again. By default the persistence is
set to scrolling.

大致意思如下：

　　定義繪圖的快取的持久性。 繪圖緩衝可能由一個 ViewGroup 在特定情況下為其所有的子類啟用，例如在一個滾動的過程中。 此屬性可以保留在記憶體中的緩衝後其初始的使用。 堅持緩衝會消耗更多的記憶體，但可能會阻止頻繁的記憶體回收是反覆建立緩衝。 預設情況下持續存在設定為滾動。

　　其屬性值只有以下幾種：

　　Constant   Value   Description

        none            0x0     The drawing cache is not persisted after use.

　　animation   0x1     The drawing cache is persisted after a layout animation.

　　scrolling     0x2     The drawing cache is persisted after a scroll.

　　all                0x3     The drawing cache is always persisted.