android:persistentDrawingCache (Google官方译文)
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.
定义绘图的高速缓存的持久性。 绘图缓存可能由一个在特定情况下为其所有的子类启用，例如在一个滚动的过程中。 此属性可以在初次使用后保留在其在内存中的缓存。 坚持缓存会消耗更多的内存，但可能会阻止频繁的垃圾回收是反复创建缓存。 默认情况下持续存在设置为滚动。
Must be one or more (separated by ‘|’) of the following constant values.
Xml文件中可以使用一下的值：
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